title: Hyperbaric oxygen does not improve cerebral function when started 2 or 4 hours after cerebral arterial gas embolism in swine.
abstract: OBJECTIVE
  Hyperbaric oxygenation is the accepted treatment for cerebral arterial gas embolism. Although earlier start of hyperbaric oxygenation is associated with better outcome, it is unknown how much delay can be tolerated before start of hyperbaric oxygenation. This study investigates the effect of hyperbaric oxygenation on cerebral function in swine when initiated 2 or 4 hours after cerebral arterial gas embolism.
  
  
  METHODS
  Prospective interventional animal study.
  
  
  METHODS
  Surgical laboratory and hyperbaric chamber.
  
  
  METHODS
  Twenty-two Landrace pigs.
  
  
  METHODS
  Under general anesthesia, probes to measure intracranial pressure, brain oxygen tension (PbtO2), and brain microdialysis, and electrodes for electroencephalography were placed. The electroencephalogram (quantified using temporal brain symmetry index) was suppressed during 1 hour by repeated injection of air boluses through a catheter placed in the right ascending pharyngeal artery. Hyperbaric oxygenation was administered using U.S. Navy Treatment Table 6 after 2- or 4-hour delay. Control animals were maintained on an inspiratory oxygen fraction of 0.4.
  
  
  RESULTS
  Intracranial pressure increased to a mean maximum of 19 mm Hg (SD, 4.5 mm Hg) due to the embolization procedure. Hyperbaric oxygenation significantly increased PbtO2 in both groups treated with hyperbaric oxygenation (mean maximum PbtO2, 390 torr; SD, 177 torr). There were no significant differences between groups with regard to temporal brain symmetry index (control vs 2-hr delay, p = 0.078; control vs 4-hr delay, p = 0.150), intracranial pressure, and microdialysis values.
  
  
  CONCLUSIONS
  We did not observe an effect of hyperbaric oxygenation on cerebral function after a delay of 2 or 4 hours. The injury caused in our model could be too severe for a single session of hyperbaric oxygenation to be effective. Our study should not change current hyperbaric oxygenation strategies for cerebral arterial gas embolism, but further research is necessary to elucidate our results. Whether less severe injury benefits from hyperbaric oxygenation should be investigated in models using smaller amounts of air and clinical outcome measures.
authors: Diving Medical Center, Royal Netherlands Navy, Den Helder, The Netherlands. r.p.weenink@amc.nl
authors: Robert P
authors: RP
authors: Weenink
authors: Markus W
authors: MW
authors: Hollmann
authors: Xavier C E
authors: XC
authors: Vrijdag
authors: Krijn P
authors: KP
authors: Van Lienden
authors: Diederick W
authors: DW
authors: De Boo
authors: Markus F
authors: MF
authors: Stevens
authors: Thomas M
authors: TM
authors: Van Gulik
authors: Robert A
authors: RA
authors: Van Hulst
mesh_terms: D000818:Animals; D004569:Electroencephalography; D004618:Embolism, Air / Q000503:physiopathology / Q000628:therapy*; D005260:Female; D006931:Hyperbaric Oxygenation / Q000379:methods*; D020766:Intracranial Embolism / Q000503:physiopathology / Q000628:therapy*; D007427:Intracranial Pressure; D017551:Microdialysis; D013552:Swine; D013997:Time Factors