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

Abstract

Long- and short-term adverse outcomes in hemodialysis (HD) have been associated with intradialytic hypotension, a common HD complication and significant cause of morbidity. It has been suggested that knowledge of absolute blood volume (ABV) could be used to significantly improve treatment outcomes. Different dilution-based protocols have been proposed for estimating ABV, all relying on the classic mono-exponential back-extrapolation algorithm (BEXP). In this paper, we introduce a dialysate dilution protocol and an estimation algorithm based on a variable-volume, two-compartment, intravascular blood water content kinetic model (VVKM). We compare ABV estimates derived using the two algorithms in a dialysate dilution study including three arterio-venous (AV) and three central-venous (CV) access patients, and multiple bolus injection tests (3-5) within each of several (2-6) HD treatments. The distribution of differences between ABV estimated from the two methods showed negligible systematic difference between the mean values of ABVs estimated from the BEXP and VVKM algorithms, however, the VVKM estimates were 53% and 42% more precise for the CV and AV patients, respectively. Good agreement was observed between measured and VVKM-estimated blood water concentration with the root-mean-square error (RMSE) less than 0.02 kg/kg (2%) and 0.03 kg/kg (3%) for AV and CV patients, respectively. The dilution protocol and the new VVKM-based estimation algorithm offer a noninvasive, inexpensive, safe, and practical approach for ABV estimation in routine HD settings.

Hemodialysis-induced changes in hematocrit, hemoglobin and total protein: Implications for relative blood volume monitoring

“…The latter can be measured by a standard dilution technique with radioisotope tracers (e.g. radio iodinated albumin and 51 Cr-labeled red blood cells) [17], but as a more feasible alternative, absolute BV changes during HD may be estimated based on RBV recordings before and after a step change in ultrafiltration rate [35,36,37,38,39] or following dialysate infusion [40,41,42].…”

Feasibility of Dialysate Bolus-Based Absolute Blood Volume Estimation in Maintenance Hemodialysis Patients

“…Here we employed a previously published method to estimate the ABV by applying an intradialytic bolus of ultrapure dialysate. In our understanding, the present study adds important information to the existing literature, not only by representing a larger population size than the earlier reports (32)(33)(34)(35)(36)(37)39), but also because repeated measurement sessions per patient were performed, and possible pitfalls regarding insufficient sampling rates using an automatic data acquisition systems were fully disclosed. To evaluate the method, we made an effort to use as much data as possible for each analysis, implementing separate, but genuine exclusion steps, as necessary for validity.…”

“…To improve accuracy and physiological plausibility, more complex models should probably be used, taking into account the intravascular/extravascular/interstitial fluid shifts. In this vein, Samandari et al have recently published a study comparing a two compartment model to a back-extrapolation method (39).…”

“…To improve accuracy and physiological plausibility, more complex models should probably be used, taking into account the intravascular/extravascular/interstitial fluid shifts. In this vein, Samandari et al have recently published a study comparing a two compartment model to a back-extrapolation method ( 39 ). While not explicitly addressed, a main figure in their paper shows that ABV-DB values were consistently estimated lower in patients with a central catheter, using either of the modeling approaches they employed.…”

Feedback control of absolute blood volume: A new technical approach in hemodialysis

“…Therefore, we developed a method to determine absolute BV in everyday dialysis sessions . Meanwhile, several working groups have used his method with different clinical aims …”