Noninvasive pressure support versus proportional assist ventilation in acute respiratory failure

Background. Although conventional pressure ventilation (PSV) decreases the rate of intubation in acute respiratory failure, patient-ventilator dyssynchrony is a frequent cause of failure. In proportional assist ventilation (PAV), pressure is applied by the ventilator in proportion to the patient-generated volume and flow; therefore, there is automatic synchrony between the patient's effort and the ventilatory cycle. Objective. The aim of this study was to compare the effects of PSV and PAV during noninvasive ventilation in the treatment of acute respiratory failure. Design. Prospective randomised study. Setting. A multidisciplinary 24-bed intensive care unit of an acute-care teaching hospital in Alicante, Spain. Patients. This study included 117 consecutive adult patients with acute respiratory failure randomised to noninvasive ventilation delivered by PSV (n = 59) or PAV (n = 58). Measurements and results. There were no statistically significant differences between patients assigned to each mode of ventilation with regard to baseline parameters and aetiological diagnoses of acute respiratory failure. With regard to outcome data, no significant differences were observed between PSV and PAV in the frequency of intubation (37% vs 34%), mortality rate (29% vs 28%), and mean length of stay. Subjective comfort (0-10 visual analogue scale) was rated higher and intolerance occurred less frequently (3.4% vs 15%, P = 0.03) in the PAV than in the PSV mode. Conclusions. Although PAV seems more comfortable and intolerance occurred less frequently, no major differences exist in terms of physiological improvement or in terms of outcomes when comparing PSV and PAV.