Anaesthesia and the liver: History and Epidemiology

Abstract

A PROVEN DAMAGING EFFECT of an anaesthetic agent on the human liver is an adverse drug reaction, and must receive its final evaluation by studies, conducted in sick human populations, of both the efficacy and the toxicity of the drug. Such studies fall within the province of the epidemiologist, and must rely on the techniques he has developed for their conduct. MacMahon e t al. 1,2 have divided the Strategy of Epidemiology into four steps. First, descriptive epidemiology, or the search for variables associated with a disease, and second, formulation of hypotheses, or the drawing up of tentative theories regarding the most direct causal associations possible between the disease and the variables associated with it. The final two steps, aimed at testing hypotheses, are analytic epidemiology (non-experimental studies ), and experimental epidemiology (prospective randomized clinical trials). Non-experimental studies can be of two types, case-control (case-history) studies and cohort studies. In case-control studies, two groups of patients, one affected with the disease under study and the other not so affected, are selected: the incidence of exposure to the suspected causal factor is then compared. In cohort studies, two groups of patients, one of which suffers exposure to the causal factor under study and the other of which does not, are selected. The groups are then observed to determine the proportion of each group that develops the disease under study. These studies may be either retrospective or prospective in nature; case-control studies are of necessity retrospective in nature. The effect of halothane upon the human liver has only been investigated satisfactorily by means of cohort studies.