Chest
Volume 127, Issue 3, March 2005, Pages 710-715
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Clinical Investigations: Sleep and Breathing
Daytime Hypercapnia in Adult Patients With Obstructive Sleep Apnea Syndrome in France, Before Initiating Nocturnal Nasal Continuous Positive Airway Pressure Therapy

https://doi.org/10.1378/chest.127.3.710Get rights and content

Context

Daytime hypercapnia in patients with obstructive sleep apnea syndrome (OSAS) has a highly variable prevalence in the published studies, and is usually thought to be the consequence of an associated disease, COPD, or severe obesity

Study objectives

To assess the prevalence of daytime hypercapnia in a very large population of adult patients with OSAS, free of associated COPD, and with a wide range of body mass index (BMI), and to evaluate the relationship between daytime hypercapnia and the severity of obesity and obesity-related impairment in lung function

Design

Retrospective analysis of prospectively collected data

Methods

The database of the observatory of a national nonprofit network for home treatment of patients with chronic respiratory insufficiency (Association Nationale pour le Traitement aè Domicile de l'Insuffisance Respiratoire Chronique) was used. Collected data at treatment initiation were age, apnea-hypopnea index, BMI, FEV1, vital capacity (VC), and arterial blood gases. The study included 1,141 adult patients with OSAS treated in France with nocturnal nasal continuous positive airway pressure (CPAP), FEV1 ≥ 80% predicted, FEV1/VC ≥ 70%, and absence of restrictive respiratory disease other than related to obesity

Results

The prevalence of daytime hypercapnia (PaCO2 ≥ 45 mm Hg) before initiating CPAP therapy was 11% in the whole study population. The prevalence of daytime hypercapnia was 7.2% (27 of 377 patients) with BMI < 30, 9.8% (58 of 590 patients) with BMI from 30 to 40, and 23.6% (41 of 174 patients) with BMI > 40. Patients with daytime hypercapnia had significantly higher BMI values and significantly lower VC, FEV1, and PaO2 values than the normocapnic patients. Stepwise multiple regression showed that PaO2, BMI, and either VC or FEV1 were the best predictors of hypercapnia, but these variables explained only 9% of the variance in PaCO2 levels

Conclusion

Daytime hypercapnia was observed in > 1 of 10 patients with OSAS needing CPAP therapy and free of COPD, and was related to the severity of obesity and obesity-related impairment in lung function. However, other mechanisms than obesity are probably involved in the pathogenesis of daytime hypercapnia in OSAS

Section snippets

Materials and Methods

We used the database of the observatory of a national nonprofit network for home treatment of patients with chronic respiratory insufficiency (Association Nationale pour le Traitement A Domicile de l'Insuffisance Respiratoire chronique [ANTADIR]). ANTADIR was set up in France in the 1970s as a nonprofit network for the home treatment of patients with chronic respiratory insufficiency. Home treatment of patients with OSAS was started in 1985. ANTADIR has collected clinical data on treated

Results

During the study period, 88,548 patients with chronic respiratory insufficiency and 30,131 patients with OSAS needing CPAP therapy were included in the ANTADIR observatory. The values of FEV1, VC, and arterial blood gases were available in 2,217 adult patients with OSAS, defined by an AHI ≥ 10 events/h, and free of a restrictive respiratory disease other than that related to obesity. Age, sex ratio, BMI, and AHI did not significantly differ between the patients with OSAS in whom pulmonary

Discussion

This study shows that the prevalence of daytime hypercapnia for OSAS is 11% in the absence of associated COPD, in a very large group of adult patients with OSAS, before initiating CPAP therapy. The prevalence of daytime hypercapnia is particularly high (24%) for OSAS associated with massive obesity. Apart from the PaO2, the predictive variables of PaCO2 are the BMI, and the VC or the FEV1. However, these variables can only explain < 10% of the PaCO2 variance, and daytime hypercapnia has been

Conclusion

The prevalence of daytime hypercapnia was 11% in a very large group of patients with OSAS needing CPAP therapy and free of COPD. The prevalence of daytime hypercapnia was related to the severity of obesity and obesity-related impairment in lung function, and was especially high (> 20%) in patients with massive obesity. However, daytime hypercapnia was also demonstrated in patients without obesity, with a prevalence of 7%. Further studies should be performed to estimate the prevalence of daytime

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