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.

Methods: In 16 neurosurgical patients (8 anesthetized with isoflurane and 8 with sevolflurane), 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 hr.

Results: There was no significant difference in CBF equivalent at 0.5 MAC between isoflurane (20 +/- 4ml blood.ml oxygen) groups. With increasing anesthetic depth from 0.5 to 1.0 MAC, the CBF equivalent significantly (P<0.5) 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 4h. 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 was maintained with no difference between the two agents during 4h of neurosurgery.