A New Method to Evaluate Patient Characteristic Response to Ultrafiltration during Hemodialysis

Abstract

Background. Several factors are involved in the pathogenesis of dialysis discomfort interfering with optimal fluid removal and reducing the efficacy of the treatment; the most important one is a decrease in blood volume caused by an imbalance between ultrafiltration (UF) and plasma refilling (PR) rates. Objectives. This study is aimed at devising a method to tailor the dialysis therapy to each individual patient, by analyzing the relationship between PR and UF during the sessions in stable patients and widening the knowledge of fluid exchanges during the treatment. Methods. Thirty stable patients undergoing maintenance hemodialysis were enrolled. Three dialysis sessions were monitored for each patient; systemic pressure, blood composition, blood volume % variation, weight loss and conductivity were recorded repeatedly. A Plasma Refilling Index (PRI), defined and calculated by means of parameters measured throughout the dialysis, was introduced as a novel instrument to study plasma refilling phenomena. Results. The PRI provides understanding of patient response (in terms of plasma refilling) to the set UF. In the monitored sessions, the PRI trend is found to be characteristic of each patient; a PRI course that is at variance with the characteristic trend is a signal of inadequate or unusual dialysis scheduling. Moreover, statistical analysis highlights two different PRI trends during the first hour and during the rest of the treatment, suggesting the presence of different treatment phases. Conclusion. The main advantage of the PRI index is that it is non-invasive peculiar to each patient and easy to compute in a dialysis routine based on online data recorded by the monitor. A deviation from the characteristic trend may be a warning for the clinician. The analysis of the PRI trend also suggests how to modulate UF as a function of interstitial to intravascular fluid removal balance during dialysis.

Does the plasma refilling coefficient change during hemodialysis sessions?

“…In Figure 4 (top), µ( ) t is plotted against time. This term, according to equation (6), represents the difference between Lp and Kr exp ; this quantity decreased in a way similar to Kr th and Kr exp , suggesting that the decrease observed in Kr exp by us and other authors might be related to changes in µ( ) t rather than in Lp. µ( ) t is equal to 1 at t = 0, thus making Kr th theoretically equal to Lp; the impossibility of calculating Kr exp exactly at t = 0 makes hard to verify if this value can be a reliable estimate of Lp.…”

“…1,2 One of the mechanisms contributing to hemodynamic stability is the plasma refilling process, by which fluid is recalled from the interstitium to the vascular space, proportionally to the net of the oncotic and hydraulic pressure gradients at the sides of the capillary wall (the so-called Starling forces). 3 To express the impact of such process, several indices have been proposed, such as the ratio between total blood volume change and weight loss (or ultrafiltration volume) at the end of an HD session; 4,5 Casagrande et al 6 developed a plasma refilling index equal to the ratio between blood and total body water volumes, and showed it can identify stable HD patients. However, if one wants to truly quantify the mechanism of plasma refilling, the most direct approach is to estimate the refilling coefficient of the microvasculature, Lp , which expresses the proportionality between changes in the refilling flow and changes in the Starling forces.…”

Kinetics of Plasma Refilling During Hemodialysis Sessions with Different Initial Fluid Status

“…3,[6][7][8][9][10][11][12][13][14] Continuous on-line blood volume monitoring was applied by some authors to obtain qualitative characteristics of the process of refilling and its relation to hypotensive episodes. 3,[15][16][17][18][19][20][21] The quantitative analysis of the refilling process may be based on a two-compartment model to describe the rate of plasma refilling through the application of the Starling equation to the kinetics of plasma volume, V p , during dialysis session 22 :…”

Cardiovascular stability and patient dependent mass transfer during dialysis

“…Figure 4 shows the repeatable PRI trend in six different sessions recorded for the same patient. No symptomatic hypotension episodes took place during the monitored sessions, therefore these recordings did not allow to verify the capability of the index to detect symptomatic hypotension episodes [8]. Moreover, statistical analysis confirmed the presence of two different PRI trends during the first hour and during the rest of the treatment already highlighted in [8].…”

“…Based on the whole set of recorded data the Plasma Refilling Index PRI was calculated [8]. This index was defined as the ratio between instantaneous blood volume (calculated based on Hemoscan® outputs) and total body water and supplies the plasma refilling rate variation with respect to the set ultrafiltration rate.…”