Normal distributions of data will be assessed using Kolmogorov-Smirnov test. Student's paired t-test or the Wilcoxon signed-rank test will be used to compare hemodynamic variables obtained at the 2 time points (T0, T1) before and after volume expansion. Hemodynamic variables between responders and non-responders within the group at each time point will be compared using Student independent t-test or Mann-Whitney U-test where appropriate. The x2 test will be used when indicated. The Pearson rank method tests linear correlations between SVV before volume loading (T0) and absolute changes in SVV (∆SVV) and percentage change in SVI (∆SVI) after volume. The responders are defined as those patients who demonstrates a ≥ 15% increase in CI after volume expansion between T0 and T1.16 A ROC curve for each variable will be generated and an area under the ROC curve will be calculated. Using this analysis, the optimal threshold value, sensitivity and specificity of SVV during each study intervention could be determined. The ROC curves will be compared using the DeLong test. Data will be expressed as mean ± SD, medians [IQR], or number (%). A value of p< 0.05 is considered to be statistically significant.