Survival benefit of CPAP favors hypercapnic patients with the overlap syndrome

Background: Patients with the combination of chronic obstructive pulmonary disease (COPD) and obstructive sleep apnea (OSA), known as the "overlap syndrome," have a substantially greater risk of morbidity and mortality compared to those with either COPD or OSA alone. The study's objective was to report on the long-term outcome of hypercapnic (PaCO₂ ≥ 45 mmHg) and normocapnic patients with the overlap syndrome treated with continuous positive airway pressure (CPAP). Methods: A nonconcurrent cohort of consecutive patients with the overlap syndrome was followed for a median duration of 71 months (range 1-100) at a VA sleep center. All patients were managed according to the prevailing recommendations of both diseases. The end point of the study was all-cause mortality. Results: Of the 271 patients identified, 104 were hypercapnic (PaCO₂ = 51.6 ± 4.3 mmHg). Both normocapnic and hypercapnic patients had comparable apnea-hypopnea indexes (AHI) (29.2 ± 23.8 and 35.2 ± 29.2/h, respectively; p = 0.07) and similar adherence rates to CPAP (43 and 42 %, respectively, p = 0.9). Survival analysis revealed that hypercapnic patients who were adherent to CPAP had reduced mortality compared to nonadherent hypercapnic patients (p = 0.04). In contrast, the cumulative mortality rate for normocapnic patients was not significantly different between the adherent and the nonadherent group (p = 0.42). In multivariate analysis, the comorbidity index was the only independent predictor of mortality in normocapnic patients with the overlap syndrome [hazard ratio (HR) 1.68; p < 0.001] while CPAP adherence was associated with improved survival (HR 0.65; p = 0.04). Conclusions: CPAP mitigates the excess risk of mortality in hypercapnic patients but not in normocapnic patients with the overlap syndrome.