To systematically evaluate factors associated with daytime hypercapnia in obese patients with obstructive sleep apnea (OSA).
Our Meta-analysis included studies evaluating the association between clinical and physiological variables and daytime hypercapnia (PaCO2≥ 45mmHg) in obese patients (BMI>30 kg/m2) with OSA (AHI>5) and <10% prevalence of COPD. Two investigators conducted independent literature searches using Medline, Web of Science and Scopus until July 31, 2008. We excluded studies that only evaluated patients with COPD or overlap syndrome, studies with <10 patients in the hypercapnic and eucapnic groups and studies in which the main/only purpose of the publication was to evaluate a treatment or intervention. The association between individual factors and hypercapnia was expressed as mean difference (MD). Random effects models were used to account for heterogeneity.
Fifteen studies (n= 4250) 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% CI [1.9, 4.4]) and AHI (MD 12.5 [6.6, 18.4]) than eucapnic patients. Patients with hypercapnia had lower FEV1% predicted (MD −11.2 [−15.7, −6.8]), lower vital capacity (VC %) predicted (MD −8.1 [−11.3, −4.9]), and lower total lung capacity (TLC %) predicted (MD −6.4 [−10.0, −2.7]). FEV1/FVC% was not different between hypercapnic and eucapnic patients (MD −1.7 [−4.1, 0.8]), but mean overnight oxygen saturation by pulse oximetry (SpO2) was significantly lower in hypercapnic patients (MD -4.9 [-7.0, -2.7]).
In obese patients with OSA and mostly without COPD, daytime hypercapnia was associated with severity of OSA, higher BMI, lower overnight SpO2 and degree of restrictive chest wall mechanics.
In summary, a growing number of studies originating from various geographical regions have reported a high prevalence of hypercapnia among obese patients with OSA. The prevalence of hypercapnia is likely to increase due to the global obesity epidemic. A high index of suspicion should be maintained in patients with these risk factors, as early recognition and appropriate treatment can improve outcomes.
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