title: Moderate hyperventilation during intravenous anesthesia increases net cerebral lactate efflux.
abstract: BACKGROUND
  Hyperventilation is known to decrease cerebral blood flow (CBF) and to impair cerebral metabolism, but the threshold in patients undergoing intravenous anesthesia is unknown. The authors hypothesized that reduced CBF associated with moderate hyperventilation might impair cerebral aerobic metabolism in patients undergoing intravenous anesthesia.
  
  
  METHODS
  Thirty male patients scheduled for coronary surgery were included in a prospective, controlled crossover trial. Measurements were performed under fentanyl-midazolam anesthesia in a randomized sequence aiming at partial pressures of carbon dioxide of 30 and 50 mmHg. Endpoints were CBF, blood flow velocity in the middle cerebral artery, and cerebral metabolic rates for oxygen, glucose, and lactate. Global CBF was measured using a modified Kety-Schmidt technique with argon as inert gas tracer. CBF velocity of the middle cerebral artery was recorded by transcranial Doppler sonography. Data were presented as mean (SD). Two-sided paired t tests and one-way ANOVA for repeated measures were used for statistical analysis.
  
  
  RESULTS
  Moderate hyperventilation significantly decreased CBF by 60%, blood flow velocity by 41%, cerebral oxygen delivery by 58%, and partial pressure of oxygen of the jugular venous bulb by 45%. Cerebral metabolic rates for oxygen and glucose remained unchanged; however, net cerebral lactate efflux significantly increased from -0.38 (2.18) to -2.41(2.43) µmol min 100 g.
  
  
  CONCLUSIONS
  Moderate hyperventilation, when compared with moderate hypoventilation, in patients with cardiovascular disease undergoing intravenous anesthesia increased net cerebral lactate efflux and markedly reduced CBF and partial pressure of oxygen of the jugular venous bulb, suggesting partial impairment of cerebral aerobic metabolism at clinically relevant levels of hypocapnia.
authors.affiliation: From the Department of Anesthesiology, Erasmus MC, Rotterdam, The Netherlands (F.G., R.J.S.); Department of Anesthesiology, Critical Care, and Emergency Medicine, University of Göttingen, Göttingen, Germany (S.K., H.S.); and Department of Anesthesiology, Critical Care, Emergency, and Pain Medicine, Klinikum Oldenburg, Oldenburg, Germany (A.W.).
authors.forename: Frank
authors.initials: F
authors.lastname: Grüne
authors.forename: Stephan
authors.initials: S
authors.lastname: Kazmaier
authors.forename: Hans
authors.initials: H
authors.lastname: Sonntag
authors.forename: Robert Jan
authors.initials: RJ
authors.lastname: Stolker
authors.forename: Andreas
authors.initials: A
authors.lastname: Weyland
mesh_terms: D000328:Adult; D000332:Aerobiosis / Q000502:physiology; D000368:Aged; D000771:Anesthesia, Intravenous / Q000009:adverse effects*; D001784:Blood Gas Analysis; D001923:Brain Chemistry / Q000502:physiology*; D002245:Carbon Dioxide / Q000097:blood; D002560:Cerebrovascular Circulation; D018592:Cross-Over Studies; D017666:Deuterium Oxide / Q000378:metabolism; D023381:Endpoint Determination; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D006985:Hyperventilation / Q000378:metabolism*; D019344:Lactic Acid / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D015656:Respiratory Mechanics / Q000502:physiology; D018401:Sample Size
chemical_list: D002245:Carbon Dioxide; D019344:Lactic Acid; D017666:Deuterium Oxide