A physiologic comparison of proportional assist ventilation with load-adjustable gain factors (PAV plus ) versus pressure support ventilation (PSV)

To compare patient-ventilator interaction during PSV and PAV+ in patients that are difficult to wean. This was a physiologic study involving 11 patients. During three consecutive trials (PSV first trial-PSV1, followed by PAV+, followed by a second PSV trial-PSV2, with the same settings as PSV1) we evaluated mechanical and patient respiratory pattern; inspiratory effort from excursion Pdi (swing(Pdi)), and pressure-time products of the transdiaphragmatic (PTPdi) pressures. Inspiratory (delay(trinsp)) and expiratory (delay(trexp)) trigger delays, time of synchrony (time(syn)), and asynchrony index (AI) were assessed. Compared to PAV+, during PSV trials, the mechanical inspiratory time (Ti-flow) was significantly longer than patient inspiratory time (Ti-pat) (p < 0.05); Ti-pat showed a prolongation between PSV1 and PAV+, significant comparing PAV+ and PSV2 (p < 0.05). PAV+ significantly reduced delay(trexp) (p < 0.001). The portion of tidal volume (VT) delivered in phase with Ti-pat (VTpat/VTmecc) was significantly higher during PAV+ (p < 0.01). The time of synchrony was significantly longer during PAV+ than during PSV (p < 0.001). During PSV 5 patients out of 11 showed an AI greater than 10%, whereas the AI was nil during PAV+. PAV+ improves patient-ventilator interaction, significantly reducing the incidence of end-expiratory asynchrony and increasing the time of synchrony.