Objective:To investigate the value of bedside transthoracic echocardiography(TTE) in volume reactivity assessment of children with septic shock.Methods:A total of 41 children aged from 1 to 5 years with septic shock requiring mechanical ventilation admitted to PICU from January 2017 to June 2020 were prospectively included.Under the condition of complete mechanical ventilation, full sedation and analgesia, and no spontaneous breathing(tidal volume 8 to 10 mL/kg), volume expansion was given to children.Hemodynamic indexs such as cardiac index(CI), stroke volume index(SVI) and stroke volume variability(SVV) were measured before and after volume expansion by noninvasive cardiac output monitoring(NICOM) and TTE.Moreover, aortic flow velocity time integral variable degrees(ΔVTI), inferior vena cava variability(ΔIVC) and inferior vena cava dilation index(dIVC) were also measured by TTE.Patients were considered to be responsive to volume expansion if SVI NICOMincreased≥15%.Based on the responsiveness of volume expansion, all the patients were divided into response group and non-response group.The value of SVV TTE, ΔVTI, ΔIVC, dIVC, ΔCVP and SVV NICOMin predicting volume responsiveness were analysed. Results:(1) There were 23 cases in response group and 18 cases in non-response group.Before volume expansion, there were no statistically significant differences in general hemodynamic indexes HR, MAP, CVP, EF, CI NICOM, and CI TTEbetween two groups( P>0.05). (2) In response group, HR, MAP, CI, SVI and CVP were all improved after volume expansion( P<0.001). In non-response group, only CVP was significantly increased after volume expansion, while other indexes were not improved( P>0.05). (3)Before the volume expansion, SVV TTE, ΔVTI, ΔIVC, and dIVC in response group were higher than those in non-response group( P<0.001). After volume expansion, these indicators were significantly reduced in response group.In non-response group, only ΔIVC significantly reduced after volume expansion.(4) The receiver-operating characteristic curve analysis showed that the area under the curve of SVV TTEand ΔVTI was 0.971, with 12.04% as the threshold, the sensitivity was 0.957 and the specificity was 0.944. The area under the curve of ΔIVC was 0.981, with 25.98% as the threshold, the sensitivity was 0.870 and the specificity was 1.000.The area under the curve of dIVC was 0.980, with 29.86% as the threshold, the sensitivity was 0.870 and the specificity was 1.000. The area under the curve of ΔCVP was 0.778, with 2.5 cmH 2O(1 cmH 2O=0.098 kPa) as the threshold, the sensitivity was 0.913 and the specificity was 0.556. The area under the curve of SVV NICOMwas 0.874, with 12.50% as the threshold, the sensitivity was 0.869 and the specificity was 0.778. Conclusion:The dynamic indexes SVV, ΔVTI, ΔIVC and dIVC monitored by TTE have good accuracy in evaluating children′s volume responsiveness, among which the accuracy of ΔIVC and dIVC is relatively the highest; the value of ΔCVP in predicting volume responsiveness is limited.