Noninvasive proportional assist ventilation compared with noninvasive pressure support ventilation in hypercapnic acute respiratory failure

Objectives: To compare short-term administration of noninvasive proportional assist ventilation (NIV-PAV) and pressure support ventilation (NIV-PSV). Design: Prospective, crossover, randomized study. Setting: Medicosurgical intensive care unit in a nonteaching hospital. Patients: Twelve chronic obstructive pulmonary disease patients admitted for hypercapnic acute respiratory failure. Intervention: NIV-PSV and NIV-PAV given in a randomized order after baseline evaluation in continuous positive airway pressure. Using a flow-triggering ventilator, NIV-PAV was adjusted using the runaway method and compared with NIV-PSV at similar peak inspiratory airway pressure. Measurements and Main Results: Flow, airway pressure, and changes in esophageal pressure were measured and the tidal volume, the patient's inspiratory work of breathing, and the esophageal pressure-time product were calculated. Arterial pH and Paco(2) were measured and breathing comfort was assessed using a visual analogic scale. Peak inspiratory airway pressure (17 +/- 3 cm H2O) and tidal volume were similarly increased with the two modalities with no change in respiratory rate. The change in esophageal pressure was similarly decreased (from 20 8 cm H2O in continuous positive airway pressure to 12 7 in NIV-PSV and 10 +/- 5 cm H2O in NIV-PAV) as well as inspiratory muscle effort indexes. Arterial pH and PaCO2 were similarly improved. Breathing comfort was significantly improved in NIV-PAV (+38 38%) but not in NIV-PSV (+ 11 +/- 23%). The tidal volume was more variable in NIV-PAV (89 +/- 18%) than in NIV-PSV (15 +/- 8%) and changes in tidal volume variability were significantly correlated (P=.02) with changes in breathing comfort. Conclusions: In chronic obstructive pulmonary disease patients with hypercapnic acute respiratory failure, NIV-PAV was able to unload inspiratory muscles similarly to NIV-PSV but may be more comfortable than NIV-PSV.