Automation of expiratory trigger sensitivity in pressure support ventilation.

Patients under pressure support ventilation sometimes encounter patient-ventilator asynchrony in the transition from inspiration to expiration, that is, expiratory asynchrony. This problem is caused by the incompatibility of the fixed level of expiratory trigger sensitivity termination criteria (i.e., flow termination criteria) in the ICU ventilators to various patient conditions. The user-adjustable expiratory trigger sensitivity implemented in some newly released ventilators has been experienced to be difficult to use and unable to adapt ever-changing patient conditions without user intervention, although it provides more flexibility. This article elucidates the rationale for automatic control of the expiratory trigger sensitivity and evaluates the automation system with a bench setup. The evaluation data suggest that good expiratory synchronies can be achieved through automatic adjustments of expiratory trigger sensitivity.