Prognostic significance of oxygen saturation/fraction of inspired oxygen 3 days after initiation of tocilizumab treatment in patients with COVID-19

Abstract

Background: Tocilizumab is effective in treating severe coronavirus disease 2019 (COVID-19). However, the specific time point it acts as a valid indicator of treatment efficacy remains unclear. This study aimed to determine the optimal day for assessing the prognostic value of the oxygen saturation/fraction of inspired oxygen (SpO₂/FiO₂) and ratio of respiratory rate-oxygenation (ROX) index in patients receiving tocilizumab for COVID-19.

Methods: All patients admitted to our hospital from March 2020 to July 2021 who received tocilizumab for COVID-19 were retrospectively identified from hospital charts. Biodata, medical history, and laboratory tests results were obtained from medical records. The prognostic values of the SpO₂/FiO₂ and ROX index for predicting mortality were assessed. Cox proportional hazard and receiver operating characteristic curve models were utilized.

Results: Of the 84 included patients, 34 died within 7 days after discharge. The patients who recovered had a mean age of 65 years and were younger than those who died. The multivariate analysis indicated that multiple comorbidities, cancer history, CURB-65 score, neutrophil and lymphocyte counts, neutrophil/lymphocyte ratio, and lactate dehydrogenase levels were higher in those who died compared with those who survived. No significant differences were found in dyspnea or total bilirubin levels between the two groups. The SpO₂/FiO₂ at 3 days post-tocilizumab initiation was strongly associated with survival.

Conclusions: The SpO₂/FiO₂ on day 3 post-tocilizumab initiation was a predictor of COVID-19 prognosis, which could be employed in determining clinical decisions. Prompt alternative interventions should be considered when this ratio does not improve.

Keywords: COVID-19; Fraction of inspired oxygen; Oxygen saturation; ROX index; Tocilizumab.