PREMEDICATION WITH FAMOTIDINE AUGMENTS CORE HYPOTHERMIA DURING GENERAL-ANESTHESIA

Background: Animal studies have provided considerable evidence to support a role of histamine in the central nervous system in thermoregulation, and premedication with a histamine H-2 receptor antagonist before general anesthesia is used to reduce the risk of acid aspiration. The authors investigated whether premedication with famotidine had an effect on thermoregulation during general anesthesia. Methods: In a randomized, placebo-controlled study, 30 ASA physical status 1 or 2 patients, scheduled for open abdominal surgery, were given either placebo or 40 mg oral famotidine 3 h before induction of anesthesia. Epidural buprenorphine (4 mu g/kg) was injected, and anesthesia was maintained with 0.4-0.6% isoflurane and 66% nitrous oxide in oxygen. The tympanic membrane temperature was measured to assess core temperature, and forearm-fingertip and calf-toe skin-surface temperature gradients were used to assess peripheral vasoconstriction. Tympanic membrane temperature triggering initial vasoconstriction (a skin temperature gradient of 0 degrees C) identified the vasoconstriction threshold. Results: Tympanic membrane temperature during surgery in the patients premedicated with famotidine was significantly less than those in the patients without famotidine. Famotidine significantly reduced the thermoregulatory threshold for vasoconstriction in the leg (35.0 +/- 0.5 degrees C, P < 0.05), compared to that in the placebo group (36.4 +/- 0.6 degrees C) Once triggered, thermoregulatory vasoconstriction produced a core-temperature plateau and no further hypothermia was observed for the duration of the study. Neither mean arterial pressure nor heart rate were significantly different between the two groups. Conclusions: Premedication with famotidine augments intraoperative hypothermia. The mechanism appears to be inhibition of centrally mediated thermoregulatory control.