Time to Lung Volume Stability After Pressure Change During High-Frequency Oscillatory Ventilation

OBJECTIVES: Clinicians have little guidance on the time needed before assessing the effect of a mean airway pressure change during high-frequency oscillatory ventilation. We aimed to determine: 1) time to stable lung volume after a mean airway pressure change during high-frequency oscillatory ventilation and 2) the relationship between time to volume stability and the volume state of the lung. DESIGN: Prospective observational study. SETTING: Regional quaternary teaching hospital neonatal ICU. PATIENTS: Thirteen term or near-term infants receiving high-frequency oscillatory ventilation and muscle relaxants. INTERVENTIONS: One to two cm H(2)O mean airway pressure changes every 10 minutes as part of an open lung strategy based on oxygen response. MEASUREMENTS AND MAIN RESULTS: Continuous lung volume measurements (respiratory inductive plethysmography) were made during the mean airway pressure changes. Volume signals were analyzed with a biexponential model to calculate the time to stable lung volume if the model R(2) was greater than 0.6. If volume stability did not occur within 10 minutes, the model was extrapolated to maximum 3,600 s. One-hundred ninety-six mean airway pressure changes were made, with no volume change in 33 occurrences (17%). One-hundred twenty-five volume signals met modeling criteria for inclusion; median (interquartile range) R(2), 0.96 (0.91–0.98). The time to stable lung volume was 1,131 seconds (718–1,959 s) (mean airway pressure increases) and 647 seconds (439–1,309 s) (mean airway pressure decreases), with only 17 (14%) occurring within 10 minutes and time to stability being longer when the lung was atelectatic. CONCLUSIONS: During high-frequency oscillatory ventilation, the time to stable lung volume after a mean airway pressure change is variable, often requires more than 10 minutes, and is dependent on the preceding volume state.