Admission oxygen saturation and all-cause in-hospital mortality in acute myocardial infarction patients: data from the MIMIC-III database

BACKGROUND: Acute myocardial infarction (AMI) is mainly caused by a mismatch of blood oxygen supply and demand in the myocardium. However, several studies have suggested that excessively high or low arterial oxygen tension could have deleterious effects on the prognosis of AMI patients. Therefore, the relationship between blood oxygenation and clinical outcomes among AMI patients is unclear, and could be nonlinear. In the critical care setting, blood oxygen level is commonly measured continuously using pulse oximetry-derived oxygen saturation (SpO(2)). The present study aimed to determine the association between admission SpO(2) levels and all-cause in-hospital mortality, and to elucidate the optimal SpO(2) range with real-world data. METHODS: Patients diagnosed with AMI on admission in the Medical Information Mart for Intensive Care III (MIMIC-III) database were included. A generalized additive model (GAM) with loess smoothing functions was used to determine and visualize the nonlinear relationship between admission SpO(2) levels within the first 24 hours after ICU admission and mortality. Moreover, the Cox regression model was constructed to confirm the association between SpO(2) and mortality. RESULTS: We included 1,846 patients who fulfilled our inclusion criteria, among whom 587 (31.80%) died during hospitalization. The GAM showed that the relationship between admission SpO(2) levels and all-cause in-hospital mortality among AMI patients was nonlinear, as a U-shaped curve was observed. In addition, the lowest mortality was observed for an SpO(2) range of 94–96%. Adjusted multivariable Cox regression analysis confirmed that the admission SpO(2) level of 94–96% was independently associated with decreased mortality compared to SpO(2) levels <94% [hazard ratio (HR) 1.352; 95% confidence interval (CI): 1.048–1.715; P=0.028] and >96% (HR 1.315; 95% CI: 1.018–1.658; P=0.030). CONCLUSIONS: The relationship between admission SpO(2) levels and all-cause in-hospital mortality followed a U-shaped curve among patients with AMI. The optimal oxygen saturation range was identified as an SpO(2) range of 94–96%, which was independently associated with increased survival in a large and heterogeneous cohort of AMI patients.