Effects of Different Pressure Support Termination on Patient-Ventilator Synchrony

Abstract

Background

In pressure support ventilation (PSV), ventilators terminate their flow when the inspiratory flow decays to a certain flow (flow criteria) or when the airway pressure rises a certain amount above the set pressure support level (pressure criteria). There are significant differences among intensive care unit ventilators in regard to these termination criteria.

Purpose

In this adult simulation study, we investigated if the termination criteria used in intensive care unit ventilators affect the patient-ventilator synchrony in the transition to exhalation.

Methods

A two-compartment lung model was used to simulate spontaneous breathing of the patient with high demand (peak flow of 60 L/min) or low demand (peak flow of 30 L/min). Three ventilators with different flow criteria and pressure criteria in the inspiratory termination were alternately attached to the test lung: the Nellcor Puritan Bennett 7200ae (NPB7200ae), the Siemens Servo300 (SV300), and the Newport Wave E200 (E200). During testing, the PSV level was set at 10 cm H₂O with positive end-expiratory pressure of 0 or 5 cm H₂O. The termination delay time, termination type, inspiratory muscle work, plateau and peak inspiratory pressures, and inspiratory area percent were measured. The tests were conducted at the compliance of 20, 40, and 80 mL/cm H₂O, with a resistor of R5 or R20.

Results

In most of the experimental settings, all three ventilators terminated their flow within 0.1 second before or after the end of the 'patient' inspiratory effort. In the 'patient' with long time constant, termination criteria in the SV300 delayed the inspiratory termination by 0.5 second. In all settings in the NPB7200ae and some settings in the E200, the ventilator flow was terminated by the pressure criteria, not by the flow criteria. The NPB7200ae showed pressure undershoot during the first half of the inspiration and required the highest patient work in all settings, especially at high patient demand. In the SV300, the actual support level was higher than the set level. Its peak inspiratory airway pressure was also the highest among the three ventilators. There was a trigger dyssynchrony in the E200 at high demand with high resistance/ high compliance.

Conclusion

In most settings, the termination criteria used in PSV in the three ventilators provided a relatively reasonable patient-ventilator synchrony in the transition to exhalation. The marked delay in the ventilator inspiratory termination may occur under the conditions of long time constant with low demand in the SV300, which resulted mainly from the combination of the inappropriate pressure criteria and flow criteria.