Triaging Acute Chest Syndrome Clinical Decision-Making Using Bedside SaO2/FiO2 Ratio

• The ratio of peripheral oxygen saturation to the fraction of inspired oxygen (SaO2/FiO2) was a useful measure for acute chest syndrome.

• The bedside SaO2/FiO2 ratio is an inexpensive biomarker to assess acute chest severity and guiding transfer to the intensive care unit.

Acute chest syndrome (ACS) severity is inconsistently defined and its clinical course difficult to predict. This retrospective observational study evaluated the utility of the ratio of the pulse oximetry oxygen saturation to the fraction of inspired oxygen (SaO2/FiO2) in adult patients with ACS and its association with the clinical outcome of intensive care unit (ICU) transfer. Across all ACS hospitalizations at a tertiary medical center from 2017-2021, we characterized the SaO2/FiO2 ratio at 3 timepoints: emergency department (ED) presentation, diagnosis with ACS, and antibiotic initiation. Of the 227 hospitalizations identified, 54% were female, mean age was 29, 70% had Hgb SS, and 9% had obesity. While ICU transfer was not strongly associated with the SaO2/FiO2 ratio at ED presentation (AUC 0.59), it was strongly associated with the SaO2/FiO2 ratio at ACS diagnosis (AUC 0.73) and antibiotic initiation (AUC 0.74). Given the highest sensitivity at ACS diagnosis, a diagnostic SaO2/FiO2 cutoff of 310 was proposed for triaging likely ICU transfer (sensitivity 63%, specificity 82%, aOR 8.94, 95% CI 2.12-37.6, adjusted HR 4.86, 95% CI 1.91-12.4) with models adjusting for obesity, lung disease, and blood counts. This cutoff corresponds to an SpO2 below 90% on 2 L/min nasal cannula support. We propose using the SaO2/FiO2 ratio cutoff of 310 prospectively as a simple bedside triage tool for adult patients with sickle cell disease hospitalized with ACS to be transferred to a higher level of care.