Variable-Volume Kinetic Model to Estimate Absolute Blood Volume in Patients on Dialysis Using Dialysate Dilution

Area of Science:

• Nephrology
• Biomedical Engineering
• Medical Devices

Background:

• Intradialytic hypotension is a common complication in hemodialysis (HD), leading to significant morbidity and adverse outcomes.
• Accurate estimation of absolute blood volume (ABV) is crucial for improving HD treatment efficacy and patient safety.
• Current ABV estimation methods often rely on the classic back-extrapolation algorithm (BEXP), which has limitations.

Purpose of the Study:

• To introduce and validate a novel dialysate dilution protocol and estimation algorithm (VVKM) for ABV measurement.
• To compare the precision and accuracy of the VVKM algorithm against the traditional BEXP algorithm for ABV estimation.
• To assess the feasibility of VVKM for noninvasive, routine ABV monitoring in hemodialysis patients.

Main Methods:

• A dialysate dilution protocol was employed with a variable-volume, two-compartment, intravascular blood water content kinetic model (VVKM).
• ABV estimates from the VVKM algorithm were compared with those from the classic BEXP algorithm.
• The study included patients with arterio-venous (AV) and central-venous (CV) access, with multiple bolus injections during several HD treatments.

Main Results:

• The VVKM algorithm demonstrated significantly higher precision in ABV estimation compared to BEXP, with 53% improvement for CV and 42% for AV access patients.
• Negligible systematic differences were found between mean ABV values estimated by both methods.
• VVKM-estimated blood water concentration showed good agreement with measured values, with root-mean-square errors below 2% for AV and 3% for CV patients.

Conclusions:

• The VVKM-based algorithm provides a more precise and accurate method for estimating absolute blood volume during hemodialysis.
• This novel approach offers a noninvasive, inexpensive, safe, and practical alternative for routine ABV monitoring in clinical settings.
• Improved ABV estimation can potentially lead to better management of intradialytic hypotension and enhanced patient outcomes in hemodialysis.