Cerebral Circulation and Metabolism during Enflurane Anesthesia in Humans

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Abstract
The effects of enflurane anesthesia on cerebral blood flow (CBF) and cerebral metabolic rate for O2 (CMRO2) were studied in 17 patients. The patients were divided into 2 groups according to the depth of anesthesia. Cerebral perfusion pressure was maintained above 60 mmHg with phenylephrine. Group 1 (arterial enflurane concentration, 15 mg/dl) patients were studied before surgery while in group 2 (enflurane concentration, 27 mg/dl), the measurements were performed before and during surgery. In group 1, mean CBF and CMRO2 were 53 and 2.8 ml/100 g per min, respectively. These values were not significantly different from CBF (46 ml/100 per min) and CMRO2 (3.1 ml/100 g per min) values previously obtained in awake patients. In group 2 before surgery, mean CBF and CMRO2 were 61 and 2.6 ml/100 g per min, respectively, and were significantly different from the awake values, while the EEG showed frequent spikes and suppression. In group 2 during surgery, mean CBF and CMRO2 did not differ from the values obtained before surgery, despite significant EEG changes. Apparently, enflurane is a cerebral vasodilator and causes an increase in CBF and a decrease in CMRO2 in humans at an anesthetic level characterized by frequent spikes and suppression on the EEG.