Intubation Timing in COVID-19 Based on ROX Index and Association With Patient Outcomes

Abstract

Background: Timing of intubation in COVID-19 is controversial. We sought to determine the association of the ROX (Respiratory rate-OXygenation) index defined as [Formula: see text] divided by [Formula: see text] divided by breathing frequency at the time of intubation with clinical outcomes.

Methods: We conducted a retrospective cohort study of patients with COVID-19 who were intubated by using a database composed of electronic health record data from patients with COVID-19 from 62 institutions. Multivariable logistic regression was used to evaluate the impact of ROX index score on mortality. We analyzed the ROX index as a continuous variable as well as a categorical variable by using cutoffs previously described as predicting success with high-flow nasal cannula.

Results: Of 1,087 subjects in the analysis group, the median age was 64 years, and more than half had diabetes; 55.2% died, 1.8% were discharged to hospice, 7.8% were discharged to home, 27.3% were discharged to another institution, and 7.8% had another disposition. Increasing age and a longer time from admission to intubation were associated with mortality. After adjusting for sex, race, age, comorbidities, and days from admission to intubation, an increasing ROX index score at the time of intubation was associated with a lower risk of death. In a logistic regression model, each increase in the ROX index score by 1 at the time of intubation was associated with an 8% reduction in odds of mortality (odds ratio 0.92, 95% CI 0.88-0.95). We also found an odds ratio for death of 0.62 (95% CI 0.47-0.81) for subjects with an ROX index score ≥ 4.88 at the time of intubation.

Conclusions: Among a cohort of subjects with COVID-19 who were ultimately intubated, a higher ROX index at the time of intubation was positively associated with survival.

Keywords: ARDS; COVID-19; intubation; mechanical ventilation; outcomes.

Fig. 1.

Flow chart.

Fig. 2.

Relationship between the ROX (Respiratory rate– OXygenation) index score for intubation and hospital mortality. The solid line shows the line of best fit generated by a multivariable model for the association between the ROX index score and mortality. The higher the ROX index score, the lower the estimated the probability of death. The shaded area shows the 95% CIs. Because fewer subjects were intubated at ROX index values > 5, the 95% CI widens as the ROX index scores increase.

Fig. 3.

Lines of best fit generated by a multivariable model for the association between the ROX (Respiratory rate – OXygenation) index score and mortality subjects with and without acute kidney injury. Although the risk of mortality was higher in the subjects with acute kidney injury at all ROX index values, the relationship between the ROX index score before intubation and mortality remained similar.