Cerebral Hypometabolism Obtained with Deep Pentobarbital Anesthesia and Hypothermia (30 C)

Cerebral metabolic and vascular effects of hypothermia (30 C) and deep pentobarbital anesthesia, separately and combined, were evaluated in 15 mongrel dogs. External cardiovascular support was not used, and mean arterial blood pressures remained greater than 60 torr. Normothermic deep pentobarbital anesthesia, characterized by an electroencephalographic (EEG) frequency of less than 1 Hz, was associated with 30% decreases in cerebral metabolic rates for oxygen (CMRO2) and glucose (CMRG) from lightly anesthetized control values. Hypothermia (30 C) alone caused similar decreases in CMRO2 and CMRG in the presence of an active EEG. The use of pentobarbital anesthesia and hypothermia combined achieved significantly greater (P less than 0.05) decreases in CMRO2 (70%) and CMRG (72%) from the control state. Cerebral vascular resistance (CVR) increased by 70% (P less than 0.05) during hypothermia and about 20% when pentobarbital was administered to normothermic dogs. In hypothermic animals the addition of pentobarbital had a minimal effect on CVR. No alteration in the oxygen-glucose or lactate-glucose index indicative of cerebral hypoxia occurred in any experimental group. This study indicates that barbiturates combined with hypothermia decrease cerebral metabolism to a greater extent than hypothermia or barbiturate alone. When cerebral hypometabolism is therapeutically necessary, barbiturates may be indicated as an adjunct to moderate hypothermia.