Echography of the inferior vena cava is a simple and reliable tool for estimation of 'dry weight' in haemodialysis patients.

Using echography, the diameter of the inferior vena cava (IVC) and its decrease on deep inspiration (collapse index) were evaluated in haemodialysis patients. The diameter of the IVC was expressed as an index to the body surface area (VCD) in mm/m2. Non-linear regression analysis in predicting mean right atrial pressure by VCD (mm/m2) and collapse index revealed a good correlation (r = 0.92; P less than 0.001) in both measurements. These results indicate that the IVC indices can be used as a parameter for both high and low filling pressures. Over-hydration (mean right atrial pressure greater than 7 mmHg) was defined as a collapse index of less than 40% and a VCD of more than 11.5 mm/m2, and underhydration (mean right atrial pressure less than 3 mmHg) as a VCD of less than 8 mm/m2 and collapse index of above 75%. In 22 patients in whom dry weight was determined on clinical grounds, only six had a correct dry weight according to IVC indices. Reliability of IVC indices for estimation of body fluid status was proved by the fact that during haemodialysis with fluid removal, postdialysis underhydrated patients according to IVC indices showed a decrease of mean arterial pressure and stroke volume, and an increase of heart rate. No such changes were observed in postdialysis normovolaemic and hypervolaemic patients, according to the vena cava indices. Furthermore, blood volume in normo- and hypervolaemic patients decreased much less than in hypovolaemic patients, despite the same amount of ultrafiltration. Total blood volume (ml/m2) and VCD (mm/m2) correlated significantly (r = 0.61; P less than 0.001), whereas there was no significant correlation between collapse index and blood volume.(ABSTRACT TRUNCATED AT 250 WORDS)