Abstract: ob＜x＞jective To explore the reliability of ultrasonographic measurement of carotid corrected blood flow time (FTc) and inferior vena cava respiratory variability (dIVC) in predicting fluid responsiveness of mechanically ventilated patients following abdominal surgery. Methods A total of 65 mechanically ventilated patients after elective abdominal surgery, aged 25-75 years, ASA physical status Ⅱ-Ⅲ, with BMI 20-26 kg/m2, and admitted in the anesthesia ICU (AICU) were enrolled in this study. According to the changes of cardiac output (CO) increased ≥15% or not after the 5ml/kg of a compound sodium chloride infusion within 15minutes, patients were classified as responder group (group R) or non-responder group (group NR). The end-inspiratory maximum diameter of IVC (IVCmax), the end-expiratory minimum diameter of IVC (IVCmin), FTC and CO measured by ultrasonography, and the immediate hemodynamic parameters were recorded before and after the volume expansion test. Receiver operating characteristic (ROC) curve analysis and gray area approach were performed to access the value of related indicators in predicting fluid responsiveness. Results Twenty-nine patients (44.6%) responded to fluid challenge, while the rest thirty-six patients (55.4%) did not. There was no statistical difference in the demographic and intraoperative characteristics between the two groups (P>0.05). Before fluid replacement, IVCmax, IVCmin in group R was lower than that in group NR, while dIVC in group R was higher than that in group NR (P<0.05). The areas under the ROC curve (AUC) of dIVC, IVCmin and FTc were 0.781 (0.661-0.874, P<0.001), 0.746 (0.62-0.846, P<0.001), 0.542 (0.413-0.666，P>0.05), respectively. AUCFTc were significantly decreased when compared with AUCdIVC and AUCIVCmin (P<0.05). The optimal cutoff values were 17.36% for dIVC and 1.24 cm for IVCmin .The gray zone for dIVC was 10.10% to 23.71% and included 41.5% of patients and that for IVCmin was 1.01 to 1.68 cm and included 47.7% of patients. Conclusion The accuracy of dIVC in predicting fluid responsiveness of mechanically ventilated patients after abdominal surgery is better than that of FTc, and the volume status can be better evaluated when combined with the end-expiratory minimum diameter of IVC.