Cerebrovascular carbon dioxide reactivity during general anesthesia: A comparison between sevoflurane and isoflurane

We compared cerebrovascular carbon dioxide reactivity during the administration of sevoflurane and isoflurane anesthesia by measuring cerebral blood flow velocity (CBFV) as an indirect measurement of cerebral blood flow. Thirty patients, 20-70 yr old, undergoing lower abdominal surgery and without known cerebral or cardiovascular system disease, were randomly assigned to either sevoflurane or isoflurane treatment groups. Anesthesia was induced with thiopental 5 mg/kg IV and maintained with either sevoflurane or isoflurane in 67% nitrous oxide and oxygen. The CBFV and pulsatility index (PI) of the left middle cerebral artery were monitored with transcranial Doppler. The PETCO₂ was increased stepwise from 20 to 50 mm Hg by changing the respiratory rate with a constant tidal volume. At every 5-mm Hg stepwise change in PETCO₂, CBFV and PI were recorded. CBFV increased with increasing PETCO₂. CBFV was significantly smaller in the isoflurane group at PETCO₂ = 20-40 mm Hg than in the sevoflurane group. The rate of change of CBFV with changes in CO₂ was larger in the isoflurane group than in the sevoflurane group. PI was constant over time and was not different between groups. In conclusion, hypocapnia-induced reduction of intracranial pressure might be more effective during the administration of isoflurane than sevoflurane. Implications: Changes in cerebral blood flow caused by the changes of carbon dioxide tension are greater during the administration of isoflurane anesthesia compared with sevoflurane anesthesia. Attempts to decrease intracranial pressure by decreasing carbon dioxide tension may be more successful during isoflurane than sevoflurane anesthesia administration.