Harmful effects of early hyperoxaemia in patients admitted to general wards: an observational cohort study in South Korea

Objectives We evaluated the association between hyperoxaemia induced by a non-invasive oxygen supply for 3 days after emergency department (ED) arrival and the clinical outcomes at day 5 after ED arrival. Design Observational cohort study. Setting and patients Consecutive ED patients >= 16 years of age with available arterial blood gas analysis results who were admitted to our hospital were enrolled from January 2010 to December 2016. Interventions The highest (PaO2MAX), average (PaO2AVG) and median (PaO2MED) PaO2 (arterial oxygen pressure) values within 72 hours and the area under the curve divided by the time elapsed between ED admittance and the last PaO2 result (AUC(72)) were used to assess hyperoxaemia. The AUC(72) values were calculated using the trapezoid rule. Outcomes The primary outcome was the 90-day in-hospital mortality rate. The secondary outcomes were intensive care unit (ICU) transfer and respiratory failure at day 5 after ED arrival, as well as new-onset cardiovascular, coagulation, hepatic and renal dysfunction at day 5 after ED arrival. Results Among the 10 141 patients, the mortality rate was 5.8%. The adjusted ORs of in-hospital mortality for PaO2MAX, PaO2AVG, PaO2MED and AUC(72) were 0.79 (95% CI 0.61 to 1.02; p=0.0715), 0.92 (95% CI 0.69 to 1.24; p=0.5863), 0.82 (95% CI 0.61 to 1.11; p=0.2005) and 1.53 (95% CI 1.25 to 1.88; p<0.0001). All of the hyperoxaemia variables showed significant positive correlations with ICU transfer at day 5 after ED arrival (p<0.05). AUC(72) was positively correlated with respiratory failure, as well as cardiovascular, hepatic and renal dysfunction (p<0.05). PaO2MAX was positively correlated with cardiovascular dysfunction. PaO2MAX and AUC(72) were negatively correlated with coagulation dysfunction (p<0.05). Conclusions Hyperoxaemia during the first 3 days in patients outside the ICU is associated with in-hospital mortality and ICU transfer at day 5 after arrival at the ED.