Ebm Methodology And Hyperbaric Medicine

EBM methodology has gained a widespread acceptance and is presently an integral part of modern medical practice. The approach and tools used in EBM involve using double-blind randomized prospective controlled clinical studies to provide answers to specific questions, grading rather than providing a general estimation of results to conclude clinical studies and finally collecting results into a meta-analysis to smooth variations between studies. It is typically based on 3 axes:

1- the level of evidence (i.e. quality of available data),

2- interpretation of the evidence (i.e. what the data suggest and how concordant these data are regarding a particular problem),

3- the type or strength of the recommended practice (i.e. the extent to which a physician is able to recommend a particular intervention on the basis of the first two considerations). This method may be used either by an individual physician or by a group of experts who could be expected to arrive at the same conclusion.

For clinical research the various levels of evidence are the following:

Level A: At least 2 concordant, large, double-blind, controlled randomized studies with no or little methodological bias

Level B: Double-blind controlled, randomized studies but with methodological flaws; studies with only small samples, or one study only

Level C: Consensus opinion of experts

Level D: Only uncontrolled studies with no consensus opinion of experts

Level E: No evidence of beneficial action, or methodological or interpretation bias precluding any conclusion

Level F: procedure not indicated by existing evidence

Unfortunately, this method only gives clinically useful recommendations when high quality randomized controlled clinical studies are available. When there is no such data, as in the HBO field no firm recommendation (level A or B) can be issued and the clinician in left without any guidelines. In those cases, the search of a consensus within experts is the method the most widely chosen. The expert consensus method is regarded as the best surrogate to EBM methods to assess procedures under the following circumstances:

1- where a particular procedure, unsupported by a high level of evidence, has become universally accepted to such an extent that it would be considered a violation of accepted standards of care to deny a patient the benefit of the therapy for the purpose of a study.

2- where the disease or condition of interest is so complex or where there are so many variables that it would be impossible to design a study sufficiently powerful to assess any single procedure.

3- where the application of the therapy is so logical that it would be grossly inappropriate to consider omitting it to establish proof of efficacy

4- where no current higher level of evidence exists, but experts are able to report, not only from their own experiences but also by producing comprehensive literature reviews from which consensus can provisionally be reached, pending the outcome of future studies.

Even if an enormous effort has been made by the hyperbaric medicine community in order to achieve high quality clinical studies, we are forced to recognize that in our field, many questions remain without sufficient evidence to give a definite answer. It is therefore hardly surprising to note that to this day, only a small proportion of therapy procedures conventionally used in hyperbaric medicine is supported by the highest level of evidence. Each therapy has its own imperatives. Physicians should remember that where therapy is concerned, clinical decision-making is usually based on the existence of evidence, rather than on the level of evidence required for establishing proof. No evidence of a benefit is not the same as evidence of no benefit. Finally, there is a hierarchy in levels of evidence : from the evidence which is strong enough to support clinical decision-making, through to the highest level where evidence is supported by many extensive clinical studies. A number of pathologies for which HBO is indicated have not undergone the stringent scrutiny of double-blind randomized prospective controlled clinical study but the considerable amount of available data in favour of the use of HBO for these pathologies justifies their choice as indications. Obviously the results of current or future research can alter the current list of indications. Lastly the actual conception of clinical studies is essential to assess the effectiveness of a therapy such as HBO, all the more so when ethical considerations further complicate the issue. Here clostridial myonecrosis is a significant example. There are no double-blind randomized prospective controlled clinical studies with human subjects in this field but the scientific and medical community does agree, in view of the microbiology, animal experimentation and considerable clinical experience, that HBO has transformed the vital and functional prognosis of this terrible gangrene disease - so much so that such a study would now be considered pointless, dangerous and in contradiction with medical ethics.

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