Defining prognosis in medical coma.

Defining prognosis in medical comaThe advent of cardiopulmonary resuscitation during the 1960s together with advances in intensive care medicine focussed interest on the development of clinical and laboratory methods to identify prognosis early in the course of coma.The fear that large numbers of patients resuscitated after drug overdose, trauma or anoxic injury might survive in a chronic vegetative state or that costly support would be wasted on patients who were insentient resulted in many attempts to develop clinical scales, electrophyiological techniques and laboratory tests that would predict the likely outcome in individual patients.'It is disappointing that most of the reports ofprognostic signs in coma are on such small numbers of patients, retrospective or poorly defined so that adequate statistical validation is impossible.Few reports provide details of confidence limits.The specificity of such tests, that is the avoidance of false positive error in predicting a poor outcome in a patient who recovers, has been widely recognised to be more important than their sensitivity, or risk of a false negative error.However, few reports in the literature document these important figures for their own findings.2The original clinical studies, which were retrospective, proposed the length of coma or lack of motor response to pain as indicators of a poor prognosis but the inaccuracies were high and the criteria consequently of little use.5