Does the plasma refilling coefficient change during hemodialysis sessions?

Abstract

The filtration coefficient in the Starling equation is an important determinant of plasma refilling during hemodialysis. A method for calculating from clinical data an estimate of the filtration coefficient, called the refilling coefficient, was proposed in the past. The assumption behind this method was that the only drive for refilling is the increase in plasma oncotic pressure, and the remaining Starling forces have negligible effect. The refilling coefficient was observed to decrease during hemodialysis, and this was interpreted as a change in the filtration coefficient. The purpose of our study was providing an alternative explanation for the behavior of the refilling coefficient and, using clinical data and mathematical modeling, to predict the values of the immeasurable Starling forces and provide the theoretical basis for the interpretation of the refilling coefficient as the filtration coefficient. Blood volume and bioimpedance data from 23 patients undergoing hemodialysis were used to calculate the refilling coefficient according to the original formulation and to fit a two-compartment model of protein and fluid transport. The changes in the other Starling forces were non-negligible, ranging from 19% to 60% of plasma oncotic pressure. The results showed that the decrease observed in the refilling coefficient is likely caused by neglecting important changes in the Starling forces while deriving the equation for the refilling coefficient. When these Starling forces were taken into account, constant filtration coefficient and dynamic refilling coefficient provided an equivalent description of the data in most cases. However, this was not true for a subgroup of sessions, which suggests that additional factors may also be responsible for the observed decrease in the refilling coefficient.

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

“…Even though our study showed no significant difference between changes in HGB and TBP, the TBP-based method of estimating RBV changes may be additionally biased by a possible variation of the amount of plasma proteins within the circulatory system due to protein refilling from the interstitium during HD (through the lymphatic system and transcapillary fluid absorption) [23,24,25,26]. Apparently this was not the case in the present study, given that the relative PV changes estimated from TPP variation were highly correlated with the PV changes calculated from HGB and HCT variation with the regression line being very close to the identity line (see Fig 6B).…”

Vascular refilling coefficient is not a good marker of whole-body capillary hydraulic conductivity in hemodialysis patients: insights from a simulation study

“…It was shown previously by Pietribiasi et al that the decrease in Kr observed during HD could be largely explained by the assumed lack of intradialytic changes in the interstitial Starling forces and the flow of lymph (except for patients with the highest initial Kr) 46 . They also showed that those assumptions could be valid only if the capillary blood pressure (assumed constant) decreased during dialysis approximately three times more than the interstitial fluid pressure 46 , which is rather unlikely given the autoregulatory capacity of the capillary beds 24 .…”

“…It was shown previously by Pietribiasi et al that the decrease in Kr observed during HD could be largely explained by the assumed lack of intradialytic changes in the interstitial Starling forces and the flow of lymph (except for patients with the highest initial Kr) 46 . They also showed that those assumptions could be valid only if the capillary blood pressure (assumed constant) decreased during dialysis approximately three times more than the interstitial fluid pressure 46 , which is rather unlikely given the autoregulatory capacity of the capillary beds 24 . The present study provides a more complete mathematical analysis of the vascular refilling process, given that in our model the capillary blood pressure is a variable that depends on the state of the whole cardiovascular system (particularly the venous system), as opposed to a constant value assumed in the model with one plasma compartment.…”

Impact of the nature of the capillary wall on plasma refilling during hemodialysis

“…22,23 In these reports, refilling coefficients decreased with ultrafiltration. Pietribiasi et al 24 claimed that there is no need to assume a decreasing nature of refilling coefficients if lymphatic flow is taken into consideration with 3PM. Although in our study a constant value of LpS during ultrafiltration was also assumed, there were faint but significant correlations between LpS and BIA-derived pre-HD volume overload such as excess fluid mass.…”