Amphotericin selectively increases peritoneal ultrafiltration

Pharmacologic Modification of Transperitoneal Movement of Water

Investigations concerning the influence of pharmacologic agents on transperitoneal water movement are predominantly undertaken in the hope that their results can help in a restoration of net ultrafiltration (UF) volume toward normal in cases with declining UF during long-term dialysis treatment. Net UF volume represents the difference between net transcapillary UF and lymphatic absorption.

The choice of a pharmacological agent for enhancing UF depends on the mechanisms responsible for net UF loss, which include: (a) early dissipation of the transperitoneal osmotic gradient; (b) decrease in the peritoneal surface area; (c) Iymphomonokine overproduction; (d) enhanced lymphatic absorption; (e) high residual volumes left in the peritoneal cavity; or (f) a combination of these factors. Leakage of dialysate to the abdominal wall sometimes occurring in peritoneally dialysed patients (1), according to a definition of net UF volume, cannot be regarded as a true UF loss.

Does Impaired Transcellular Water Transport Contribute to Net Ultrafiltration Failure during CAPD?

Objectives

To assess the contribution of transcellular water transport in net ultrafiltration failure during continuous ambulatory peritoneal dialysis (CAPD).

Design

Retrospective.

Setting

Renal Unit, Academic Medical Center, Amsterdam.

Patients

One group of 6 patients with clinical severe ultrafiltration loss and a group of 10 stable CAPD patients without ultrafiltration problems.

Intervention

In all patients, two peritoneal permeability tests were done within one week, using glucose 1.36% dialysate on one day and glucose 3.86% on the other day. Dextran 70 was used as a volume marker.

Results

The difference in net ultrafiltration between 3.86% glucose and 1.36% glucose dialysate was 569±51 mL (control) and 153±1 03 mL (poor ultrafiltration group; p < 0.005). The dialysatelplasma (DIP) concentration ratios increased in both groups with glucose 1.36%. When using 3.86% glucose, the DIP ratio decreased in the control group with a median minimum value one hour after completion of inflow. It is possible that sieving of sodium was due to transcellular water transport by crystalloid osmosis during the hypertonic dwell, as a dissociation between the transport of water and sodium is unlikely to occur in transport through the much larger intercellular pores. The DIP sodium ratio after one hour was related to the mass transfer area coefficient (MTC) of creatinine and the percentage of glucose absorption in the control group. No decrease in DIP ratio was found in the poor ultrafiltration group. This suggests impairment of transcellular water transport. No significant differences were present between both groups with regard to MTC creatinine (10.2 and 14.0 mL/min), glucose absorption (71% and 71%), effective lymphatic absorption rate (1.34 and 1.01 mL/min), and residual volume (248 and 178 mL). Only 1 patient in the ultrafiltration loss group continued with CAPD. The others had to be transferred to hemodialysis; 1 of them developed sclerosing peritonitis.

Conclusion

The sieving of sodium during CAPD may be caused by transcellular water transport. Deficient sieving as assessed by the absence of a decreased DIP ratio after one hour of a hypertonic dwell suggests impairment of transcellular water transport. This is asso ciated with severe ultrafiltration failure. It indicates that failure of transcellular water transport, possibly by glycosylation of specific proteins on the cell membrane, may be considered one of the causes of ultrafiltration failure during CAPD.

Effect of Fluid Supplementation and Modality on Peritoneal Permeability Characteristics in a Rat Peritoneal Dialysis Model

Objective

Hemoconcentration may influence peritoneal permeability parameters in anesthetized animals without fluid supplementation. Therefore, the aim of this study was to investigate the effects of fluid supplementation on peritoneal permeability in an acute peritoneal dialysis model in anesthetized rats.

Design

To study the effect of fluid supplementation on peritoneal permeability characteristics, 24 anesthetized male Wistar rats were investigated in 3 groups during a 4-hour standardized peritoneal permeability analysis with a 3.86% glucose dialysis solution (SPARa). The groups included a control group with no fluid supplementation (None, n = 8), a group with continuous subcutaneous infusion of 0.9% NaCl 3 mL/hr (SC, n = 9), and a group with continuous intravenous infusion of 0.9% NaCl 3 mL/hr (IV, n = 7). Inflow, sampling, and outflow of the dialysate during the SPARa occurred via a cannula inserted intraperitoneally in the lower left quadrant of the abdomen. Blood was drawn at the end of the dwell. Baseline blood samples were obtained from six separate untreated rats.

Results

Plasma osmolality was significantly lower in the IV group (334 ± 1.4 mOsm/kg) compared to the None group (348 ± 0.7 mOsm/kg, p < 0.01), and not different from the SC group (335 ± 6.4 mOsm/kg), but higher than baseline (314 ± 5.3 mOsm/kg, p < 0.001). Urine production during the dwell was not different among the groups: None 10.6 ± 5.3 mL; SC 8.0 ± 6.0 mL; and IV 10.5 ± 5.6 mL. Transcapillary ultrafiltration after 4 hours was significantly higher in the IV group ( p < 0.05) compared to the other two groups. Net ultrafiltration and effective lymphatic absorption were similar in all groups. Mass transfer area coefficient of urea (MTACurea) was significantly greater in the IV group (155 ± 23.2 μL/minute, p < 0.003), but not different between the None (118 ± 16.2 μL/min) and SC (123 ± 25.9 μL/min) groups. Correcting these for the baseline plasma concentration resulted in higher values, but the IV data remained greater than the SC and None groups ( p < 0.01). The glucose absorption, albumin, and IgG clearances and the sieving of sodium were alike in all groups.

Conclusion

It can be concluded that IV fluid supplementation is more effective in preventing dehydration than SC supplementation, and it enhanced some peritoneal permeability characteristics in anesthetized rats during a 4-hour investigation. It is therefore important to standardize fluid supplementation in experiments with anesthetized animals.

Experimental models in peritoneal dialysis: a European experience

BACKGROUND

The development of adequate animal models is important for the in vivo study of selected aspects of peritoneal dialysis (PD) that cannot be evaluated by an in vitro model, such as peritoneal membrane transport, the influence of local defense mechanisms, and for testing new osmotic agents and their biocompatibilities.

METHODS

Our experience with animal models for PD, including the acute Stockholm model in non-uremic rats, the acute and chronic Amsterdam model in non-uremic rats, and the chronic Gent model in uremic rats, is described.

RESULTS

The Stockholm model proved to be useful in understanding the normal physiology of peritoneal transport, and for testing new dialysis solutions and their biocompatibilities. It is a rather simple and inexpensive model, and thus is suitable for screening new solutions and additives. The Amsterdam model permits the study of chemokines and mesothelial cell regeneration in vivo, and is applied in a model of chronic peritonitis. The results of the Gent model suggest that chronic peritoneal dialysis in uremic rats is feasible for at least eight weeks. This model is, however, very laborious, time consuming, and expensive.

CONCLUSION

Further improvement of the technique and increase of the dialysis dose should result in a better and more realistic model for peritoneal dialysis. It is hoped that in the future these models will be useful to test the effects of long-term intraperitoneal application of different dialysis solutions and additives in uremic animals.