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Excessive daytime sleepiness in patients with sleep-disordered breathing

King Saud University, Riyadh, Saudi Arabia.

To the Editors:

I read with interest the article by Mediano et al. 1 about excessive daytime sleepiness (EDS) in patients with obstructive sleep apnoea (OSA). In order to investigate the determinants of EDS in OSA patients, the authors compared the demographics and polysomnographic variables of two groups of OSA patients who had a similar apnoea/hypopnoea index (AHI), age and body mass index (BMI). Nocturnal hypoxaemia was reported to be a major determinant of EDS in patients with OSA.

I would like to point out that the possible coexistence of obesity hypoventilation syndrome (OHS), which is a known cause of EDS, was not ruled out in the studied group 2. Hida et al. 3 have shown that OHS patients have a significantly higher Epworth Sleepiness Scale score compared with pure OSA patients matched for age, BMI and AHI. It is well documented that 70–90% of patients with OHS have predominantly obstructive events during sleep 4. Therefore, to rule out coexisting OHS, measurement of daytime blood gases and nocturnal monitoring of carbon dioxide arterial tension, as well as the observation for oxygen desaturation during sleep that is not explained by apnoeic or hypopnoeic events, become imperative.

Mediano et al. 1 reported that patients with EDS had lower nocturnal oxygen saturation and mean arterial saturation. However, the desaturation index was not reported. As patients with hypoventilation may have frequent episodes of desaturation without obstructive apnoeic or hypopnoeic events, it becomes important to compare the desaturation index in both groups. The group with EDS was found to have a longer apnoea duration, which the authors attributed to intrinsic differences in arousal thresholds or increased sleep pressure 1.

It is known that patients with OHS exhibit periods of sustained sleep hypoxaemia 5. Sustained hypoxaemia has been suggested as a cause of delayed arousal from sleep 6, which may explain the longer apnoea duration in the EDS group. The fact that patients with and without EDS had a similar age, BMI and AHI does not imply that they have the same underlying sleep-disordered breathing 1. A recent large study 7 reported no difference in AHI between OHS patients and pure OSA patients matched for BMI. In another recently published study 8, patients with OHS and hypercapnic respiratory failure were compared with patients with pure OSA matched to each subject using BMI, age and AHI measured at the time of diagnosis. Compared with pure OSA patients, OHS patients spent more time with arterial oxygen tension <90%, had lower mean saturation, a higher desaturation index and their lowest recorded oxygen saturation was significantly lower 8. We agree with Mediano et al. 1 that nocturnal hypoxaemia may play a role in the pathogenesis of EDS; however, we feel that OHS was not ruled out as a cause of EDS in the studied group.

Data suggest that obesity hypoventilation syndrome is both under recognised and underdiagnosed 2. To overcome these problems, the serum bicarbonate level should be measured in patients with sleep-disordered breathing, excessive daytime sleepiness and significant desaturation. An elevated serum bicarbonate level suggests the presence of obstructive sleep apnoea and should warrant measurement of daytime blood gases 9.

Statement of interest

None declared.

REFERENCES

1. Mediano O, Barceló A, de la Peña M, Gozal D, Agustí A, Barbé F. Daytime sleepiness and polysomnographic variables in sleep apnoea patients. Eur Respir J 2007;30:110–113.[Abstract/Free Full Text]
2. Olson AL, Zwillich C. The obesity hypoventilation syndrome. Am J Med 2005;118:948–956.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]
3. Hida W, Okabe S, Tatsumi K, et al. Nasal continuous positive airway pressure improves quality of life in obesity hypoventilation syndrome. Sleep Breath 2003;7:3–12.[CrossRef][Medline] [Order article via Infotrieve]
4. Chouri-Pontarollo N, Borel JC, Tamisier R, Wuyam B, Levy P, Pépin JL. Impaired objective daytime vigilance in obesity-hypoventilation syndrome: impact of noninvasive ventilation. Chest 2007;131:148–155.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]
5. Piper AJ, Grunstein RR. Current perspectives on the obesity hypoventilation syndrome. Curr Opin Pulm Med 2007;13:490–496.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]
6. Hlavac MC, Catcheside PG, McDonald R, Eckert DJ, Windler S, McEvoy RD. Hypoxia impairs the arousal response to external resistive loading and airway occlusion during sleep. Sleep 2006;29:624–631.[Web of Science][Medline] [Order article via Infotrieve]
7. Akashiba T, Akahoshi T, Kawahara S, et al. Clinical characteristics of obesity-hypoventilation syndrome in Japan: a multi-center study. Intern Med 2006;45:1121–1125.[CrossRef][Medline] [Order article via Infotrieve]
8. BaHammam A, Syed S, Al-Mughairy A. Sleep-related breathing disorders in obese patients presenting with acute respiratory failure. Respir Med 2005;99:718–725.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]
9. Mokhlesi B, Tulaimat A. Obesity hypoventilation syndrome: prevalence and predictors in patients with obstructive sleep apnea. Sleep Breath 2007;11:203–204.[CrossRef][Web of Science]

This article has been cited by other articles:

				P. Castiglioni, C. Lombardi, M. Di Rienzo, E. Lugaresi, P. Montagna, P. Cortelli, and G. Parati What are the causes of excessive daytime sleepiness in patients with sleep-disordered breathing? Eur. Respir. J., August 1, 2008; 32(2): 526 - 527. [Full Text] [PDF]

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Permissions Request Permissions Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (1) Citing Articles via Google Scholar Google Scholar Articles by BaHammam, A. Search for Related Content PubMed PubMed Citation Articles by BaHammam, A.