The Efficacy of Nasal Continuous Positive Airway Pressure in the Treatment of Obstructive Sleep Apnea Syndrome Is Not Proven

John Wright

Clinical Epidemiology and Public Health, Bradford Hospitals NHS Trust, Bradford, United Kingdom

Trevor Sheldon

Department of Health Studies, University of York, York, United Kingdom

	A LABEL IN SEARCH OF AN ILLNESS

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Until recently the common definition used for sleep apnea was to take an apnea-hypopnea index (AHI) cutoff of 15. However, population-based studies have found that 10-20% of middle-aged men have sleep apnea by this criterion (1). In addition there is poor correlation between AHI and sleepiness. For example, the prevalence of excessive daytime sleepiness has been found to be about 40% in people with and without sleep-disordered breathing (3).

Because both excessive daytime sleepiness and having an AHI > 15 is common, many people will have both by chance, even without there being a causal relationship between the two. In addition, many patients with sleepiness caused by sleep apnea have an AHI of less than 15. A definition that incorporates daytime sleepiness has replaced the arbitrary and narrow earlier definition. However, once sleepiness becomes integral to the definition we cannot discuss the causal relationship between sleep apnea and sleepinessit is now tautological. This also creates uncertainty as to how we classify severity of disease. Furthermore, in elderly populations, the prevalence of sleep-disordered breathing has been found to be up to 60%, making it almost normal (4).

Defining what is normal and what constitutes disease is often problematic, especially when a new syndrome is evolving. In such cases definitions are often best linked to the benefits of treatment rather than to arbitrary measurements.

	AN ILLNESS IN SEARCH OF A DISEASE

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Traditional reviews in leading medical journals have made claims about the importance of sleep apnea in causing death and disability (5). One editorial writer claimed that the "staggering" public health impact of sleep apnea was as big as that of smoking (5).

Our systematic review (8) demonstrated that the evidence of causal association with disease was weak and contradictory. Evidence of a causal link with road traffic accidents was stronger but still flawed and our conclusion was reiterated in a recent call for "properly designed studies to investigate the association with injury and identify effective preventive strategies" (9).

Although considering treatment for excessive sleepiness, the main reason for presentation, is legitimate, our review reassured patients alarmed that nonadherence might cause them to "die in your sleep" (10).

	A DISEASE IN SEARCH OF A TREATMENT

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Our systematic review also highlighted the paucity of good-quality clinical trials evaluating the clinical effectiveness of continuous positive airway pressure (CPAP). The challenge to researchers to obtain better evidence is being answered. Two studies have demonstrated therapeutic benefit in (mostly male) patients with fairly severe disease (11, 12). CPAP was shown to improve sleepiness, mood, and quality of life measures. The importance of including comparable (sham CPAP) placebos was also demonstrated (11).

The real uncertainty exists in the extension of treatment to patients with milder disease. As with all new treatments there is a danger of an inexorable "technology creep" and diffusion for use in patients outside evaluated inclusion criteria. This problem is exacerbated in sleep apnea, for which there is definitional uncertainty and financial incentives to overtreat. Extending treatment from the few with severe disease to the many with mild disease will have major implications for the use of health resources. There is a danger that such a change in clinical practice will become entrenched before objective evaluation assesses the benefits.

Treatment of patients with mild sleep apnea can improve some symptom scores but has poor acceptability among patients (13). Such evidence does not support claims that CPAP is of proven benefit for the large population with daytime sleepiness (14). Further good-quality trials using appropriate outcome measures are needed to evaluate the clinical and cost effectiveness of treatment for these patients with milder disease.

	TREATMENTS IN SEARCH OF AN EVALUATION

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Although CPAP is an effective treatment for fairly severe sleep apnea, it is an uncomfortable, noisy, intrusive intervention with poor adherence and well described, occasionally serious, side effects. However, trials have demonstrated that patients with mild to moderate sleep apnea prefer treatment with oral prostheses over CPAP (15, 16). Patients should have accurate information to enable them to make an informed choice between alternative treatments rather than face a lottery with the intervention dependent on the type of specialist they consult.

The association between severity of disease and obesity is strong, consistent, and causal. Losing weight not only improves sleep apnea, but may cure it (17). For most patients, therefore, sleep apnea is a symptom of obesity and it is common sense that whenever possible we should treat the underlying cause rather than the symptom.

This is particularly true from a public health perspective approach, as the causal association between obesity and vascular disease is strong and well established. By treating the obesity of patients, we can reduce their risk of heart disease and stroke as well as treat their sleep apnea. This approach could improve the health of the overall population as well as that of individuals.

Unfortunately there are no magic pills or machines to treat obesity. Doctors tend to be nihilistic about persuading patients to lose weight. It is not surprising that common approaches to "go away and lose weight" rarely work (18). There are effective interventions (19); however, those involved in the first-line treatment of sleep apnea (e.g., respiratory physicians) are unlikely to have sufficient knowledge or experience to treat obesity effectively.

	CONCLUSIONS

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Our understanding of sleep-disordered breathing is in its infancy. Although trials show that CPAP relieves symptoms in patients with fairly severe sleep apnea, definitional problems and the lack of good evaluation of less severely affected patients leave much uncertainty.

If we look at other common diseases such heart disease and the effectiveness of thrombolysis, aspirin, angioplasty, and bypass surgery we find trials of hundreds or thousands of patients. These trials tell us which patients benefit, how great this benefit is and what the costs of alternative therapeutic options are. Similar research is still needed before CPAP is used to treat the large number of people with mild disease.

	References

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