Metabolic acidosis in the critically ill

The processes that lead to increased blood lactate concentration in shock and critical illness are complex. Although it is widely believed that lactic acidosis develops because of tissue hypoxia and reduced aerobic metabolism, a number of workers have shown that lactate oxidation rate is actually increased. Lactate production is also increased and this is probably the cause of increased blood lactate concentration. The clinical usefulness of lactate estimation in critical illness is also obscure. Suggestions that whole blood lactate concentration is an accurate predictor of the outcome of an episode of shock are unconvincing. At best this method may differentiate between groups of patients. However, the rate of improvement in lactate concentration with intensive resuscitation probably correlates better with survival, and further investigation of this possibility is suggested.