Comparative Physiologic Effects of Noninvasive Assist-Control and Pressure Support Ventilation in Acute Hypercapnic Respiratory Failure

To compare the effects of noninvasive assist-control ventilation (ACV) and pressure support ventilation (PSV) by nasal mask on respiratory physiologic parameters and comfort in acute hypercapnic respiratory failure (AHRF). A prospective randomized study. A medical ICU. Fifteen patients with COPD and AHRF were consecutively and randomly assigned to two noninvasive ventilation (NIV) sequences with ACV and PSV mode, spontaneous breathing (SR) via nasal mask being used as control. ACV and PSV settings were always subsequently adjusted according to patient's tolerance and air leaks. Fraction of inspired oxygen did not change between the sequences. ACV and PSV mode strongly decreased the inspiratory effort in comparison with SR. The total inspiratory work of breathing (WOBinsp) expressed as WOBinsp/tidal volume (VT) and WOBinsp/respiratory rate (RR), the pressure time product (PTP), and esophageal pressure variations (ΔPes) were the most discriminant parameters (p