special subjects
Evidence Based Medicine and Clinical Guidelines
Evidence Based Medicine
EBM is not the blind application of advice gleaned from recently published literature to individual patient problems. It does not imply a "one size fits all" model of care. Rather, EBM requires the use of a series of steps to gather sufficiently useful information to answer a carefully crafted question for an individual patient. Fully integrating the principles of EBM also incorporates the patient’s value system, which includes such things as costs incurred, the patient’s religious or moral beliefs, and patient autonomy. Applying the principles of EBM typically involves the following steps: Formulating a clinical question Gathering evidence to answer the question Evaluating the quality and validity of the evidence Deciding how to apply the evidence to the care of a specific patient Questions must be specific. Specific questions are most likely to be addressed in the medical literature. A well-designed question specifies the population, intervention (diagnostic test, treatment), comparison (treatment A vs treatment B), and outcome. “What is the best way to evaluate someone with abdominal pain?” is not an overly useful question to pursue in the literature. A better, more specific question may be “Is CT or ultrasonography preferable for diagnosing acute appendicitis in a 30-year-old male with acute lower abdominal pain?” A broad selection of relevant studies is obtained from a review of the literature. Standard resources are consulted (eg, MEDLINE or PubMed for primary references, the Cochrane Collaboration [treatment options often for specific questions], ACP Journal Club). Not all scientific studies are of equal value. Different types of studies have different scientific strengths and legitimacy, and for any given type of study, individual examples often vary in quality of the methodology, internal validity, generalizability of results, and applicability to a specific patient (external validity). Levels of evidenceare graded 1 through 5 in decreasing order of quality. Types of studies at each level vary somewhat with the clinical question (eg, of diagnosis, treatment, or economic analysis), but typically consist of the following: Level 1 (the highest quality): Systematic reviews or meta-analyses of randomized controlled trials and high-quality, single, randomized controlled trials Level 2: Well-designed cohort studies Level 3: Systematically reviewed case-control studies Level 4: Case series and lesser-quality cohort and case-control studies Level 5: Expert opinion not based on critical appraisal, but based on reasoning from physiology, bench research, or underlying principles For EBM analysis, the highest level of evidence available is selected. Ideally, a significant number of large, well-conducted level 1 studies are available. However, because the number of high-quality, randomized, controlled trials is vanishingly small compared with the number of possible clinical questions, less reliable level 4 or 5 evidence is very often all that is available. Lower-quality evidence does not mean that the EBM process cannot be used, just that the strength of the conclusion is weaker. Because the best available evidence may have come from patient populations with different characteristics from those of the patient in question, significant judgment is required when applying results from a randomized trial to a specific patient. Additionally, patients’ wishes regarding aggressive or invasive tests and treatment must be taken into account as well as their tolerance for discomfort, risk, and uncertainty. For example, even though an EBM review may definitively show a 3-month survival advantage from an aggressive chemotherapy regimen in a certain form of cancer, patients may differ on whether they prefer to gain the extra time or avoid the extra discomfort. The cost of tests and treatments may also influence physician and patient decision making, especially when some of the alternatives are significantly costlier for the patient. Two general concerns are that patients who voluntarily participate in clinical trials are not the same as patients in general practice, and care delivered in a clinical trial environment is not identical to general care in the medical community. Dozens of clinical questions are faced during the course of even one day in a busy practice. Although some of them may be the subject of an existing EBM review available for reference, most are not, and preparing a formal EBM analysis is too time-consuming to be useful in answering an immediate clinical question. Even when time is not a consideration, many clinical questions do not have any relevant studies in the literature. 