Direct cerebrovasodilatory effects of halothane, isoflurane, and desflurane during propofol-induced isoelectric electroencephalogram in humans.

BACKGROUND

The effect of volatile anesthetics on cerebral blood flow depends on the balance between the agent's direct vasodilatory action and the indirect vasoconstrictive action mediated by flow-metabolism coupling. To compare the intrinsic action of volatile anesthetics, the effect of halothane, isoflurane, and desflurane on flow velocity in the middle cerebral artery during propofol-induced isoelectricity of the electroencephalogram was examined.

METHODS

In 21 ASA physical status 1-2 patients, anesthesia was induced with 2.5 mg/kg propofol, 3 micrograms/kg fentanyl, and 0.1 mg/kg vecuronium and maintained with a propofol infusion to preserve an isoelectric electroencephalogram. End-tidal carbon dioxide and blood pressure were maintained constant throughout the study period. A transcranial Doppler was used to measure blood flow velocity in the middle cerebral artery, and a catheter was inserted in a retrograde direction into the jugular bulb for oxygen saturation measurements. After 15 min of isoelectric electroencephalogram, arterial and jugular venous blood samples were drawn, and flow velocity in the middle cerebral artery was recorded. Patients were randomly allocated to receive 0.5 MAC halothane, isoflurane, or desflurane, and after 15 min of equilibration, all variables were measured again. The concentration of the volatile agent was increased to 1.5 MAC, and after 15 min of equilibration, the measurements were repeated.

RESULTS

Halothane, isoflurane, and desflurane significantly increased flow velocity in the middle cerebral artery (baseline 28 +/- 4, 30 +/- 4, and 29 +/- 3 cm/s, respectively) at 0.5 MAC (19 +/- 1.5%, 21 +/- 2%, and 23 +/- 3%, respectively; P < 0.05) and at 1.5 MAC (48 +/- 3%, 75 +/- 7%, and 74 +/- 4%, respectively; P < 0.05). Changes in the cerebral arteriovenous oxygen content difference are consistent with these findings.

CONCLUSIONS

Halothane, isoflurane, and desflurane have intrinsic, dose-related cerebral vasodilatory effects. Whereas all three agents are similar at 0.5 MAC, isoflurane and desflurane have greater vasodilatory effects than halothane at 1.5 MAC.