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Anesth Analg 2001;92:787-794
© 2001 International Anesthesia Research Society

REVIEW ARTICLE

Evidence-Based Medicine in Anesthesiology

Peter J. Pronovost, MD, PhD*, Sean M. Berenholtz, MD{dagger}, Todd Dorman, MD{ddagger}, William T. Merritt, MD, MBA{dagger}, Elizabeth A. Martinez, MD{dagger}, and Gordon H. Guyatt, MD, MSc§

*Department of Anesthesiology and Critical Care Medicine, Surgery, and Health Policy and Management, Johns Hopkins University, Baltimore, Maryland; {dagger}Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University, Baltimore, Maryland; {ddagger}Department of Anesthesiology and Critical Care Medicine, Medicine, and Surgery, Johns Hopkins University, Baltimore, Maryland; and §Departments of Clinical Epidemiology and Biostatistics, and Medicine, McMaster University, Hamilton, Ontario, Canada

Address correspondence to Peter J. Pronovost, MD, PhD, The Johns Hopkins University, 600 N. Wolfe St., Meyer Building, Rm. 295, Baltimore, MD 21289-7294. Address e-mail to ppronovo @jhmi.edu.


   Evidence-Based Medicine
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 Evidence-Based Medicine
References
 
All of us practice anesthesiology and medicine on the basis of evidence from our personal experience of treating patients over the years and from our personal knowledge base that includes information that can be as old as a medical school course or as recent as an article we just read. How we tackle the responsibility of evaluating the quality of this evidence and of combining the evidence with patient preferences represents the substance of the practice of medicine. The application of evidence-based medicine (EBM) principles can help us with this daunting task that challenges us daily. Although EBM principles have been applied at the anesthesia society levels, we believe that the principles and tools of EBM can be applied in our daily practice to improve the care we provide to our patients. In this review, we will provide a general overview of what EBM is, demonstrate how it can be applied to the daily practice of anesthesiology, explore its limitations, and propose strategies on how we can train residents and attending physicians in the practice of EBM.

What is EBM?
EBM is an approach to caring for patients that involves the explicit and judicious use of the clinical research literature combined with an understanding of pathophysiology, clinical experience, and patient preferences to aid in clinical decision making (1). The philosophical foundation for EBM lies in clinical epidemiology championed in a book by Sackett et al. (2) titled A Basic Science for Clinical Practice. This approach to patient care may improve clinical decision making by incorporating the best available scientific literature, reducing bias that occurs when medical decision making is based on unsystematic observations (when more systematic observations are available), weighing the risks and benefits of a clinical decision, and incorporating patient preferences into a risk/benefit assessment (3).

EBM deemphasizes (but does not eliminate) intuition, unsystematic clinical experience, and physiologic reasoning as sufficient grounds for clinical decision making and emphasizes the systematic evaluation of evidence from clinical research (1). EBM asks us to seek the best evidence and, when randomized trials are unavailable, to fall back on observational studies; when observational studies are unavailable, it asks us to fall back on our less systematic clinical observations and on pathophysiologic reasoning. The philosophy underlying EBM suggests that a formal set of rules must complement our medical training and clinical experience to effectively apply the results of clinical research (4). In this light, EBM can be viewed as a set of tools that must be incorporated with patient values when evaluating the benefits and risks of alternative treatment decisions. The practitioner of EBM must be able to understand the patient’s situation, identify knowledge gaps, ask questions to address those gaps, conduct an efficient literature search, critically appraise the research, incorporate patient values, and apply the research to patient care (5).

On the Need for Evidence-Based Anesthesiology
Professional societies in anesthesiology (including the Anesthesia Patient Safety Foundation) have attempted to apply the principles of EBM to improve patient care. As a result, anesthesiologists are recognized as leaders in the development and widespread adoption of practice guidelines that may have contributed to major, sustained, widespread reductions in morbidity and mortality attributed to the administration of anesthesia (6–9). Nonetheless, it is difficult to establish a causal relationship between the activities of these organizations and improved patient outcomes.

The application of EBM in our daily clinical practice remains a challenge and requires a very structured approach to clinical care. EBM provides us with the tools to find and systematically evaluate the evidence from which we make our clinical decisions. The better we understand the quality of the evidence we use to make clinical decisions, the better we will be able to judge whether the evidence should be incorporated into our practice. For example, when reviewing a preoperative electrocardiogram in a patient with left bundle branch block and atypical chest pain, it is helpful to know the sensitivity of the electrocardiogram for detecting myocardial ischemia in this setting (10). By consciously and explicitly discussing the medical decision making process, we may improve patient care (11).

Because of the paucity of valid randomized clinical trials to help inform anesthesia practice, many decisions in the operating room (OR) are based on evidence from pathophysiologic reasoning or evidence obtained from studies of animals, healthy volunteers, or observational studies focusing on biologic (arterial blood pressure, heart rate, pulmonary artery occlusion pressure) or patient (mortality, morbidity, functional status) outcomes. EBM sees evidence broadly. There is always evidence; however, it is often unsystematic or physiologic. Dispersed literature sources and insufficient clinical research data enhance the need for evidence-based anesthesiology, whereas the need to make critical decisions under the pressure of time challenges the application of EBM in anesthesiology.

Literature Sources
The body of literature pertaining to anesthesiology is dispersed across multiple journals, including journals in general medicine, medical subspecialties, critical care, anesthesiology, pediatrics, and surgery, as well as basic science journals such as cell, shock, and circulation journals. This diversity increases the need for efficient methods to access and search relevant literature. Techniques for improving efficiency when searching the medical literature have been published (12). Many clinicians rely on alternative strategies for accessing relevant clinical literature, such as evidence summaries (for example, Intensive Care Monitor) that screen journals relevant to their particular field and summarize the information to facilitate critical appraisal. Both the breadth of knowledge required for anesthesiology and the diverse sources of clinical literature demand efficient access and evaluation of relevant literature.

Need for Rapid Decisions
The need to make rapid clinical decisions may complicate the application of EBM in the OR or intensive care unit (ICU). Sackett and Straus (13) explored the ability of an "evidence cart," i.e., readily accessible texts and literature, etc., to enhance clinical decision making. This work was partly driven by the concern that EBM, though attractive in theory, may be limited in application simply because of the time and effort required to systematically appraise the literature before a decision is made. Though their study showed that making evidence quickly available to clinicians increased the extent to which evidence was sought and incorporated into patient care decisions, it was conducted on a general medical ward.

In the OR and ICU, decisions are routinely made faster than on a general medical ward, and there are few data regarding whether EBM can be applied practically where rapid decisions are required. There are some data suggesting that EBM treatment and diagnostic protocols may be used effectively even in the treatment of acute processes such as acute respiratory distress syndrome (14). Without such protocols, practical applications of EBM in the OR and ICU will be limited to problems we see repeatedly.

Below, we have presented a clinical scenario to demonstrate how we might apply EBM in our daily clinical practice.

Clinical Scenario
A 55-yr-old woman presents for a repair of an abdominal aortic aneurysm. She smoked a pack of cigarettes per day for 20 yr, but she quit 6 yr ago and walks a mile per day. She is without other medical disease. She is seen on the morning of surgery, and the anesthesiologist explains the risks of the procedure and anesthesia to the patient. When the risk of perioperative blood transfusion is explained, the patient asks how it would be decided if she were to receive blood. The patient has never received a blood transfusion and would like to avoid this if at all possible. How might the physician proceed?

Pathophysiologic Reasoning
The resident anesthesiologist explains that she will transfuse the patient to maintain a hemoglobin of 9.0 g/dL to decrease the risk of perioperative morbidity. The resident explains that the stress of surgery increases myocardial oxygen demand and decreases myocardial oxygen supply, thus creating a risk for myocardial ischemia. In addition, the anesthesiologist explains that most patients having abdominal aortic surgery have coronary artery disease that further increases the risk of perioperative cardiac morbidity and mortality. The patient accepts this explanation and proceeds with the surgery.

EBM Reasoning
The attending physician for the case would like to know if the transfusion trigger of 9 g/dL is based on clinical research. She proceeds to the computer in the recovery room and, by using Best Evidence, a database of clinical trials that has been screened for quality and is available on our hospital network, enters the key words transfusion, critical illness, and allogeneic, and she downloads an article about transfusion in critically ill patients (15).

After reading the article, she asks herself three questions:

  1. 1. Is the evidence from this randomized trial valid?
  2. 2. If valid, is the evidence important?
  3. 3. If valid and important, can I apply this evidence in caring for my patient?

To assist with answering these questions, she uses the EBM worksheet for evaluating a study about a therapy (http://cebm.jr2.ox.ac.uk), which is described in Figure 1.



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  		Figure 1. Completed therapy worksheet.

 
Back to the Scenario
The attending physician tells the resident that she would not transfuse the patient until her hemoglobin decreased to <7 g/dL, because transfusion to a higher hemoglobin is not associated with reduced mortality and transfusions have risks that the patient is concerned about. The attending physician states that this study evaluated critically ill patients in an ICU and may not apply to patients in the OR. The resident asks whether patients in the OR are sufficiently like critically ill patients in an ICU so the results might apply. After some discussion, the attending physician agrees and asks the resident if she could present this information at the weekly case conference.

The resident accepts the offer and wants to introduce EBM to the case conference. She organizes her findings into a critically appraised topic. An example of this one-page summary of the evidence supporting a clinical research question is presented in Figure 2. The clinical director of the department is in the audience and likes this evidence-based approach. He creates a task force (that includes the resident) to develop an evidence-based guideline for transfusion practices using the critically appraised topic and other existing evidence-based summaries, such as the ASA practice guidelines (http://www.asahq.org).



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  		Figure 2. Critically appraised topic (CAT).

 
How Might We Apply EBM in Anesthesiology?
The practice of EBM can supplement our current daily clinical practice, in our journal clubs and case conferences, and in our teaching and role modeling (1). In our daily practice, we can train residents and new faculty how to critically appraise the literature, providing access to computerized literature searches and incorporating the literature into our work. Anesthesiologists can change their journal clubs and case conferences from unsystematic reviews to case-based critical reviews that focus on a clinical problem and critically appraise the literature to address that problem.

Applying the Results of Clinical Trials to Our Daily Practice
When critically appraising an article about therapy, readers must decide whether the results of a clinical trial apply to their patient or whether their patient is so different that the study results would not apply. In most cases, the results may be applied with a quantitative difference (one of degree), rather than a qualitative difference, i.e., a different conclusion would be reached for the applicability to the individual patient (16,17). Most clinical trials are efficacy studies in that they evaluate how something works in an artificial world that controls multiple variables. Although this control is necessary to maintain the internal validity of the study, it may limit our ability to apply the results of the clinical trial to a population of patients outside the trial. However, effectiveness studies evaluate how a treatment works in the real world; have less internal validity, i.e., ability to make an inference without random or systematic error; and have increased generalizability, or external validity.

This difference between efficacy studies and effectiveness studies and the potential problem of assuming applicability of results of a randomized clinical trial to a population of patients is illustrated in the carotid endarterectomy story. The Asymptomatic Carotid Atherosclerosis Study found that the 30-day mortality for asymptomatic patients having carotid endarterectomy was 1 in 1000 (18). Coincident with the publication of this trial, there was a significant increase in the rate of this operation between 1989 and 1995 (19). However, an effectiveness study of Medicare patients revealed that the mortality for asymptomatic patients having a carotid endarterectomy was 1 in 100, 10 times more than in the clinical trial (20). This difference in mortality is likely caused by the strict entry criteria for the clinical trial, because patients with comorbid diseases, patients over 79 yr old, and hospitals and surgeons with poor outcomes were excluded from the clinical trial.

The carotid endarterectomy story demonstrates the need for effectiveness studies to ensure that results achieved in randomized trials are being achieved in regular clinical practice. When deciding whether the results of a study on therapy apply to your patient, you must explicitly consider the risks and benefits for the patient. In procedure-oriented specialties such as anesthesiology, the skill of the provider and hospital-level factors may affect risk and should be considered in the risk/benefit analysis (21). For example, if a clinical trial demonstrated that regional anesthesia for patients having carotid endarterectomy is associated with reduced mortality, but the anesthesiologist is not comfortable with regional anesthesia, he or she may elect to do general anesthesia because the risks of an unskilled provider performing regional anesthesia may outweigh the potential benefits of improved patient outcomes with regional anesthesia.

What Are the Requirements for the Practice of EBM?
All the traditional medical skills are required for the practice of EBM. Clinicians must have a sound understanding of pathophysiology to evaluate the ability to apply clinical research findings to a particular patient and to help inform clinical practice in the absence of clinical studies. In general, current training in anesthesiology places more emphasis on teaching pathophysiologic reasoning and less emphasis on teaching systematic evaluation of the literature. In addition, the evidence-based clinician, like all clinicians, must be sensitive to the patient’s values. The practice of EBM is a systematic process that will require physicians to learn new skills.

Requirements for the New System

  1. 1. We need to be able to define a clinical question that includes a patient population, intervention, and outcome. Clinical experience and background knowledge of the disease are required to make a diagnosis and to define the relevant treatment options and outcomes.
  2. 2. We need to train residents and new faculty in efficiently searching the literature (12). Most medical libraries can provide this training. In addition, we can hold workshops at national meetings to teach EBM to a broad audience.
  3. 3. We need efficient means of providing access to scientific literature. Many decisions in anesthesiology need to be made rapidly, and we must be able to access literature without hindering patient care. The growth of on-line computer access to full-text journals and other evidence-based resources will facilitate this. Nonetheless, we must be careful not to compromise vigilance while providing patient care.
  4. 4. We need to be able to critically appraise the available literature. Traditional undergraduate and graduate medical training generally does not provide physicians with these skills.
  5. 5. We need to increase clinical research to provide additional evidence for clinical practice. Most of what we do in medicine is not supported in science (22,23), and EBM can help identify areas in need of clinical research.
  6. 6. We need to be able to decide whether we can apply research evidence to our patients. Clinical experience is critical for this. Clinicians must judge the extent to which differences in expertise, the availability of technology, or patient characteristics may affect estimates of benefits and risk that come from the published literature (4). Furthermore, clinicians must decide if all of the important outcomes were considered, if patient follow up was sufficiently long, and if the study compared the experimental therapy with the most commonly used alternative.
  7. 7. We must understand how the patient’s values affect the balance of the advantages and disadvantages of the available treatment options and the ability to appropriately involve the patient in decision making (5). We need compassion, good listening skills, and a broad perspective to help us understand the patient’s illness in the context of his or her experience, personality, and culture (5). Although clinical experience is necessary to provide these skills, further research is needed on the process of eliciting patient values and incorporating them into clinical decision making.

Does the Practice of EBM Improve Patient Care?
Emerging literature suggests that the practice of EBM does improve patient care. Over the last 40 yr, reliable and valid knowledge from randomized clinical trials about therapies that are associated with improved outcomes has become the basis for medical practice (24,25). Despite this knowledge, a gap remains between what the evidence recommends and what is practiced, and significant effort is spent helping physicians translate the evidence into practice (22). A systematic review of educational strategies suggests that didactic measures, often used in traditional medical education, are generally ineffective at changing physician behavior (26). However, case-based methods are more effective at changing physician behavior (27).

Nonetheless, there is no evidence from randomized clinical trials that the practice of EBM is associated with improved patient outcomes. Such a study would need to overcome significant methodological hurdles, including sample size, contamination, blinding, and long-term follow-up (3). As a result, it would be exceedingly expensive and difficult to conduct, and it would likely meet significant ethical challenges. If such a study were conducted, would it be appropriate to withhold scientific evidence in the control group?

There is evidence from effectiveness studies that patients who receive evidence-based therapies have better outcomes than those who do not. For example, myocardial infarction patients who are prescribed aspirin and ß-blockers (evidence-based therapies) have less mortality than those patients not receiving these therapies. In addition, internal medicine residents trained in EBM are more likely to practice according to evidence-based practice guidelines than those not trained in EBM (28). Furthermore, the use of evidence-based, computerized decision support systems can change physician behavior and improve patient outcome (29,30).

We are not aware of an anesthesiology training program that has formally implemented an EBM program and thus, there are no such data for anesthesiology. Although there is strong biologic plausibility that incorporating the best available scientific evidence and patient preferences into patient care will likely improve outcomes, there are no data suggest-ing that EBM will improve the clinical practice of anesthesiology.

What is the Potential Negative Impact of Practicing EBM?
Although the authors believe it would be beneficial to incorporate EBM into anesthesia practice, the potential negative impact of investing in EBM must be considered. The practice of EBM will require capital investment in computers so that physicians can access the litera-ture. This investment will likely decrease funding in other areas and may negatively affect a training or community-based program. In addition, training residents in the practice of EBM may decrease the time available for didactic lectures. Although didactic lectures are not effective at changing physician behavior, they provide residents with the background information they need to safely practice anesthesiology. We are not suggesting eliminating didactic lectures. Rather, we would encourage that evidence-based, case-based learning supplement didactic lectures. This may allow residents to bring new knowledge to patient care, improving their clinical decision making.

Another potentially negative impact of EBM is that evidence may be viewed as static rather than dynamic. Guidelines are increasingly influencing medical practice, yet these guidelines require frequent review and revision to incorporate new literature. Unfortunately, the sponsors of many guidelines do not have the resources to continuously support such a review process. The use of out-of-date guidelines may be associated with decreased quality of care compared with the use of more recent evidence. As such, it is imperative that anesthesiologists have the ability to critique guidelines and the medical literature to determine whether the guideline is valid and current.

What Resources Are Available to Help Practice EBM?
The challenge for us is to translate existing knowledge into practice as well as generate new knowledge about practice that is not presently supported by evidence. EBM can help us by summarizing existing knowledge with systematic reviews and evidence-based clinical recommendations and by identifying clinical decisions that are not supported by clinical research, thus prioritizing future research agendas (31). Anesthesiology has been a leader in implementing practice standards (32) and is well positioned to broadly translate evidence into practice.

Nonetheless, we generally do a poor job of translating research into practice, and this results in increased morbidity and mortality (22,33–35). For example, it is estimated that 18,000 people die each year in the United States, in part from a failure to receive ß-blockers after acute myocardial infarction (36). Given that physicians have difficulty keeping abreast of current literature, and that nonsystematic reviews found in text books and some journals have a several year lag in recommending effective therapies and that they continue to recommend ineffective therapies, we need systematic summaries of primary research to help guide clinical decision making (37). One such type of systematic review that incorporates a quantitative summary of the evidence is metaanalyses that are increasingly being performed and have well described methods for their conduct (38,39). Indeed, the Cochrane collaboration maintains and updates a collection of systematic reviews of randomized trials of interventions in health care from around the world (http://hiru.mcmaster.ca/cochrane/cochrane/resource. htm). For example, this database contains a metaanalysis of the outcomes of patients having carotid endarterectomy performed under local anesthesia versus general anesthesia. Systematic reviews are a very efficient means of evaluating a clinical question. The number of systematic reviews pertaining to anesthesiology is increasing, and the Cochrane collaboration has recently created an anesthesiology work group to conduct systematic reviews that are relevant to anesthesiology (40,41).

In addition, the users’ guides to the medical literature series in JAMA provides templates on how to use a variety of studies, including primary studies on therapy, prognosis, and diagnosis, as well as systematic reviews, decision analyses, cost-effectiveness analyses, and practice guidelines. Furthermore, many medical societies are attempting to evaluate and synthesize the literature, according to rigorous evidence-based principles and grades of evidence, into evidence-based practice guidelines or clinical recommendations. The guidelines developed by the ASA on preoperative fasting and blood component therapy are examples of using an evidence-based approach to guideline development (42).

Alternatives to EBM
EBM asks us to incorporate valid scientific literature into our practice without significant data and tells us that such an approach improves patient outcomes. The practice of EBM takes time and may detract from other educational initiatives. Therefore, it is appropriate to reflect on some alternatives to the practice of EBM. A recent review of alternatives to EBM demonstrates the shortcomings of practice approaches that do not attempt to incorporate valid scientific evidence into practice (43). In the absence of scientific literature to guide clinical decision making, personality characteristics such as seniority (eminence-based medicine) drive clinical decision making. Indeed, traditional medicine uses the lack of scientific evidence of efficacy as a defense against alternative forms of medicine.

Summary
By making the clinical decision making process explicit, conscious, and science based, we may avoid confusing opinion with evidence. EBM may help sharpen our critical appraisal skills and thus improve the way we practice, teach, and conduct research. Nevertheless, EBM will need to supplement rather than substitute for other approaches to patient care and teaching (31). EBM may better incorporate patients’ values into clinical decision making, and this may be especially important in anesthesiology, where we are in need of valid evidence about important clinical issues such as preoperative testing and postoperative analgesia (44,45). By incorporating valid scientific evidence and patients’ values into clinical decision making, we may improve patient outcomes. Outside of internal medicine, the literature suggesting that the practice of EBM improves outcomes is sparse, though increasing (28,46). Future studies to critically evaluate the practice of EBM in anesthesiology and critical care would be helpful.

Appendix 1: Other Resources for the Practice of EBM

The Centre for Evidence-based Medicine Web site (http://cebm.jr2.ox.ac.uk) is an excellent source of practical information for the practice of EBM.
The American Society of Anesthesiology Web site (http://www.asahq.org) contains several evidence-based practice guidelines.
The Cochrane Library and McMaster: (http://hiru. mcmaster.ca/cochrane/cochrane/resource.htm)
University of Alberta Center for EBM (http://www.med.ualberta.ca/ebm/ebm.htm): This Web site contains an EBM tool kit and is very practical and helpful.
Best Evidence: This is a CD-ROM produced by the American College of Physicians that contains a critical review of randomized clinical trials since the early 1990s. This is a very efficient means of identifying a clinical trial in a particular area.
Critical Care Medicine: Users’ Guides to the Medical Literature: This series, based on the JAMA publications, presents a unique opportunity for the reader to learn how to critically evaluate the literature by critiquing an article. This series is well done and should be read by all critical care practitioners.
Journal of the American Medical Association: Rational Clinical Examination Series: This series critically evaluates clinical decision making and is very helpful in making clinical decision making explicit.
Critical Care Clinics; 1998:14. This entire issue was devoted to evidence-based critical care and provides an evidence-based review of several specific critical care topics.


   References
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Accepted for publication November 27, 2000.




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Lippincott, Williams & Wilkins Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999 HighWire Press