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Heliox does not affect gas exchange during high-frequency oscillatory ventilation if tidal volume is held constant
Andrew L Katz1, Michael A Gentile, Damian M Craig
1Duke University Medical Center, Durham, NC, USA.
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.
Design:
Randomized, crossover trial.
Setting:
University animal research laboratory.
Subjects:
Ten swine (4.4-5.4 kg).
Interventions:
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.
Measurements And Main 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.