Intracranial Pressure and Internal Carotid Blood Flow During Halothane Anesthesia in the Dog

Abstract

The effect of halothane anesthesia on internal carotid blood flow and intracranial pressure was studied in the dog. Internal carotid vascular resistance was calculated as the ratio between mean blood pressure and mean internal carotid blood flow/minute. Control of arterial PCO2, with a maximal decrease of 5 mm of Hg for halothane determinations, was maintained. Administration of CO2 was used as a reference point for the changes induced by halothane. Halothane decreased vascular resistance, as measured in the internal carotid artery, a change related to the depth of anesthesia. The maximal decrease in resistance was [long dash]56.4% with a reduction of 40.7% in the mean blood pressure. This effect is roughly similar to that produced by 60 mm of Hg in arterial PCO2. However, it was difficult todi fferentiate between the effects of hypotension of halothane itself on the internal carotid vascular resistance. Intracranial pressure rose sharply and returned to new levels in accordance with the altered cerebrovascular hemodynamics and not with the changes in venous pressure alone. The intracranial pressure was high during light anesthesia and normal or low during deep anesthesia.