case study peer observation

Peer Observation as a Collaborative Vehicle for Innovation in Incorporating Educational Technology into Teaching

A Case Study

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• Sven Venema 4 ,
• Steve Drew 5 &
• Jason M. Lodge 6 , 7  

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We provide a case study using peer review and observation of teaching (PRO-Teaching) as a vehicle to develop both a scholarly approach to teaching as well as providing a framework to gather data for ongoing change to facilitate scholarship of learning and teaching.

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Venema, S., Drew, S., Lodge, J.M. (2015). Peer Observation as a Collaborative Vehicle for Innovation in Incorporating Educational Technology into Teaching. In: Klopper, C., Drew, S. (eds) Teaching for Learning and Learning for Teaching. Professional Learning. SensePublishers, Rotterdam. https://doi.org/10.1007/978-94-6300-289-9_13

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• Published: 04 May 2012

Peer observation of teaching as a faculty development tool

• Peter B Sullivan 1 ,
• Alexandra Buckle 1 ,
• Gregg Nicky 1 &
• Sarah H Atkinson 1  

BMC Medical Education volume  12 , Article number:  26 ( 2012 ) Cite this article

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Peer observation of Teaching involves observers providing descriptive feedback to their peers on learning and teaching practice as a means to improve quality of teaching. This study employed and assessed peer observation as a constructive, developmental process for members of a Pediatric Teaching Faculty.

This study describes how peer observation was implemented as part of a teaching faculty development program and how it was perceived by teachers. The PoT process was divided into 4 stages: pre-observation meeting, observation, post-observation feedback and reflection. Particular care was taken to ensure that teachers understood that the observation and feedback was a developmental and not an evaluative process. Twenty teachers had their teaching peer observed by trained Faculty members and gave an e-mail ‘sound-bite’ of their perceptions of the process. Teaching activities included lectures, problem-based learning, small group teaching, case-based teaching and ward-based teaching sessions.

Teachers were given detailed verbal and written feedback based on the observer’s and students’ observations. Teachers’ perceptions were that PoT was useful and relevant to their teaching practice. Teachers valued receiving feedback and viewed PoT as an opportunity for insight and reflection. The process of PoT was viewed as non-threatening and teachers thought that PoT enhanced the quality of their teaching, promoted professional development and was critical for Faculty development.

Conclusions

This study demonstrated that PoT can be used in a constructive way to improve course content and delivery, to support and encourage medical teachers, and to reinforce good teaching.

Peer Review reports

The General Medical Council which regulates medical practice in the United Kingdom has, in its 2009 report ‘Tomorrow’s Doctors’, set the standards that it will use to judge the quality of undergraduate teaching and assessments in individual medical schools. Two quotations from this report give indications of this which are relevant to the present paper:

"‘Everyone involved in educating medical students will be appropriately selected, trained, supported and appraised’" "‘The medical school must ensure that appropriate training is provided…and that staff development programmes promote teaching and assessment skills’"

The aim of this study was to address both of these issues within the context of an undergraduate pediatric course. As part of an ongoing process of course and faculty development a peer observation of teaching (PoT) process was offered as a developmental opportunity for members of the teaching Faculty.

PoT involves observers providing descriptive feedback to their peers on learning and teaching practice [ 1 ] and can be seen as a means by which the quality of teaching and learning process in higher education establishments is both accounted for and improved [ 2 ]. PoT has attracted increasing attention in higher education in recent years. This arises, in part, to help prepare for internal or external audit of teaching as, for instance, in HEFCE-driven assessments of university teaching and is also partly a reflection of the awareness of the need to foster teacher development and professional growth and to adapt to the changing demands of the higher education system [ 3 ].

A consequence of these two drivers is the potential for confusion or conflict about the role of the observer. On the one hand, with evaluation and audit-driven process there is the possibility that observation may acquire a threatening, confrontational dimension, which may alienate the teacher. On the other hand, and probably depending in large measure on how it is approached, the peer observation process may be perceived by the teacher as a constructive, developmental adjunct to their teaching, which improves opportunities for student learning.

In view of this possible controversy, there is a need for clear focus and goals: ‘we should be very clear about exactly what our objectives are for the implementation of peer observation, and the best way to achieve these, before espousing a potentially divisive and detrimental procedure’ [ 3 ]. Shortland states that ‘an inappropriate choice of methodology – may lead to de-motivating feedback, presenting a dilemma within observation practice’ [ 1 ]. This is obviously a major concern and one that is not only represented in the literature, but in actual practice. At its worst, the aims of this exercise introduce ‘conflict’ in a system that is meant to inspire ‘confidence, enthusiasm and a sense of professional worth’ [ 3 ]. As one case report states: ‘Peer observation was designed to meet the twin aims of teacher development and quality assurance. Teachers’ views suggest these two aims may conflict’ [ 4 ].

Ramsden points out that ‘there can be no single right answer to the problem of improving the quality of university teaching’ [ 5 ]. If peer observation feedback is to achieve its goal of being motivating and helping people to learn [ 5 ], then it must be remembered that it is not an ‘automatic recipe for enhanced learning and development’ [ 1 ]. However, research unequivocally indicates that ‘classroom observation methodologies…can provide a different perspective on the observation process and thus play a part in developing observers as reflective practitioners of teaching and learning’ [ 1 ]. Irrespective of the reason for observation of teaching, it is imperative that the process is conducted in a structured and managed fashion. As Fullerton observes, ‘The aim of the observation is to help improve the skills of the observed, therefore quality feedback is essential’ [ 6 ].

Despite a large literature on PoT, there are few accounts of its implementation in clinical teaching [ 7 ] and as far as we are aware no accounts of clinical teachers’ perceptions of PoT. The aims of this project were firstly to implement PoT methods as a constructive, developmental process for members of the Pediatric Teaching Faculty and secondly to assess teachers’ perceptions of the PoT process. Our overall aim was to improve opportunities for student learning in pediatrics in our institution.

Peer observation was undertaken by Faculty members (PBS and SHA) with specific training in PoT provided by a Fellow of the Higher Education Academy with specialist knowledge of PoT. There was one-to-one training in the techniques involved followed by peer observation of trainee observers’ teaching. Our 8 week pediatric course is presented 6 times a year with the ensuing danger of becoming mechanical and stale. We therefore assessed that there was a need for PoT to keep our course material and lectures up to date and to affirm the efforts of our teaching Faculty. Critically, and this was emphasized to teaching Faculty, the PoT process was developed to be constructive and developmental. As discussed in the literature [ 1 ], an inappropriate methodology might lead to de-motivating feedback and would not achieve our aim of improving student learning.

Between October 2008 and January 2011, 15 Consultants (by PBS), 3 Clinical Lecturers and 2 Specialist Registrars (by SHA) were peer observed. Only 4 Consultants regularly contributing to the undergraduate course declined the invitation. The reasons given for declining were: from the most senior (n = 2) “not necessary”; from the most junior “too busy” and the fourth misunderstood the process and has subsequently agreed to participate. The teaching activities observed included 10 lectures, 2 problem-based teaching sessions, 3 small group teaching activities, 3 case-based teaching sessions and 2 ward-based teaching rounds. The teaching sessions were generally about one hour long. The pre-observation meeting generally took between 15 and 20 minutes and the post-observation feedback about 25–30 minutes. Each observation therefore took about 2 hours.

The general approach that was adopted for peer observation of teaching was based on Bell’s model [ 8 ]. Figure 1 illustrates the cyclical nature of the process.

Peer Observation Process (Bell 2002, [ 8 ] ]).

This approach will now be discussed under these four sub-headings:

· Pre-observation meeting

· Observation

· Post observation feedback

· Reflection

Pre-observation meeting

Prior to the observations, a pre-observation meeting was held to clarify the process and enquire of the teacher what they required from the review and to establish the context of the teaching event. Topics covered at this meeting were;

· Context of the teaching; how the session fits into the course

· The content and its place within the curriculum of the unit and the programme of study

· To what extent is this session relied upon to deliver teaching on the whole topic

· Identify specific learning objectives for this session

· Teaching approach to be adopted, anticipated student activities, time plan for the session

· Any potential difficulties or areas of concern

· Any particular aspects that the tutor wishes to have observed

· How the observation is to be conducted

· The way in which the students will be informed and incorporated into the observation

· Any particular concerns that either the observer or the observed might have about undertaking the observation.

This pre-observation meeting is an essential component in establishing a ‘contract’ with the teacher to underline that this is intended to be a developmental exercise and not an evaluative/assessment process [ 9 ].

Observation

During the observation notes were taken on the content, style and delivery of the teaching and these were used to inform the post observation feedback. With the teacher’s approval a short questionnaire scored with a Likert scale and with space for free text comments (Additional file 1 : Appendix 1) was administered to the students at the end of each observed session. The purpose of this was to help validate any observation made by the observer.

Post observation feedback

The model of feedback for each peer observation was broadly based on the revised Pendleton rules [ 10 ]. The purpose of giving feedback has been well summarized by King (1999), ‘Giving feedback is not just to provide a judgment or evaluation… It is to provide insight’ [ 11 ]. If feedback is to be effective certain criteria must be met. Feedback should be:

· Descriptive - of the behavior rather than the personality

· Specific - rather than general

· Sensitive - to the needs of the receiver as well as the giver

· Directed - towards behavior that can be changed

· Timely - given as close to the event as possible

· Selective - addressing one or two key issues rather than too many at once

At the end of the feedback session the observer and the observee examined and discussed the results of the student questionnaire. Potential solutions to any concerns raised were collaboratively identified and discussed by the observer and observee. Each teacher received a letter providing a written summary of the outcome of the observation process assimilating both the observer’s comments and the students’ comments together with potential solutions to any concerns raised.

An important component of peer observation is the opportunity for teachers to reflect on their teaching in the light of feedback from observation. All participants were invited to reflect on their observation and to send an email with comments on their experience of the process and what, if any, value it had for them as teachers. This informal approach was considered to be more likely to achieve a response rather than any structured or formal approach such as using a questionnaire.

Data analysis

Reflective feedback from the teaching faculty on PoT was analyzed using qualitative methods. Key themes in the data were identified and content analysis was carried out via systematic coding using NVivo Version 9 (QSR International Pty Ltd, Doncaster, Australia). Data were analyzed using a grounded theory approach [ 12 ] with constant comparison. The use of direct quotation gave additional richer perspectives on how, when and why certain observations were made [ 13 ].

Post-PoT recommendations

Observation of teaching activities provided an opportunity to examine both content and delivery of individual course components so that suggestions could be made as to how these might be improved or refined. Some examples of these post-PoT recommendations to individual teachers are listed:

· Ensure that learning objectives for the session are defined

· Refinement of slides by updating old slides and removing unnecessary ones

· Embed video clips in PowerPoint rather than switching to VHS format mid-lecture

· Convert Video to DVD to prevent further deterioration of useful teaching material

· Improve interaction with students

· Update teaching materials on course website e.g. use up to date growth charts

· Avoid “contamination” in small group sessions too close together in a small room

· Improve session structure with less jumping backwards and forwards between topics

· Identify what adult medicine teaches (e.g. Diabetic Ketoacidosis) and ensure consistency

The following letter extracts give a sense of how suggestions for improvement were handled:

"‘One of the disadvantages, of course, of using the white board is that one can end up talking to the white board with one’s back to the students’" "‘I thought a couple of slides which you used could be ditched and we discussed that in our post-observation de-brief. I think this will help deal with some of the time pressures that you were experiencing’"

The Peer Observation process was also useful to reinforce good teaching as the following letter extracts demonstrate:

"‘The presentation was very lively and interactive and well illustrated with case studies. I particularly liked your stick diagram to illustrate the differential diagnosis of Wilms’ tumor and neuroblastoma’"

What about the observees?: the reflective component of PoT

The device of using an email ‘sound-bite’ to document evidence of the reflective component of Peer Observation was vindicated by the 100% response rate from observees. Seven major themes emerged from the data. These were: usefulness and relevance; value of feedback, insight and reflection; non-threatening process; enhanced teaching quality; professional development; and the necessity of peer observation for Faculty development.

Usefulness and relevance

PoT was overwhelmingly described by the Teaching Faculty as extremely useful, valuable and relevant to their teaching practice.

"‘I actually thought that the whole process was extremely useful and relevant’"

Value of feedback

A major theme was that of the value of feedback. Teachers strongly valued receiving feedback from the observer and from students and thought that it improved their performance. An important component of this was receiving ‘immediate feedback’.

"‘One very rarely gets feedback – positive or negative on teaching so it was an interesting and worthwhile experience’" "‘Live feedback can only improve one’s teaching overall’" "‘Useful to have feedback from the perspective of both the students and another teacher’"

Promotion of insight and reflection

Another major theme was that PoT gave teachers insight and promoted reflection on their teaching practice.

"‘Peer review is an essential way of gaining a perspective on one’s teaching’" "‘It made me look critically at the presentation…think more clearly about my objectives’" "‘All too often teaching takes place without the opportunity for this kind of reflection’."

Non-threatening process of PoT

The overwhelming majority of teachers thought that the process of PoT was constructive and non-threatening, although the potential for the process to be threatening was acknowledged. The peer aspect of the process was also appreciated.

"‘Helpful and non-threatening feedback on teaching skills’" "‘The way in which the observation was conducted was considerate and unobtrusive’" "‘Less threatening than a more ‘senior’ member of the teaching faculty sitting in on a session’" "‘When done in a sympathetic, but informed way, this is a helpful tool’"

Enhanced teaching quality

Teachers described the tangible improvement in their teaching practice that had resulted from the detailed and specific feedback they had received from PoT. The overwhelming perception of the teachers was that these changes had resulted in enhanced quality of learning for the students.

"‘I was able to make some useful changes to the lecture that has already led to improvements in the session’" "‘Forced me into improving my audio-visual aids…which I had been meaning to do’" "‘Resulted in a more effective teaching experience for the students’"

Professional development and worth

Teachers thought that PoT enhanced their professional development and feelings of worth. ‘I was fairly confident that students liked my presentations and that it was a fairly interactive session, but hearing from them and you formally just boosted that belief and confidence’

A necessary and important process

Finally, PoT was described by teachers as a necessary and important process in a Teaching Program. The teachers advocated that PoT should be more widely implemented.

"‘If we do not do this we are at risk of doing the same old thing without variation. I am sure that there are some academics who give the same talk today as 20 years ago – is this the way ahead? I think not. If you are not open to learning then you should not teach’" "‘I would recommend peer review to all teachers…should be used more widely’"

Benefit for the observers

The process of training to be an observer and implementing peer observation was also of benefit to the observers’ professional development. It promoted awareness and reflection on one’s own teaching style and content and it was useful to learn from and borrow teaching techniques from other teachers.

This study has shown that PoT can be used as a technique both to update and refine the content and delivery of a well-established teaching course, and to provide useful feedback to teaching Faculty. This technique is useful therefore, to Course Directors who rarely get on opportunity to see the fine detail of the content of course materials or to witness the interaction of teaching faculty and students in the front line. As a result of frequent repetition (our 8 week course is presented 6 times each year) it is easy for lectures to become stale and mechanical. Power Point-based lectures may be inherited from previous teachers and/or repeated from course to course and from year to year without being updated as new information arises. An example of this last point was the use of the 1990 Growth Charts for children rather than the World Health Organization growth charts in widespread use since 2009 in a teaching module on Normal Growth and Development. Introduction of an impartial but informed observer into the teaching session has been shown to be a relatively straightforward way of keeping the course material up to date and refreshing and reaffirming the teaching style of the lecturers. An important part of the process is ‘building a partnership’ or ‘working alliance’ between the observer and observee [ 14 ], and giving specific feedback that is focused on the task and in line with personal goals [ 15 ]. In agreement with a study on the implementation of PoT in pharmaceutical education we found that a particular strength of the process was the pre-observation meeting which allowed for ‘customization of the process to meet the Faculty member’s specific needs’ [ 16 ].

Teaching Faculty unanimously described the PoT process as very useful and relevant to their teaching practice and teachers appreciated the opportunity to discuss their teaching and to have constructive feedback. The success of this process was in no small measure related to the efforts expended on emphasizing that it was not an evaluative assessment but being applied by an equal as a professional developmental tool. There is little doubt that when used in such a positive way peer observation encourages and supports teaching Faculty. However, as a GP questionnaire revealed, anxiety is likely to be provoked if PoT is imposed from outside and is not conducted by a peer [ 4 ]. Moreover, as noted in another study, PoT also gave the observing teachers the opportunity to reflect on their own teaching practice and to borrow effective teaching techniques [ 7 ].

This study has also shown how important it is to individual lecturers to receive immediate feedback from students. At the end of each course students are required to complete the Oxford Course Evaluation Questionnaire which is used to assess the students’ perceptions about teaching, workload, goals, standards and assessment methods [ 17 ]. It is based on this ongoing evaluation that we know that the course is successful in achieving its stated aims and objectives and that the great majority of students are satisfied with the organization and delivery of the course. Nevertheless, only occasionally do individual teachers get singled out for special mention so the immediate feedback provided by the simple questionnaire designed for this study enabled lecturers to see how their own lecture was received by the students. Not all comments from students were positive. Examples included ‘spoke too quickly’, ‘too many slides’, ‘rushed at the end’, but when used in conjunction with the feedback from the observation these comments had a confirmatory effect and were taken constructively by the lecturers.

The advantages of PoT when adopted in this developmental way are clear. Teachers described tangible improvements in the quality of their teaching and an enhancement of their professional development and worth. Nevertheless, it is important to emphasize the limitations of PoT. The successful application of PoT requires expertise, time and commitment. The fact that it took 30 months to complete 20 observations (at 2 hours each) indicates that the time factor is a significant limitation. This is in agreement with another study which has emphasized concern regarding ‘the time it will add to an already heavy workload’ [ 16 ]. In future it is intended that PoT will be offered to all new lecturers and re-offered to existing lecturers either on request or every five years. It is also hoped that other Faculty members may be willing to acquire the skills necessary to undertake PoT and so share the workload.

This study had a number of limitations. The department of Pediatrics is relatively small and only three peer observers have been trained to date although there are plans for more Faculty members to be trained in this process. There was also a challenge with other time pressures to complete the post-observation meeting and letter in a timely fashion. However, we believe that giving immediate feedback is one of the most important aspects of the process and consequently prioritized the post-observation feedback. Another potential limitation of the study was the lack of anonymity with the e-mail ‘sound-bite’ received from the teachers. We do not think that this is likely to have influenced our results as feedback revealed that teachers felt very comfortable with the peer aspect of PoT and did not view the process as threatening.

In summary, our study showed that PoT can be effectively implemented within an undergraduate pediatric curriculum for the development of the teaching staff and ultimately to improve the quality of student teaching.

Practice points

Peer Observation of Teaching can be used to:

· identify the need to update teaching course materials

· demonstrate to students departmental commitment to good teaching practice

· reaffirm good teaching skills of teaching faculty

· provide developmental feedback to help faculty refine teaching methods

· maintain high standards in undergraduate teaching

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Department of Paediatrics, Children’s Hospital, University of Oxford, Oxford, OX3 9DU, UK

Peter B Sullivan, Alexandra Buckle, Gregg Nicky & Sarah H Atkinson

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PS is Director of Teaching, Learning and Assessment and Head of the University of Oxford, Department of Paediatrics. He is a qualified Physician Educator of the Royal College of Physicians of London and a Fellow of the Higher Education Academy. He conceived and carried out the study and wrote the paper. AB is tutor at the University of Oxford and holds the University’s Postgraduate Diploma in Learning and Teaching in Higher Education and is a Fellow of the Higher Education Academy. She has a special interest in Peer Observation and advised on the design of the study and contributed to writing the manuscript. NG is Course Administrator for the undergraduate paediatric course in the University of Oxford, Department of Paediatrics and was responsible for the logistic and administrative arrangements of the study. SA is a Clinical Lecturer in the Department of Paediatrics, University of Oxford with a special interest in Medical Student Education. She contributed to carrying out the study, analysis of data and writing of the manuscript. All authors read and approved the final manuscript.

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Sullivan, P.B., Buckle, A., Nicky, G. et al. Peer observation of teaching as a faculty development tool. BMC Med Educ 12 , 26 (2012). https://doi.org/10.1186/1472-6920-12-26

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Observational Studies: Cohort and Case-Control Studies

Jae w. song.

1 Research Fellow, Section of Plastic Surgery, Department of Surgery The University of Michigan Health System; Ann Arbor, MI

Kevin C. Chung

2 Professor of Surgery, Section of Plastic Surgery, Department of Surgery The University of Michigan Health System; Ann Arbor, MI

Observational studies are an important category of study designs. To address some investigative questions in plastic surgery, randomized controlled trials are not always indicated or ethical to conduct. Instead, observational studies may be the next best method to address these types of questions. Well-designed observational studies have been shown to provide results similar to randomized controlled trials, challenging the belief that observational studies are second-rate. Cohort studies and case-control studies are two primary types of observational studies that aid in evaluating associations between diseases and exposures. In this review article, we describe these study designs, methodological issues, and provide examples from the plastic surgery literature.

Because of the innovative nature of the specialty, plastic surgeons are frequently confronted with a spectrum of clinical questions by patients who inquire about “best practices.” It is thus essential that plastic surgeons know how to critically appraise the literature to understand and practice evidence-based medicine (EBM) and also contribute to the effort by carrying out high-quality investigations. 1 Well-designed randomized controlled trials (RCTs) have held the pre-eminent position in the hierarchy of EBM as level I evidence ( Table 1 ). However, RCT methodology, which was first developed for drug trials, can be difficult to conduct for surgical investigations. 3 Instead, well-designed observational studies, recognized as level II or III evidence, can play an important role in deriving evidence for plastic surgery. Results from observational studies are often criticized for being vulnerable to influences by unpredictable confounding factors. However, recent work has challenged this notion, showing comparable results between observational studies and RCTs. 4 , 5 Observational studies can also complement RCTs in hypothesis generation, establishing questions for future RCTs, and defining clinical conditions.

Levels of Evidence Based Medicine

From REF 1 .

Observational studies fall under the category of analytic study designs and are further sub-classified as observational or experimental study designs ( Figure 1 ). The goal of analytic studies is to identify and evaluate causes or risk factors of diseases or health-related events. The differentiating characteristic between observational and experimental study designs is that in the latter, the presence or absence of undergoing an intervention defines the groups. By contrast, in an observational study, the investigator does not intervene and rather simply “observes” and assesses the strength of the relationship between an exposure and disease variable. 6 Three types of observational studies include cohort studies, case-control studies, and cross-sectional studies ( Figure 1 ). Case-control and cohort studies offer specific advantages by measuring disease occurrence and its association with an exposure by offering a temporal dimension (i.e. prospective or retrospective study design). Cross-sectional studies, also known as prevalence studies, examine the data on disease and exposure at one particular time point ( Figure 2 ). 6 Because the temporal relationship between disease occurrence and exposure cannot be established, cross-sectional studies cannot assess the cause and effect relationship. In this review, we will primarily discuss cohort and case-control study designs and related methodologic issues.

Analytic Study Designs. Adapted with permission from Joseph Eisenberg, Ph.D.

Temporal Design of Observational Studies: Cross-sectional studies are known as prevalence studies and do not have an inherent temporal dimension. These studies evaluate subjects at one point in time, the present time. By contrast, cohort studies can be either retrospective (latin derived prefix, “retro” meaning “back, behind”) or prospective (greek derived prefix, “pro” meaning “before, in front of”). Retrospective studies “look back” in time contrasting with prospective studies, which “look ahead” to examine causal associations. Case-control study designs are also retrospective and assess the history of the subject for the presence or absence of an exposure.

COHORT STUDY

The term “cohort” is derived from the Latin word cohors . Roman legions were composed of ten cohorts. During battle each cohort, or military unit, consisting of a specific number of warriors and commanding centurions, were traceable. The word “cohort” has been adopted into epidemiology to define a set of people followed over a period of time. W.H. Frost, an epidemiologist from the early 1900s, was the first to use the word “cohort” in his 1935 publication assessing age-specific mortality rates and tuberculosis. 7 The modern epidemiological definition of the word now means a “group of people with defined characteristics who are followed up to determine incidence of, or mortality from, some specific disease, all causes of death, or some other outcome.” 7

Study Design

A well-designed cohort study can provide powerful results. In a cohort study, an outcome or disease-free study population is first identified by the exposure or event of interest and followed in time until the disease or outcome of interest occurs ( Figure 3A ). Because exposure is identified before the outcome, cohort studies have a temporal framework to assess causality and thus have the potential to provide the strongest scientific evidence. 8 Advantages and disadvantages of a cohort study are listed in Table 2 . 2 , 9 Cohort studies are particularly advantageous for examining rare exposures because subjects are selected by their exposure status. Additionally, the investigator can examine multiple outcomes simultaneously. Disadvantages include the need for a large sample size and the potentially long follow-up duration of the study design resulting in a costly endeavor.

Cohort and Case-Control Study Designs

Advantages and Disadvantages of the Cohort Study

Cohort studies can be prospective or retrospective ( Figure 2 ). Prospective studies are carried out from the present time into the future. Because prospective studies are designed with specific data collection methods, it has the advantage of being tailored to collect specific exposure data and may be more complete. The disadvantage of a prospective cohort study may be the long follow-up period while waiting for events or diseases to occur. Thus, this study design is inefficient for investigating diseases with long latency periods and is vulnerable to a high loss to follow-up rate. Although prospective cohort studies are invaluable as exemplified by the landmark Framingham Heart Study, started in 1948 and still ongoing, 10 in the plastic surgery literature this study design is generally seen to be inefficient and impractical. Instead, retrospective cohort studies are better indicated given the timeliness and inexpensive nature of the study design.

Retrospective cohort studies, also known as historical cohort studies, are carried out at the present time and look to the past to examine medical events or outcomes. In other words, a cohort of subjects selected based on exposure status is chosen at the present time, and outcome data (i.e. disease status, event status), which was measured in the past, are reconstructed for analysis. The primary disadvantage of this study design is the limited control the investigator has over data collection. The existing data may be incomplete, inaccurate, or inconsistently measured between subjects. 2 However, because of the immediate availability of the data, this study design is comparatively less costly and shorter than prospective cohort studies. For example, Spear and colleagues examined the effect of obesity and complication rates after undergoing the pedicled TRAM flap reconstruction by retrospectively reviewing 224 pedicled TRAM flaps in 200 patients over a 10-year period. 11 In this example, subjects who underwent the pedicled TRAM flap reconstruction were selected and categorized into cohorts by their exposure status: normal/underweight, overweight, or obese. The outcomes of interest were various flap and donor site complications. The findings revealed that obese patients had a significantly higher incidence of donor site complications, multiple flap complications, and partial flap necrosis than normal or overweight patients. An advantage of the retrospective study design analysis is the immediate access to the data. A disadvantage is the limited control over the data collection because data was gathered retrospectively over 10-years; for example, a limitation reported by the authors is that mastectomy flap necrosis was not uniformly recorded for all subjects. 11

An important distinction lies between cohort studies and case-series. The distinguishing feature between these two types of studies is the presence of a control, or unexposed, group. Contrasting with epidemiological cohort studies, case-series are descriptive studies following one small group of subjects. In essence, they are extensions of case reports. Usually the cases are obtained from the authors' experiences, generally involve a small number of patients, and more importantly, lack a control group. 12 There is often confusion in designating studies as “cohort studies” when only one group of subjects is examined. Yet, unless a second comparative group serving as a control is present, these studies are defined as case-series. The next step in strengthening an observation from a case-series is selecting appropriate control groups to conduct a cohort or case-control study, the latter which is discussed in the following section about case-control studies. 9

Methodological Issues

Selection of subjects in cohort studies.

The hallmark of a cohort study is defining the selected group of subjects by exposure status at the start of the investigation. A critical characteristic of subject selection is to have both the exposed and unexposed groups be selected from the same source population ( Figure 4 ). 9 Subjects who are not at risk for developing the outcome should be excluded from the study. The source population is determined by practical considerations, such as sampling. Subjects may be effectively sampled from the hospital, be members of a community, or from a doctor's individual practice. A subset of these subjects will be eligible for the study.

Levels of Subject Selection. Adapted from Ref 9 .

Attrition Bias (Loss to follow-up)

Because prospective cohort studies may require long follow-up periods, it is important to minimize loss to follow-up. Loss to follow-up is a situation in which the investigator loses contact with the subject, resulting in missing data. If too many subjects are loss to follow-up, the internal validity of the study is reduced. A general rule of thumb requires that the loss to follow-up rate not exceed 20% of the sample. 6 Any systematic differences related to the outcome or exposure of risk factors between those who drop out and those who stay in the study must be examined, if possible, by comparing individuals who remain in the study and those who were loss to follow-up or dropped out. It is therefore important to select subjects who can be followed for the entire duration of the cohort study. Methods to minimize loss to follow-up are listed in Table 3 .

Methods to Minimize Loss to Follow-Up

Adapted from REF 2 .

CASE-CONTROL STUDIES

Case-control studies were historically borne out of interest in disease etiology. The conceptual basis of the case-control study is similar to taking a history and physical; the diseased patient is questioned and examined, and elements from this history taking are knitted together to reveal characteristics or factors that predisposed the patient to the disease. In fact, the practice of interviewing patients about behaviors and conditions preceding illness dates back to the Hippocratic writings of the 4 th century B.C. 7

Reasons of practicality and feasibility inherent in the study design typically dictate whether a cohort study or case-control study is appropriate. This study design was first recognized in Janet Lane-Claypon's study of breast cancer in 1926, revealing the finding that low fertility rate raises the risk of breast cancer. 13 , 14 In the ensuing decades, case-control study methodology crystallized with the landmark publication linking smoking and lung cancer in the 1950s. 15 Since that time, retrospective case-control studies have become more prominent in the biomedical literature with more rigorous methodological advances in design, execution, and analysis.

Case-control studies identify subjects by outcome status at the outset of the investigation. Outcomes of interest may be whether the subject has undergone a specific type of surgery, experienced a complication, or is diagnosed with a disease ( Figure 3B ). Once outcome status is identified and subjects are categorized as cases, controls (subjects without the outcome but from the same source population) are selected. Data about exposure to a risk factor or several risk factors are then collected retrospectively, typically by interview, abstraction from records, or survey. Case-control studies are well suited to investigate rare outcomes or outcomes with a long latency period because subjects are selected from the outset by their outcome status. Thus in comparison to cohort studies, case-control studies are quick, relatively inexpensive to implement, require comparatively fewer subjects, and allow for multiple exposures or risk factors to be assessed for one outcome ( Table 4 ). 2 , 9

Advantages and Disadvantages of the Case-Control Study

An example of a case-control investigation is by Zhang and colleagues who examined the association of environmental and genetic factors associated with rare congenital microtia, 16 which has an estimated prevalence of 0.83 to 17.4 in 10,000. 17 They selected 121 congenital microtia cases based on clinical phenotype, and 152 unaffected controls, matched by age and sex in the same hospital and same period. Controls were of Hans Chinese origin from Jiangsu, China, the same area from where the cases were selected. This allowed both the controls and cases to have the same genetic background, important to note given the investigated association between genetic factors and congenital microtia. To examine environmental factors, a questionnaire was administered to the mothers of both cases and controls. The authors concluded that adverse maternal health was among the main risk factors for congenital microtia, specifically maternal disease during pregnancy (OR 5.89, 95% CI 2.36-14.72), maternal toxicity exposure during pregnancy (OR 4.76, 95% CI 1.66-13.68), and resident area, such as living near industries associated with air pollution (OR 7.00, 95% CI 2.09-23.47). 16 A case-control study design is most efficient for this investigation, given the rarity of the disease outcome. Because congenital microtia is thought to have multifactorial causes, an additional advantage of the case-control study design in this example is the ability to examine multiple exposures and risk factors.

Selection of Cases

Sampling in a case-control study design begins with selecting the cases. In a case-control study, it is imperative that the investigator has explicitly defined inclusion and exclusion criteria prior to the selection of cases. For example, if the outcome is having a disease, specific diagnostic criteria, disease subtype, stage of disease, or degree of severity should be defined. Such criteria ensure that all the cases are homogenous. Second, cases may be selected from a variety of sources, including hospital patients, clinic patients, or community subjects. Many communities maintain registries of patients with certain diseases and can serve as a valuable source of cases. However, despite the methodologic convenience of this method, validity issues may arise. For example, if cases are selected from one hospital, identified risk factors may be unique to that single hospital. This methodological choice may weaken the generalizability of the study findings. Another example is choosing cases from the hospital versus the community; most likely cases from the hospital sample will represent a more severe form of the disease than those in the community. 2 Finally, it is also important to select cases that are representative of cases in the target population to strengthen the study's external validity ( Figure 4 ). Potential reasons why cases from the original target population eventually filter through and are available as cases (study participants) for a case-control study are illustrated in Figure 5 .

Levels of Case Selection. Adapted from Ref 2 .

Selection of Controls

Selecting the appropriate group of controls can be one of the most demanding aspects of a case-control study. An important principle is that the distribution of exposure should be the same among cases and controls; in other words, both cases and controls should stem from the same source population. The investigator may also consider the control group to be an at-risk population, with the potential to develop the outcome. Because the validity of the study depends upon the comparability of these two groups, cases and controls should otherwise meet the same inclusion criteria in the study.

A case-control study design that exemplifies this methodological feature is by Chung and colleagues, who examined maternal cigarette smoking during pregnancy and the risk of newborns developing cleft lip/palate. 18 A salient feature of this study is the use of the 1996 U.S. Natality database, a population database, from which both cases and controls were selected. This database provides a large sample size to assess newborn development of cleft lip/palate (outcome), which has a reported incidence of 1 in 1000 live births, 19 and also enabled the investigators to choose controls (i.e., healthy newborns) that were generalizable to the general population to strengthen the study's external validity. A significant relationship with maternal cigarette smoking and cleft lip/palate in the newborn was reported in this study (adjusted OR 1.34, 95% CI 1.36-1.76). 18

Matching is a method used in an attempt to ensure comparability between cases and controls and reduces variability and systematic differences due to background variables that are not of interest to the investigator. 8 Each case is typically individually paired with a control subject with respect to the background variables. The exposure to the risk factor of interest is then compared between the cases and the controls. This matching strategy is called individual matching. Age, sex, and race are often used to match cases and controls because they are typically strong confounders of disease. 20 Confounders are variables associated with the risk factor and may potentially be a cause of the outcome. 8 Table 5 lists several advantages and disadvantages with a matching design.

Advantages and Disadvantages for Using a Matching Strategy

Multiple Controls

Investigations examining rare outcomes may have a limited number of cases to select from, whereas the source population from which controls can be selected is much larger. In such scenarios, the study may be able to provide more information if multiple controls per case are selected. This method increases the “statistical power” of the investigation by increasing the sample size. The precision of the findings may improve by having up to about three or four controls per case. 21 - 23

Bias in Case-Control Studies

Evaluating exposure status can be the Achilles heel of case-control studies. Because information about exposure is typically collected by self-report, interview, or from recorded information, it is susceptible to recall bias, interviewer bias, or will rely on the completeness or accuracy of recorded information, respectively. These biases decrease the internal validity of the investigation and should be carefully addressed and reduced in the study design. Recall bias occurs when a differential response between cases and controls occurs. The common scenario is when a subject with disease (case) will unconsciously recall and report an exposure with better clarity due to the disease experience. Interviewer bias occurs when the interviewer asks leading questions or has an inconsistent interview approach between cases and controls. A good study design will implement a standardized interview in a non-judgemental atmosphere with well-trained interviewers to reduce interviewer bias. 9

The STROBE Statement: The Strengthening the Reporting of Observational Studies in Epidemiology Statement

In 2004, the first meeting of the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) group took place in Bristol, UK. 24 The aim of the group was to establish guidelines on reporting observational research to improve the transparency of the methods, thereby facilitating the critical appraisal of a study's findings. A well-designed but poorly reported study is disadvantaged in contributing to the literature because the results and generalizability of the findings may be difficult to assess. Thus a 22-item checklist was generated to enhance the reporting of observational studies across disciplines. 25 , 26 This checklist is also located at the following website: www.strobe-statement.org . This statement is applicable to cohort studies, case-control studies, and cross-sectional studies. In fact, 18 of the checklist items are common to all three types of observational studies, and 4 items are specific to each of the 3 specific study designs. In an effort to provide specific guidance to go along with this checklist, an “explanation and elaboration” article was published for users to better appreciate each item on the checklist. 27 Plastic surgery investigators should peruse this checklist prior to designing their study and when they are writing up the report for publication. In fact, some journals now require authors to follow the STROBE Statement. A list of participating journals can be found on this website: http://www.strobe-statement.org./index.php?id=strobe-endorsement .

Due to the limitations in carrying out RCTs in surgical investigations, observational studies are becoming more popular to investigate the relationship between exposures, such as risk factors or surgical interventions, and outcomes, such as disease states or complications. Recognizing that well-designed observational studies can provide valid results is important among the plastic surgery community, so that investigators can both critically appraise and appropriately design observational studies to address important clinical research questions. The investigator planning an observational study can certainly use the STROBE statement as a tool to outline key features of a study as well as coming back to it again at the end to enhance transparency in methodology reporting.

Acknowledgments

Supported in part by a Midcareer Investigator Award in Patient-Oriented Research (K24 AR053120) from the National Institute of Arthritis and Musculoskeletal and Skin Diseases (to Dr. Kevin C. Chung).

None of the authors has a financial interest in any of the products, devices, or drugs mentioned in this manuscript.

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Peer observation

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The use of the resources on this page is optional. They can be a useful reference point for future planning and improvement if appropriate to the needs of the school.

About peer observation

Peer observation is about teachers observing each others’ practice and learning from one another. It aims to support the sharing of best practice and build awareness about the impact of your own teaching.

​Effective peer observation (including feedback and reflection):

• focuses on teachers' individual needs and gives an opportunity to learn from, and give feedback to peers      
• is a core component of creating a professional community and building collective efficacy
• can help teachers continue to improve their practice in ways that better promote student learning
• is a developmental learning opportunity.

For principals and school leaders: Integrating peer observation within existing structures, such as your school strategic plan, will facilitate a greater line of sight between personal and collective improvement goals.

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• give quality feedback to colleagues
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Chelsea Heights Primary School

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Roxburgh College

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Verney Road School

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• Open access
• Published: 10 April 2024

Bronchiectasis-associated infections and outcomes in a large, geographically diverse electronic health record cohort in the United States

• Samantha G Dean 1 ,
• Rebekah A Blakney 1 ,
• Emily E Ricotta 1 ,
• James D Chalmers 2 ,
• Sameer S Kadri 3 ,
• Kenneth N Olivier 4 , 5 &
• D Rebecca Prevots 1  

BMC Pulmonary Medicine volume  24 , Article number:  172 ( 2024 ) Cite this article

Metrics details

Bronchiectasis is a pulmonary disease characterized by irreversible dilation of the bronchi and recurring respiratory infections. Few studies have described the microbiology and prevalence of infections in large patient populations outside of specialized tertiary care centers.

We used the Cerner HealthFacts Electronic Health Record database to characterize the nature, burden, and frequency of pulmonary infections among persons with bronchiectasis. Chronic infections were defined based on organism-specific guidelines.

We identified 7,749 patients who met our incident bronchiectasis case definition. In this study population, the organisms with the highest rates of isolate prevalence were Pseudomonas aeruginosa with 937 (12%) individuals, Staphylococcus aureus with 502 (6%), Mycobacterium avium complex (MAC) with 336 (4%), and Aspergillus sp. with 288 (4%). Among persons with at least one isolate of each respective pathogen, 219 (23%) met criteria for chronic P. aeruginosa colonization, 74 (15%) met criteria for S. aureus chronic colonization, 101 (30%) met criteria for MAC chronic infection, and 50 (17%) met criteria for Aspergillus sp. chronic infection. Of 5,795 persons with at least two years of observation, 1,860 (32%) had a bronchiectasis exacerbation and 3,462 (60%) were hospitalized within two years of bronchiectasis diagnoses. Among patients with chronic respiratory infections, the two-year occurrence of exacerbations was 53% and for hospitalizations was 82%.

Conclusions

Patients with bronchiectasis experiencing chronic respiratory infections have high rates of hospitalization.

Peer Review reports

Bronchiectasis is a pulmonary disease defined by the irreversible dilation of the bronchi [ 1 , 2 ]. Patients typically have a chronic, productive cough and recurring respiratory infections [ 1 ], with an associated increased risk of mortality [ 3 ]. The current estimated prevalence of bronchiectasis in the United States is up to 213 cases per 100,000 [ 4 ] across all age groups, and 700 per 100,000 among adults aged > 65 years [ 5 ]. Bronchiectasis has multiple causes including infectious, inflammatory, autoimmune, allergic, and congenital disorders [ 6 , 7 ]. Recurrent respiratory infections are common and result from impaired mucociliary clearance [ 8 ]. These infections trigger inflammation, which in turn worsens underlying damage. Consequently, this vicious cycle leads to increased frequency of exacerbations [ 1 , 8 , 9 ].

Although certain organisms such as Pseudomonas aeruginosa and Staphylococcus aureus have been associated with exacerbations of bronchiectasis [ 10 ], systematic evaluations of bronchiectasis-associated infections in large community and non-tertiary referral populations are lacking. Understanding the etiology and impact of bronchiectasis has implications for effectively treating patients and managing disease [ 11 ]. Ongoing cohort studies are expanding our knowledge about the landscape of infections among bronchiectasis patients. In the United States (US), data collected through the US Bronchiectasis Research Registry (BRR) describe infections and treatment among bronchiectasis patients [ 12 ]. The European Multicentre Bronchiectasis Audit and Research Collaboration (EMBARC) registry in Europe has recruited more than 20,000 patients as of September 2020 and will provide further insight regarding infections in bronchiectasis patients [ 13 , 14 ]. However, the US BRR and the EMBARC registry are both based primarily in specialist bronchiectasis clinics and therefore may be biased towards more severe manifestations of the disease. In this study we use a large, nationally distributed Electronic Health Record (EHR) dataset, including microbiological data, to describe bronchiectasis-associated infections and selected outcomes.

Study population

Our study population comprised patients in the Cerner HealthFact s Electronic Health Record (EHR) database with at least two International Classification of Diseases 9th or 10th revision (ICD9/10) codes for bronchiectasis from 2009 to 2017 (Fig.  1 ), with no ICD9/10 codes for cystic fibrosis, and where all encounters were in inpatient or outpatient healthcare facilities reporting microbiology data. Facility characteristics are described in Table  1 . We considered bronchiectasis cases to be incident if no prior encounters included a bronchiectasis ICD9/10 code for the two years preceding the first bronchiectasis ICD9/10 code (Fig.  1 ). We included microbiology isolates from only respiratory sites and subset to the most common species isolated, after removing non-pathogenic species and non-speciated results (Table  2 ). We used text searches for chronic obstructive pulmonary disease (COPD), asthma, and lung cancer to identify ICD codes for these conditions. We defined time under observation as the duration of time between the incident bronchiectasis encounter and the end of the study period.

Study population flowchart. a ICD9/10 codes: 494.0, 494.1, 494, 011.50, 011.54, 748.6, 011.51, 011.53, 011.52, 011.55, 011.5, 011.56, J47, J47.9, J47.1, J47.0, Q33.4

Data analysis

To estimate the prevalence of organisms associated with bronchiectasis [ 12 ], we summed the number of persons in our population with at least one isolate of the selected organisms on or after the date of their first bronchiectasis diagnosis. Whether frequent detection of an organism is considered “infection” or “colonization” varies by organism, thus we also assessed the prevalence using organism-specific definitions of chronic infection or chronic colonization from the literature and expert opinion. For Mycobacterium avium complex (MAC) and M. abscessus , we defined chronic infection as two or more isolates on separate days within two years of one another [ 15 ]. For Aspergillus sp [ 16 ]. and Stenotrophomas maltophilia [ 17 ] we defined chronic infection as two or more isolates on separate days within one year of one another. For Pseudomonas aeruginosa , we used the definition of chronic colonization established by international consensus and also used in the bronchiectasis severity index (BSI), which counts the number of individuals who had at least two isolates of P. aeruginosa three or more months apart within a year [ 18 , 19 ]. For the remaining species where a more specific definition was not available, we continued to use the EMBARC/BRR chronic colonization definition (Table  2 ). For calculations of the prevalence of at least one isolate of the specified organism the population denominator was the 7,749 persons who met our case definition for incident bronchiectasis. For purposes of clarity, for the remainder of this paper we will refer to the organism-specific definitions of chronic colonization and chronic infection as “chronic infection.” For calculations of chronic infection prevalence, the population denominator was all persons with at least one isolate of the specified organism.

To describe the impact of chronic infections on clinical outcomes, we evaluated hospitalizations and exacerbations among patients with chronic infection for the most common organisms. For all analyses of chronic infection, we included the 5,795 patients (75% of study population) with at least two years of follow up time after their initial bronchiectasis diagnosis. Hospitalizations were defined as any inpatient encounter. Exacerbations were defined as one or more ICD9/10 codes for bronchiectasis with acute exacerbation or acute respiratory infection, COPD with acute exacerbation, or asthma with acute exacerbation. Codes for asthma and COPD were included to increase the sensitivity of capturing exacerbations. We included a thirty day “window” prior to the incident bronchiectasis diagnosis encounter to include hospitalizations and exacerbations that may have contributed to the identification of bronchiectasis. Rates of hospitalization and exacerbations were calculated for the duration of the study period following the incident bronchiectasis encounter. In addition, because MAC and P. aeruginosa are of particular concern among persons with bronchiectasis, we calculated the total time hospitalized using the cumulative time across inpatient encounters. Analysis was completed using R version 3.6.1. We assessed the significance of the difference in proportions of exacerbations and hospitalizations among chronic infection subgroups using two-proportion z-tests with a one-sided alternative and significance assessed at p  < 0.05. Relative risks of exacerbations and hospitalizations comparing chronic infection vs. no infection were estimated using a univariate negative binomial regression.

We identified 7,749 persons with incident bronchiectasis, which comprised our study population (Fig.  1 ). Of these, 5,050 (65%) were women and 5,030 (65%) were aged ≥ 65 years. Concurrent pulmonary disease was common: 3,848 (50%) were diagnosed with COPD, 2,741 (35%) with asthma, and 537 (7%) with lung cancer (Table  3 ). Overall, persons sought care at 260 unique healthcare facilities, and 65% had all encounters at a single facility within the EHR system during the study period. An additional 24% received care at two facilities.

Prevalence of infecting pathogens

Of the 7,749 persons in our study population, 4,369 (56%) had at least one pulmonary sample taken for microbiology analysis over an average observation time of 3.6 years per person. Among patients with at least one pulmonary culture, the median number of samples per person was 4 (IQR 2–7): 890 (20%) had one culture, 1597 (37%) had 2–4, 807 (19%) had 5–7, and 1075 (25%) had more than 7. The most commonly identified organisms were P. aeruginosa with 937 (12%) individuals, S. aureus with 502 (6%), MAC with 336 (4%), and Aspergillus sp. with 288 (4%). Of persons with at least one isolate of each respective pathogen, those who met definitions for chronic infection were as follows: 219 (23%) for P. aeruginosa colonization, 74 (15%) for S. aureus , 101 (30%) for MAC, and 50 (17%) for Aspergillus sp. (Fig.  2 ).

Prevalence of organism isolation and chronic infection for commonly isolated pathogens following incident bronchiectasis diagnosis. See Table  2 for organism-specific definitions of chronic colonization/chronic infection

Infections and clinical outcomes

Of the 5,795 patients with two years of follow up, 1,521 (26%) had an exacerbation within one year and cumulatively, 1,861 (32%) had an exacerbation within two years following the incident bronchiectasis diagnosis (Table  4 ). Hospitalizations were common, with 3,016 (52%) hospitalized within one year and 3,462 (60%) hospitalized within two cumulative years. A total of 3,954 (68%) patients were hospitalized at any point in the study period after the incident bronchiectasis diagnosis, with a rate of 0.6 hospitalizations per person-year. Among these patients, 920 (23%) had an inpatient encounter including an intensive care unit admission and the 30-day readmission rate was 0.1 per person-year. Inpatient discharge disposition was coded as expired or discharged to hospice for 706 (18%) patients during the study period after the incident bronchiectasis diagnosis.

The 139 patients with chronic P. aeruginosa infection experienced significantly more severe clinical outcomes than patients with chronic MAC infection or no chronic infections, with 69 (50%) experiencing exacerbations within one year, compared with 15 (27%) for chronic MAC ( p  < 0.0029) and 89 (64%) experiencing exacerbations within two years compared with 21 (38%) for chronic MAC ( p  < 00064) (Table  4 ). Patients with chronic P. aeruginosa infection also experienced hospitalization more frequently: 113 (81%) patients were hospitalized within one year, compared with 30 (54%) for MAC ( p  = 0.000078) and 121 (87%) were hospitalized within two years, compared with 64% for MAC ( p  < 0.0029). The rates of exacerbations and hospitalizations during the study period were 0.9 and 1.4 per person-year, respectively. The median total duration of hospitalization following incident bronchiectasis diagnosis was longer in the group with P. aeruginosa (median 32.6 days, IQR 14.3–61.6) than in the group with MAC (median 10.9 days, IQR 5.3–18) or among patients not chronically infected with any organism of interest (median 11.7 days, IQR 4.8–24.1). Overall, relative to those with no chronic infection,, those with chronic infection with any of the organisms were at a significant 70% increased risk of exacerbations at one and two years of follow-up, and at a significant 40% (one year) to 50% (two years) increased risk of hospitalizations relative to those with no chronic infections (Table  4 ).

Our study characterized pulmonary infections in a large cohort of patients with bronchiectasis identified through an electronic healthcare record database. Existing estimates of infections and chronic infections among persons with bronchiectasis are based primarily on studies or registries from tertiary care centers with more intensive follow-up, notably the Bronchiectasis Research Registry (BRR) in the US [ 12 ] and the European Bronchiectasis Registry (EMBARC). We found that among patients with two years of follow-up, 32% had exacerbations and 60% were hospitalized. Our estimates are similar to a study of bronchiectasis among Medicare patients, which found that 41% of patients had at least one inpatient hospital admission in the 12 months prior to their bronchiectasis diagnosis [ 5 ]. Thus, our finding is consistent with another large, population-based sample, particularly given that worsening disease may prompt patients to seek healthcare. Further, a study of a prospective cohort of bronchiectasis with four years of follow up found that 82% of patients with P. aeruginosa had a hospitalization related to a severe exacerbation during the study period [ 18 ]. This aligns with our finding that 87% of P. aeruginosa patients were hospitalized within two years. The high rate of hospitalization following incident bronchiectasis suggests that disease is already somewhat severe by the time of diagnosis. Earlier screening and identification could provide the opportunity for interventions to limit disease progression.

Among incident bronchiectasis cases, the most commonly identified pathogens were P. aeruginosa , MAC, S. aureus, Aspergillus species. However, the prevalence of infections and chronic infections is likely an underestimate, given that only 56% of patients had any pulmonary sample associated with any encounter over the 9-year study period, with a median of 7 months between diagnosis and first isolate, and only 48% of patients with 2 or more years of observation had more than one isolate. This highlights the need for improved and more systematic evaluation of persons with bronchiectasis, including collection of samples for microbiological analysis.

Eradication therapy for P. aeruginosa is recommended to reduce the frequency of poor clinical outcomes such as exacerbation, hospitalization, and mortality, with long-term inhaled antibiotics recommended [ 20 ]. Patients with P. aeruginosa with frequent exacerbations have worse clinical outcomes, particularly mortality, versus patients with P. aeruginosa and without frequent exacerbations. Questions remain regarding how much exacerbations mediate the morbidity and mortality of patients with P. aeruginosa and if treatment strategies should vary among patients with P. aeruginosa and frequent exacerbation versus those chronically infected but not experiencing frequent exacerbations [ 21 ]. The high rate of hospitalization with P. aeruginosa may reflect the severity of the infection, the severity of the underlying lung disease or the fact that P. aeruginosa is inherently resistant to most oral drugs and therefore intravenous therapy is often required at exacerbation.

Although our dataset represents a large, nationally distributed population, our findings are still subject to limitations inherent in this EHR system. First, because our data are limited to hospitals using the Cerner HealthFacts system, we do not have a closed population with regular follow-up. Persons categorized as incident cases of bronchiectasis in our dataset may have an earlier diagnosis in a hospital not represented in this system. The lack of regular follow up also limits our ability to ascertain the sequence of bronchiectasis disease and infection onset. Rather than receiving medical care as disease or infections arise, individuals may have multiple health problems identified at a single, irregular visit. This approach could be an underestimate because we may not have identified persons who had bronchiectasis but were not coded as such, persons who sought care at a facility outside of the Cerner system, or healthcare encounters unrelated to bronchiectasis with no associated bronchiectasis ICD9/10 code. In addition, bronchiectasis ICD9/10 codes have unknown sensitivity and specificity, but are unlikely to identify all true bronchiectasis cases, and could possibly identify more severe cases (given the rarity of this condition relative to other more common pulmonary diagnoses like COPD). Given the small sample size of persons with chronic infections, we could not assess the impact of bacterial coinfections for some pathogens (e.g. Aspergillus). Finally, persons with CF but without an ICD code may have been included in our dataset, with some potential different distribution of organisms; we are unable to evaluate this potential for misclassification in our current dataset. Despite these limitations, the large sample size and the comparability of our findings to other population-based studies speaks to the robust nature of these estimates of infection prevalence. Additionally, our study contributes findings regarding bronchiectasis patients receiving standard clinical care, which is likely more generalizable to all bronchiectasis patients than findings from those patients referred to tertiary care facilities.

We found a high prevalence of infections and severe outcomes in a nationally distributed population of persons with bronchiectasis, who are likely more representative of all persons with bronchiectasis compared with those enrolled in specialized registries at tertiary care centers. These findings speaks to the need for continued monitoring of lung infections among all persons with bronchiectasis.

Data availability

The data that support the findings of this study are available from The Cerner Health Facts, whose dataset was leased by the authors following a Data Use Agreement with the Cerner corporation and as such are not publicly available based on the legal terms of the Data Use Agreement. Interested persons maybe contact the company at the following link: https://www.cerner.com/ap/en/solutions/data-research .

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Acknowledgements

This work was supported in part by the National Institute of Allergy and Infectious Disease and National Heart, Lung, and Blood Institute Intramural Research Programs, and by the Clinical Center, National Institutes of Health.

No outside funds were obtained for this work, which was supported in part by the intramural programs of the National Institute of Allergy and Infectious Disease, National Heart, Lung, and Blood Institute, and the Clinical Center, National Institutes of Health.

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Samantha G Dean, Rebekah A Blakney, Emily E Ricotta & D Rebecca Prevots

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Study conception: DRP. Data acquisition: DRP, ER, SD, SK. Study design and data analysis: DRP, SD, RB, ER, KO, JC. All authors contributed to data interpretation, manuscript drafting and revision for important intellectual content. All authors approve of the final submitted manuscript version and agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

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Dean, S.G., Blakney, R.A., Ricotta, E.E. et al. Bronchiectasis-associated infections and outcomes in a large, geographically diverse electronic health record cohort in the United States. BMC Pulm Med 24 , 172 (2024). https://doi.org/10.1186/s12890-024-02973-3

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Slow magnetic relaxation in a europium(II) complex

• Dylan Errulat 1   na1 ,
• Katie L. M. Harriman 1   na1 ,
• Diogo A. Gálico   ORCID: orcid.org/0000-0003-3722-2996 1 ,
• Elvin V. Salerno 2 ,
• Johan van Tol   ORCID: orcid.org/0000-0001-6972-2149 2 ,
• Akseli Mansikkamäki   ORCID: orcid.org/0000-0003-0401-4373 3 ,
• Mathieu Rouzières   ORCID: orcid.org/0000-0003-3457-3133 4 ,
• Stephen Hill   ORCID: orcid.org/0000-0001-6742-3620 2 , 5 ,
• Rodolphe Clérac   ORCID: orcid.org/0000-0001-5429-7418 4 &
• Muralee Murugesu   ORCID: orcid.org/0000-0002-5123-374X 1  

Nature Communications volume  15 , Article number:  3010 ( 2024 ) Cite this article

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• Inorganic chemistry
• Magnetic materials

Single-ion anisotropy is vital for the observation of Single-Molecule Magnet (SMM) properties (i.e., a slow dynamics of the magnetization) in lanthanide-based systems. In the case of europium, the occurrence of this phenomenon has been inhibited by the spin and orbital quantum numbers that give way to J  = 0 in the trivalent state and the half-filled population of the 4f orbitals in the divalent state. Herein, by optimizing the local crystal field of a quasi-linear bis(silylamido) Eu II complex, the [Eu II (N{SiMePh 2 } 2 ) 2 ] SMM is described, providing an example of a europium complex exhibiting slow relaxation of its magnetization. This behavior is dominated by a thermally activated (Orbach-like) mechanism, with an effective energy barrier of approximately 8 K, determined by bulk magnetometry and electron paramagnetic resonance. Ab initio calculations confirm second-order spin-orbit coupling effects lead to non-negligible axial magnetic anisotropy, splitting the ground state multiplet into four Kramers doublets, thereby allowing for the observation of an Orbach-like relaxation at low temperatures.

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Introduction

Single-molecule magnets (SMMs) have garnered much attention owing to their potential application in molecular-level memory storage devices as well as for quantum information technologies 1 , 2 , 3 , 4 . These SMM properties arise from an intrinsic energy barrier to the reorientation of the magnetic moment. The strong unquenched orbital contribution of the core 4f-orbitals leads to large inherent magnetic anisotropy in many of the lanthanide series, and the half-integer angular momentum projection of ions such as Dy III ( 6 H 15/2 ) ensures a doubly degenerate ground state, as dictated by Kramers theorem 5 . Recently, the use of lanthanide (Ln) ions in the design of SMMs has led to significant breakthroughs in performance and operation temperatures beyond that of liquid nitrogen ( T  = 77 K) 6 , 7 , 8 , 9 . These remarkable improvements are largely thanks to the exceptional synthetic control of the crystal field splitting and axiality (i.e., ligand design and coordination geometry) 10 .

Beyond the crystal field, the inherent magnetic moment of the metal center is an important consideration, as a greater magnitude of J can reduce ground-state quantum tunneling of the magnetization (QTM) between degenerate states and lead to overall improvements in the coercivity and blocking temperature 11 , 12 . However, altering the effective magnetic moment of a given 4f ion is challenging as the trivalent oxidation state is the most stable for Ln ions 13 . New discoveries in synthetic 4f chemistry have resulted in the expansion of accessible oxidation states 14 , 15 . These discoveries have led to record magnetic moments for the divalent complexes [(Cp’) 3 Ln II ] - (Cp’ = trimethylsilylcyclopentadienyl, Ln = Dy II , Ho II ), originating from the 4f n 5d 1 configuration 16 . Despite this attractive feature, [(Cp’) 3 Ln II ] - do not display slow magnetization dynamics. Nevertheless, ab initio calculations have recently demonstrated that divalent complexes have the potential to possess very strong magnetic anisotropy and very large magnetization blocking barriers (∆ /k B  > 3000 K) when the geometry around the metal ion is highly symmetric and/or low coordinate 17 . As an illustration, the divalent metallocene [Tb II (Cp i Pr5 ) 2 ] (Cp i Pr5 = pentaisopropylcyclopentadienyl, Ln = Tb II ) possesses an impressive barrier of 1738 K (1205 cm –1 ) and a blocking temperature of 52 K 18 . Ultimately, a clear trend has yet to be established for the effects of oxidation states on the splitting of the ground and excited states, as well as variations in metal-ligand covalency 19 , 20 .

The spin contribution to the magnetic moment is the highest in the case of a half-filled 4f-shell (4f 7 ), such as Gd III . However, this electronic configuration is largely considered to be magnetically isotropic as a result of the spherically symmetric charge density of the 8 S 7/2 ground state that lacks orbital angular momentum ( S  = 7/2, L  = 0). Nonetheless, some Gd III complexes displaying slow magnetization relaxation have been documented 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 . Combined with the inclusion of the isoelectronic Tb IV , the 4f 7 valence series (Eu II , Gd III , and Tb IV ) provides unique insight into the minutia that govern the electronic properties of lanthanides beyond the trivalent oxidation state, serving as an excellent model to examine the precise effects of the coordination environment on the electronic structures of Ln ions with uncommon oxidation states. However, until now, the magnetic studies of Eu-based complexes have been limited to their static susceptibility properties. In order to expand the prevalence of elements displaying slow magnetization relaxation, we present herein the quasi-linear complex, [Eu II {N(SiMePh 2 ) 2 } 2 ] ( 1 ), which is to the best of our knowledge, the first example of a europium SMM.

Results and discussions

Synthesis and structural analysis.

Compound 1 was prepared by the reaction of one equivalent of EuI 2 with two equivalents of K(THF)N(SiMePh 2 ) 2 in THF, in accordance with the previously reported procedure for [Yb II {N(SiMePh 2 ) 2 } 2 ] (Fig.  1a ) 36 . Crystallization from an n- hexane solution gave [Eu II {N(SiMePh 2 ) 2 } 2 ] ( 1 ) as orange crystals in ~68% yield.

a Reaction scheme for the synthesis of 1 . b ORTEP molecular model with 50% thermal probability ellipsoids. H-atoms have been omitted for clarity. Orange, europium; teal, silicon; blue, nitrogen; gray, carbon. The solid orange line represents the orientation of the principal anisotropy axis of the zero-field split 8 S 7/2 multiplet.

Single-crystal X-ray diffraction reveals 1 crystallizes in the monoclinic P 2 1 /c space group (Supplementary Table  1 ). The complex has a near-linear geometry with an N–Eu–N angle of 169.808(83)° and metal-nitrogen distances of 2.4884(26) Å and 2.4612(26) Å, comparable to the Yb II analog 36 . The slightly longer bond lengths in 1 compared to the Yb II analogue is consistent with the increased ionic radius of the Eu II ion. Two phenyl moieties from each – N(SiMePh 2 ) 2 ligand act to encapsulate the metal ion with Eu•••C interactions between 2.93 and 3.04 Å, preventing any further aggregation or interactions with solvent molecules. The individual complexes are well separated in the lattice by a distance of 10.64 Å (Supplementary Fig.  1 ).

Photoluminescence spectroscopy

The excitation spectrum of 1 obtained at 10 K (Supplementary Fig.  2 ) reveals a broad signal in the UV range at 270 nm due to the ligand and Eu II 5d centered absorptions. A single component centred at 518 nm (19,305 cm −1 ) is observed in the emission spectrum (Supplementary Fig.  3a ), characteristic of Eu II 5d → 4f transitions. A blue shift of the transition is observed at 293 K, with the center being shifted to 496 nm (20,161 cm −1 ). At room temperature, the emitter level lifetime is 2.45 µs (Supplementary Fig.  4 ). It is noteworthy that vibrational components are observable at room temperature, suggesting strong vibronic coupling. Deconvolution of the emission band results in seven different components equally separated (~1550 cm −1 ), suggesting possible vibronic coupling between the excited 5d state and the vibration located at 1561 cm −1 in the FT-IR (Supplementary Fig.  3b ). Attempts to oxidize the divalent complex 1 using silver salts, particularly AgAl{OC(CF 3 ) 3 } 4 , resulted in the formation of a silver mirror (Ag I → Ag 0 ) and strong red emission visible to the naked eye when excited under a 405 nm UV laser. At first glance, this result might suggest the successful oxidation of 1 to the trivalent oxidation state with the characteristic red emission of Eu III . While single crystals of the oxidized product could not be isolated, the excitation spectrum of the obtained crude oil was collected in C 6 H 5 F (Supplementary Fig.  5 ). The characteristic broad emission of the Eu II 5d → 4f transitions was observed with the band red-shifted to 756 nm (13,227 cm −1 ). This drastic red shift indicates a significant change in the metal’s coordination environment, suggesting that a ligand-centred oxidation is taking place in the presence of Ag I . As the Eu II/III redox potential (−0.35 V vs . SCE) is the most positive of the lanthanides, the divalent oxidation state is particularly stable 37 . In fact, the reaction of K(THF)N(SiPh 2 Me) 2 with AgAl{OC(CF 3 ) 3 } 4 in the absence of oxidizable Eu II still resulted qualitatively in the formation of Ag 0 and an intractable product whose structure could not be determined. This echoes several of the challenges observed in previous reports by Mills and co-workers when attempting to oxidize bis(silylamido) Eu II complexes, where the bis(silylamide) ligands undergo non-reversible oxidation in place of the metal center 38 , 39 .

Computational studies

The electronic structure of 1 was studied by computational methods (see Methods section), confirming a ground electronic configuration of 4f 7 , which would be expected to give rise to an isotropic 8 S 7/2 multiplet 40 . However, linear coordination geometries have recently been shown to stabilize states with multiple open shell configurations in coordination complexes of divalent lanthanide ions 18 . Therefore, this possibility was also considered for 1 . At the hybrid DFT level using the PBE0 exchange-correlation functional, all seven unpaired electrons are found to reside in orbitals with more than 88% 4f character. Furthermore, ab initio multireference calculations were performed 41 , 42 , demonstrating that the 8 S 7/2 ground spin multiplet is weakly split under second-order spin-orbit coupling (SOC) effects into four Kramers doublets spanning an energy range of 3–4 cm –1 (4–6 K). The calculated g tensor of the 8 S 7/2 multiplet is almost isotropic with principal values of 1.9975, which only differ in the fifth decimal. The second-order zero-field splitting (ZFS) parameters are calculated to be D / k B  = –0.40 K and E / k B  = +0.008 K, indicating the presence of axial anisotropy. The higher-order ZFS parameters are negligible. The principal axis of the ZFS tensor is oriented along the molecular N–Eu–N pseudo axis (Fig.  1b ), implying that 1 possesses non-negligible magnetic axiality, owing to the quasi linear environment provided by the bis(silylamide) ligands. It can therefore be anticipated that the ZFS will result in slow relaxation of magnetization via an Orbach-like mechanism at low temperatures.

High-field EPR measurements

Due to the inferred magnetic anisotropy of 1 , temperature-dependent continuous-wave (CW) high-field electron paramagnetic resonance (EPR) measurements were performed on an unconstrained polycrystalline sample, at frequencies of 128 and 256 GHz (Fig.  2 ) 43 , 44 . Seven dominant resonances are observed in the spectra recorded at each frequency, corresponding to the 2 S allowed EPR (Δ m S  = ±1) transitions within the eight (= 2 S  + 1) spin projection states associated with the S  = 7/2 Eu II ion (Fig.  2 ); note that weakly allowed Δ m S  = ±2 transitions are also observed in the half-field region of the spectrum (Fig.  2 , inset). Excellent spectral simulations are obtained with the following ZFS parameters: g z  = 1.998(5), D / k B  = −0.659(4) K ( D/hc  = −0.458(3) cm −1 ), in good agreement with the above calculations and the magnetization data discussed below. In order to reproduce the observed intensity patterns, D -strain, σ D  = 0.004 cm −1 , and a peak-to-peak linewidth, σ lw  = 15 mT, were included in the 4.5 K simulations (σ D  = 0.001 cm −1 and Δ lw  = 45 mT at 50 K). These simulations assume alignment of the crystallites within the powder sample, which is to be expected due to the magnetic torque on the anisotropic Eu II species. However, the glide plane in the unit cell of 1 gives rise to symmetry equivalent molecules that are not collinear (Supplementary Fig.  1a ). Consequently, the field aligns along the average anisotropy direction of the bulk crystals, which intersects the principal magnetic axes of the two sites 45 . The most accurate simulations were achieved when the angle ( θ ) between the applied field and the principal axes of the ZFS ( D ) tensors of the molecules in the unit cell was set to 16.6(2)°. Because of this alignment, only the axial spin Hamiltonian parameters, g z and D , could reliably be determined from the simulations. Due to the reactivity of 1 , several attempts to constrain the sample to prevent torquing proved unsuccessful. As such, the bulk crystals were left unconstrained in order to avoid potential decomposition.

Unconstrained powder sample recorded in derivative mode (d I /d H , where I is the microwave intensity transmitted through the sample and H the applied field) at 4.5 K & 128 GHz (top), 50 K & 128 GHz (second from top), 4.5 K & 256 GHz (second from bottom), and 50 K & 256 GHz (bottom). In addition, the optimal simulations (depicted in red) are presented, generated following the procedure outlined in the main text. The spectra are offset for clarity. The inset shows an expanded view of the low-field region of the 256 GHz, 50 K spectrum, highlighting weakly allowed Δ m S  = ±2 transitions that are also captured by the simulations. Source data are provided as a Source Data file.

The obtained D parameter gives a magnetization reversal barrier, ∆ EPR / k B  = ( S 2 – 1 / 4 ) ∣ D ∣ / k B  = 7.9 K, which is in almost perfect agreement with the value determined from the ac susceptibility studies discussed below (∆ ac / k B  = 8.2 K, vide infra). Finally, we note that the simulated peak positions enable an unambiguous determination of the magnitude of D . However, in order to determine its sign, one must compare temperature-dependent spectra. As can be seen from the spectra in Fig.  2 , spectral weight shifts from high- to low-field upon cooling, which is fully consistent with a negative D parameter 46 .

Magnetic measurements

To probe the magnetic properties, direct current (dc) magnetic susceptibility measurements were performed on 1 . At room temperature, a χT product of 7.8 cm 3 K mol −1 is observed (Supplementary Fig.  6 ), which is in good agreement with the S  = 7/2 ground state expected for an isolated Eu II ion with a 4f 7 ground state configuration (7.875 cm 3 K mol −1 ). The χT product remains constant down to 50 K, whereafter it decreases slightly to reach 6.3 cm 3 K mol −1 at 1.85 K and 1000 Oe. This low-temperature behavior is likely the result of ZFS, as predicted by the computational results and confirmed by EPR (vide supra), and has been observed in related linear Eu II complexes 47 . Magnetization as a function of applied magnetic field (between 0 and 70 kOe; Supplementary Fig.  7 ) in the temperature range of 1.85–8 K exhibits a high-field linear variation and non-complete saturation at 70 kOe, indicative of magnetic anisotropy. A near saturation close to 7.0 μ B at 1.85 K and 70 kOe is in good agreement with the S  = 7/2 ground state. Non-superposition of the isothermal lines of the reduced magnetization plot (Supplementary Fig.  7 ) further suggests the presence of non-negligible ZFS. An attempt was made to fit the experimental M vs. H/T and χT vs. T data to the simplest S  = 7/2 model with the \(\widehat{H}=D \hat{S}_{T,z}^{2}\) Hamiltonian (Supplementary Fig.  8 ). The experimental data are qualitatively reproduced with D / k B  = −0.58(5) K ( D / hc  = −0.40(7) cm −1 ), in agreement with EPR data and computational results.

Alternating current (ac) susceptibility measurements were performed on 1 . In the absence of an applied magnetic field, the ac susceptibility does not exhibit any sign of slow relaxation of the magnetization down to 1.9 K and up to 10 kHz. Upon application of a static dc field, a clear signal in the out-of-phase component is observed, indicating the presence of slow paramagnetic relaxation. (Supplementary Fig.  9 ). The frequency dependence of the ac susceptibly data measured at different magnetic fields up to 10 kOe was fitted to the generalized Debye model (Supplementary Eqs. 1 and 2; Supplementary Figs.  9 and 10 ) from which the relaxation times ( τ ) were extracted (Supplementary Fig.  11 ) 48 . To elucidate the contribution of the individual relaxation mechanisms on the spin dynamics of 1 , the relaxation times were fit to the sum of individual QTM ( B 1 , B 2 ), Direct ( A ), Raman ( C , C 1, C 2), and Orbach-like ( τ 0 , ∆) relaxation mechanisms. These pathways are the most frequently used in the phenomenological models used to describe the relaxation dynamics of SMMs, which is expressed by the rate equations (Eqs. 1 and 2 ) 49 , 50 , 51 :

At fields below 1 kOe, the relaxation time increases with an \({H}^{2}\) dependence (Supplementary Fig.  11 ), which is consistent with the field dependence of a QTM process described by the first term in Eq. ( 2 ). Fitting of the experimental τ between 0 and 800 Oe leads to the following parameters: B 1  = 1.8(1) 10 4  s −1 and B 2  = 22.8(2.3) kOe −2 (Supplementary Fig.  11 ). At higher fields, the variation does not follow an \({H}^{-4}\) dependence that would indicate a Direct process, nor an \({H}^{-2}\) field-dependence characteristic of Raman relaxation. Indeed, this field variation of the relaxation time is modest, suggesting the presence of a thermally activated (Orbach-like) relaxation process (last term in Eq. ( 2 )). To elucidate the relaxation dynamics of 1 , ac magnetic susceptibility as a function of temperature was measured under an applied dc field 800 Oe (Fig.  3 and Supplementary Fig.  12 ), for which the relaxation time is the longest and the effects of ground state QTM are minimized.

a Frequency dependence of the in-phase (χ ′ ) ac magnetic susceptibility in the range of 1.9 K – 8 K, collected at a constant applied field of 800 Oe. b Frequency dependence of the out-of-phase ( χ “) ac magnetic susceptibility from 1.9 K–8 K, collected at a constant applied field of 800 Oe. The solid lines represent the fit to the generalized Debye model at each temperature. (Inset) The average τ as a function of inverse temperature at 800 Oe, fitted from 1.9 K to 5 K. The estimated standard deviation (ESD) of the relaxation times are represented as vertical solid bars calculated from the α -parameters of the generalized Debye fits and the log-normal distributions 87 . The blue line represents the best fit ( R 2  = 0.9998) to a model considering both thermally activated (Orbach-like) and QTM relaxation processes (Eqs. 1 and 2). Source data are provided as a Source Data file.

The obtained temperature dependence of τ can be modeled between 1.9 and 5 K considering a thermally activated (Orbach-like) relaxation process with an energy gap of 8.2(5) K (or 5.7(3) cm −1 ; τ 0  = 3.1(6) 10 −6  s; Supplementary Figs.  13 – 15 ) and a contribution from a QTM relaxation process ( B 1 and B 2 being fixed to the values obtained from the fit of the field dependence). This result indicates unambiguously that the thermally activated relaxation is dominant in this temperature region, which agrees with the analysis of the field dependence of the relaxation. Nonetheless, two factors suggest the presence of additional relaxation mechanisms: (i) the obtained pre-exponential factor ( τ 0 ) of 3.1(6) 10 −6  s is larger than expected for an Orbach-like relaxation regime; and (ii) the field dependence of the relaxation time above 1 kOe is complex and could not be reproduced by fitting to Eq. ( 2 ). Attempts to fit the experimental data with relaxation models including Raman and direct processes lead to overparameterization and did not improve the theory-experiment agreement above 0.1 T (Supplementary Fig.  15 ).

The Eu II complex presented herein exhibits slow relaxation of the magnetization, expanding the elements of the 4f 7 valence series capable of behaving as an SMM beyond Gd III . This divalent complex belongs to a rare and synthetically challenging class of low-coordinate SMMs that continues to attract interest. An Orbach-like mechanism dominates the relaxation dynamics of 1 , with a relaxation barrier of 8.2 K. The highly axial coordination environment, combined with second order spin-orbit coupling, gives rise to a weak axial ZFS interaction that provides the origin of the paramagnetic relaxation. These results underscore the significance of crystal field effects in lanthanide ions, which allows us to harness the magnet-like behavior of the Eu II ion.

General methods

All operations were performed in an M. Braun glovebox under an atmosphere of purified dinitrogen or using high vacuum standard Schlenk techniques. Solvents were dried using a J.C. Meyer solvent system, degassed with successive freeze-pump-thaw cycles, and stored over activated 4 Å molecular sieves prior to use. EuI 2 was purchased from Sigma Aldrich in anhydrous form at ≥ 99.9% purity. Celite used for filtration was dried under vacuum while heating to 180 °C for 5 days. [K{N(SiMePh 2 ) 2 }THF] n was prepared according to literature procedure 52 . [Eu{N(SiMePh 2 ) 2 } 2 ] ( 1 ) was prepared based on our previously published synthetic procedure 36 . A brief description of the synthesis is detailed below. FT-IR spectra were recorded on a Nicolet Nexus 550 FT-IR spectrometer using transmission mode in the 4000-600 cm −1 range; solid samples were prepared in an inert atmosphere and sandwiched between transparent NaCl plates. Elemental analyses were performed by Midwest Microlab.

Synthesis of [Eu{N(SiMePh 2 ) 2 } 2 ] (1)

A solution of [K{N(SiMePh 2 ) 2 }THF] n (128 mg, 0.246 mmol) in THF (5 mL) was added to EuI 2 (50 mg, 0.123 mmol) in 5 mL of THF. The mixture was allowed to stir for 16 h, followed by the removal of the solvent under reduced pressure. The crude solid was suspended in n-hexane, followed by filtration through Celite. The solvent was then removed under reduced pressure until incipient crystallization was observed. The product is obtained as crystalline orange blocks in 68% yield (81 mg, 0.083 mmol). CHN Anal. Calcd. for C 52 H 52 N 2 Si 4 Eu: C, 64.43; H, 5.41; N, 2.89. Found: C, 62.85; H, 5.43; N, 3.01. FT-IR (neat, cm −1 ): 487(w) 596(w), 627(w), 662(w), 703(s), 729(s), 775(s), 799(s), 852(w), 870(w), 967(m), 1031(w), 1060(w), 1110(m), 1153(w), 1183(w), 1251(w), 1298(w), 1330(w), 1423(w), 1477(w), 1561(w), 1581(w).

Crystal growth and single-crystal X-ray diffraction analysis

Crystal growth of [Eu{N(SiMePh 2 ) 2 } 2 ] was accomplished by concentration of a solution of 1 in n -hexane, from which bright orange blocks suitable for X-ray crystallographic study were obtained. X-ray diffraction data represents the most reliable datasets obtained from multiple trials. The crystal was submerged in Parabar 10312 (Paratone N) oil and mounted on a MiTeGen Microloop. The X-ray diffraction data for 1 was collected on a Bruker KAPPA APEX II single crystal diffractometer equipped with a sealed Mo tube source (λ = 0.71073 Å) APEX II CCD detector at a temperature of 200 K. The structure was solved by direct method with SHELXT 53 and refined based on F 2 with SHELLXL 54 . Hydrogen atom positions were calculated based on the geometry of related non-hydrogen atoms and treated as idealized contributions during the refinement.

Luminescence measurements

The photoluminescence data was obtained using a QuantaMaster 8075-21 spectrofluorometer (Horiba). An ozone-free PowerArc energy 75 W xenon lamp was used as the radiation source. The excitation spectra were corrected in real-time according to the lamp intensity and the optical system of the excitation monochromator using a silicon diode as a reference. The emission spectra were corrected according to the optical system of the emission monochromator and the photomultiplier response (Hamamatsu R13456 red extended PMT). Low-temperature measurements were performed with the samples mounted inside a CS202*E-DMX-1AL closed-cycle helium cryostat system (Advanced Research Systems) controlled via a LakeShore 335 temperature controller. For the emission decay curve, we excited the sample with a 275 nm LED (Thorlabs M275L4) controlled with a LED driver (Thorlabs DC2200 Driver) and collected the emission with an Andor iStar 334 ICCD camera installed in a Shamrock SR750 spectrograph. The LED was pulsed with a 20 kHz frequency (one pulse every 50 µs) and a pulse width of 2.5 µs.

CW EPR spectrometry

The sample was ground to a fine powder under inert atmosphere using a mortar and pestle. It was then placed in a polyethylene cup with a Teflon stopper, then shipped to the NHMFL in an ampoule which was sealed under inert atmosphere. Just prior to measurement, the ampoule was opened, and the sample quickly mounted in the spectrometer and cooled under a helium atmosphere. The transmission type spectrometer 43 employs a 17 T sweepable superconducting magnet. Microwave frequencies in the range 128–256 GHz were generated using a tunable phase-locked source followed by a series of frequency multipliers (Virginia Diodes Inc., Charlottesville, VA). The field-modulated EPR signal was generated using a wound copper coil and the signal detected using an InSb hot-electron bolometer (QMC Ltd., Cardiff UK). The final derivative-mode (d I /d H , where I is the microwave intensity transmitted through the sample and H is the applied magnetic field) EPR signal was demodulated using a lock-in amplifier at 50 kHz (Stanford Research Systems, Sunnyvale, CA). The temperature was regulated via a continuous flow helium cryostat in combination with an ITC 503 controller (Oxford Instruments, Oxford UK).

Magnetometry

Magnetic susceptibility measurements were performed on a Quantum Design SQUID MPMS-XL magnetometer and PPMS-9 susceptometer housed at the Centre de Recherche Paul Pascal at temperatures between 1.85 and 300 K and dc magnetic fields ranging from −7 to +7 T. The ac magnetic susceptibility measurements were performed in an oscillating ac field of 1 to 6 Oe with frequencies between 0.1 Hz and 10 kHz and various dc fields (including zero). The measurements were carried out on polycrystalline samples of [Eu{N(SiMePh 2 ) 2 } 2 ] ( 1 ) (16.9 and 9.8 mg) suspended in mineral oil (typically 10-12 mg) and introduced in a sealed double layered polyethylene/polypropylene bag (3 × 0.5 × 0.02 cm; 25.5 and 20.1 mg). The consistent and reproducible dc and ac measurements on these samples were combined into a single extended set. Prior to the experiments, the field-dependent magnetization was measured at 100 K to exclude the presence of bulk ferromagnetic impurities. In fact, common paramagnetic or diamagnetic materials should exhibit a perfectly linear dependence of the magnetization at 100 K that extrapolates to zero at zero dc field; the samples appeared to be free of any ferromagnetic impurities. The magnetic susceptibilities were corrected for the sample holder, the mineral oil, and the intrinsic diamagnetic contributions.

Computational details

The geometry of 1 was extracted from the crystal structure. The positions of hydrogen atoms were optimized using density functional theory (DFT), while the positions of heavier atoms were kept frozen to their crystal-structure coordinates. The optimization was carried out using the Amsterdam Modeling Suite (AMS) version 2020.101 55 , 56 , 57 , 58 . The pure GGA exchange-correlation functional PBE 59 , 60 was used along with Grimme’s DFT-D3 dispersion correction 61 with the Becke–Johnson damping function 62 . Scalar relativistic effects were treated using the zeroth-order regular approximation (ZORA) 63 , 64 , 65 . The default Slater-type basis sets designed for ZORA calculations were used in all DFT calculations 66 . A valence-polarized triple-ζ quality basis (TZP) was used for the Eu ion with all orbitals up to 5 p treated as a frozen core. Valence-polarized double-ζ quality basis sets were used for the remaining atoms. The 1 s electrons in C and N atoms and all electrons up to 2 p in Si were treated as frozen cores. In order to study the electron configuration, a final single-point DFT calculation was carried out on 1 using the hybrid PBE0 exchange-correlation functional and all-electron triple-ζ quality basis sets with two sets of polarization functions (TZ2P) for all atoms 67 , 68 .

The electronic structure of 1 was further studied by multireference ab initio calculations. These were conducted using the OpenMolcas code version 21.02 69 , 70 . Two state-averaged complete active space self-consistent field (SA-CASSCF) calculations were carried out 71 , 72 , 73 , 74 , 75 . The active space consisted of the seven 4f orbitals and seven 4f electrons. In the first calculation, the high spin octet state was solved and, in the second calculation, all 48 sextet states were solved for. These were then mixed under the effect of spin-orbit coupling (SOC) using the well-established spin-orbit restricted active space state interaction (SO-RASSI) approach 76 . The zero-field splitting (ZFS) parameters and the g tensors were extracted from the ab initio results using the SINGLE_ANISO module 77 , 78 .

Relativistically contracted atomic natural orbital basis sets (ANO-RCC) were used in the multireference calculations 79 , 80 , 81 . A valence-polarized quadruple-ζ basis (VQZP) was used for the Eu ion, valence-polarized triple-ζ basis sets (VTZP) were used for the N and Si atoms while valence-polarized double-ζ basis sets (VDZP) were used for the remaining atoms. Cholesky decomposition with a threshold of 10 –8 atomic units was used in the integral storage. Scalar relativistic effects were introduced using the scalar exact two-component (X2C) approach 82 , 83 , 84 . The atomic mean-field integral (AMFI) formalism was used in the construction of the SOC operator used in the SO-RASSI procedure 85 , 86 .

Data availability

The crystallographic data generated in this study have been deposited in the Cambridge Structural Database under deposition number 2284168. Copies of the data can be obtained free of charge via https://www.ccdc.cam.ac.uk/structures/ . The EPR data and ac magnetic susceptibility generated in this study are provided in as Source Data files. Source data for the Supplementary Figs. can be provided upon request.  Source data are provided with this paper.

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Acknowledgements

D.E., K.L.M.H. and M.M. thank the University of Ottawa, the CFI, and NSERC for financial support of this work. A.M. acknowledges the funding provided by the Academy of Finland (grant no. 332294) and the University of Oulu (Kvantum Institute). Computational resources were provided by CSC-IT Center for Science in Finland and the Finnish Grid and Cloud Infrastructure (persistent identifier urn:nbn:fi:research-infras-2016072533). R.C. and M.R. thank the University of Bordeaux, the Centre National de la Recherche Scientifique (CNRS), the Région Nouvelle Aquitaine, Quantum Matter Bordeaux (QMBx), and the Association Française de Magnétisme Moléculaire. E.V.S. and S.H. acknowledge support from the US Department of Energy, Basic Energy Sciences (DE-SC0020260). Work performed at the National High Magnetic Field Laboratory is supported by the US National Science Foundation (DMR-2128556) and the State of Florida.

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These authors contributed equally: Dylan Errulat, Katie L. M. Harriman.

Authors and Affiliations

Department of Chemistry and Biomolecular Sciences, University of Ottawa, Ottawa, Ontario, K1N 6N5, Canada

Dylan Errulat, Katie L. M. Harriman, Diogo A. Gálico & Muralee Murugesu

National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL, 32310, USA

Elvin V. Salerno, Johan van Tol & Stephen Hill

NMR Research Unit, University of Oulu, P. O. Box 3000, 90014, Oulu, Finland

Akseli Mansikkamäki

Univ. Bordeaux, CNRS, CRPP, UMR 5031, F-33600, Pessac, France

Mathieu Rouzières & Rodolphe Clérac

Department of Physics, Florida State University, Tallahassee, FL, 32306, USA

Stephen Hill

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Contributions

D.E., K.L.M.H. and M.M. conceived the study. D.E. and K.L.M.H. synthesized and characterized the compounds. D.E. and K.L.M.H. collected X-ray diffraction data on 1, and D.E. performed structure determination and refinement. M.R. and R.C. collected and interpreted the magnetic data. A.M. performed the ab initio calculations and analysis. D.A.G. collected and interpreted the luminescence data. E.V.S, J.v.T. and S.H. collected and interpreted the EPR data. M.M. supervised all aspects of the project. The manuscript was written with contributions from all authors.

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Correspondence to Stephen Hill , Rodolphe Clérac or Muralee Murugesu .

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Errulat, D., Harriman, K.L.M., Gálico, D.A. et al. Slow magnetic relaxation in a europium(II) complex. Nat Commun 15 , 3010 (2024). https://doi.org/10.1038/s41467-024-46196-w

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Received : 09 August 2023

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DOI : https://doi.org/10.1038/s41467-024-46196-w

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