Sevoflurane induces less cerebral vasodilation than isoflurane at the same A-line autoregressive index level.
BACKGROUND
The use of sevoflurane in neuroanesthesia is still under debate. Comparison of dose-dependent vasodilatory properties between sevoflurane and isoflurane, the more traditional neuroanesthetic agent, requires comparable dosing of the agents. A-line autoregressive index (AAI) provides reproducible individual measurement of anesthetic depth.


METHODS
Sevoflurane and isoflurane, in randomized order, were titrated to a stable AAI of 15-20 in each of 18 ASA I or II patients. The mean flow velocity (Vmca) and pulsatility index (PI) in the middle cerebral artery were measured with transcranial Doppler at an end-tidal CO2 of 4.5%.


RESULTS
For sevoflurane Vmca was 18% lower [95% confidence interval (CI) 12-22%; P < 0.00001] and PI was 23% higher (95% CI 12-33%; P = 0.0013) than for isoflurane. Mean arterial blood pressure did not differ between the two agents. The minimum alveolar concentration (MAC) fraction necessary to reach the intended AAI level was 13% higher (95% CI 5-20%; P = 0.0079) with sevoflurane than with isoflurane.


CONCLUSIONS
Sevoflurane induced less cerebral vasodilation than isoflurane at the same depth of anesthesia, measured by AAI, and hence seems more favorable for clinical neuroanesthesia. In our opinion the difference between sevoflurane and isoflurane in the MAC fraction required to attain the same AAI level demonstrates the limitations of MAC in defining the level of anesthesia.
Holmström
A
A
Department of Anesthesia and Intensive Care, Malmö University Hospital, Lund University, Malmö, Sweden. anders.holmstrom@skane.se
Akeson
J
J
D000328:Adult; D000368:Aged; D000465:Algorithms; D018685:Anesthetics, Inhalation / Q000009:adverse effects; D002560:Cerebrovascular Circulation / Q000187:drug effects*; D004311:Double-Blind Method; D004562:Electrocardiography; D004594:Electrophysiology; D005260:Female; D006439:Hemodynamics / Q000187:drug effects; D006801:Humans; D007530:Isoflurane / Q000009:adverse effects*; D008297:Male; D008738:Methyl Ethers / Q000009:adverse effects; D008875:Middle Aged; D020768:Middle Cerebral Artery / Q000000981:diagnostic imaging / Q000187:drug effects / Q000502:physiology; D016343:Monitoring, Intraoperative; D000077149:Sevoflurane; D017585:Ultrasonography, Doppler, Transcranial; D014664:Vasodilation / Q000187:drug effects*
D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D000077149:Sevoflurane; D007530:Isoflurane