Canine Cerebral Metabolic Tolerance during 24 Hours Deep Pentobarbital Anesthesia

Abstract

The impact of tolerance on cerebral metabolism during prolonged pentobarbital-induced anesthesia was evaluated in 16 dogs. Cerebral metabolic rate for O2 was calculated from direct measurements of venous blood flow rate and the difference in blood O2 content between arterial and venous blood during 4 periods of continuous and unvarying deep pentobarbital anesthesia.sbd.0-3 h, 3-6 h, 12-15 and 21-24 h. During 0-3 h, the metabolic rate was 1.8-2.0 ml O2/100 g brain per min. This increased to 2.3-2.6 ml/100 per min during 3-6, 12-15, and 21-24 h. In all studies, the ECG indicated a constant deep burst-suppression level at 2-6 burst/min and blood pentobarbital levels were unchanged at 4.9-5.9 mg/dl throughout the entire period of anesthesia. The sustained increase in cerebral metabolism that occurred after 3 h and continued through 24 h of pentobarbital anesthesia is presumably due to tolerance. This was a phenomenon in which metabolism increased during steady deep anesthesia with unchanged blood levels of pentobarbital, rather than one in which greater blood levels were necessary to maintain the same level of anesthesia.