Thermoregulatory response in female patients during lower abdominal surgery in the head-down tilt position

Background: The head-down tilt (HDT) position suppresses sympathetic nervous activity. We investigated the effect on thermoregulation of the HDT position during lower abdominal surgery under general anaesthesia. Methods: Tympanic membrane temperature was measured to assess core temperature, and forearm-fingertip and calf-toe temperature gradients were used to assess peripheral vaso-constriction in 30 female patients less than 60 years of age. Results: During surgery in the HDT position (n = 10), the tympanic membrane temperature was similar to that of patients in the supine position (n = 10) (36.2 degrees C and 36.2 degrees C), but in patients operated in the HDT position and premedicated with an angiotensin converting enzyme inhibitor (5 mg of enalapril, n = 10) it was reduced (35.7 degrees C, P<0.05). Ln both groups of patients operated in the HDT position, forearm and calf skin-surface temperature gradients were lower by 2-3 degrees\C than those in patients operated in the supine position (P<0.05). Conclusions: During lower abdominal surgery the head-down tilt position does not augment core hypothermia in spite of suppressed peripheral vasoconstriction, and the renin-angiotensin system may be of importance for thermoregulation.