SpO2/FIO2 ratio 3 days after treatment with tocilizumab is a prognostic factor in patients with COVID-19: A retrospective cohort study

Abstract

Abstract Background: Tocilizumab is considered a critical treatment for severe COVID-19. Thus far, there are no established means of predicting outcomes of administering tocilizumab. Our goal was to determine the factors that predict the prognosis of patients with COVID-19 receiving tocilizumab. Methods: All patients admitted to our hospital from March 2020 to July 2021 who had received tocilizumab for COVID-19 were retrospectively identified from hospital charts. We identified 92 patients who were eligible for this observational cohort study. We assessed age, dyspnoea, number of comorbidities, history of cancer, neutrophil and lymphocyte counts, neutrophil/lymphocyte ratio, lactate dehydrogenase, and total bilirubin. We also analysed the relationship between mortality and oxygen saturation/fraction of inspired oxygen (SpO2/FIO2) and ratio of oxygen concentration to respiratory rate (ROX index). We assessed these data using the Cox proportional hazard and ROC curve models. Results: Survivors (n = 56; mean age 65 years) were younger than those who died (n = 36; mean age 78 years). According to multivariable analysis, multiple comorbidities, history of cancer, CURB-65 score, neutrophil and lymphocyte counts, neutrophil/lymphocyte ratio, and lactate dehydrogenase were all greater in those who died than in those who survived. There were no significant differences in dyspnoea and total bilirubin. The SpO2/FIO2 ratio 3 days after treatment with tocilizumab was strongly associated with subsequent mortality. According to multivariate analysis, of the variables analysed, only the SpO2/FIO2 ratio 3 days after treatment with tocilizumab was significantly associated with mortality rate (p = 0.029; hazard ratio = 0.987, 95% confidence interval 0.977–0.997). Conclusions: The SpO2/FIO2 ratio 3 days after treatment with tocilizumab is a useful prognostic indicator in patients with COVID-19. Our findings indicate that aggressive respiratory therapy and/or additional treatment should be instigated when the SpO2/FIO2 ratio has not improved 3 days after treatment with tocilizumab.