Study objective: To determine whether an exhalation valve designed to minimize rebreathing improves daytime or nocturnal gas exchange or improves symptoms compared with a traditional valve during nocturnal nasal ventilation delivered using a bilevel pressure ventilation device.
Design: Prospective direct comparison trial with each patient sequentially using both valves, during a 2-week run-in period with a traditional valve, a 2-week trial with the nonrebreathing valve, and a 2-week washout period with the traditional valve.
Setting: Outpatient pulmonary function laboratory and home nocturnal monitoring.
Patients: Seven patients who received long-term (> 1 year) nocturnal nasal bilevel pressure ventilation with an expiratory pressure of ≤ 4 cm H2O.
Intervention: Symptoms, pulmonary function, and arterial blood gas levels were assessed at each of three daytime sessions after the sequential 2-week periods using the different valves. Nocturnal studies used a multichannel recorder that measured heart rate, chest wall impedance, nasal airflow, and oximetry. End-tidal Pco2 (Petco2) from the mask and transcutaneous Pco2 (Ptcco2) were also monitored nocturnally.
Results: Seven patients with a variety of neuromuscular, chest wall, and obstructive defects were enrolled. No mean differences in daytime arterial blood gas levels, pulmonary functions, nocturnal vital signs or oximetry, or Ptcco2 were apparent regardless of the exhalation valve used. The multichannel recording was indicative of an air leak at least one third of the time, and the Petco2 tracing detected a blunted signal or no signal from the mask during the majority of the recording time.
Conclusion: The use of an exhalation valve designed to minimize rebreathing did not improve daytime or nocturnal gas exchange or symptoms in patients receiving long-term nasal bilevel pressure ventilation in comparison with a traditional exhalation valve, most likely because of air leakage and escape of CO2 via other routes.