title: Head-up tilt and hyperventilation produce similar changes in cerebral oxygenation and blood volume: an observational comparison study using frequency-domain near-infrared spectroscopy.
abstract: OBJECTIVE
  During anesthesia, maneuvers which cause the least disturbance of cerebral oxygenation with the greatest decrease in intracranial pressure would be most beneficial to patients with intracranial hypertension. Both head-up tilt (HUT) and hyperventilation are used to decrease brain bulk, and both may be associated with decreases in cerebral oxygenation. In this observational study, our null hypothesis was that the impact of HUT and hyperventilation on cerebral tissue oxygen saturation (SctO2) and cerebral blood volume (CBV) are comparable.
  
  
  METHODS
  Surgical patients without neurological disease were anesthetized with propofol-remifentanil. Before the start of surgery, frequency-domain near-infrared spectroscopy was used to measure SctO2 and CBV at the supine position, at the 30° head-up and head-down positions, as well as during hypoventilation and hyperventilation.
  
  
  RESULTS
  Thirty-three patients were studied. Both HUT and hyperventilation induced small decreases in SctO2 [3.5 (2.6)%; P < 0.001 and 3.0 (1.8)%; P < 0.001, respectively] and in CBV [0.05 (0.07) mL x 100 g(-1); P < 0.001 and 0.06 (0.05) mL x 100 g(-1); P < 0.001, respectively]. There were no differences between HUT to 30° and hyperventilation to an end-tidal carbon dioxide (ETCO2) of 25 mmHg (from 45 mmHg) in both SctO2 (P = 0.3) and CBV (P = 0.4).
  
  
  CONCLUSIONS
  The small but statistically significant decreases in both SctO2 and CBV caused by HUT and hyperventilation are comparable. There was no correlation between the decreases in SctO2 and CBV and the decreases in blood pressure and cardiac output during head-up and head-down tilts. However, the decreases in both SctO2 and CBV correlate with the decreases in ETCO2 during ventilation adjustment.
authors.affiliation: Department of Anesthesiology & Perioperative Care, University of California Irvine Medical Center, 101 The City Drive South, Bldg. 53, Rm. 227, Orange, CA 92868, USA. meng.lingzhong@gmail.com
authors.forename: Lingzhong
authors.initials: L
authors.lastname: Meng
authors.forename: William W
authors.initials: WW
authors.lastname: Mantulin
authors.forename: Brenton S
authors.initials: BS
authors.lastname: Alexander
authors.forename: Albert E
authors.initials: AE
authors.lastname: Cerussi
authors.forename: Bruce J
authors.initials: BJ
authors.lastname: Tromberg
authors.forename: Zhaoxia
authors.initials: Z
authors.lastname: Yu
authors.forename: Kathleen
authors.initials: K
authors.lastname: Laning
authors.forename: Zeev N
authors.initials: ZN
authors.lastname: Kain
authors.forename: Maxime
authors.initials: M
authors.lastname: Cannesson
authors.forename: Adrian W
authors.initials: AW
authors.lastname: Gelb
mesh_terms: D000328:Adult; D000368:Aged; D001810:Blood Volume; D001921:Brain / Q000378:metabolism*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D006801:Humans; D006985:Hyperventilation / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000378:metabolism*; D011187:Posture; D019265:Spectroscopy, Near-Infrared / Q000379:methods*
chemical_list: D010100:Oxygen