For each episode of suspected hypovolaemia, defined as PPV >13% and SVV >12% [5], VE was performed using a Calcitriol 32222-06-3 500-mL bolus of hydroxyethylstarch delivered over a 15-minute period. Fluid responsiveness was defined as an increase in SV of ��15% [3]. Before and after each VE, an additional set of measurements was obtained (PAS, PAD, PAM, CI, SV, baseline StO2, desStO2, recStO2 and hyperaemia recovery area).Statistical analysisWe subdivided the population into two groups based on the percentage increase in SV after intravascular VE: (1) positive response to fluid challenge when SV was ��15% and (2) negative response to fluid challenge when SV was <15%. The results were tested for normality using the one-sample Kolmogorov-Smirnov goodness-of-fit test.

Normally distributed data are presented as means �� standard deviation (SD) or and non-normally distributed data as medians with 25th and 75th percentiles. The ��2 test was used to compare categorical data. Quantitative data were compared using analysis of variance (ANOVA) when the distributions were normal and the variances were equivalent; otherwise, they were compared using the Kruskal-Wallis H-test. The paired Student’s t-test was used to compare data at two different time points, with adjustment of the t-statistics whenever indicated, to take into account the presence of several measurements in the patient studied. The within-group effect of fluid loading was analysed using ANOVA or the Kruskal-Wallis H-test as appropriate.

To assess the reproducibility of VOT-derived StO2 variables, the coefficient of variability was calculated to obtain the StO2 recovery slopes for both positive and negative responses to fluid loading [22]. Differences between groups were assessed using Student’s t-test or a Mann-Whitney U test as appropriate. A mixed model using the restricted maximum likelihood method was used to estimate covariance components, taking into account the random effects of patient and time (before and after fluid loading) and the covariate interaction group �� time. The receiver operating characteristic (ROC) curve was also generated for the StO2 recovery slope, and area under the ROC curve, sensitivity, specificity, positive predictive value and negative predictive value were calculated for recStO2. When applicable, correlations were evaluated on the basis of the Spearman’s �� coefficient.

Statistical analysis was performed using SEM version 2.0 software [23]. P < 0.05 was considered statistically significant.ResultsTable Table11 summarises the baseline demographic clinical characteristics of the 24 patients. On the basis of the passive leg-raising test, no patient was considered GSK-3 preload-dependent before induction of anaesthesia. The duration of the surgical procedures ranged from 75 to 300 minutes (median, 120 minutes). Table Table22 shows the baseline macrocirculatory and thenar StO2 curve variables, which were recorded after induction of anaesthesia.