Determinants of tidal volume during high-frequency oscillation

Objective. High-frequency oscillation has been proposed for use in adult acute respiratory distress syndrome. However, limited data are available on the effect of pressure amplitude and rate (Hz) on tidal volumes delivered during high-frequency oscillation in adults. Design. Prospective, animal model, lung injury study. Setting. Large-animal laboratory of a university-affiliated medical center. Subjects. Nine sheep (29.2 +/- 2.4 kg). Interventions. Severe lung injury was induced by repeated saline lung lavage. After stabilization, high-frequency oscillation was initiated at a mean airway pressure equal to the point of maximum curvature on the deflation limb of the pressure-volume curve (26 +/- 1.9 cm H2O). Tidal volume at all combinations of rates of 4, 6, 8, and 10 Hz, pressure amplitudes of 30, 40, 50, and 60 cm H2O, and inspiratory/expiratory ratios of 1:1 and 1:2 (using the Sensormedics 3100B oscillator) were measured. Flow was measured by a pneumotachometer, amplified and digitized at 1000 Hz. Three breaths were analyzed at each setting. Measurements and Main Results. At both inspiratory/expiratory ratios, tidal volume was directly proportional to pressure amplitude and inversely proportional to frequency. During an inspiratory/expiratory ratio of 1:1, at 60 cm H2O pressure amplitude and 4 Hz, a tidal volume of 129.1 +/- 34.8 mL (4.4 +/- 1.2 mL/kg) was delivered. Conclusions. At low rates and high-pressure amplitudes in this model, tidal volumes approaching conventional mechanical ventilation can be delivered during high-frequency oscillation.