Background: Continuous positive airway pressure (CPAP)
is widely applied as a home treatment during sleep. Conventional CPAP
devices are based on a blower to generate nasal pressure and to
maintain air washout from the circuit. Because common CPAP systems do
not incorporate alarms, failure in the device or in the electric supply
could result in rebreathing.
Aim: To assess the
potential rebreathing to which a patient could be subjected after CPAP
Methods: Four conventional CPAP devices,
PV100 (Breas Medica; Molnlycke, Sweden), CP90 (Taema; Antony, France),
and SoloPlus and BiPAP (Respironics, Murrysville, PA), and three
common exhalation ports (Whisper Swivel [Respironics], Plateau[
Respironics], and 4-mm orifice) were tested in a bench study.
Rebreathing after failure was assessed by measuring the resistance of
the exhalation port (Rep) and the resistance of the tubing
plus CPAP device (Rtub), and by measuring O2
and CO2 concentrations in the nasal mask in a subject
breathing through a CPAP system.
Rep was much higher (approximately 30 cm
H2O × s/L) than Rtub (approximately 1 cm
H2O × s/L). Most (approximately 90%) of the breathing
tidal volume would flow from/to the tubing plus CPAP device, which
represents a dead space (≥ 0.5 L) similar to the patient’s tidal
volume. After CPAP failure, end-tidal O2 in the mask
changed from 16.8 to 9.2% and end-tidal CO2 in the mask
changed from 4.2 to 6.2%. By contrast, O2 and
CO2 did not change when a nonrebreathing valve was placed
in the mask.
Conclusions: Common CPAP systems run a
risk of inducing rebreathing in case of failure. This risk could be
easily avoided by including a passive valve in the