Assisted ventilation in patients with acute respiratory distress syndrome: Lung-distending pressure and patient-ventilator Interaction

Background: In ARDS patients, use of assisted mechanical ventilation is subject of debate. Assisted ventilation has benefits over controlled ventilation, such as preserved diaphragm function and improved oxygenation. Therefore, higher level of 9patient control9 of ventilator assist may be preferable. However, assisted modes may also increase risk of high tidal volumes and lung-distending pressures. This study quantifies how differences in freedom to control the ventilator, affect lung protective ventilation, breathing pattern, and patient ventilator-interaction. Methods: Twelve ARDS patients were randomly ventilated with assist pressure control ventilation (PCV), pressure support ventilation (PSV) and neurally adjusted ventilatory assist (NAVA). Transpulmonary pressure, tidal volume, respiratory variability, and patient-ventilator interaction were measured. Results: Mean delta inspiratory transpulmonary pressure was lower with NAVA (10.3±0.7, 11.2±0.7, and 9.4±0.7 cmH2O for PCV, PSV, and NAVA; P<0.01). Tidal volume was similar for PCV, PSV, and NAVA (6.6 [5.7-7.0], 6.4 [5.8-7.0] and 6.0 [5.6-7.3] ml/kg), but respiratory variability was higher with NAVA (8.0 [6.4-10.0], 7.1 [5.9-9.0], and 17.0 [12.0-36.1] % for PCV, PSV, and NAVA; P<0.001). Patient-ventilator interaction improved with NAVA (6 [5-8] % error) compared to PCV (29 [14-52] % error) and PSV (12 [9-27] % error); P<0.0001. Conclusions: In mild to moderate ARDS patients, increasing freedom to control the ventilator maintains lung protective ventilation in terms of tidal volume and lung-distending pressure, but improves patient-ventilator interaction and preserves respiratory variability.