Improvement in hypercapnia does not predict survival in COPD patients on chronic noninvasive ventilation

It has recently been shown that chronic noninvasive ventilation (NIV) improves a number of outcomes including survival, in patients with stable hypercapnic COPD. However, the mechanisms responsible for these improved outcomes are still unknown. The aim of the present study was to identify parameters associated with: 1) an improved arterial partial pressure of carbon dioxide (PaCO₂) and 2) survival, in a cohort of hypercapnic COPD patients treated with chronic NIV.

Data from 240 COPD patients treated with chronic NIV were analyzed. Predictors for the change in PaCO₂ and survival were investigated using multivariate linear and Cox regression models, respectively.

A higher level of bicarbonate before NIV initiation, the use of higher inspiratory ventilator pressures, the presence of anxiety symptoms, and NIV initiated following an exacerbation compared to NIV initiated in stable disease were associated with a larger reduction in PaCO₂. A higher body mass index, a higher FEV₁, a lower bicarbonate before NIV initiation, and younger age and NIV initiation in stable condition were independently associated with better survival. The change in PaCO₂ was not associated with survival, neither in a subgroup of patients with a PaCO₂ >7.0 kPa before the initiation of NIV.

Patients with anxiety symptoms and a high bicarbonate level at NIV initiation are potentially good responders in terms of an improvement in hypercapnia. Also, higher inspiratory ventilator pressures are associated with a larger reduction in PaCO₂. However, the improvement in hypercapnia does not seem to be associated with an improved survival and emphasizes the need to look beyond PaCO₂ when considering NIV initiation.