In vitro performance characteristics of high-frequency oscillatory ventilators

This study aimed to examine the performance characteristics of four high-fr equency oscillatory-type ventilators, using an in vitro model of the intuba ted neonatal respiratory system. Each ventilator was examined across its op erative range of settings and at varying model lung compliance (C) and resi stance. The oscillatory pressure waveform was measured at the airway openin g (Pao). Tidal volume (VT) and flow were determined from pressure changes w ithin the model lung (Delta PA). The spectral content of the Pao waveform d iffered between ventilators. The maximum ventilator VT ranged from 3.7 to 1 1.1 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 i n VT and marked increase in Delta PA from 0.1 to 0.8 ml/cm H2O. The influen ce 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 t he specific ventilator used. Substantive differences exist between oscillat ory ventilators that need to be considered in their clinical application. T he rapid establishment of optimal lung volume and oscillatory frequency is important in minimizing barotrauma during high-frequency oscillatory ventil ation.