CHEST. 2003;123(3) 

In This Article

Continuous Positive Airway Pressure

Treatment of obstructive sleep apnea with continuous positive airway pressure (CPAP) is less than ideal, not because the concept is incorrect but because the delivery is cumbersome and patients find it difficult to adapt to its use. Apart from being anchored to a mask, tubing, and a potentially noisy pressure-generating device, there may be nasal dis-comfort, nasal congestion, nasal obstruction, claustrophobia, the feeling of being either overventilated or underventilated, and mouth and mask leaks that make acceptance and adherence with nasal CPAP difficult for many patients. Several approaches[1,2,3,4] have had some success in overcoming the disadvantages of CPAP including heated humidification, chin straps, treatment of nasal congestion both pharmacologically and surgically, use of hypnotics, different types of interfaces such as nasal cannulas, or a full-face mask (also called an oronasal mask). Despite these approaches, adherence and acceptance are less than ideal.[5]

An alternative that would avoid nasal congestion and obstruction and potentially would lessen the claustrophobic feeling from a confining mask would be to deliver CPAP through the mouth. However, although there are at least two devices available in the United States that permit oral CPAP, a search of the literature fails to identify a single peer-reviewed study using such an approach. One of these devices is a combination anterior mandibular advancement dental device with an orifice for optional CPAP.[6] The other device is the oral mask, similar to the one examined in the study by Smith et al in this issue of CHEST (see page 689), which fits over the lips and seals the mouth with an orifice for delivery of CPAP and an oral retainer that depresses the anterior portion of the tongue. Although the technology is available, many questions about its use remain to be answered.

Smith et al have made a small but important step forward in validating that oral CPAP is a potentially viable method of treating patients with obstructive sleep apnea. This preliminary study of seven subjects (five men and two women) addresses a focused and relevant question. Does the use of an oral interface to deliver CPAP produce equivalent pressure-flow curves of the upper airway, indicating that nasal and oral CPAP are potentially therapeutically equivalent? Although it might seem intuitive that "splinting" the airway with pressure from the nose or mouth would lead to similar results, the differing anatomy and geometry of the oral route vs the nasal route raised the possibility that differing pressures would be required. The data from this small sample suggest that there are not marked differences in the pressure required to keep the airway from collapsing and to maintain airway patency without flow limitation (ie, without continued partial upper airway obstruction) during tidal breathing. The authors also allowed subjects to sleep with the oral device without the nose clip, which was used during pressure-flow curve measurements. There was no apparent loss of effectiveness (pressure-flow curves were not measured) of oral CPAP. Of note, the pressure that eliminated flow limitation in this group of subjects with severe obstructive sleep apnea averaged 11 cm H2O.

While this is a promising start, many questions remain. Those include, among others, patient comfort with differing pressures, the obligatory need to keep the mouth sealed shut all night with the device, further examination of the position of the tongue that might potentially occlude the airway orifice on an individual basis, the possible need for heated or room-temperature humidification, the need for a nose clip to prevent nasal breathing or leakage on an individual basis, its use with an edentulous patient, the potential that the flexibility of the soft tissues of the mouth such as the cheeks may produce discom-fort with distension from mouth pressure (particularly if higher pressures are required), and the possibility of sex differences in response to oral CPAP. Furthermore, although the study suggests that the airway mechanics are similar during oral and nasal CPAP during non-rapid eye movement sleep, only a select few measurements were made, and there is no description of whether body or head position or rapid eye movement (REM) sleep had any effect on the results. These conditions may potentially affect the results by putting pressure or stress on the mouth (head position), by relaxing the upper airway (REM sleep), or by increasing pressures to prevent airway collapse and maintain airway patency (head position, body position, or REM sleep). In addition, as with any occlusion of the mouth, there is the hypothetical possibility of the aspiration of stomach contents should the patient regurgitate during the night and not be able to expel the emesis through an occluded mouth. Of note, this is also a hypothetical possibility with a full-face mask[1,2] but there are few if any documented cases of this occurrence.

Until there have been properly performed randomized and comparative trials -- including attention to long-term maintenance of CPAP levels, adaptability to autotitrating CPAP systems, general sleep architecture, the durability of the oral mask, body and head position, airway characteristics and effectiveness during REM sleep, daytime sleepiness, other outcomes such as health status and ideally cardiovascular complications -- the use of oral CPAP will remain experimental. To date, there is no published peer-reviewed documentation of the potential side effects and general therapeutic effectiveness of oral CPAP. If one decides to treat a patient with oral CPAP, there should be careful follow-up with close questioning of the patient and documentation regarding the safety and effectiveness of the treatment, including a provision for follow-up polysomnography. Whether patients will prefer oral CPAP is not known. For example, full-face masks are in use for patients, usually those who do not respond to nasal CPAP. However, there are data to suggest that patients generally prefer nasal CPAP and are more adherent to therapy when compared to the use of a full-face mask as the initial approach to treatment.[7] Similarly, until studied, it is not clear whether oral or nasal CPAP would be preferred by the majority of patients.

One of the available devices is intriguing in that it combines mandibular advancement with the potential for oral CPAP. The mandibular advancement feature may modify the geometry of the airway so that it is hypothetically possible that this would lead to lower CPAP pressures than with the use of oral or nasal CPAP without mandibular advancement. This hypothesis should be tested since it is a common experience that tolerance declines in some patients with higher CPAP pressures.

In summary, nasal and oronasal CPAP treatment are effective when tolerated. Unfortunately, many patients find CPAP difficult to tolerate and, even when tolerated, may have difficulty keeping the mask in place. Oral delivery may hypothetically benefit such patients as an alternative to the nasal and oronasal delivery of CPAP. Unfortunately, we have barely progressed beyond the hypothetical stage to a practical and documented understanding of the place, if any, for the oral delivery of CPAP. To state it another way, caveat emptor (buyer beware)!

Michael R. Littner, MD, FCCP, Los Angeles, CA

Dr. Littner is affiliated with the Pulmonary, Critical Care, and Sleep Medicine Division, Veterans Affairs Greater Los Angeles Healthcare System, and is Professor of Medicine, David Geffen School of Medicine, University of California at Los Angeles. Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (e-mail: permissions@chestnet.org).

Correspondence to: Michael R. Littner, MD, FCCP, Pulmonary Department, 16111 Plummer St (111P), Building 200, Room 3534, North Hills, CA 91343.

  1. Prosise GL, Berry RB. Oral-nasal continuous positive airway pressure as a treatment for obstructive sleep apnea. Chest 1994; 106:180-186

  2. Sanders MH, Kern NB, Stiller RA, et al. CPAP therapy via oronasal mask for obstructive sleep apnea. Chest 1994; 106:774-779

  3. Zozula R, Rosen R. Compliance with continuous positive airway pressure therapy: assessing and improving treatment outcomes. Curr Opin Pulm Med 2001; 7:391-398

  4. Massie C, Hart W, Peralez K, et al. Effects of humidification on nasal symptoms and compliance in sleep apnea patients using continuous positive airway pressure. Chest 1999; 116:403-408

  5. Reeves-Hoche MK, Meck R, Zwillich CW. Nasal CPAP: an objective evaluation of patient compliance. Am J Respir Crit Care Med 1994; 149:149-154

  6. OPAP Inc. Oral pressure appliance. Available at: www. opap.com. Accessed February 6, 2003

  7. Mortimore IL, Whittle AT, Douglas NJ. Comparison of nose and face mask CPAP therapy for sleep apnoea. Thorax 1998; 53:290-292