Annual decline in arterial blood oxygen predicts development of chronic respiratory failure in COPD with mild hypoxaemia: A 6-year follow-up study

Abstract

Background and objective: Chronic respiratory failure (CRF) with hypoxaemia is an important pathophysiology in patients with chronic obstructive pulmonary disease (COPD), and existing mild hypoxaemia may be a sign of future CRF development. However, little is known about the trajectory of partial arterial pressure of oxygen (PaO₂ ) decline in patients with COPD. We assessed decline in PaO₂ and the impact of short-term reductions in PaO₂ to predict future decline in PaO₂ .

Methods: A total of 172 outpatients with COPD from a prospective cohort study were enrolled. Pulmonary function tests and arterial blood gas (ABG) analyses were conducted at baseline and 1 year after enrolment and changes in PaO₂ (ΔPaO₂ ) and other parameters were calculated. Survival and incidence of CRF (as assessed by prescription of long-term home oxygen therapy) were monitored for 6 years.

Results: A total of 164 patients completed the observation period and 101 patients had mild hypoxaemia (PaO₂ < 80 Torr) at baseline. No patients with normal PaO₂ (≥80 Torr) developed CRF, and 10 patients with mild hypoxaemia developed CRF in 6 years. Baseline airflow limitation and diffusion capacity were significantly associated with development of CRF. Receiver-operating characteristic curve analysis showed that ΔPaO₂ of -3.05 Torr/year is a useful cut-off value to predict development of CRF in 6 years (hazard ratio (HR): 12.6, 95% CI: 3.48-58.73, P < 0.0001).

Conclusion: Patients with COPD and mild hypoxaemia may benefit from repeat ABG after 1 year. Although PaO₂ trajectories widely varied, significant annual changes in PaO₂ of at least -3.0 Torr/year were predictive of CRF development.

Keywords: arterial blood gas; chronic obstructive pulmonary disease; emphysema; pulmonary function test; respiratory failure.