Statistical analyses
Continuous data were tested for normality with the Shapiro-Wilk test. Parametric data are presented as mean ± SD and non-parametric data as median [interquartile range]. The accuracy of the sensors was determined by comparing somatic regional oxygen saturation readings from the O3 sensor and blood reference oxygen saturation values and calculating the root-mean-square error accuracy. Additionally, the agreement was evaluated by Bland-Altman plots, allowing the calculation of bias and limits of agreement between the O3-derived oxygen saturation values and invasive reference values. To account for repeated measures and missing values, we used the Parker method to calculate the weighted mean bias and the total SD of the bias (calculated as the square root of the sum of the within-subject and between-subject variances) [