Tuesday, January 24, 2012

Evidence based medicine

When I came across the phrase “evidence based medicine” for the first time many years ago, I was somewhat bewildered. Was medicine we had learned in the college and practiced since not based on evidence?! Are there two types of medicine, one evidence based and one not?! Shouldn’t all medicine be evidence based?!
The key to the answer to these questions lies in the word “evidence”. Like almost any word in the language (any language), evidence can mean different things to different people or in different contexts. In the field of medicine, evidence can come through reasoning from known (thought to be known) pathophysiological facts. For example, in heart failure the heart does not pump blood to the tissues efficiently. Digitalis increases the force of myocardial contraction. So digitalis should be useful to patients with heart failure. Evidence can be the result of opinions of experienced doctors who obtained it from their practice. It may come from opinions of patients who expressed their satisfaction or dissatisfaction of a certain medical intervention. Evidence can also come from planned scientific experimentation.
During the last century and especially in the latter half of it, a trend towards examining medical interventions (drugs, surgical operations, diagnostic tests, life style changes etc) in a planned scientific way following the steps of the scientific method appeared and evolved. It aimed at properly evaluating the benefits and harms of various medical interventions. The trend became more powerful with the evolution and increasing use of clinical trials (including controlled clinical trials). Doctors, and increasingly the public, are not any more satisfied with the results of mere reasoning or opinions of experts. Reasoning that an intervention should be useful because it sounds logical according to our knowledge of medical facts is not enough. Our knowledge is not necessarily complete or perfect and usually, if not always, it is not. Opinions of experts and patients can be, and usually are, biased. The intervention should be tried on people under strictly controlled conditions and the results interpreted in a proper scientific way to find out if the intervention is really useful. And even if it is, we should make sure that it has no adverse effects that outweigh its benefits.
Medicine based on this kind of evidence is what is called evidence based medicine. This should not mean that the rest of medicine is not based on evidence but it means that the evidence for it is not satisfactory. The phrase does not express this in a clear unambiguous way. But that is language, however meticulous and careful one tries to be, language remains liable to be interpreted in various ways!
Should we conclude that evidence obtained from properly controlled clinical trials is infallible? Certainly not. We regularly hear of drugs withdrawn from the market and processes abandoned after being properly and scientifically evaluated and after years of use. Nothing in life is infallible.