Minimizing troublesome side effects is the key to long-term patient use of CPAP.

Treatment of obstructive sleep apnea (OSA) with nasal continuous positive airway pressure (CPAP) has proven to be both effective and safe, but difficult to use. The majority of patients experience significant side effects, particularly in the early stages. Wearing a tight-fitting mask attached to a noisy machine is not most people’s formula for a good night’s sleep, and it is unlikely that many people would use CPAP if it did not result in such large improvements in daytime alertness.

Many patients currently using CPAP await a more comfortable form of treatment. Unfortunately, the alternatives available are less reliable and present their own set of side effects, and there is no promising new therapy on the horizon. For the time being, CPAP is the gold standard treatment of OSA.

Contraindications For CPAP

Serious side effects with CPAP are very rare but do occur. One contraindication for CPAP is communication between the upper airway and meningeal space, and there are case reports of both pneumoencephalitis1 and meningitis occurring in these patients.2 There is a high prevalence of ischemic heart disease in patients treated with CPAP, but important cardiac side effects have not been reported. There is one published case study3 of atrial arrhythmias developing in CPAP patients. Respiratory disease is also common, but CPAP has proven safe even in patients with advanced respiratory failure. There is the potential for excessive CPAP pressure to induce hypoventilation and central apnea, but this can be avoided by careful pressure setting, and serious complications have not been reported. A case of massive epistaxis due to CPAP has been published.4

Patients starting CPAP usually experience a multitude of irritating problems that may ultimately reduce their compliance with treatment (Table 1, page 76). Many of the problems mentioned, however, are not true side effects but are caused by a lack of familiarity with the equipment and tend to resolve spontaneously over time. (For the purposes of this article, they will be called side effects.) Patients who are poorly compliant with treatment from the start often have difficulty identifying exactly what it is about CPAP therapy they dislike. For some, the entire experience of being attached to a machine while they are asleep is unpleasant, and there is no particular aspect of therapy they can identify as irksome. This may be one reason published studies have not regularly found a relationship between specific side effects and poor compliance.

Equipment Problems

There are four categories of side effects: mask problems, upper airway symptoms, positive pressure problems, and machine and tubing problems. The most common side effects are related to mask problems and upper airway symptoms, which each affect 40 percent to 65 percent of patients starting CPAP.5-7

The nasal mask–the interface between the patient and the equipment–can be a source of numerous problems. A feeling of claustrophobia upon wearing a mask is a significant problem in many patients and may lead to early rejection of CPAP. Slowly introducing the mask, then the pressure, during the daytime and giving patients adequate time to acclimatize before they undergo their pressure-setting study can alleviate this problem. A great deal of reassurance and support may be required, but compliance generally improves in a few days.

A well-fitted mask is essential to avoid some of the most annoying side effects of CPAP. Several design advances have been made over the past decade that have improved both mask comfort and the range of alternatives available. There is a variety of soft silicon nasal masks available, which are preferred by many patients. The seal between the mask and the patient’s face also has been improved. There are now masks that have a thin silicon membrane that follows facial contours rather than flattening them out. These masks generally provide a good seal without the headgear pressure required with standard silicon masks, but are more likely to be dislodged during changes in body position.

A mask with a silicon membrane and tubing attached to the headgear to reduce the risk of the mask dislodging has recently been marketed and has been popular with patients. The seal between mask and face may also be improved by using a gel-filled mask. Some patients, however, find the increased weight of these masks uncomfortable. Also, there have been problems with gel leaks. Adams circuits, with a seal provided by nasal pillows, provide an alternative to nasal masks and are preferred by some patients.

Despite improvements in mask design, leaks are still a problem for some patients, particularly those with a narrow nasal bridge, deep labial folds, an asymetrical face, or facial hair. In an effort to reduce leaks, patients may tighten the headgear to increase pressure on the mask. This usually does not fix the leak but may lead to pain and ulceration of the bridge of the nose and pain in the gums and teeth.

Reducing Side Effects

More than half the patients starting CPAP experience worsened or new upper airway symptoms including epistaxis, nasal congestion, and dry nose, throat, and mouth.5-7 These symptoms are caused by mouth leaks. There is a high prevalence of chronic nasal disease among patients referred to a sleep laboratory, and as a result, many are chronic mouth breathers. This normally has no consequences, but on CPAP, mouth breathers develop mouth leaks. They may be surprisingly difficult to detect by observation but frequently exceed 30 L/min. High unidirectional airflow overwhelms the ability of the mucosa to remain hydrated, leading to symptoms of dryness. Excessive drying of the nasal mucosa can lead to the release of inflammatory mediators resulting in nasal congestion. Increasing nasal congestion increases the propensity to mouth breathe, creating a vicious circle. Upper airway symptoms are most common in winter when reduced temperatures decrease the water content of room air.

Nasal congestion and large increases in nasal resistance can be induced by short periods of mouth leak but are prevented by fully humidifying inspired air with a hot water bath humidifier. Cold passover humidifiers produce insufficient humidity
to prevent mucosal drying.

Nasal symptoms should be viewed not only as annoying, but also as an indicator that treatment is possibly being compromised. Changes in nasal resistance sufficient to reduce pharyngeal pressures by
5 cm H2O are readily induced by short periods of mouth leak using room air. Reduction of pharyngeal pressure may lead to treatment failure in patients who develop nasal congestion while using CPAP.

A number of methods may be employed to reduce upper airway symptoms. Preexisting nasal disease should be treated vigorously to reduce nasal congestion. Topical nasal treatments such as steroids, decongestants, and ipratropium are all ineffective against the effects of drying but may be useful in treating preexisting disease. Warming the bedroom can be helpful. Methods aimed at reducing mouth leaks may also be tried. Chin straps may be effective but many patients find them uncomfortable, particularly mouth breathers who do not like their mouth being held shut. Full face masks are available, but they are difficult to seal and are unpopular with patients.

Cold passover humidifiers are relatively cheap but produce modest levels of humidity and are often ineffective. Heated humidifiers produce high levels of humidity even at high flow rates. There may be problems with condensation, but this can be minimized by reducing heat loss from the tubing. They provide the most effective and reliable means of eliminating upper airway symptoms.

Most patients have difficulties early in treatment learning to exhale against positive pressure. This can often be overcome by asking patients to take three or four very large breaths while using CPAP. The aim is to increase functional residual capacity (FRC), which stretches the chest wall and assists expiration. Most CPAP machines include an option to increase pressure gradually during the early stages of sleep. Many patients find this option useful, particularly during the first few weeks of treatment. Most patients can adjust their breathing to feel comfortable exhaling against positive pressure, but for the minority who cannot, bilevel positive airway pressure (BiPAP) systems are an option. Aerophagia (air swallowing) can be a problem, resulting in abdominal discomfort and flatulence. It can be treated by having a patient lie on his or her side.

Pressure-Related Side Effects

Although there is no evidence that side effects are proportional to the level of pressure, very high pressures are difficult to tolerate and are undoubtedly associated with a higher incidence of side effects such as mask and mouth leaks. Some sleep laboratories use heated humidification in patients who require very high pressures to control respiratory disturbances. The aim is to minimize nasal resistance and therefore keep mask pressure as low as possible. In general, there is little to be gained by making small pressure adjustments in an effort to improve comfort and compliance.

Noise is frequently reported by patients and their bed partners as a troublesome side effect. It is curious that bed partners are sometimes affected when the noise of the CPAP machine is more constant and quieter than the snoring it replaces. Problems with noise tend to resolve spontaneously with increasing familiarity, but if they are persistent, earplugs may provide a simple solution. If necessary, the CPAP machine may be moved away from the bedside with the addition of extra tubing, but mask pressure should be rechecked whenever extra tubing is fitted. With improvements in technology, CPAP machines are becoming quieter, and most now produce around 50 dB of noise.


Some initial studies9 of CPAP compliance reported low rates of use. Most recent studies, however, show good rates of acceptance, with between 70 percent and 85 percent10-12 of patients becoming regular users with an average daily use of 5 to 6 hours. It is very difficult to predict before treatment who will have difficulty with compliance. Patients who are not sleepy before treatment and those who have had a previous uvulopalatopharyngoplasty (UPPP) are generally identified as being poorly compliant. Factors such as severity of OSA, presence of comorbidity, and characteristics such as age and level of education are, surprisingly, not associated with compliance.

Compliance is determined early on, probably within the first few days of treatment. In one study, CPAP use at 4 days predicted use at 3 months. Clearly, the patient’s very early experience with CPAP has a strong and lasting effect. The obvious corollary to this observation is that any interventions are likely to have a greater impact on compliance if performed early in treatment.

There is a weak relationship between reported side effects and compliance. In one study6 noncompliant patients voiced significantly more complaints about CPAP equipment than those who kept it, but there were no specific problems that led to noncompliance. In other studies “nonphysical” side effects such as claustrophobia were weakly associated with noncompliance. In another,5 “nuisance symptoms,” such as machine noise, were weakly associated with noncompliance. In general, there are no specific side effects that predict poor compliance.

There are surprisingly few studies of interventions designed to improve compliance, particularly given the importance payors place on this issue. The only published studies of interventions have involved intensive support and education of CPAP users. There are now three published studies, two of which are positive.13-15 There is little doubt that support and education are vital in achieving compliance, and that they should be carried out early in treatment. There are no published studies showing that new-generation masks, CPAP or bilevel positive pressure systems, or any accessories are associated with an improvement in compliance.


Most patients starting CPAP experience side effects that may ultimately reduce their compliance with treatment. Although many side effects resolve spontaneously, the initial period of treatment is important in determining long-term compliance, so problems should be addressed without delay. Improvements in technology have increased the comfort of equipment, but the main determinant of compliance is, and is likely to remain, the quality of support and education patients receive.

Glenn Richards, MB, ChB, FRACP, is a respiratory and sleep physician at Green Lane Hospital, in Auckland, New Zealand.


1. Jarjour NN, Wilson P. Pneumocephalus associated with nasal continuous positive pressure in a patient with sleep apnea syndrome. Chest. 1989;96:1425-1426.

2. Bamford CR, Quan SF. Bacterial meningitis–a possible complication of nasal continuous positive airway pressure therapy in a patient with obstructive sleep apnea syndrome and a mucocele. Sleep. 1993;16:31-32.

3. Meurice JC, Mergy J, Rostykus C, et al. Atrial arrhythmia as a complication of nasal CPAP. Chest. 1992;102:640-642.

4. Strumpf PA, Harrop P, Dobbin J, Millman RP. Massive epistaxis from nasal CPAP therapy. Chest. 1989;95:1141.

5. Engleman HM, Asgari-Jirhandeh N, McLeod A, Ramsay CF, Dearly IJ, Douglas NJ. Self-reported use of CPAP and benefits of CPAP therapy. Chest. 1996;109:1470-1476.

6. Pepin JL, Leger P, Veale D, Langevin B, Robert D, Levy P. Side effects of nasal continuous positive airway pressure in sleep apnea syndrome. Chest. 1995;107:375-381.

7. Hoffstein V, Viner S, Mateika S, Conway J. Treatment of obstructive sleep apnea with nasal continuous positive airway pressure–patient compliance, perception of benefits and side effects. Am Rev Respir Dis. 1992;145:841-845.

8. Richards GN, Cistulli P, Ungar RG, Berthon-Jones M, Sullivan C. Mouth leak with nasal continuous positive airway pressure increases nasal airway resistance. Am J Respir Crit Care Med. 1996;154:182-186.

9. Waldhorn RE, Herrick TW, Nguyen MC, O’Donnell AE, Sodero J, Potolicchio SJ. Long term compliance with nasal continuous positive airway pressure therapy of obstructive sleep apnea. Chest. 1990;97:33-38.

10. Rolfe I, Olsen LG, Saunders NA. Long term acceptance of continuous positive airway pressure in obstructive sleep apnea. Am Rev Respir Dis. 1991;144:1130-1133.

11. Kribbs NB, Pack AL, Kline LR, et al. Objective measurement of patterns of nasal CPAP use by patients with obstructive sleep apnea. Am Rev Respir Dis. 1993;147:887-895.

12. 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.

13. Fletcher EC, Luckett RA. The effects of positive reinforcement on hourly compliance in nasal continuous positive airway pressure users with obstructive sleep apnea. Am Rev Respir Dis. 1991;143:936-941.

14. Likar LL, Panciera TM, Erickson AD, Rounds S. Group education sessions and compliance with nasal CPAP therapy. Chest. 1997;111:1273-1277.

15. Chervin RD, Theut S, Bassetti C, Aldrich MS. Compliance with nasal CPAP can be improved with simple interventions. Sleep. 1997;20:284-289.