Association of Early Oxygenation Levels with Mortality in Acute Ischemic Stroke - A Retrospective Cohort Study

Abstract

Background: Ischemic stroke is an emergency with elevated risk for morbidity and mortality. Hypoxia is harmful in acute ischemic stroke. Recent evidence raises concerns regarding hyperoxia as well in acute illness, and for supplemental oxygen therapy when SpO₂greater than 92%. Current AHA/ASA guidelines recommend maintaining SpO₂greater than 94%. In this study, we aimed to assess the relationship between the oxygenation levels within the first 6-hour of ischemic stroke admission and mortality.

Methods: With the approval of the Human Studies Committee (IRB #: 13.0396), we performed a retrospective cohort study of ischemic stroke patients consecutively admitted to our hospital in the years 2013-14 and 2017-18 (n = 1479). Relationship between the first 6 hours oxygenation status and in-house mortality was assessed. SpO₂/FiO₂ ratio was used as the oxygenation outcome parameter. Patients who were intubated at admission were excluded. Additionally, demographics, baseline confounding factors, neurological status, and laboratory values on admission were examined for their association with mortality in a multivariate logistic regression analysis.

Results: Mean age of patients was 64 ± 15 years. Time interval from last seen normal to hospital admission was 7 ± 5 hours (mean ± standard deviation). NIHSS on arrival was 4^1-9 (median-IQR). Fourteen percent of patients received IV alteplase and 6% were treated with mechanical thrombectomy. Baseline SpO₂ was 97 ± 2%, and 47% of the patients required supplemental oxygen treatment per AHA/ASA guidelines. In hospital mortality rate of this cohort was 5.7%. Lower mean SpO₂ /FiO₂ levels were strongly correlated with increasing mortality rates (R² = .973). Age (1.048 [1.028-1.068]), NIHSS (1.120 [1.088-1.154]), WBC (1.116 [1.061-1.175]) and Mean SpO₂/FiO₂ (.995 [.992-.999]) independently risk associated with mortality.

Conclusions: Baseline oxygenation varies within the acute ischemic stroke patient population. In this retrospective cohort study, we are reporting a strong association between lower SpO₂/FiO₂ levels in the first few hours of admission and mortality. In the light of these results, we plan to prospectively assess the role of oxygenation further in the context of recanalization status of stroke.

Keywords: Oxygen; SpO(2)/FiO(2) ratio; hyperoxia; hypoxia; mortality; oxygenation; stroke.