The rationale and utility of neurophysiological investigations in clinical monitoring for brain and spinal cord ischaemia during surgery and intensive care.

This review concerns the role of neurophysiological monitoring in prevention of damage to the brain or spinal cord from inadequate supply of oxygenated blood during surgery and intensive care. The spontaneous and evoked electrical activity from neurones depends on oxidative metabolism of glucose, the substrate being delivered via the arterial blood supply and not stored locally. In critical situations electrical activity declines as oxygen delivery fails. Since this happens before neuronal death occurs it can provide early warning of risk. Methods for signal processing of EEG for this purpose must include time domain assessment and recognition of burst suppression pattern, as well as frequency domain information, and provide multivariate pattern recognition. Models for monitoring systems require analysis of data sets based on clinical studies where accurate outcome data is available so that valid comparisons between different approaches can be made. Neurophysiological features must be considered in the context of other relevant clinical parameters in the design of effective warning systems for prevention of brain damage due to inadequate oxygen supply.