title: Heliox does not affect gas exchange during high-frequency oscillatory ventilation if tidal volume is held constant.
abstract: OBJECTIVE
  To compare gas exchange with heliox and oxygen-enriched air during high-frequency oscillatory ventilation, while controlling for tidal volume, in a pediatric swine model of acute lung injury. We hypothesized that when tidal volume delivery is held constant, heliox does not alter gas exchange.
  
  
  METHODS
  Randomized, crossover trial.
  
  
  METHODS
  University animal research laboratory.
  
  
  METHODS
  Ten swine (4.4-5.4 kg).
  
  
  METHODS
  Acute lung injury (A-a gradient of >300 mm Hg) was created using repeated saline lavage during conventional mechanical ventilation. The animals were then administered high-frequency oscillatory ventilation and ventilated with 60% oxygen/40% helium and 60% oxygen/40% nitrogen in a randomized, crossover trial. When changing gas mixtures within each animal, mean airway pressure (Paw = 16.8 +/- 0.3 cm H(2)O) and frequency (10 Hz) were held constant. Oscillation amplitude (DeltaP) was adjusted to maintain constant tidal volume delivery as measured by respiratory inductive plethysmography. Next, the animals were ventilated with 40% oxygen/60% helium and 40% oxygen/60% nitrogen in a randomized crossover trial, again controlling for tidal volume.
  
  
  RESULTS
  Gas exchange was assessed by arterial blood gas analysis after ventilation with each gas mixture. We demonstrated no significant difference in Paco(2) or Pao(2) between the heliox and oxygen-enriched air with either the 40% or 60% oxygen mixtures. The oscillation amplitude required to achieve the same tidal volume delivery was significantly less with heliox.
  
  
  CONCLUSIONS
  We conclude that if tidal volume delivery is maintained constant, heliox does not alter gas exchange when compared with oxygen-enriched air. However, to achieve the same tidal volume delivery, a lower oscillation amplitude is required with heliox. The clinical benefit of heliox administration during high-frequency oscillatory ventilation has yet to be determined. Possible advantages of heliox include improved ventilation of larger patients when approaching the power limitations of the Sensormedics 3100A oscillator and a potential reduction in the oscillation amplitude delivered to the more proximal gas exchange units.
authors.affiliation: Duke University Medical Center, Durham, NC, USA.
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Katz
authors.forename: Michael A
authors.initials: MA
authors.lastname: Gentile
authors.forename: Damian M
authors.initials: DM
authors.lastname: Craig
authors.forename: George
authors.initials: G
authors.lastname: Quick
authors.forename: Ira M
authors.initials: IM
authors.lastname: Cheifetz
mesh_terms: D000818:Animals; D002245:Carbon Dioxide / Q000097:blood; D004305:Dose-Response Relationship, Drug; D006371:Helium / Q000494:pharmacology*; D006611:High-Frequency Jet Ventilation; D009991:Oscillometry; D010100:Oxygen / Q000097:blood / Q000494:pharmacology*; D011659:Pulmonary Gas Exchange / Q000187:drug effects*; D013552:Swine; D013990:Tidal Volume
chemical_list: D002245:Carbon Dioxide; D006371:Helium; C038949:heliox; D010100:Oxygen