Estimation of Excess Extracellular Fluid Volume Using Blood Volume Monitoring: A Comparison With Bioimpedance Spectroscopy. A Pilot Study.

BACKGROUND

Excess extracellular fluid volume (excess VECF ) is associated with poor prognosis in dialysis patients. Although bioimpedance spectroscopy is widely used to assess excess VECF  , it requires specialized equipment. The aim of this study was to develop a novel method to estimate excess VECF based on blood volume monitoring data.

METHODS

We constructed a mathematical model to estimate excess VECF using the relative blood volume at the end of dialysis. The estimated excess VECF at the end of dialysis was compared with the bioimpedance spectroscopy-derived excess VECF measured immediately after the same dialysis session. The correlation and agreement between the two methods were evaluated.

RESULTS

A significant correlation was observed between blood volume-based and bioimpedance spectroscopy-derived excess VECF (r 2 = 0.7526, p < 0.0001). Bland-Altman analysis showed a fixed bias, indicating that blood volume-based excess VECF systematically overestimated bioimpedance spectroscopy-derived excess VECF at the end of dialysis, but no proportional bias was observed (mean difference = +0.86 L/m2; 95% limits of agreement = -1.10 to +2.82 L/m2; r = 0.046).

DISCUSSION: Possible sources of estimation error in blood volume-based excess VECF include the assumption of isotonicity during dialysis and variability in the f-cell ratio.

CONCLUSION

The proposed blood volume-based method for estimating excess VECF demonstrated a significant correlation with bioimpedance spectroscopy-derived values and may serve as a useful tool for volume assessment in dialysis patients. However, further validation is needed before it can be considered a substitute for bioimpedance spectroscopy as a standard method.