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Correspondence |

Positive Airway Pressure Therapy and Daytime Hypercapnia in Patients With Sleep-Disordered Breathing Response FREE TO VIEW

Ahmed BaHammam, MD, FCCP
Author and Funding Information

Affiliations: King Saud University, College of Medicine, Riyadh, Saudi Arabia,  Graduate School of Medicine, Chiba University, Chiba, Japan

Correspondence to: Ahmed BaHammam, MD, FCCP, King Saud University, College of Medicine, Riyadh, Saudi Arabia; e-mail: ashammam2@gmail.com


Chest. 2008;134(1):218-219. doi:10.1378/chest.08-0570
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Published online

I read with interest the article by Kawata and colleagues1 about daytime hypercapnia in obstructive sleep apnea syndrome (OSAS). Based on the response to continuous positive airway pressure (CPAP) therapy, the authors classified the patients as good responders (a decrease in Paco2 by 5 mm Hg) or poor responders (a decrease of < 5 mm Hg). A similar apnea-hypopnea index (AHI) was reported in the two groups. However, average and lowest nocturnal arterial oxygen saturation (Sao2) values were significantly lower in the poor responders.,1The investigators did not rule out the possibility of coexisting severe obesity-hypoventilation syndrome (OHS) in the poor responders. It is well documented that 70 to 90% of OHS patients have predominantly obstructive events during sleep.2Additionally, OHS patients exhibit lower nocturnal and mean Sao2 compared to patients with pure OSAS matched for AHI.4 Therefore, it is possible that OHS was more prevalent or more severe among the poor responders, which in turn might have accounted for the higher daytime Paco2. A recent study5 suggests that CPAP may not be effective in severe cases of OHS. Additionally, the authors did not report desaturation index, nocturnal carbon dioxide, and AHI in the poor responders after applying CPAP. As patients with hypoventilation may have frequent episodes of desaturation without obstructive apneic or hypopneic events, it becomes important to compare the desaturation index in both groups. The fact that poor and good responders had similar AHI does not imply that they have the same underlying sleep-disordered breathing.34 The response to CPAP therapy in OHS patients has not been well investigated, and no study has demonstrated the intermediate and long-term effects of CPAP in these patients. Future studies aiming to investigate the physiologic responses to CPAP in patients with sleep-disordered breathing should differentiate between patients with pure OSAS and patients with OHS and OSA.

The author has no conflicts of interest to disclose.

The authors have reported to the ACCP that no significant conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Kawata, N, Tatsumi, K, Terada, J, et al (2007) Daytime hypercapnia in obstructive sleep apnea syndrome.Chest132,1832-1838
 
Chouri-Pontarollo, N, Borel, JC, Tamisier, R, et al Impaired objective daytime vigilance in obesity-hypoventilation syndrome: impact of noninvasive ventilation.Chest2007;131,148-155
 
Akashiba, T, Akahoshi, T, Kawahara, S, et al Clinical characteristics of obesity-hypoventilation syndrome in Japan: a multi-center study.Intern Med2006;45,1121-1125
 
BaHammam, A, Syed, S, Al-Mughairy, A Sleep-related breathing disorders in obese patients presenting with acute respiratory failure.Respir Med2005;99,718-725
 
Banerjee, D, Yee, BJ, Piper, AJ, et al Obesity hypoventilation syndrome: hypoxemia during continuous positive airway pressure.Chest2007;131,1678-1684
 
To the Editor:

We thank Dr. BaHammam for his comments on our recent article in CHEST (December 2007).1 The responses to continuous positive airway pressure (CPAP) therapy could be different among the patients with obstructive sleep apnea syndrome (OSAS), partly due to the presence of daytime hypercapnia and the severity of obesity. Daytime hypercapnia was corrected in some patients with severe OSAS after 3 months of CPAP therapy, indicating the presence of good responders (ie, a decrease in Paco2 of ≥ 5 mm Hg) and poor responders (ie, a decrease in Paco2 of < 5 mm Hg).,1Most patients with obesity hypoventilation syndrome (OHS) exhibit predominantly obstructive sleep apnea;2however, CPAP therapy may be less effective in patients with severe OHS.3

In our subjects, 4 of 18 poor responders to CPAP therapy had severe OHS and none of 19 good responders had severe OHS. Poor responders exhibited more severe sleep oxygen desaturation; thus, they did not have the same underlying sleep-disordered breathing, although the mean (± SE) 4% desaturation index was similar between the groups (good responders, 51.1 ± 6.5; poor responders, 56.4 ± 6.8). Our OHS subjects showed predominant obstructive events during sleep, while they rarely showed hypoventilation without obstructive apnea or hypopnea. It is likely that CPAP therapy could not normalize oxygen saturations during sleep in subjects with severe OHS, probably resulting in a poor response to CPAP therapy. The coexistence of severe OHS could partly explain the poor awake Paco2 response to CPAP therapy.

When considering the responses to CPAP therapy, we should remember that OSAS and OHS are not single disease entities. Further studies are needed to clarify the spectra of OSAS and OHS.

References
Kawata, N, Tatsumi, K, Terada, J, et al Daytime hypercapnia in obstructive sleep apnea syndrome.Chest2007;132,1832-1838
 
Akashiba, T, Akahoshi, T, Kawahara, S, et al Clinical characteristics of obesity-hypoventilation syndrome in Japan: a multicenter study.Intern Med2006;45,1121-1125
 
Banerjee, D, Yee, BJ, Piper, AJ, et al Obesity hypoventilation syndrome: hypoxemia during continuous positive airway pressure.Chest2007;131,1678-1684
 

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References

Kawata, N, Tatsumi, K, Terada, J, et al (2007) Daytime hypercapnia in obstructive sleep apnea syndrome.Chest132,1832-1838
 
Chouri-Pontarollo, N, Borel, JC, Tamisier, R, et al Impaired objective daytime vigilance in obesity-hypoventilation syndrome: impact of noninvasive ventilation.Chest2007;131,148-155
 
Akashiba, T, Akahoshi, T, Kawahara, S, et al Clinical characteristics of obesity-hypoventilation syndrome in Japan: a multi-center study.Intern Med2006;45,1121-1125
 
BaHammam, A, Syed, S, Al-Mughairy, A Sleep-related breathing disorders in obese patients presenting with acute respiratory failure.Respir Med2005;99,718-725
 
Banerjee, D, Yee, BJ, Piper, AJ, et al Obesity hypoventilation syndrome: hypoxemia during continuous positive airway pressure.Chest2007;131,1678-1684
 
Kawata, N, Tatsumi, K, Terada, J, et al Daytime hypercapnia in obstructive sleep apnea syndrome.Chest2007;132,1832-1838
 
Akashiba, T, Akahoshi, T, Kawahara, S, et al Clinical characteristics of obesity-hypoventilation syndrome in Japan: a multicenter study.Intern Med2006;45,1121-1125
 
Banerjee, D, Yee, BJ, Piper, AJ, et al Obesity hypoventilation syndrome: hypoxemia during continuous positive airway pressure.Chest2007;131,1678-1684
 
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