Statistical Analysis
The quantitative data were described as the mean ± standard deviation (SD), or as the median (min-max). A sample size calculation was performed based on our observed results by using a one-sided McNemar’s test. A sample size of 447 individuals, at least 49 in each arm, is found to be sufficient to detect a clinically significant difference between groups with 80% power and a 5% level of significance. The qualitative data were described by the number of cases (proportion, %). Patient characteristics were compared using the χ2 test or Fisher’s exact test for categorical data and the Mann Whitney U test for continuous data. Cox proportional-hazards regression models were used to estimate the association between QCB use and the composite endpoint of intubation or death. Statistical significance was accepted when the probability (P) value was <0.05 and changes were referred to as significant at this P-value.