Influence of Dwell Time, Osmolality, and Volume of Exchanges on Solute Mass Transfer and Ultrafiltration in Peritoneal Dialysis

Calcium Carbonate as a Phosphate Binder: Is There a Need to Adjust Peritoneal Dialysate Calcium Concentrations for Patients Using CaCO3?

The widespread use of calcium carbonate as a phosphate binder is limited by its tendency to develop hypercalcemia in some patients using effective dosages needed to control hyperphosphatemia. Most common continuous ambulatory peritoneal dialysis (CAPD) regimens using dialysis solutions containing 3.5 mEqlL of calcium result in net absorption of calcium from the dialysis solution and, hence limit the amount of oral calcium that can be administered. Peritoneal dialysis solutions with reduced calcium levels are needed for effective use of CaCO3 to control hyperphosphatemia in some dialysis patients.

Hormonal, Blood Pressure, and Peritoneal Transport Response to Short -Term Ace Inhibition

Objectives

To evaluate the hormonal, blood pressure, and peritoneal transport effects of intraperitoneal enalaprilat and oral enalapril.

Design

A nonrandomized, nonblinded, prospective clinical trial was performed.

Setting

The study was conducted at the Clinical Research Unit at the Medical College of Virginia, a tertiary care center.

Patients

Six continuous ambulatory peritoneal dialysis (CAPD) patients with hypertension were enrolled in the study. All 6 patients received intraperitoneal enalaprilat. Five of the patients also received oral enalapril.

Interventions

Hormonal, clinical, and transport parameters were investigated in patients given intraperitoneal enalaprilat and oral enalapril. Standardized 2-L exchanges were performed during a control period, following 2.5 mg intraperitoneal enalaprilat and after a week of oral enalapril. Inulin, blood urea nitrogen (BUN) and creatinine clearances, and glucose absorption were determined during these exchanges.

Results

After intraperitoneal enalaprilat, both systolic and diastolic blood pressure significantly declined, reaching maximal decreases of -21.7±14.2% at 95±92 minutes, and of -23.3±15.4% at 105±105 minutes, respectively. Plasma angiotensin converting enzyme (ACE) activity was suppressed below detectable limits at four hours following intraperitoneal enalaprilat, and remained suppressed throughout all sampling time points following oral enalapril treatment. There was no significant change in drain volumes, glucose absorption, or BUN, creatinine, or inulin clearances, whether enalaprilat was administered intraperitoneally or enalapril orally.

Conclusion

This study demonstrates that intraperitoneal administration of enalaprilat is a rapidly effective route of administration of this ACE inhibitor. There were no changes in peritoneal transport characteristics demonstrated.

Intra-abdominal pressure, peritoneal dialysis exchange volume, and tolerance in APD

Automated peritoneal dialysis (APD) is increasingly popular compared to continuous ambulatory peritoneal dialysis (CAPD). It not only can provide more solute clearance and ultrafiltration than its CAPD counterpart, but it is conducive to a more convenient lifestyle as well. Using relatively smaller-volume daytime dwells, with the use of larger-volume exchanges while the patient is recumbent during the night, is an attractive approach. Advantages of supine exchanges include greater small molecule clearances for equivalent flow rates and decreased intra-abdominal pressure per volume of dialysate (as intraperitoneal pressure parallels intraperitoneal volume). Urea nitrogen clearance can be optimally increased on APD by increasing both the exchange volume and the frequency of exchanges at night. This is even true for anuric low transporters. This approach allows daytime exchanges and volumes to be minimized. Historic studies in peritoneal dialysis including flow rate analysis, clearance and adequacy studies, as well as tolerance have primarily involved CAPD. As a result, there is a paucity of investigations involving APD. More research is required in APD related to these subjects.

Evaluation of peritoneal membrane permeability

Total removal of fluid and solutes during peritoneal dialysis depends on both the dialysis prescription (ie, the number, length, and timing of the dwells and the volume and contents of the dialysis solution) and the permeability of the peritoneal membrane. Peritoneal membrane permeability determines the rate of solute equilibration between body fluids and the solution within the peritoneal cavity and is, therefore, a significant determinant of the solute removal rate. The relationship between fluid removal during peritoneal dialysis and the properties of the peritoneal membrane is more complex; peritoneal ultrafiltration is inversely related to the permeability of the peritoneal membrane to osmotic solutes but is directly related to the hydraulic conductivity of the peritoneal membrane. The peritoneal equilibration test (PET) is widely used as the standard method for evaluating peritoneal membrane permeability, and results from the PET can be used to determine the type of peritoneal dialysis therapy optimal for the permeability characteristics of the patient's peritoneal membrane. Simple extrapolations from the PET can only provide qualitative estimates of the dialysis dose required for various types of peritoneal dialysis. More accurate estimates of the required dialysis dose can be provided by mathematical models of peritoneal fluid and solute transport, but these models require calculation of the permeability-area product or mass transfer-area coefficient of the peritoneal membrane. Although the latter approach shows promise for improving peritoneal dialysis prescriptions, determination of the delivered dose of peritoneal dialysis can, at present, only be assessed by directly measuring total 24-hour solute and fluid removal.

Peritoneal dialysis. Current technology and techniques

The use of chronic peritoneal dialysis has increased greatly in recent years. The procedure has few contraindications, and complications such as mild peritonitis respond quickly to intraperitoneal antibiotics. At present, a continuous ambulatory regimen, which can be performed by the patient anywhere, is the predominant form of peritoneal dialysis.