Antioxidants in critical care medicine.

Critically ill patients in the intensive care unit (ICU) present with a variety of different pathologies, and mortality is high despite extensive multi-organ supportive treatment. Reactive oxygen species (ROS) are believed to play a pivotal role in the pathophysiology of organ dysfunction in the ICU. In particular, the role of ROS as a final common pathway of cell damage has been increasingly emphasised in the adult respiratory distress syndrome (ARDS), in central nervous system traumatic and hypoxic states, and as a cause of ischaemic neurological deficits after subarachnoid haemorrhage. Measurement of total antioxidant status (TAS) has shown improved survival of patients with high TAS and poorer outcomes for those with lower values. Attempts to supplement endogenous antioxidant defences have not demonstrated clear benefits in randomised clinical trials, and the use of free radical scavenging agents have had similar mixed results. Considering the wide variation in the nature and severity of illness in the intensive care population, it is not surprising that clear evidence of the efficacy of antioxidant therapies in improving survival has not been clearly demonstrated. However, single component therapies for complex pathophysiological processes are rarely successful, and the role of antioxidants in the critically ill should be thought of as only part of a rational and logical therapeutic approach.