Trajectory of the arterial-alveolar oxygen gradient in COPD for a decade

Abstract

BACKGROUND: Chronic respiratory failure (CRF) is a critical complication in patients with chronic obstructive pulmonary disease (COPD) and is characterized by an increase in the arterial-alveolar oxygen gradient (A-aDO₂). The long-term trajectory and prognostic significance remain unclear. This study aimed to assess the prognostic impact of A-aDO₂ and elucidate its trajectory over ten years. METHODS: We enrolled 170 outpatients with COPD from a prospective cohort study. Arterial blood gas (ABG) analyses were conducted annually for ten years while monitoring the development of CRF. RESULTS: 157 patients completed the observation period, of whom 21 developed CRF (CRF group) and 136 did not (non-CRF group). In the CRF group, there was a gradual increase in A-aDO₂ along with decreases in partial pressure of oxygen (PaO₂) and partial pressure of carbon dioxide (PaCO₂) over ten years, although there were no changes in the non-CRF group. The CRF group had higher baseline A-aDO₂ and higher ΔA-aDO₂ in the first year than the non-CRF group (3.76 vs. 0.42 Torr/year, p = 0.030). Kaplan-Meier analyses, and multivariate Cox proportional hazards analysis revealed that both baseline A-aDO₂ and ΔA-aDO₂ were significantly associated with the development of CRF. Retrospective tracking from the initiation of long-term oxygen therapy (LTOT) revealed significant increases in A-aDO₂ from 5 years prior to LTOT initiation in the CRF group when compared to the non-CRF group. CONCLUSIONS: An increasing trend in A-aDO₂ may be a significant sign for the future development of CRF. A transition of the annual change of A-aDO₂ from a stable state to a deterioration phase can serve as a prognostic factor for developing CRF within 5 years.