Local cortical blood flow and oxygen consumption during isoflurane-induced hypotension

ABSTRACT

Cerebral cortical blood flow (ICoBF) and metabolic rate for oxygen (1CoMRO₂) were studied in eight patients undergoing intracranial aneurysm clipping. The patients were anesthetized with fentanyl 10 μg/kg and 70% nitrous oxide combined with 30% oxygen. Hypotension was induced with isoflurane. A thermal diffusion probe was used to measure ICoBF, and arterial and cerebral venous blood samples were obtained for measurement of arterio-cerebral venous O₂ content difference. Measurements were made prior to hypotension, during hypotension (to mean arterial pressure approximately 50 mmHg), and posthypotension. Mean ICoBF decreased from 69 ± 20 mL/100 g/min at normotension to 59 ± 13 mL/100 g/min during hypotension (P <.03, NS) and was 61 ± 18 mL/100 g/min upon return to normotension (all values mean ± 1 SD). The lCoMRO₂ averaged 3.9 ± 1.6 mL/100 g/min and 3.1 ± 1.5 mL/100 g/min, respectively (P <.03, NS) for normotension v hypotension. Values for cerebral venous PO₂ and O₂ saturation also did not differ significantly between study periods. These results indicate that isoflurane-induced hypotension during fentanyl-nitrous oxide anesthesia allows maintenance of a constant ICoBF and oxygen delivery.