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GENERAL ARTICLES

Thermoregulatory Response to Intraoperative Head-Down Tilt

Yasufumi Nakajima, MD PhD^*, Toshiki Mizobe, MD PhD^*, Takashi Matsukawa, MD PhD, Daniel I. Sessler, MD, Yoshihiro Kitamura, MD PhD^*, and Yoshifumi Tanaka, MD PhD^*

*Department of Anesthesiology, Kyoto Prefectural University of Medicine, Kyoto, Japan; Department of Anesthesiology, Yamanashi Medical University, Yamanashi, Japan; and Outcomes Research^TM Institute, Department of Anesthesiology, University of Louisville, Kentucky, and Ludwig Boltzmann Institute, University of Vienna, Austria

Address correspondence and reprint requests to Toshiki Mizobe, MD, PhD, Department of Anesthesiology, Kyoto Prefectural University of Medicine, Kawaramachi Hirokoji, Kamigyo-ku, Kyoto 602-8566, Japan. Address e-mail to toshim{at}koto.kpu-m.ac.jp

Thermoregulation interacts with cardiovascular regulation within the central nervous system. We therefore evaluated the effects of head-down tilt on intraoperative thermal and cardiovascular regulation. Thirty-two patients undergoing lower-abdominal surgery were randomly assigned to the 1) supine, 2) 15°–20° head-down tilt, 3) leg-up, or 4) combination of leg-up and head-down tilt position. Core temperature and forearm minus fingertip skin-temperature gradients (an index of peripheral vasoconstriction) were monitored for 3 h after the induction of combined general and lumbar epidural anesthesia. We also determined cardiac output and central-venous and esophageal pressures. Neither right atrial transmural pressure nor cardiac index was altered in the Head-Down Tilt group, but both increased significantly in the Leg-Up groups. The vasoconstriction threshold was reduced in both leg-up positions but was not significantly decreased by head-down tilt. Final core temperatures were 35.2°C ± 0.2°C (mean ± SEM) in the Supine group, 35.0°C ± 0.2°C in the Head-Down Tilt group, 34.2°C ± 0.2°C in the Leg-Up group (P < 0.05 compared with supine), and 34.3°C ± 0.2°C when leg-up and head-down tilt were combined (P < 0.05 compared with supine). These results confirm that elevating the legs increases right atrial transmural pressure, reduces the vasoconstriction threshold, and aggravates intraoperative hypothermia. Surprisingly, maintaining a head-down tilt did not increase right atrial pressure.

IMPLICATIONS: Intraoperative hypothermia is exaggerated when patients are maintained in the leg-up position because the vasoconstriction threshold is reduced. However, head-down tilt (Trendelenburg position) does not reduce the vasoconstriction threshold or aggravate hypothermia. The head-down tilt position thus does not require special perioperative thermal precautions or management unless the leg-up position is used simultaneously.

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