[Effect on inspiratory cycling-off synchronization with different expiratory trigger sensitivity level during pressure-support ventilation: a lung model study].

OBJECTIVE

To compare the inspiratory cycling-off synchronization with different expiratory trigger sensitivity (ETS) setting during noninvasive pressure support ventilation (PSV) under the conditions of system leak.

METHODS

Ventilators were connected to a lung model (Hans Rudolph Series1101 simulator). And its mechanics was set in two models of obstructive and restrictive ventilatory dysfunction. All ventilators were set at 15 cmH2O (1 cmH2O = 0.098 kPa) pressure support and 5 cmH2O positive end-expiratory pressure (PEEP). Tests were conducted at the level of air leaks (24-28 L/min). Cycling delay time, tidal volume and airflow were collected.

RESULTS

Compared with Curative Flexo ST 30 with the ETS setting at the most sensitive level, the use of digital Auto-Trak(TM) system (Respironics Synchrony) was associated with milder delay cycling ((68.9 ± 13.3) vs (121.4 ± 13.2) ms, P < 0.05) in obstructive condition. The tidal volume (VT), inspiratory time (TI vent) and peak expiratory flow (PEF) increased after adjusting the ETS level. Premature cycling was detected in restrictive condition with both ventilators. Peak inspiratory flow (PIF) and PEF significantly increased as VT and TI vent decreased. Delay cycling ((64.3 ± 15.3) ms) was present in Flexo ST 30 when ETS was at most insensitive level.

CONCLUSIONS

There are significant differences in performances and cycling-off in obstructive and restrictive conditions among 2 bilevel ventilators. And it may be due to the software of algorithm. Modifications of ETS can affect the ventilatory parameters to improve patient-ventilator synchrony in the presence of air leaks. The Auto-Trak system during PSV show similar results and better synchronzation compared with conventional adjustments.