Abstract: Objective:To evaluate the correlation between inferior vena cava diameter index （VCD）， defined as the ratio of the inferior vena cava diameter （IVCD） to body surface area （BSA）， and ideal water ratio （ECW/TBW） after dialysis in maintenance hemodialysis patients， and to explore the value of ultrasonic measurement of inferior  vena  cava  in evaluating the  volume  load  degree  of  hemodialysis  patients.      Methodology: A  total  of  232  patients  from  the  Blood Purifcation Center of Zhongda Hospital Afiliated to Southeast University were enrolled and their ECW/TBW was measured within 0.5-1 h after  dialysis  using  InBody720  body  composition  analysis  instrument.  After  the  measurement， the  inferior vena cava diameter （IVCD）and respiratory variation rate （ΔIVCD）were measured by ultrasound immediately. Meanwhile， the height  and  weight  data  of  patients  were  collected  to  calculate  the  body  surface  area （BSA）.  The  diameter  index  of inferior vena cava was calculated.  The differences of ECW/TBW in different ΔIVCD groups was analyzed.  The correlation between VCD and ECW/TBW was analyzed， the receiver characteristic curve （ROC） of ideal ECW/TBW （value range: 0.380 ~ 0.385） for VCD diagnosis was drawn， and the detection efficiency was analyzed.    Results:In the 232 patients， 22 cases of inferior vena cava were not clear on ultrasound. Finally， complete data of 210 patients were collected.  Among the patients， 71 cases had an ECW/TBW ratio exceeding the ideal range after dialysis， accounting for 33.8%. There were 30 patients with ΔIVCD≤50%  and 180 patients with>50%. ECW/TBW in ΔIVCD≤50% group was significantly higher than that in ΔIVCD> 50%  group  （0.388 ± 0.011  vs  0.383 ± 0.011，  P = 0.023）.  There  were  significant  differences  in  VCD between the two groups  （9.083± 2.168  vs  6.336± 2.131，  P< 0.001）. VCD  was  significantly  correlated  with  ECW/TBW
（r = 0.321， P<0.001）， and the correlation coefficient of ΔIVCD≤50% group was higher than that of ΔIVCD>50% group
（r = 0.455 vs r = 0.278）.The optimal cut-off value of VCD for ideal ECW/TBW of 0.380 was 6.48 mm/m2 ， with an area under the curve was 0.805， and the sensitivity and specificity were 65.6% and 86.7%， respectively （P < 0.001）. The optimal cut-off value of VCD for the ideal ECW/TBW of 0.385 was 7.12 mm/m2 ， with an area under the curve of 0.790， and the sensitivity and specificity  were  66.3%  and  78.7%  respectively  （P < 0.001） .     Conclusion: VCD  is  related  to ECW/TBW After dialysis， which has certain clinical value in evaluating the degree of volume load.

Key words: ultrasound,  ,  , maintenance hemodialysis ,  ,  inferior vena cava diameter index,  ,  , water ratio,  ,  , volume load