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

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 (38.0degreesC). Thereafter, cranial heating was discontinued. Brain-to-core temperature gradients during the 3 h study were greatest in the right subdural area, averaging -2.5degreesC +/- 0.9degreesC in HN, -2.5degreesC +/- 0.8degreesC in HH, and -4.1degreesC +/- 1.1degreesC 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 -0.8degreesC +/- 0.5degreesC to - 1.1degreesC +/- 0.6degreesC for both HN and HH but were twice this amount in PN (-1.9degreesC +/- 0.5degreesC to -2.1degreesC +/- 0.7degreesC) (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 cerebro-protective properties of the barbiturates.