Ultrafiltration and Small Solute Transport at Initiation of PD: Questioning the Paradigm of Peritoneal Function

Abstract

Background Human peritoneal function on commencing peritoneal dialysis (PD) is not yet adequately understood. The objective of this study was to determine peritoneal functional patterns on commencing PD. Methods 367 end-stage renal disease (ESRD) patients on PD for the first time were studied between their initial second to sixth weeks on PD. Urea and creatinine mass transfer area coefficients (MTAC) and standardized ultrafiltration (UF) capacity were determined. Results Mean parametric values were MTAC urea 22.9 ± 7.04 mL/min, MTAC creatinine 10.31 ± 4.68 mL/min, and UF 896 ± 344 mL. Gender, patient size, and diabetes or kidney disease did not affect these parameters. The relationship between values of MTAC creatinine and UF reached statistical significance, although with a low value for Pearson's coefficient ( r=–0.30, p = 0.001). Age showed a significant inverse linear correlation with UF capacity ( r = –0.15, p = 0.003) and MTAC urea ( r = –0.11, p < 0.05). Logistic regression analysis demonstrated that UF below 400 mL was independently related to a high MTAC creatinine and older age. Diabetes was least frequent in patients with the lowest UF. However, in the analysis of MTAC creatinine quintiles, UF values did not follow the expected inverse pattern. The lack of differences in UF between the second and third to fourth MTAC creatinine quintiles is remarkable; MTAC creatinine ranged from 6.71 to 13.54. Conclusions The functional characteristics of human peritoneum varied markedly and there was a less intense than expected relationship between solute and water transports. This mild inverse relationship is intriguing and suggestive of the necessity of redefining some basic concepts. Age was associated with a lower peritoneal UF capacity, in part independently of small solute transport.

Renal Association Clinical Practice Guideline on peritoneal dialysis in adults and children

“…(See Appendix for methodological description of membrane function tests). This is for the following reasons: There is considerable between-patient variability in both solute transport and ultrafiltration capacity that translates into real differences in achieved solute clearance and ultrafiltration unless they are accounted for in prescription practice [ 78 – 81 ] Membrane function is an independent predictor of patient survival; specifically high solute transport and low ultrafiltration capacity are associated with worse outcomes [ 82 – 86 ] Membrane function changes with time on therapy. There are early changes – usually during the first few weeks of treatment that can be avoided by performing tests 6 weeks after commencing PD.…”

Mitigating peritoneal membrane characteristics in modern peritoneal dialysis therapy

“…Nevertheless, as can be seen in Figure 1, the amount of variability in ultrafiltration explained by variability in solute transport is only B18%; even if we allow for the measurement of ultrafiltration capacity being less precise, it is clear that solute transport is only one, albeit important and easily measured aspect of membrane function. 3,6 So what are the clinical characteristics that are associated with variability in solute transport at the start of PD? Several studies have looked at this and their findings are summarized in Table 1.…”

“…Several studies have looked at this and their findings are summarized in Table 1. 3,[6][7][8][9][10] Before discussing these in detail, two things should be noted. First, in general, although statistically significant relationships are found, they explain relatively little of the variance in solute transport.…”

Peritoneal Membrane Structural and Functional Changes during Peritoneal Dialysis

“…(17) documented that approximately two‐thirds of PD patients have an average transport rate, while the remaining one‐third are almost equally distributed between fast and slow transport. This significant interpatient variability in baseline PM characteristics has been confirmed (42,48,55–59), raising the critical question of what determines that variability.…”