Longitudinal analysis of peritoneal fluid transport and its determinants in a cohort of incident peritoneal dialysis patients

Abstract

Background and objectives: There is a paucity of large longitudinal studies on the time course of peritoneal fluid transport. The aim of the present study was to longitudinally analyze changes in fluid transport and relevant solute transport parameters in patients treated with a conventional peritoneal dialysis (PD) fluid and, to mimic clinical reality, not selected for the presence or absence of ultrafiltration (UF) failure.

Methods: This prospective single-center cohort study followed 138 consecutive incident PD patients from July 1994 until censoring in August 2004. The design was longitudinal, with repeated measures over time in each patient. Patients had undergone at least 1 and a maximum of 5 annual standard peritoneal permeability analyses (SPAs) using 3.86% glucose dialysate. A linear mixed model was used to analyze the longitudinal data.

Results: No differences in patient characteristics were present at baseline in relation to the number of available SPAs. There were also no differences in patient withdrawal during the years of follow-up. A gradual decline in fluid transport, expressed as free water transport (FWT), small-pore fluid transport (SPFT), and transcapillary UF (TCUF), was observed with duration of PD. The decline was mainly attributable to patients who developed UF failure. The time courses for the determinants of fluid transport, such as the reflection coefficient (σ) and the UF coefficient (LpA), were not different. However, they were associated with an increase in the mass transfer area coefficient of creatinine, reflecting the peritoneal vascular surface area.

Conclusions: Fluid profiles for FWT and SPFT during a dwell can be explained by current knowledge of the three-pore model. Fluid transport declines with the duration of PD because of an increase in the vascular surface area, leading to a rapid dissipation of glucose as the osmotic agent. The absence of a trend in the time course of osmotic conductance and its constituents-that is, LpA and σ-suggests that, in an unselected population, these parameters are affected only late in the time course of PD.

Keywords: Peritoneal fluid transport; free water transport: small-pore fluid transport; linear mixed model; prospective longitudinal study; standard peritoneal permeability analysis.

Figure 1 —

Flowchart of patient selection. PD = peritoneal dialysis; SPA = standard peritoneal permeability analysis.

Figure 2 —

The reasons for withdrawal from peritoneal dialysis. HD = hemodialysis; UFF = ultrafiltration failure.

Figure 3 —

The time course of transcapillary ultrafiltration (TCUF), small-pore fluid transport (SPFT), and free water transport (FWT). A gradual decline occurred in all parameters (p < 0.05), being most prominent after 4 years of follow-up. SPA = standard peritoneal permeability analysis.

Figure 4 —

The number of patients with ultrafiltration (UF) failure according to the number of standard peritoneal permeability analyses (SPAs).

Figure 5 —

Time course of free water transport (FWT), small-pore fluid transport (SPFT), reflection coefficient (sigma), and LpA (hydraulic permeability of peritoneal membrane multiplied by surface area) according to the number of standard peritoneal permeability analyses (SPAs). The number of SPAs did not influence these parameters.

Figure 6 —

Time course of the determinants of fluid transport. Only the mass transfer-area coefficient (MTAC) of creatinine showed a significant increase with the duration of peritoneal dialysis (p < 0.01). LpA = hydraulic permeability of peritoneal membrane multiplied by surface area; SPA = standard peritoneal permeability analysis; sigma = reflection coefficient.