Oxygen therapy and inpatient mortality in COPD exacerbation

Emerg Med J. 2021 Mar;38(3):170-177. doi: 10.1136/emermed-2019-209257. Epub 2020 Nov 26.

Abstract

Background: In hospitalised patients with exacerbation of Chronic Obstructive Pulmonary Disease, European and British guidelines endorse oxygen target saturations of 88%-92%, with adjustment to 94%-98% if carbon dioxide levels are normal. We assessed the impact of admission oxygen saturation level and baseline carbon dioxide on inpatient mortality.

Methods: Patients were identified from the prospective Dyspnoea, Eosinopenia, Consolidation, Acidaemia and Atrial Fibrillation (DECAF) derivation study (December 2008-June 2010) and the mixed methods DECAF validation study (January 2012 to May 2014). In six UK hospitals, of 2645 patients with COPD exacerbation, 1027 patients were in receipt of supplemental oxygen at admission. All had a clinical history of COPD and obstructive spirometry. These patients were subdivided into the following groups: admission oxygen saturations of 87% or less, 88%-92%, 93%-96% or 97%-100%. Inpatient mortality was calculated for each group and expressed as ORs. The DECAF score and National Early Warning Score 2 (excluding oxygen saturation) were used in binary logistic regression to adjust for baseline risk.

Results: In patients with COPD receiving supplemental oxygen, oxygen saturations above 92% were associated with higher mortality and an adverse dose-response. Compared with the 88%-92% group, the adjusted risk of death (OR) in the 93%-96% and 97%-100% groups was 1.98 (95% CI 1.09 to 3.60, p=0.025) and 2.97 (95% CI 1.58 to 5.58, p=0.001). In the subgroup with normocapnia, the mortality signal remained significant in both the 93%-96% and 97%-100% groups.

Conclusions: Inpatient mortality was lowest in those with oxygen saturations of 88%-92%. Even modest elevations in oxygen saturations above this range (93%-96%) were associated with an increased risk of death. A similar mortality trend was seen in both patients with hypercapnia and normocapnia. This shows that the practice of setting different target saturations based on carbon dioxide levels is not justified. Treating all patients with COPD with target saturations of 88%-92% will simplify prescribing and should improve outcome.

Trial registration number: UKCRN ID 14214.

Keywords: COPD; death/mortality; resuscitation.