In vitro performance characteristics of high-frequency oscillatory ventilators

This study aimed to examine the performance characteristics of four high-frequency oscillatory-type ventilators, using an in vitro model of the intubated neonatal respiratory system. Each ventilator was examined across its operative range of settings and at varying model lung compliance (C) and resistance. The oscillatory pressure waveform was measured at the airway opening (Pao). Tidal volume (VT) and flow were determined from pressure changes within the model lung (Delta PA). The spectral content of the Pao waveform differed between ventilators. The maximum ventilator VT ranged from 3.7 to 11.1 ml at 15 Hz and a mean airway pressure (Paw) of 12 cm H2O to oscillate a model lung (C = 0.4 ml/cm H2O) through a 3.0-mm internal diameter (i.d.) endotracheal tube (ETT). A small drop in C was associated with a decrease in VT and marked increase in Delta PA from 0.1 to 0.8 ml/cm H2O. The influence of C on VT and Delta PA and the pressure cost of ventilation (Delta PA/f.VT2) was dependent on the oscillatory frequency, ETT inner diameter, and the specific ventilator used. Substantive differences exist between oscillatory ventilators that need to be considered in their clinical application. The rapid establishment of optimal lung volume and oscillatory frequency is important in minimizing barotrauma during high-frequency oscillatory ventilation.