Background Patients with low Body Mass Index (BMI) on maintenance hemodialysis have a higher mortality risk than patients with elevated BMI. We investigated the use of kinetic modeling to test different hypotheses which have been advanced to explain this relationship. Methods Equations from a three-pool urea-kinetic mathematical model (hepatic mass, extracellular fluid, muscle mass and adipose tissue) were solved to yield predictive profiles of solute and putative toxin concentrations versus time for patients of different body weights. Results For the interdialytic interval, our mathematic model suggests that extracellular solute/toxin concentration increases more rapidly in small patients. Additionally, time average concentration (TAC) is higher for this cohort. A lower value of the muscle mass and adipose tissue mass-transfer coefficient (KMMAT), which determines the rate of solute release into the extracellular fluid, exacerbates this difference. Conclusion These results suggest that higher mortality for smaller dialysis patients may be mediated by higher time average toxin concentration, especially for solutes with a low mass-transfer coefficient value.

Background: Currently, ultraflitration during peritoneal dialysis is determined from direct measurement of weight differences between the initial filling and final draining volumes. A new technique based on segmental bioimpedance analysis (SBIA) has been developed to accurately measure intraperitoneal volume continuously during peritoneal dialysis. Methods: Twenty-two peritoneal dialysis patients were studied in 6 supine position during peritoneal dialysis consisting of 4 tidal exchanges (TPD). For bioimpedance measurements, 4 electrodes were placed, 1 on each hand and foot, to inject an alternating current. Sensing electrodes were placed on the lower ribs and the buttocks on both sides of the body. Calibration of the SBIA method was performed by first filling a known volume of dialysate to establish the relationship between change in resistance and a known fluid volume in the peritoneal cavity. The increase of fluid volume in the peritoneal cavity during dwell time Was considered to be equal to net ultrafiltration volume occurring during this period. These measurements. were compared with those obtained by the difference in weight between the total filling and draining volumes. Results: The. change in intraperitoneal volumes measured by differences in weight (0.39 +/- 0.29 L) did not differ significantly from those established from SBIA (0.41 +/- 0.31 L). Bland-Altman analysis I yielded limits of agreement of 0.12 L. Conclusion: The SBIA technique provides a continuous noninvasive approach to the measurement of changes in intraperitoneal fluid volume. (C) 2003 by the National Kidney Foundation, Inc.

Purpose. The advent of 2 hr and 8 hr daily dialysis may result in inadequate or excessive JiP. We found that normalized time averaged iP concentration (Cpi) as a function of t (nTACiP=it) for CpiPt/CpiPo, where t is elapsed time of dialysis, was independent of dialyzer iP clearance (KiP) over range 100–160 ml/min and conformed to a function of the form y = 1- a[l-exp-(bt)]. Our purpose was to study this function over a wide range of spKt/ViP for modeling JdiP. Methods. Patients on 3 X weekly HD (n = 13) with CoiP 5–6 mg/dl, Vip 8 to 16 L (est as .20Vurea + wt gain) dialyzed with Optiflux200 polysulfone dialyzers. Blood inlet, outlet and dialysate iP (Cbi, Cbo & Cdo) were measured every 1/2 hr to calculate: KdiP = CdoQdo/Cbi and effective iP distribution volume flow rate (QeiP) across the dialyzer from Qdo(Cdo)/(Chi-Cbo) compared to blood water (Qbw) nTACiP=f(t) and KdiP(t)ViP = f(t). Total dialysate iP was measured (JdTiP) and compared to total JvTiP calculated by solution of variable volume single pool ViP model for sum of mobilization of iP(MiPT) outside VIP and removal from its volume of distribution (d(CiPViP). Results (M±SD). KdiP = 188±40 Qe/Qbw = .8.5±.30 nTACiP=1–0.44[1-exp(−1.28KdiPt/ViP)], n = 117, range of KdiPt/Vip= 0 to 4.5 JdTiP= 11301±542 d(CiPViP) = 538±179 MiPT =919 ± 462 JvTiP=1452±472 JvTiP=.88(JdTiP)±365,r = .96,n = 13, p<.001. Conclusions. The QeiP averages 85% of Qbw the JvTiP correlated well with JdTiP JdiPT, mg/day, can he modeled as JdiPT = [KdiP CoiP[1−.44(exp(−1.28KiPt/ViP)] t NJ/7 where N is number of dialyses per week and t is duration of dialysis in minutes.

Accumulation of β2-M in ESRD correlates with the development of dialysis related amyloidosis. HFD membranes have more efficient mass transfer, mostly by convection, of β2-M than cuprophane. However HFD is only able to remove 50% of daily β2-M generation. A biocompatible polymer adsorbent hemoperfusion (HP) device (BetaSorbTM) containing 300 ml of a polystyrene-like adsorbent with efficient removal of β2-M was inserted upstream of a HFD (HF80, Fresenius, Bad Homburg) in the blood circuit in 2 ESRD patients, during one routine hemodialysis (HD). During combined HP/HD β2-M was measured at timed intervals, as were platelet and white cell counts. Blood flow rates were 405 ml/min and 380 ml/min in patients #1 and #2 respectively. Single pool (sp) Kt/Vβ-M was calculated, and compared to the high-flux arm (F80 dialyzers, Fresenius, Bad Homburg) of the HEMO study.TableCombined HP/HD was well tolerated by both pts. Neither platelets nor WBC (corrected for ultrafiltration) changed significantly. spKt/Vβ2-M was 1.7 and 1.37, while rebound equilibrium of β2-M would be achieved in 87 mins and 108 mins, in patients #1 and #2 respectively. β2-M concentrations were similar to, but spKt/Vβ-M, exceeded, that observed in the large HEMO study of HFD. This is the first resin HP device not associated with a fall in platelet count. In view of the efficient removal of β2-M a multicenter study of this device combined with HFD is planned.

A closed system kinetic modeling set (KMS) has been fabricated which permits collection of a small 100-mL aliquot from each exchange. The KMS was used to collect aliquots from 65 exchanges in 13 patients. The concentrations of urea nitrogen (UN), creatinine (Cr), glucose (G), and total protein (TP) were measured in each individual aliquot (Cka) and drain bag (Cba), and all aliquots for each dialysis treatment were used to calculate the concentrations expected in total batched dialysate (BaC) for the treatment and were compared to the measured concentrations (BaM) in mixed total dialysate. The ratios Cka/Cba [mean+/- two times coefficient of variation (mean +/- 2CV)] were 1.00 +/- 5%, 1.00 +/- 5%, 1.01 +/- 10%, and 1.00 +/- 6%, respectively, for UN, Cr, G, and TP (each, n = 61). The ratios BaC/BaM (mean +/- 2CV) were 1.00 +/- 2%, 1.00 +/- 5%, 1.01 +/- 3%, and 0.99 +/- 5%, respectively, for UN, Cr, G, and TP (each, n = 15). We concluded that the KMS aliquots can be reliably used for kinetic and total clearance calculations without mixing and transporting large volumes of dialysate.

Dialyzer reprocessing with heated water (100 to 105 degrees C) for 20 h can be used safely in lieu of chemical methods for disinfection. All infective agents including spores are destroyed and depyrogenation may occur. However, these temperatures may result in structural damage to the dialyzer, limiting reuse. Dialyzer reprocessing by using 1.5% citric acid heated to 95 degrees C for 20 h is an alternative method that produces equivalent microbiologic effects. Citric acid is well known as a disinfecting agent used for dialysis equipment. Because there is little structural damage to dialyzer components at 95 degrees C, reuse statistics are improved (mean reuse increased to 12.8). Both small and large molecule clearances and the sieving coefficient for protein are insignificantly altered by the process. Whereas the procedure is relatively simple, quality-assurance indicators are essential. The method has appeal because it avoids the use of chemical germicides. However, at present it has only been tested thoroughly in polysulfone dialyzers with heat-resistant polycarbonate casings and polyurethane resin. The clinical experience is favorable.