The impact of extracorporeal technlogies on outcome in critically ill adults

Nowadays we believe that extracorporeal techniques, applied in experienced institutions, may become a feasible and promising alternative to mechanical ventilation to fully prevent VILI. The randomized controlled trials (RCTs) are experiments designed to confirm or disprove a given hypothesis. Therefore our reasoning in acquiring new knowledge in medicine may be summarized according to the following sequence: observation, inductive processes, proposal of theories and premises, deductive hypothesis and experiments to prove or disprove the hypothesis, which is implicit in the premises. The randomized controlled trials are one of the possible experiments. Testing an hypothesis deducted from wrong or vague premises leads necessarily to inconclusive results. Hence the fundamental importance of the premises when using RCTs. Let us consider, as examples, some of the major trials performed in intensive care units (ICU), by analyzing their premises, deducted hypothesis and outcome the successful trials are based on robust and well-defined hypotheses, sometimes refined with time. Good examples are the prone position trials and the high tidal volume ventilation. Many other trials, in our opinion, failed either because they were based on wrong premises (the first RCT on extracorporeal support) or were based on too vague and generic premises. The RCTs are successful, in general, only when the premises are well-defined. This obviously makes the results valid only for the restricted patient population enrolled in the study and the generalization of the results (the external validity) is problematic. Using thousands patients, studies with weak premises are usually inconclusive as the presence of subgroups in which the intervention could be of benefit may be vanished by subgroups in which the same intervention may be harmful. Therefore the effort to conduct the trial in a large population unavoidably carries the high risk of vagueness premises and useless results. In conclusion we believe that trials may be an extremely effective method to advance our knowledge when "positive" which usually occurs when the premises are carefully considered and defined, the hypothesis logical and the target population (unfortunately "restricted") adequate to test the hypothesis. In contrast the negative trials do not indicate that a given intervention per se is useless or wrong, but simply disproves the premises which usually occurs when they are too generic or wrong.