Influence of expiratory trigger sensitivity setting on inspiratory cycling-off synchronization during noninvasive pressure support ventilation with different respiratory mechanics

Abstract

Objective To compare the inspiratory cycling-off synchronization with expiratory trigger sensitivity (ETS) setting during noninvasive pressure support ventilation (PSV) under the different conditions of respiratory mechanics. Methods Bi-level pressure ventilator was connected to a lung model (Hans Rudolph Series1101 simulator). And its mechanics was set to normal, obstructive and restrictive ventilation dysfunction. Tests were performed with pressure support levels of 10 (in normal condition, 1 cmH2O = 0.098 kPa) and 15 cmH2O, 5 cmH2O positive end-expiratory pressure (PEEP). The data including cycling delay time (Td), tidal volume (TV) and airflow were collected in the presence of air leaks (24 -28 L/min). Results Significant performance on airflow was observed in various respiratory mechanics conditions. The peak inspiratory flow (PIF) and peak expiratory flow (PEF) were different, and the tidal volume, PEF and inspiratory time were increased after decreasing the ETS level. Premature cycling occurred frequently in normal and restrictive model. Delay cycling was found only when the ETS setting was at the lowest level (about 5% of PIF), at which Td were (15.20 ± 0.43) ms and (105.00 ± 15.82) ms. In obstructive model, PIF and PEF were significantly decreased, and delay cycling was always present. Td were increased after the ETS setting was changed from the most sensitive level to moderate level: (51.30 ± 12.63) ms vs. (162.40 ± 15.59) ms, as cycling-off criteria were reduced from (34.52 ± 3.36)% to (16.04 ± 2.58)% of PIF, and there were statistical differences (P <0.05). Severe delay cycling was found when the ETS level was at the lowest level. Conclusions There are significant differences in performances and cycling-off synchrony in various respiratory mechanics models during PSV. For Curative Flexo ST30 bi-level pressure ventilator, its flow cycling-off criteria range is about 5% -35% of PIF. The higher ETS level might be beneficial to improve patient-ventilator synchrony in patients with obstructive airway diseases, which could result in premature cycling in patients with restrictive disease. Key words: Respiration, artificial; Positive-Pressure Respiration; Respiratory mechanics