Measurement of Peritoneal Fluid Handling in Children on Continuous Ambulatory Peritoneal Dialysis Using Autologous Hemoglobin

Objective

Previous measurements of peritoneal fluid handling in children treated by continuous ambulatory peritoneal dialysis (CAPD) were performed with human albumin as a fluid marker. A major disadvantage of this substance is that endogenous patient albumin enters the peritoneal cavity during the dwell period. For this reason perito neal fluid kinetics were measured in a group of children on CAPD, using autologous hemoglobin as a volume marker.

Design

Autologous hemoglobin was added to dialysate containing 1.36% glucose as a volume marker. Marker clearance (MC), which is presently the best available approximation of lymphatic absorption in the clinical setting, and transcapillary ultrafiltration (TCUF) were measured during a 4-hour dwell.

Setting

University hospital.

Patients

Children on CAPD (N=9), with a median age of 8.1 years (range 2.1–13.2 years).

Results

MC was 521±166 mL/4 hour/1.73 m2, which is high compared to the literature data on adult CAPD patients. TCUF was 519±92 mL/4 hour/1.73 m2, which is similar to data concerning adult patients. TCUF reached no maximum during the 4-hour dwell, and the deviation of the TCUF curve from linear was markedly less than usually seen in adult patients.

Conclusions

MC in children treated with CAPD is higher when compared to the literature data on adults. Difficulties to achieve sufficient ultrafiltration in children could be caused by relatively small differences between MC and TCUF from the beginning to the end of the dwell.

Methods for Estimation of Peritoneal Dialysate Volume and Reabsorption Rate Using Macromolecular Markers

Reabsorption of fluid and solutes from the peritoneal cavity poses several problems for the correct estimation of peritoneal dialysate volume and ultrafiltration rate with macromolecular volume markers. Although physiological mechanisms of peritoneal reabsorption (direct lymphatic absorption vs reabsorption to the peritoneal tissue) are being currently discussed, many experimental and clinical studies have demonstrated that peritoneal reabsorption of the marker is mainly a bulk “backflow” out of the peritoneal cavity. Theoretical bases for the estimation of peritoneal dialysate volume and cumulative ultrafiltration of fluid including the correction for peritoneal reabsorption are reviewed. A widely applied simplified method which, however, neglects the impact of ultrafiltration on marker concentration is also discussed. The systematic errors involved in the application of the simplified method are usually less than 10% in the standard conditions; however, in specific cases they may be much higher. Therefore, the correct method is suggested for practical applications.

Factors Affecting Lymphatic Absorption in Chinese Patients on Continuous Ambulatory Peritoneal Dialysis (CAPD)

The pathways and physiology of lymph absorption (LA) from the peritoneal cavity are well documented; however, much uncertainty still exists as to the various clinical and demographic factors affecting LA. We studied LA measured by the albumin instillation method, in adult Chinese CAPD patients, and showed that it was independent of age, sex, body surface area, duration of dialysis, intrinsic renal disease, use of intraperitoneal drugs (heparin/antibiotics/deferroxamine) and frequency of past bacterial peritonitis. High lymph absorbers had a relatively highertranscapillary cumulative ultrafiltration than low lymph absorbers. An enhanced LA was associated with a high initial intraperitoneal volume. Assessment of diaphragmatic strength by the decrement in vital capacity on changing from an erect to a supine position failed to distinguish patients with high and low LA.

Animal Models of Peritoneal Dialysis: Thirty Years of Our Own Experience

Experimental animal models improve our understanding of technical problems in peritoneal dialysis PD, and such studies contribute to solving crucial clinical problems. We established an acute and chronic PD model in nonuremic and uremic rats. We observed that kinetics of PD in rats change as the animals are aging, and this effect is due not only to an increasing peritoneal surface area, but also to changes in the permeability of the peritoneum. Changes of the peritoneal permeability seen during chronic PD in rats are comparable to results obtained in humans treated with PD. Effluent dialysate can be drained repeatedly to measure concentration of various bioactive molecules and to correlate the results with the peritoneal permeability. Additionally we can study in in vitro conditions properties of the effluent dialysate on cultured peritoneal mesothelial cells or fibroblasts. We can evaluate acute and chronic effect of various additives to the dialysis fluid on function and permeability of the peritoneum. Results from such study are even more relevant to the clinical scenario when experiments are performed in uremic rats. Our experimental animal PD model not only helps to understand the pathophysiology of PD but also can be used for testing biocompatibility of new PD fluids.

Albumin-based solutions for peritoneal dialysis: investigations with a rat model

To evaluate albumin, an osmotic agent for peritoneal dialysis, the peritoneal fluid and solute transport were investigated during a 4-h single cycle peritoneal dialysis with albumin-based dialysis solutions. Two different albumin solutions were used in 15 normal Sprague-Dawley rats: isotonic 7.5% albumin solution (ADS 1, n = 7) and a combined 7.5% albumin and 1.35% glucose solution (ADS 2; n = 8). A standard 1.36% Dianeal solution was used to provide control values (n = 6). The rate of the intraperitoneal volume change (Qv) was positive during the initial 90 min with ADS 2 and during the initial 60 min with Dianeal 1.36% solution but negative with ADS 1. The peritoneal bulk flow reabsorption rate, Qa, was similar in all three groups. The estimated rate of transcapillary ultrafiltration (Qu = Qv + Qa) was positive with all three solutions throughout the dialysis. With ADS 1, Qu increased gradually during the initial 90 min and then remained stable, but it decreased with ADS 2 and Dianeal 1.36% solution. Qu with ADS 2 did not differ from that with Dianeal 1.36% solution during the initial 60 min, but it was significantly higher during the latter part of dialysis. The value of Qu during the last 2 h of dialysis was 0.026 +/- 0.010 and 0.025 +/- 0.009 ml/min with ADS 1 and ADS 2, respectively, and it was significantly higher than that with Dianeal 1.36% solution (0.005 +/- 0.007 ml/min; p < 0.017).(ABSTRACT TRUNCATED AT 250 WORDS)

Water transport model during CAPD: determination of parameters

To minimize the total amount of glucose required for removing the same volume of water as a bolus, a continuous infusion of glucose during CAPD was proposed and studied. Both a computer simulation of water transport through the peritoneal membrane and in vivo assessment with rats were carried out to evaluate the feasibility of the newly proposed mathematical model in which lymphatic drainage of dialysate from the peritoneal cavity to lymphatic system was considered in addition to conventional water transport. Mass transport area coefficients (KA) of 0.041 to 0.063 ml/min/100 g body wt and 0.045 to 0.066 ml/min/100 g body wt were measured for glucose and urea during CAPD with male Wistar rats. Hydraulic conductivity of peritoneal membrane (Lc) was 7.9 x 10(-5) to 1.5 x 10(-4) ml/min/mm Hg/100 g body wt, which was calculated by a linear relationship between volume and osmotic pressure. Simulated water transport model using determined parameters indicated that the ratio of lymphatic transport to convective transport would be changeable in CAPD with glucose infusion at varying infusion rates, while up to 16% of the glucose uptake could be reduced compared with that of the common CAPD at the same dwell time.

Physiology of the peritoneum. Implications for peritoneal dialysis

Solute and water transport from blood to peritoneal cavity occur by diffusion and osmotic ultrafiltration, whereas absorption to blood via lymphatics negatively affects these two processes. This article delineates the physiology of peritoneal membrane and numerous factors that influence mass transport during peritoneal dialysis, thereby affecting its therapeutic efficacy. Benefits and limitations of continuous ambulatory peritoneal dialysis (CAPD) are discussed and compared to those of hemodialysis. Survival on CAPD, its complications and imperfections are reviewed in light of the widespread acceptance of the procedure.