Chest
Volume 136, Issue 3, September 2009, Pages 787-796
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Original Research
Sleep Medicine
Determinants of Hypercapnia in Obese Patients With Obstructive Sleep Apnea: A Systematic Review and Metaanalysis of Cohort Studies

https://doi.org/10.1378/chest.09-0615Get rights and content

Background

Inconsistent information exists about factors associated with daytime hypercapnia in obese patients with obstructive sleep apnea (OSA). We systematically evaluated these factors in this population.

Methods

We included studies evaluating the association between clinical and physiologic variables and daytime hypercapnia (Paco2, ≥ 45 mm Hg) in obese patients (body mass index [BMI], ≥ 30 kg/m2) with OSA (apnea-hypopnea index [AHI], ≥ 5) and with a < 15% prevalence of COPD. Two investigators conducted independent literature searches using Medline, Web of Science, and Scopus until July 31, 2008. The association between individual factors and hypercapnia was expressed as the mean difference (MD). Random effects models were used to account for heterogeneity.

Results

Fifteen studies (n = 4,250) fulfilled the selection criteria. Daytime hypercapnia was present in 788 patients (19%). Age and gender were not associated with hypercapnia. Patients with hypercapnia had higher BMI (MD, 3.1 kg/m2; 95% confidence interval [CI], 1.9 to 4.4) and AHI (MD, 12.5; 95% CI, 6.6 to 18.4) than eucapnic patients. Patients with hypercapnia had lower percent predicted FEV1 (MD, −11.2; 95% CI, −15.7 to −6.8), lower percent predicted vital capacity (MD, −8.1; 95% CI, −11.3 to −4.9), and lower percent predicted total lung capacity (MD, −6.4; 95% CI, −10.0 to −2.7). FEV1/FVC percent predicted was not different between hypercapnic and eucapnic patients (MD, −1.7; 95% CI, −4.1 to 0.8), but mean overnight pulse oximetric saturation was significantly lower in hypercapnic patients (MD, −4.9; 95% CI, −7.0 to −2.7).

Conclusions

In obese patients with OSA and mostly without COPD, daytime hypercapnia was associated with severity of OSA, higher BMI levels, and degree of restrictive chest wall mechanics. A high index of suspicion should be maintained in patients with these factors, as early recognition and appropriate treatment can improve outcomes.

Section snippets

Study Selection

We identified all published studies that evaluated the prevalence of chronic daytime hypercapnia (Paco2, ≥ 45 mm Hg) in obese patients with OSA. OSA was defined as an AHI of ≥ 5 events per hour, obesity was defined as a body mass index (BMI) of ≥ 30 kg/m2. Two investigators (R.K. and A.V.H.) conducted independent comprehensive literature searches of Medline from 1966 to July 31, 2008, the Web of Science from 1980 to July 31, 2008, and Scopus from 1960 to July 31, 2008. A first search used text

Study Characteristics

Figure 1 provides details on how an initial search that yielded 314 potential abstracts was reduced to the 15 studies that were included in the metaanalysis (n = 4,250). The number of patients in each study ranged between 30 and 1,227 (Table 1).21, 24 All the studies were published in the last 15 years, with one exception.8 Eleven studies were performed in white populations, and 4 studies7, 21, 24, 25 (n = 1,572; 38% of total sample) were performed in Japanese patients. Most of the studies were

Main Findings

Our metaanalysis confirms that in obese patients without evidence of obstructive airways disease, chronic daytime hypercapnia is associated with the following three factors: the severity of OSA (as measured by AHI or the degree of nocturnal hypoxemia); BMI; and the degree of restrictive chest wall mechanics. More importantly, the severity of OSA and the impairment of respiratory system mechanics are closely associated with the degree of obesity. Specifically, lower FEV1, vital capacity (VC),

Acknowledgments

Author contributions: Drs. Kaw, Hernandez, and Walker contributed to the conception and design of this article. Drs. Hernandez, Kaw, and Walker were responsible for the acquisition of data. Drs. Hernandez, Kaw, Walker, Aboussouan, and Mokhlesi were responsible for the analysis and interpretation of the data. Drs. Kaw, Hernandez, Walker, and Mokhlesi contributed to the drafting of the article. Drs. Hernandez, Kaw, Walker, Aboussouan, and Mokhlesi contributed to the critical revision of the

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