title: Thermoregulatory response to intraoperative head-down tilt.
abstract: 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 degrees -20 degrees 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 degrees C +/- 0.2 degrees C (mean +/- SEM) in the Supine group, 35.0 degrees C +/- 0.2 degrees C in the Head-Down Tilt group, 34.2 degrees C +/- 0.2 degrees C in the Leg-Up group (P < 0.05 compared with supine), and 34.3 degrees C +/- 0.2 degrees 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Anesthesiology, Kyoto Prefectural University of Medicine, Kyoto, Japan.
authors.forename: Yasufumi
authors.initials: Y
authors.lastname: Nakajima
authors.forename: Toshiki
authors.initials: T
authors.lastname: Mizobe
authors.forename: Takashi
authors.initials: T
authors.lastname: Matsukawa
authors.forename: Daniel I
authors.initials: DI
authors.lastname: Sessler
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Kitamura
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Tanaka
mesh_terms: D000005:Abdomen / Q000601:surgery*; D000767:Anesthesia, Epidural; D000768:Anesthesia, General; D001831:Body Temperature; D001833:Body Temperature Regulation / Q000502:physiology*; D002302:Cardiac Output; D002496:Central Venous Pressure; D004947:Esophagus / Q000502:physiology; D005260:Female; D018475:Head-Down Tilt / Q000502:physiology*; D006801:Humans; D007432:Intraoperative Period; D008297:Male; D008365:Manometry; D008875:Middle Aged; D011187:Posture / Q000502:physiology; D012867:Skin / Q000098:blood supply; D012881:Skin Temperature; D014661:Vasoconstriction