The effect of alfentanil on cerebral blood flow velocity and intracranial pressure during isoflurane-nitrous oxide anesthesia in humans.

Background: Intravenous opioids often are used as a component of anesthesia during neurosurgical procedures. However, the cerebrovascular effects of alfentanil administered to patients are controversial. In this study, the effect of alfentanil in patients with and without intracranial pathology was studied.

Methods: Sixteen neurosurgical patients and 16 patients scheduled for orthopedic procedures were studied. Anesthesia was maintained with isoflurane (0.4-0.6 vol% inspired) and nitrous oxide (50%) in oxygen. Within each group, the patients were assigned randomly to receive either 25 or 50 micrograms/kg intravenous alfentanil. During normocapnia and without surgical stimulation, the right middle cerebral artery flow velocity, and mean arterial pressure were measured every minute for 10 min after the administration of alfentanil. In the neurosurgical patients, intracranial pressure, cerebral perfusion pressure, and cerebral arteriovenous oxygen content difference were determined also. Neurosurgical patients received intravenous phenylephrine to maintain mean arterial pressure as needed.

Results: There was no significant change in middle cerebral artery flow velocity and arteriovenous oxygen content difference in the neurosurgical patients. In the high-dose group, intracranial pressure increased by 2 mmHg at 4 min but was otherwise unchanged. Despite phenylephrine administration, there was an immediate but transient decrease in mean arterial pressure in the high-dose group and a corresponding decrease in cerebral perfusion pressure. In the orthopedic patients, mean arterial pressure decreased significantly. Middle cerebral artery flow velocity decreased in the high-dose group but remained unchanged in the low-dose group.

Conclusions: Based on the flow velocity and metabolic data, alfentanil is neither a cerebral vasodilator nor a vasoconstrictor in these doses. Furthermore, there was no clinically significant increase in intracranial pressure when alfentanil was administered in either dose.