Cerebral effects of anaesthesia and hypothermia

Cerebral blood flow, cerebral oxygen and glucose consumption, and cerebral lactate and pyruvate release were measured; spectral analysis of the EEG was recorded in 10 male patients who had coronary artery bypass surgery. The measurements were taken to evaluate the effects of fentanyl-midazolam anaesthesia during normothermia and during hypothermic nonpulsatile cardiopulmonary bypass at 26 degrees C venous blood temperature, when a temperature-corrected PaCO2-value of 5.3 kPa was maintained. Anaesthesia with fentanyl 7 micrograms/kg and midazolam 200 micrograms/kg as induction doses, followed by infusions of fentanyl 0.15 micrograms/kg/minute and midazolam 3 micrograms/kg/minute, was characterised by a decrease in fast-wave activity and an increase in high-amplitude, slow-wave activity in the EEG. There was also a decrease in cerebral blood flow (38%), oxygen consumption (22%) and glucose consumption (25%), while lactate and pyruvate production remained unchanged. Hypothermia of 26 degrees C venous blood temperature suppressed EEG almost completely and decreased oxygen and glucose consumption by a further 61% and 54%, respectively, with no changes in lactate and pyruvate production while cerebral blood flow increased by 145%. These results show that the effects of fentanyl-midazolam anaesthesia on cerebral metabolism are enhanced during hypothermic cardiopulmonary bypass while the influence of anaesthesia on cerebral blood flow is overshadowed by the practice of a temperature-corrected acid-base management.