Evolution of daytime PaCO2 in patients with neuromuscular disorders and OSA using CPAP: a retrospective study

Neuromuscular disorders (NMD) are frequently complicated by obstructive sleep apnea (OSA), which may add an obstructive ventilatory load and contribute to CO₂ retention. While non-invasive ventilation (NIV) is recommended for established hypoventilation, the impact of continuous positive airway pressure (CPAP) on daytime PaCO₂ in NMD remains poorly documented.

We conducted a retrospective single-center cohort study in a tertiary neuromuscular referral center. Consecutive adults with NMD undergoing respiratory assessment were included if they had (i) OSA treated with CPAP and (ii) daytime PaCO2 measurements before and after CPAP initiation. The primary outcome was paired PaCO₂ change. Prespecified analyses were performed in patients with baseline PaCO₂ ≥42 and ≥ 45 mmHg. Predictors of PaCO₂ decrease were explored using logistic regression.

One hundred patients were included, median AHI was 36.9/h. At a median follow-up of 13.6 months, PaCO₂ decreased from 42.0 [39.0-44.0] to 40.5 [38.3-43.0] mmHg, corresponding to a paired reduction of 1.0 mmHg (95%CI 0.3-2.0; p = 0.01). PaCO₂ decreased in 61% of patients, remained unchanged in 9%, and increased in 30%. In patients with baseline PaCO₂≥45 mmHg (n = 18), the median PaCO₂ reduction was 1.3 mmHg (95%CI 0.25-2.5; p = 0.016) and 8 patients normalized their PaCO₂ but 4 experienced a deterioration. Baseline PaCO₂ was the only independent predictor of PaCO₂ decrease.

In NMD patients with OSA, CPAP was associated with a modest but significant reduction in daytime PaCO₂. Responses were heterogeneous, supporting careful patient phenotyping and structured reassessment after CPAP initiation to avoid delayed NIV escalation in non-responders.