Anesthetic technique influences brain temperature, independently of core temperature, during craniotomy in cats.

Abstract

Because anesthetic technique has the potential to dramatically affect cerebral blood flow and metabolism (two determinants of brain thermoregulation), we tested the hypothesis that, after craniotomy, anesthetic technique would influence brain temperature independent of core temperature. Twenty-one cats (2.7 +/- 0.4 kg; mean +/- SD) undergoing a uniform right parasagittal craniotomy received 1) halothane 1.5% end-expired and normocapnia (HN), 2) halothane 1.5% and hypocapnia (HH), or 3) large-dose pentobarbital and normocapnia (PN) (n = 7 per group). Heating devices initially maintained core and right subdural normothermia (38.0 degrees C). Thereafter, cranial heating was discontinued. Brain-to-core temperature gradients during the 3 h study were greatest in the right subdural area, averaging -2.5 degrees C +/- 0.9 degrees C in HN, -2.5 degrees C +/- 0.8 degrees C in HH, and -4.1 degrees C +/- 1.1 degrees C in PN. Gradients within the unexposed left subdural area and in the right cortex 0.5 and 1.0 cm below the brain surface were -0.8 degrees C +/- 0.5 degrees C to -1.1 degrees C +/- 0.6 degrees C for both HN and HH but were twice this amount in PN (-1.9 degrees C +/- 0.5 degrees C to -2.1 degrees C +/- 0.7 degrees C) (P < 0.05 for PN versus HN and HH). Deep barbiturate anesthesia can reduce brain temperature independently of core temperature, presumably by reducing the metabolic rate and associated brain heat production. The magnitude is sufficient to augment any direct cerebroprotective properties of the barbiturates. Deep barbiturate anesthesia reduced brain temperature independently of body temperature in cats and significantly more than the reduction seen with halothane anesthesia. The magnitude of temperature reduction was sufficient to account for cerebral protection by barbiturates independently of any other properties of the drug.