Inferior vena cava diameter and left atrial diameter measure volume but not dry weight

Hypervolemia is an important and modifiable cause of hypertension. Hypertension improves with probing dry weight, but its effect on echocardiographic measures of volume is unknown.

Shortly after dialysis, echocardiograms were obtained at baseline and longitudinally every 4 weeks on two occasions. Among 100 patients in the additional ultrafiltration group, 198 echocardiograms were performed; among 50 patients in the control group, 104 echocardiograms were performed.

Baseline inferior vena cava (IVC)(insp) diameter was approximately 5.1 mm/m(2); with ultrafiltration, change in IVC(insp) diameter was -0.95 mm/m(2) more compared with the control group at 4 weeks and -1.18 mm/m(2) more compared with the control group at 8 weeks. From baseline IVC(exp) diameter of approximately 8.2 mm/m(2), ultrafiltration-induced change at 4 weeks was -1.06 mm/m(2) more and at 8 weeks was -1.07 mm/m(2) more (P=0.044). From a baseline left atrial diameter of 2.1 cm/m(2), ultrafiltration-induced change at 4 weeks was -0.14 cm/m(2) more and at 8 weeks was -0.15 cm/m(2) more. At baseline, there was no relationship between interdialytic ambulatory BP and echocardiographic parameters of volume. The reduction in interdialytic ambulatory BP was also independent of change in the echocardiographic volume parameters.

The inferior vena cava and left atrial diameters are echocardiographic parameters that are responsive to probing dry weight; thus, they reflect excess volume. However, echocardiographic volume parameters are poor determinants of interdialytic BP, and their change does not predict the BP response to probing dry weight.