Abstract： Objective To explore the correlation between radius and respiratory variation of inferior vena cava(IVC)and hemodynamic monitoring values of pulse-indicated continuous cardiac output(PiCCO)in septic shock pigs.Methods A total of 8 pigs were used to establish animal model of septic shock by intravenous infusing LPS(100 μg/kg),and fluid resuscitation was followed with normal saline.Ultrasound was used to measure the maximum radius(IVCmax)and minimum radius(IVCmin)of IVC,and respiration variation index(RVI)was calculated at basic status,septic shock,1 hour and 6 hours after fluid resuscitation,respectively.Respiratory variation index of IVC were calculated as:RVI =(IVCmax-IVCmin)/ IVCmax × 100％.Hemodynamic monitoring values,including ITBV,GEDV,SVV and CI of PiCCO,were recorded at the same time.Radius and RVI of IVC and PiCCO values between before and after fluid resuscitation were compared by LSD-t test.Correlation between radius and RVI of IVC andhemodynamic monitoring values were calculated by Pearson correlation coefficient.Results Compared with the moment of septic shock,IVC IVCmin,GEDV,ITBV and CI at 1 after hour fluid resuscitation were larger(P ＜ 0.01)and SVV and IVCrvi were smaller(P ＜ 0.01).Compared with the moment of septic shock and 1 after hour fluid resuscitation,IVC[VCmin,GEDV,[TBV and CI at 6 hours after fluid resuscitation were larger(P ＜ 0.01)and SVV and IVCrvi were smaller(P ＜ 0.01).IVCmax correlated with SVV(P=0.024)and it failed to correlate with GEDV,ITBV and CI.IVCmin correlated with GEDV(P=0.003),ITBV(P =0.001),SVV(P =0.009)and CI(P =0.015),respectively.RVI was correlated withGEDV(P＜0.01),ITBV(P＜0.01),SVV(P=0.007)and CI(P＜0.001),respectively.Conclusions Radius and RVI of IVC was correlated with hemodynamic monitoring values of PiCCO.It can serve as a parameter to rapidly estimate the blood volume.