Effects of sevoflurane and isoflurane on the ratio of cerebral blood flow/metabolic rate for oxygen in neurosurgery

Purpose. To examine the changes in cerebral blood flow (CBF) equivalent (CBF divided by cerebral metabolic rate for oxygen) during craniotomy under isoflurane and sevoflurane anesthesia in patients with intracranial disorders. Method. In 16 neurosurgical patients (8 anesthetized with isoflurane and 8 with sevoflurane), the CBF equivalent was measured while the end-tidal concentration of the selected volatile anesthetic was maintained at 0.5 and 1.0 minimum alveolar concentration (MAC) before surgery, and then 1.0 MAC during surgery, which lasted more than 4 h. Results. There was no significant difference in CBF equivalent at 0.5 MAC between the isoflurane (20 ± 4 ml blood/ml oxygen) and the sevoflurane (19 ± 4 ml blood/ml oxygen) groups. With increasing anesthetic depth from 0.5 to 1.0 MAC, the CBF equivalent significantly (P < 0.05) increased in both groups (22 ± 7 and 21 ± 5, respectively). At 1.0 MAC during operation, the CBF equivalent with both anesthetics was maintained with minimal fluctuation for 4 h. There were no significant differences in the average value of the CBF equivalent during a 4-h period at 1.0 MAC between the isoflurane (23 ± 5) and the sevoflurane (20 ± 4) groups. Conclusion. Deepening anesthesia from 0.5 to 1.0 MAC with isoflurane and sevoflurane produced a slight increase in the CBF equivalent. The CBF equivalent at 1.0 MAC was maintained with no difference between the two agents during 4 h of neurosurgery. Received: August 2, 1999 / Accepted: April 3, 2000