Effects of noninvasive positive pressure ventilatory support in non-COPD patients with acute respiratory insufficiency after early extubation

Objective: To investigate the effects of noninvasive positive pressure ventilation (NPPV) on pulmonary gas exchange, breathing pattern, intrapulmonary shunt fraction, oxygen consumption, and resting energy expenditure in patients with persistent acute respiratory failure but without chronic obstructive pulmonary disease (COPD) after early extubation. Design: Prospective study. Setting: Multidisciplinary intensive care unit of a university hospital. Patients: 15 patients after prolonged mechanical ventilation (> 72 h) with acute respiratory insufficiency after early extubation. Interventions: Criteria for early extubation were arterial oxygen tension (PaO2) greater than or equal to 40 mm Hg (fractional inspired oxygen 0.21), arterial carbon dioxide tension (PaCO2) less than or equal to 55 mm Hg, pH > 7.32, respiratory rate less than or equal to 40 breaths per min, tidal volume (V-T) greater than or equal to 3 ml/kg, rapid shallow breathing index less than or equal to 190 and negative inspiratory force greater than or equal to 20 cmH(2)O. After extubation, two modes of NPPV were applied [continuous positive airway pressure (CPAP) of 5 cmH(2)O and pressure support ventilation (PSV) with 15 cmH(2)O pressure support]. Measurements and main results: Oxygenation and ventilatory parameters improved during both modes of NPPV (p < 0.05): increase in PaO2 of 11 mm Hg during CPAP and 21 mm Hg during PSV; decrease in intrapulmonary shunt fraction of 7% during CPAP and 12% during PSV; increase in tidal volume of 1 ml/kg during CPAP and 3 ml/kg during PSV; decrease in respiratory rate 6 breaths/min during CPAP and 9 breaths/min during PSV. Oxygen consumption (15 % during CPAP, 22 % during PSV) and resting energy expenditure (12% during CPAP, 20 % during PSV) were reduced (p < 0.05). PaCO2 decreased, whereas minute ventilation and pH increased during PSV (p < 0.05). The median duration of NPPV was 2 days. Two patients had to be reintubated. Conclusions: in non-COPD patients with persistent acute respiratory failure after early extubation, NPPV improved pulmonary gas exchange and breathing pattern, decreased intrapulmonary shunt fraction, and reduced the work of breathing.