Objective: To evaluate the acute effects of noninvasive positive pressure ventilation (NPPV) in patients with stable chronic respiratory failure secondary to cystic fibrosis.
Patients: Eight patients (29+/-5 years of age) with severe airflow limitation (mean FEV1, 24+/-3% predicted) and chronic respiratory failure (PaO2=67+/-15 mm Hg and PaCO2=50+/-4 mm Hg) were evaluated.
Methods: Tidal volume, respiratory rate, minute ventilation, oxygen saturation, and transcutaneous CO2 (TcCO2) measurements were made over a 20-min period before and after the application of NPPV (inspiratory pressure of 10 to 12 cm H2O and expiratory pressure of 4 to 6 cm H2O).
Results: NPPV increased saturation from 88+/-2% to 90+/-1% (p<0.05) and decreased TcCO2 from 51+/-3 mm Hg to 50+/-2 mm Hg (p<0.05). Tidal volume increased from 219+/-20 mL to 256+/-37 mL (p=not significant [NS]) and respiratory rate decreased from 24+/-2 to 18+/-1 (p<0.01). Minute ventilation decreased from 5.3+/-0.8 L/min to 4.6+/-0.6 L/min (p=0.08). There was no change in duty cycle (32+/-5% to 34+/-5%, p=NS). In two patients, esophageal pressure measurements were also recorded. There was a decrease in pressure from -21+/-1 cm H2O to -11+/-2 cm H2O and -14+/-1 cm H2O to -7+/-1 cm H2O.
Conclusions: In patients with stable, severe cystic fibrosis, NPPV (1) acutely improves gas exchange, (2) decreases minute ventilation, suggesting either a reduction in CO2 production or an increase in alveolar ventilation, and (3) reduces work of breathing.