Does Peritoneal Protein Transport Increase with Peritoneal Dialysis Therapy Duration and Lead to Extracellular Water Overload in Peritoneal Dialysis Patients?

Abstract

Faster peritoneal transport status has been associated with adverse outcomes for peritoneal dialysis (PD) patients. Peritoneal protein clearance, through large pores, may be a surrogate marker of local inflammation. We wished to determine whether peritoneal protein transport increased with PD duration or was associated with extracellular water (ECW) expansion. We studied the relationships between 4 h Dialysate (D)/Serum (S) protein and ECW excess, using multifrequency bioelectrical impedance assessments, in 103 PD patients with up to 4 years of prospectively collected peritoneal equilibrium test (PET) results. 4 h PET D/S total protein and creatinine ratios were stable over time (K-W test, P = 0.063 and P = 0.3357, respectively). The initial PET 4 h D/S creatinine and D/S total protein correlated with ECW excess (r = 0.33, P = 0.003, and r = 0.27, P = 0.019, respectively), but thereafter there was no association. CRP and albumin did not correlate with 4 h D/S creatinine or total protein. Serial 4 h D/S total protein and 4 h D/S creatinine correlated all time points (P < 0.001). At the start of PD therapy, over-hydration (ECW excess) was observed with higher 4 h D/S creatinine and 4 h D/S total protein ratios, suggesting initial exposure to PD fluids causes faster transport. Thereafter changes in peritoneal creatinine and total protein transport mirrored each other suggesting that similar factors lead to changes in both small and large pore transport, and there was no sustained increase in larger pore transport with therapy time.

Protein Losses and Urea Nitrogen Underestimate Total Nitrogen Losses in Peritoneal Dialysis and Hemodialysis Patients

“…In keeping with previous reports of greater urea and protein losses with intermittent cycler peritoneal dialysis, we found greater losses with APD compared to CAPD [17]. Although not significantly different the protein losses were slightly greater with CAPD, reflecting the longer dwell times, as protein transport is much slower than that of urea [27].…”

Overhydration May Be the Missing Link between Peritoneal Protein Clearance and Mortality

“…Although no echocardiography was done in the present study, nor was serum NT-proBNP determined, BIA was performed in all patients and in both studies and showed similar relationships between overhydration and PPCl. Another cross-sectional analysis reported relationships between fluid overload and 4-h dialysate/serum total protein ratio, but no 24-h collections were obtained [27]. BIA results were reported in only one of the published epidemiological studies on relationships between PPCl and death [12].…”

Relationships between Peritoneal Protein Clearance and Parameters of Fluid Status Agree with Clinical Observations in other Diseases that Venous Congestion Increases Microvascular Protein Escape

“…More than 20 years ago, a study from Israel reported higher effluent total protein concentrations in patients with lower ultrafiltration rates than in those with higher ultrafiltration rates (6). Reduced ultrafiltration can lead to fluid retention and volume overload, which could then potentially explain the recently reported association between extracellular volume excess and peritoneal protein loss in PD patients during their initial peritoneal equilibration test (PET) (7). At least 4 epidemiological observational studies published in the last 15 years have reported an association between peritoneal protein loss or peritoneal protein clearance and mortality (8–11).…”