Optimal application of high-frequency ventilation in infants: a theoretical study.

A recent multicenter study of preterm infants concluded that high-frequency ventilation (HFV) applied at 15 Hz, in comparison with conventional mechanical ventilation (CMV), did not lead to reduced incidence of barotrauma, contrary to previous expectations. The primary goal of the present theoretical study was to determine whether computed estimates of lung pressures during HFV and CMV are consistent with these findings. An existing theoretical model of lung mechanics and gas transport in HFV was modified for applicability to neonates. New features, such as expiratory flow limitation and pulmonary air leak, were also incorporated. Simulations with the model were conducted assuming combinations of frequency and tidal volume that maintained a constant level of eucapnia. We found that peak alveolar pressures and the magnitude of alveolar pressure swings resulting from HFV at 15 Hz were in general comparable to those produced by CMV in healthy neonates and infants with bronchopulmonary dysplasia; peak alveolar pressures in the latter group tended to be higher with HFV than in CMV. Application of HFV at 15 Hz was even less advantageous than CMV when pulmonary air leak was also present in the infants with bronchopulmonary dysplasia. However, the model predicted the existence of an optimal range of frequencies between 2 and 4 Hz in which alveolar pressure swings and peak alveolar pressures could be minimized, and in some cases, reduced below the levels produced by CMV.