Physiologic effects of early administered mask proportional assist ventilation in patients with chronic obstructive pulmonary disease and acute respiratory failure

Objective: To evaluate the physiologic short-term effects of noninvasive pr oportional assist ventilation (PAV) in patients with acute exacerbation of chronic obstructive pulmonary disease (COPD). Design:Prospective, physiologic study. Setting: Respiratory intermediate intensive care unit. Patients: Seven patients with acute respiratory failure requiring noninvasi ve mechanical ventilation because of exacerbation of COPD. Interventions: PAV was administered by nasal mask as first ventilatory inte rvention. The setting of PAV involved a procedure to adjust volume assist a nd flow assist to levels corresponding to patient comfort. Volume assist wa s also set by means of the "run-away" procedure. Continuous positive airway pressure (CPAP) amounting to 2 cm H2O was always set by the ventilator. Th is setting of assistance (PAV) was applied for 45 mins. Thereafter, CPAP wa s increased to 5 cm H2O (PAV + CPAP-5) without any change in the PAV settin g and was administered for 20 mins. Oxygen was delivered through a port of the mask in the attempt to maintain a target Sao(2) >90%. Measurements and Main Results: Arterial blood gases, breathing pattern, and inspiratory effort were measured during unsupported breathing and at the e nd of PAV, and breathing pattern and inspiratory effort were measured after 20 mins of PAV + CPAP-5. PAV determined a significant increase in tidal vo lume and minute Ventilation (+64% and +25% on average, respectively) with u nchanged breathing frequency and a significant improvement in arterial bloo d gases (Pao, with the same oxygen supply, from 65 +/- 15 torr to 97 +/- 36 torr; Paco(2), from 80 +/- It torr to 76 +/- 13 torr; pH, from 7.30 +/- 0. 02 to 7.32 +/- 0.03). The pressure-time product calculated over a period of 1 min (from 318 +/- 87 to 205 +/- 145 cm H2O sec min(-1)) was significantl y reduced. PAV + CPAP-5 resulted in a further although not significant decr ease in the pressure-time product calculated over a period of 1 min (to 183 +/- 110 cm H2O sec min(-1)), without additional changes in the breathing p attern. Conclusions: Noninvasive PAV is able to improve arterial blood gases while unloading inspiratory muscles in patients with acute exacerbation of COPD.