Warming of insufflation gas during laparoscopic hysterectomy:: effect on body temperature and the autonomic nervous system

Background: Hypothermia is a known side effect of laparoscopic operations. It may increase the sympathetic activity of the autonomic nervous system (ANS), which can be evaluated non-invasively by heart rate variability (HRV). We tested the hypo thesis that warming of the delivered CO2 insufflation gas helps to maintain the normal body temperature. Methods: Thirty-seven healthy women undergoing laparoscopic hysterectomy were randomized into heated (37 degrees C, n=18) or unheated (24 degrees C, n=19) gas insufflation groups. Anesthesia was induced with propofol and maintained with sevoflurane in O-2-air. Tympanic (t(tymp)) temperature was recorded before, during and after the operation. Nasopharyngeal (t(naso)) temperature was recorded only during operation. Electrocardiograms were recorded and stored to evaluate changes in HRV. The individual changes in HRV were compared after decibel (dB) transformation. Results: A median decrease in tympanic temperatures during the operation was 0.7 degrees C in the heated and 0.3 degrees C in the unheated group (P=0.01 between groups), and in nasopharyngeal 0.3 degrees C and 0.1 degrees C (P=0.03), respectively. Preanesthetic tympanic values were reached within 90 min after anesthesia. After dB transformation, HRV high frequency power differed between the groups. It was better preserved in the patients receiving unheated gas. Conclusion: The heating of insufflation gas does not prevent a decrease in body temperature and is thus unnecessary during laparoscopic hysterectomy.