Admission Respiratory Rate-Oxygenation (ROX) Index and Outcome in COVID-19 Pneumonia with Acute Respiratory Failure

Abstract

Rationale: Respiratory Rate-Oxygenation Index (ROX index), defined as the ratio of oxygen saturation, fractional percentage of inspired oxygen (SpO2/FiO2) to respiratory rate (RR), has been found to be a predictor of patients who will improve with High-Flow Nasal Oxygen (HFNO) therapy. Limited information exists on ROX index in COVID-19 patients with acute respiratory failure. One study in such patients reported ROX-Index of ≥ 5.37 at four hours after admission was significantly associated with a lower risk for intubation after hour four. Objective: The objective of this study was to evaluate the ROX index at admission as an early marker of outcome in patients with COVID-19 pneumonia with acute respiratory failure. Methods: Seventy-one patients admitted to our hospital with COVID-19 and acute respiratory failure were retrospectively studied. Age, gender, admission ROX index, need for invasive mechanical ventilation (MV), hospital length of stay (LOS), and mortality were studied. Pearson's Correlation analysis was performed to determine the impact of ROX Index on need for MV, hospital LOS and mortality. p < 0.05 were deemed statistically significant. Results: Of the seventy-one (71) patients, fifty-two patients were male (71%) and mean age was 47.7 + 16.7 years. Nineteen percent (19%) of patients required MV;the mean LOS was 8.6 + 6 days, twenty-two (22%) patients expired. Mean Admission ROX index in subjects was 15 + 6.5 with ROX index 11.7 + 6 in non-survivors compared to 16 + 6 in survivors (p =0.018, independent t-test) [Figure 1]. Pearson's correlation analysis indicated a significant correlation between admission ROX index and survival (r = 0.28 ;p= 0.01), but not with hospital LOS (r=- 0.02, p=0.8). Admission ROX index in patients requiring MV was 11 + 7 and 15 + 6 in those not requiring MV (p =0.06, independent t-test). Conclusions: Higher ROX index at admission is associated with higher mortality and need for MV. Further studies are required to delineate if there is a specific value that can predict need for MV and mortality. Future studies are also needed to determine whether ROX index progression from admission in the first 48 hours can predict outcome in these patients.