Statistical analyses
Groups, defined as HFNC failure or success, were compared using Student
or Wilcoxon Mann-Whitney test for continuous variables and Chi-square or
Fisher test for categorical ones.
The accuracy of ROX index and physiological variables to predict HFNC
failure was assessed using receiver operating curve (ROC) analysis. The
area under the curve (AUC) was calculated by the Hanley method and
compared to the value 0.5 using Wilcoxon’s W statistic. For the analyses
at H1 and for changes during the first hour of HFNC delivery, all HFNC
failure patients at H1 or before were excluded.
Statistical tests were performed 2-tailed and p-values <0.05
were considered significant test results. Statistical analyses were
conducted with SAS (version 9.4, SAS Institute, Cary, NC) and R software
(R 2.3.4 for Windows). Patients’ characteristics were presented using
mean and standard deviation (SD) for the quantitative variables and
frequencies with proportions for categorical ones.