Clinical benefit of chronic non-invasive ventilation in severe stable COPD: a matter of persistent hypercapnia improvement.

Abstract

In patients with chronic obstructive pulmonary disease (COPD) treated with chronic non-invasive ventilation (NIV), the relation between improvements in nocturnal transcutaneous partial pressure of CO₂ (PtcCO₂) and daytime arterial partial pressure of CO₂ (PaCO₂) remains uncertain. Also, to what extent improvements in nocturnal PtcCO₂ result in better health-related quality of life (HRQL), exercise capacity, lung function and survival has not been investigated. Patients with COPD who were initiated on chronic NIV were prospectively followed for 6 months. Daytime PaCO₂ and nocturnal PtcCO₂ were measured before NIV initiation. NIV targeted normocapnia (PaCO₂/mean PtcCO₂<6.0 kPa) or to reduce baseline values >20%. HRQL was measured with the Severe Respiratory Insufficiency questionnaire (SRI) and exercise capacity with the 6-min walk test (6MWT). Patients were divided into three groups: group 1: neither PtcCO₂ nor PaCO₂ reductions reached the target; group 2: both PtcCO₂ and PaCO₂ targets were reached; group 3: only PtcCO₂ target was reached. 177 participants were included with both transcutaneous and daytime gas exchange data. In total, 66% reached nocturnal gas exchange targets. However, in only 17%, this also resulted in substantial daytime PaCO₂ reduction (group 2). Compared with group 1, these patients had higher baseline PtcCO₂ (7.4±0.7 vs 8.2±1.9 kPa, p=0.012) and better NIV usage (6.2±2.8 vs 8.3±2.4 hours, p=0.010). Despite comparable NIV settings, the forced expiratory volume in 1 s and 6MWT improved only in group 2, and only these participants reached a clinically relevant improvement on the SRI and experienced improved survival. Patients with COPD who can maintain improved ventilation by nocturnal NIV during daytime spontaneous breathing are most likely to experience relevant benefits on HRQL, exercise capacity, lung function and survival.