title: Does hyperventilation improve operating condition during supratentorial craniotomy? A multicenter randomized crossover trial.
abstract: BACKGROUND
  Hyperventilation has been an integral, but poorly validated part of neuroanesthetic practice. We conducted a two-period, crossover, randomized trial to evaluate surgeon-assessed brain bulk and measured intracranial pressure (ICP) in patients undergoing craniotomy for removal of supratentorial brain tumors during moderate hypocapnia or normocapnia.
  
  
  METHODS
  Two-hundred and seventy-five adult patients with supratentorial brain tumors were randomized to one of two treatment sequences: hyperventilation (arterial carbon dioxide tension, PaCO2 = 25 +/- 2 mm Hg) followed by normoventilation (PaCO2 = 37 +/- 2 mm Hg) or normoventilation followed by hyperventilation. Ventilation and end-tidal CO2 tension were kept constant for 20 min. Patients were also randomly assigned to receive a propofol infusion or isoflurane anesthesia. At the end of each study period, subdural ICP was measured and the neurosurgeon, blinded to the treatment group, was asked to rate the brain bulk using a four-point scale.
  
  
  RESULTS
  Using a generalized estimation equation model, we found that hyperventilation decreased the risk of increased brain bulk by 45%, P = 0.004, 95% confidence intervals 22% to 61%, and the number needed to treat was 8. The mean (+/-SD) ICP during hyperventilation, 12.3 +/- 8.1 mm Hg, was lower than that during normoventilation, 16.2 +/- 9.6 mm Hg, P < 0.001. Anesthetic regimen did not affect brain bulk assessment or ICP.
  
  
  CONCLUSIONS
  In patients with supratentorial brain tumors, intraoperative hyperventilation improves surgeon-assessed brain bulk which was associated with a decrease in ICP.
authors.affiliation: Department of Anesthesia and Perioperative Care, University of California San Francisco, 521 Parnassus Ave, C 450, San Francisco, CA 94143-0648, USA. gelba@anesthesia.ucsf.edu
authors.forename: Adrian W
authors.initials: AW
authors.lastname: Gelb
authors.forename: Rosemary A
authors.initials: RA
authors.lastname: Craen
authors.forename: G S Umamaheswara
authors.initials: GS
authors.lastname: Rao
authors.forename: K R Madhusudan
authors.initials: KR
authors.lastname: Reddy
authors.forename: Joseph
authors.initials: J
authors.lastname: Megyesi
authors.forename: Bibek
authors.initials: B
authors.lastname: Mohanty
authors.forename: Hari H
authors.initials: HH
authors.lastname: Dash
authors.forename: Kai C
authors.initials: KC
authors.lastname: Choi
authors.forename: Mathew T V
authors.initials: MT
authors.lastname: Chan
mesh_terms: D000328:Adult; D000368:Aged; D003399:Craniotomy / Q000379:methods*; D018592:Cross-Over Studies; D005260:Female; D006801:Humans; D006985:Hyperventilation / Q000503:physiopathology; D007427:Intracranial Pressure / Q000502:physiology; D007430:Intraoperative Care / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D015173:Supratentorial Neoplasms / Q000503:physiopathology / Q000601:surgery*