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Laboratory and Animal Investigations |

Potential Rebreathing After Continuous Positive Airway Pressure Failure During Sleep*

Ramon Farré, PhD; Josep M. Montserrat, MD; Eugeni Ballester, MD; Daniel Navajas, PhD
Author and Funding Information

*From the Unitat de Biofísica i Bioenginyeria (Drs. Farré and Navajas), Facultat de Medicina, Universitat de Barcelona; and Institut de Pneumologia i Cirurgia Toràcica (Drs. Montserrat and Ballester), Hospital Clinic, Institut d’Investigacions Biomèdiques August Pi Sunyer, Barcelona, Spain.

Correspondence to: Ramon Farré, Unitat Biofísica i Bioenginyeria, Facultat Medicina, Casanova 143, 08036 Barcelona, Spain; e-mail: farre@medicina.ub.es



Chest. 2002;121(1):196-200. doi:10.1378/chest.121.1.196
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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 failure.

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.

Results: 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 apparatus.

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