The thermoregulation of halothane versus isoflurane in humans receiving ophthalmological surgery

Although suppression of thermoregulatory mechanisms during anaesthesia is generally assumed, the extent to which thermoregulation may be inactive is unknown. Twenty unpremedicated, ASA physical status class I patients (17 men and 3 women) scheduled for retinal detachment surgery were studied to evaluate the different changes of core and two skin-surface temperatures during halothane or isoflurane anaesthesia. Anaesthesia was induced by mask inhalation of halothane or isoflurane in nitrous oxide 70% and oxygen and was maintained by mechanical ventilation during surgery with halothane or isoflurane in nitrous oxide 50% and oxygen only. Core temperature (rectus) and skin-surface temperatures (forearm and fingertip) were measured during surgery using three separate thermometers (Y.S.I.: Yellow springs instrument Co., Inc. G541-211-Y01-33A0). Operating room temperatures were recorded in every case. Significant vasoconstriction was prospectively defined by a skin-surface temperature gradient between two sampling sites > or = 4 degrees C. The result indicated that there was no significant difference between core temperatures and skin-surface temperature gradients during halothane anaesthesia and isoflurane anaesthesia. However, three of the ten patients had their skin-surface temperature gradients > or = 4 degrees C in the halothane group. None of the ten patients had their skin-surface temperature gradients > or = 4 degrees C in the isoflurane group.