Bioimpedance-based volume at clinical target weight is contracted in hemodialysis patients with a high body mass index

Abstract

To compare volume overload in stable hemodialysis (HD) patients assessed by standard clinical judgment with data obtained from bioimpedance analysis. Ultrafiltration volume (VU) was delivered as prescribed by standard clinical practice. Independently, a measure for volume overload was assessed by a clinical score (SW). The Body Composition Monitor (BCM, Fresenius Medical Care, Bad Homburg, Germany) was used to derive values for extracellular volume (VE) and volume overload (VO) before HD. Arterial pressures (P0, P1) and serum levels of NT-pro-BNP (B0, B1) were evaluated before and after HD. In 28 patients (11 women, age: 51.3 ± 13.3 y, body mass index (BMI) 18.5 - 40.9 kg/m2; VE: 17.91 ± 3.45 l) delivered VU was 2.41 ± 1.03 l and not different from VO of 2.08 ± 1.49 l derived from bioimpedance analysis. There was no correlation between VO and VU (r = -0.15, p = 0.46) but a negative correlation between the difference VO - VU (i.e., the volume overload at treatment end) and BMI (r = -0.49, p < 0.01). Positive correlations were observed between B0 and the relative volume overload (= VO/VE) (r = 0.58, p < 0.001). The well recognized relationship between cardiac natriuretic peptides and volume expansion was confirmed. The volume overload at treatment end (VO - VU) was negligible for the whole group of patients but more negative with increasing BMI. It therefore appears that in comparison to bioimpedance-based evaluation the clinical judgment overestimates volume overload in obese patients which leads to the delivery of high ultrafiltration volumes and to volume contraction at the end of a dialysis session in this group of patients.