End-tidal CO₂ tension is predictive of effective nocturnal oxygen therapy in patients with chronic heart failure and central sleep apnea

Central sleep apnea (CSA) is characterized by recurring cycles of crescendo-decrescendo ventilation during sleep, and enhances sympathetic nerve activity. Thus CSA has a prognostic impact in patients with chronic heart failure (CHF). Although nocturnal oxygen (O₂) therapy decreases frequency of CSA and improves functional exercise capacity, it is also known that some non-responders to the therapy exist. We thus aimed to identify predictors of responders to nocturnal O₂ therapy in CHF patients with CSA. In 12 CHF patients with CSA hospitalized at our department, sleep study was performed at 2 consecutive nights. Patients nasally inhaled O₂ at either the first or second night in a randomized manner. To predict the percentage reduction in apnea-hypopnea index (%Δ AHI) in response to the nocturnal O₂ therapy, we performed multiple regression analysis with a stepwise method with variables including age, brainnatriuretic peptide, circulation time, baseline AHI, hypercapnic ventilatory response and end-tidal carbon dioxide tension (P_ETCO₂). Nocturnal O₂ therapy significantly decreased AHI (from 32 ± 13/h to 12 ± 10/h, P < 0.0001). Among the possible predictors, P_ETCO₂ was the only variable that is predictive of % changes in AHI. Receiver operating characteristics analysis determined 4.25% as the optimal cutoff P_ETCO₂ level to identify responder to nocturnal O₂ therapy (> 50% reduction of AHI), with 88.9% of sensitivity and 66.7% of specificity. In conclusion, P_ETCO₂ is useful to predict the efficacy of O₂ therapy in CHF patients with CSA, providing important information to the current nocturnal O₂ therapy.