2.2. Statistical analysis
Statistical analyses were performed with Statistica v. 13 (StatSoft, Tulsa, OK, USA). Categorical data were described by frequencies and percentages. Group comparisons were performed using Pearson’s χ2 test. Continuous data (age, BMI, time of oxygenation, age of patients who died, and laboratory markers) were presented as means, standard deviations, and minimum and maximum values for some variables. The Gaussian distribution was checked with the Shapiro–Wilk test. Differences between groups were assessed using the Mann–Whitney test for continuous, non-normally distributed variables and a Student’s t-test for variables with the Gaussian distribution. A p-value of less than 0.05 was considered statistically significant.