Evaluation of inpatient oxygen therapy in hypercapnic chronic obstructive pulmonary disease

Background High concentration oxygen therapy in hypercapnic chronic obstructive pulmonary disease (COPD) is associated with increased mortality. In ward-based patients with acute exacerbation of COPD and hypercapnia, this study examines oxygen prescription and the association between high concentration oxygen therapy and adverse outcome. Aims To investigate the association between over-oxygenation and in-hospital adverse events. Methods Inpatients with acute exacerbation of hypercapnic COPD at a tertiary Australian hospital over a 1-year period were retrospectively identified. Oxygen prescription and therapy was determined based on chart review. Over-oxygenation was defined as >= 10% of nursing chart observations recording oxygen delivery with oxygen saturation above 92%. A composite adverse outcome was defined as medical emergency team response, recommencement of non-invasive ventilation or death. The association between over-oxygenation and adverse outcome was assessed using survival analysis and conditional logistic regression modelling. Results The study cohort comprised 106 unique patients and 157 admissions. Oxygen prescription was recorded in 132 (84%) and over-oxygenation occurred in 97 (62%) admissions. Over-oxygenation was higher in non-respiratory ward admissions (76% vs 57%, P = 0.03) and those without any form of oxygen prescription (84% vs 58%, P = 0.01). During follow up, 23 (22%) patients experienced an adverse event. Cox proportional hazards modelling found weak evidence for increased risk of an adverse event in over-oxygenated patients (hazard ratio 2.5; 95% confidence interval 0.8-7.3, P = 0.10). Conditional logistic regression, after matching on age, Charlson comorbidity category and length of follow up, found a similar estimate of association (hazard ratio 2.6; 95% confidence interval 0.8-8.7, P = 0.12). Conclusions Over-oxygenation to hypercapnic COPD inpatients is common and rates of oxygen prescription are suboptimal. We found weak evidence of association between over-oxygenation and adverse events, likely due to low statistical power. Larger prospective studies are needed.