Exposure to hyperoxemia and mortality in cardiac intensive care unit patients

Abstract

Abstract Funding Acknowledgements None. Background Hyperoxemia (a high PaO2, i.e. >200-300 mmHg) has been associated with adverse outcomes in general critical care settings as well as in acute cardiovascular care conditions. The association between hyperoxemia and mortality has not been characterized in the heterogeneous population admitted to the cardiac intensive care unit (CICU). We aimed to examine the association between hyperoxemia on CICU admission with in-hospital mortality. Methods We retrospectively analyzed Mayo Clinic CICU patients from January 2007 to April 2018. PaO2 closest on admission was analyzed as a continuous variable (per 100 mmHg) and categorized as: 60-100 mmHg (51.9%), 101-150 mmHg (28.6%), 151-200 mmHg (10.6%), 201-300 mmHg (6.4%), and >300 mmHg (2.5%). Those without PaO2 on admission and those with hypoxemia were excluded. The primary outcome was all-cause in-hospital mortality evaluated using logistic regression, after adjusting for age, Charlson Comorbidity Index, M-CARS, and use of IMV and NIPPV. Results A total of 3,368 patients were included (median 70.3 years, 39.4% women). Admission diagnoses included ACS (37.0%, with 19.8% STEMI), HF (67.8%), shock (33.0%) and cardiac arrest (25.3%). Median admission PaO2 was 99 (IQR 78, 136) mmHg, with no difference in median PaO2 between hospital survivors and inpatient deaths (99 versus 98, p = 0.38). A J-shaped relationship was observed between admission PaO2 and in-hospital mortality (Figure A), with slightly higher mortality below 100 mmHg and incrementally higher mortality above this threshold (esp. at >200 mmHg). The incremental association between higher PaO2 and mortality (adjusted OR 1.17 per 100 mmHg higher, 95% CI 1.01-1.34, P = 0.03) was focused in the highest PaO2 group (i.e., >300 mmHg; Figure B). Conclusion Hyperoxia (esp. PaO2 >300 mmHg) on CICU admission is associated with increased in-hospital mortality, demonstrating a J-shaped association with an inflection point of lowest mortality around 100 mmHg. Further studies are warranted to assess if specific oxygen targets influence outcomes in critically ill cardiac patients.