Reduction of cerebral blood flow and oxygen consumption with a combination of barbiturate anaesthesia and induced hypothermia in the rat.

The influence of phenobarbitone anaesthesia on cerebral blood flow (CBF) and cerebral metabolic rate for oxygen (CMRo2) during hypothermia (23 degrees C & 27 degrees C) was studied in the rat, using a modification of the Kety & Schmidt (1948) technique and arterio-venous differences for oxygen. Phenobarbitone (150 mg/kg) was found to decrease CMRo2 by 40-60% during hypothermia, when compared to N2O anaesthesia. At a body temperature of 23 degrees C, and during phenobarbitone anaesthesia, CMRo2 was reduced to about 15% of normal control value (about 10.3 ml.100g-1). CBF was reduced to about 50% of the phenobarbitone control value but was similar to the value obtained with N2O anaesthesia at 22 degrees C. It is concluded that the combination of phenobarbitone anaesthesia and hypothermia results in a more pronounced reduction in cerebral metablic rate for oxygen than can be achieved by administration of barbiturates to normothermic animals, or by reducing body temperature by 15 degrees C during superficial anaesthesia.