Pressure Support and Pressure Assist/Control: Are There Differences? An evaluation of the Newest Intensive Care Unit Ventilators

Abstract

BACKGROUND: Pressure support (PS) has been widely studied in both patients and lung models, but there is little data available evaluating pressure assist/control (P A/C, frequently referred to as PCV) and no data comparing the operational capabilities of these two modes on the newest gen- eration of ICU ventilators. We used a spontaneously breathing lung model to evaluate the response of the following new generation ventilators to varying inspiratory demand in both PS and P A/C: BEAR 1000, Dräger Evita 4, Hamilton Galileo, Nellcor Puritan-Bennett 840 and 740, Siemens Servo 300A, TBird AVS. METHODS: A bellows-in-a-box lung model was set at a respiratory rate of 12 breaths/min, inspiratory time of 1.0 second, and peak inspiratory flows (modified square wave) of 40, 60, and 80 L/min. Each ventilator was set at three levels of PS and P A/C: 10, 15, and 20 cm H2O. On all ventilators, flow-triggering was set as sensitive as possible without causing self-triggering. RESULTS: Trigger pressure, trigger pressure-time product, inspiratory trigger time delay, venti- lator-delivered peak flow, inspiratory area as a percent of the ideal inspiratory area, expiratory time delay, supraplateau expiratory pressure change, and expiratory area all varied among venti- lators and at different lung model peak flows (p < 0.01 and ≥ 10% difference). However, PS and P A/C on a given ventilator only differed with regard to expiratory variables (p < 0.01 and ≥ 10% difference). CONCLUSION: In a given ventilator little difference exists in gas delivery and response variables between PS and P A/C, but performance differences do exist among the ventilators evaluated. Ventilator performance is diminished at high lung model peak flows and low pressure settings.