The importance of stabilizing PaCO 2 during long-term non-invasive ventilation in patients with COPD

Background: In subjects with COPD, the importance of changes in PaCO 2 during long-term non-invasive ventilation (NIV) on continuation remains uncertain. We intended to elucidate whether stabilizing PaCO 2 during NPPV had an advantageous prognostic effect. Methods: Data from 54 subjects with COPD and who received long-term NIV were studied retrospectively. The annual change in PaCO 2 during NPPV was determined using a simple linear regression method for each subject who had at least two six-month intervals of PaCO 2 data. Annual changes in PaCO 2 during long-term NIV and probable confounders were analysed with discontinuation of long-term NIV as the principal consequence. Results: Thirty seven subjects who had more than two six-month intervals of PaCO 2 data were involved in this study. PaCO 2 during long-term NIV increased slightly in 19 subjects (group 1; less than 2 mmHg/y), and increased greatly in 18 subjects (group 2; more than 2 mmHg/y). In multivariate modality model, lesser annual changes in PaCO 2 (P = 0.009) and lesser PaCO 2 six months after the start of long-term NIV (P = 0.03) were associated with a significantly higher probability of continuing NPPV. The two- and five-year probabilities of continuing NIV for group-1 were 89% and 66%, respectively, while those for group-2 were 78% and 32%, respectively. Conclusion: A decrease in not only the PaCO 2 six months after the start of long-term NIV but the annual change of PaCO 2 during long-term NIV was shown to be a significantly prognostic variable.