Persistent daytime hypercapnia predicts poor prognosis in OSAS undergoing CPAP therapy

Abstract

Background: Positive airway pressure therapy (PAP) is reported to improve the mortality of OSAS with daytime hypercapnia . However, the data on long-term prognosis in hypercapnic OSAS undergoing CPAP therapy are limited.

Objective: Our study objectives were to investigate the survival and explore prognostic factors in OSAS with daytime hypercapnia undergoing CPAP therapy.

Methods: Thirty-seven patients who were diagnosed OSAS with daytime hypercapnia (PaCO₂ > 45mmHg) were enrolled. All of them are treated with CPAP therapy. The patients were divided into 2 groups according to the improvement of PaCO₂ by CPAP therapy after 3 months (the change in PaCO₂ ≥ 5mmHg; good responder, the change in PaCO₂ < 5mmHg; poor responder). Long-term mortality and predictors of survival were evaluated.

Results: During median follow-up of 125 months, All-cause mortality was 33%, in poor responder group to CPAP therapy. In contrast, all of the patients in good responder group survived (log-lank, p = 0.0115). In univariate analysis, patients with PaO₂< mmHg and PaCO₂>45 mmHg at baseline had poor prognosis (p =0.0013, p <0.0001, respectively). In Cox multivariate analysis, PaCO₂ after CPAP therapy was independent predictor of mortality (p = 0.042). In contrast, neither BMI nor results of pulmonary function tests was linked to their survival.

Conclusion: The presence of hypercapnia which is resistant to CPAP therapy predicts poor prognosis in hypercapnic OSAS.