The EEG and Evoked Potentials

Abstract

Cardiac surgery with extracorporeal circulation is associated with a series of complex changes, including hypotension, hypothermia and haemodilution. These, together with the effects of anaesthetic and other drugs, can profoundly influence cerebral function. Moderate to high doses of opioids are commonly administered by cardiac anaesthetists. These drugs produce intense miosis, which deprives the anaesthetist of information derived from changes in pupil size. Hypotension is common at the onset of bypass and may result in cerebral ischaemia unless adequately corrected, especially in patients with cerebral vascular disease. Gaseous and particulate matter arising in the extracorporeal system and the effects of haemodilution and non-pulsatile flow may also contribute to brain damage during bypass, despite careful precautions. Monitoring cerebral function is therefore an important responsibility of the cardiac anaesthetist. For this a reliable method of assessing brain activity is needed and traditionally use has been made of the electroencephalogram (EEG).