Analysis of the prevalence and causes of ultrafiltration failure during long-term peritoneal dialysis: a cross-sectional study.

BACKGROUND: Ultrafiltration failure (UFF) is a major complication of peritoneal dialysis (PD). It can occur at any stage of PD, but develops in time and is, therefore, especially important in long-term treatment. To investigate its prevalence and to identify possible causes, we performed a multicenter study in The Netherlands, where patients treated with PD for more than 4 years were studied using a peritoneal function test (standard peritoneal permeability analysis) with 3.86% glucose. UFF was defined as net UF < 400 mL after a 4-hour dwell.

RESULTS: 55 patients unselected for the presence or absence of UFF were analyzed. Mean age was 48 years (range 18 - 74 years); duration of PD ranged from 48 to 144 months (median 61 months); UFF was present in 20 patients (36%). Patients with and without UFF did not differ in age or duration of PD. Median values for patients with normal UF compared to patients with UFF were, for net UF 659 mL versus 120 mL (p < 0.01), transcapillary UF rate 3.8 versus 2.1 mL/ minute (p < 0.01), effective lymphatic absorption 1.0 versus 1.6 mL/min (p < 0.05), mass transfer area coefficient (MTAC) for creatinine 9.0 versus 12.9 mL/min (p< 0.01), dialysate-to-plasma ratio (D/P) for creatinine 0.71 versus 0.86 (p < 0.01), glucose absorption 60% versus 73% (p < 0.01), maximum dip in D/P sodium (as a measure of free water transport) 0.109 versus 0.032 (p < 0.01), and osmotic conductance to glucose 3.0 versus 2.1 microL/min/mmHg (p < 0.05). As causes for UFF, high MTAC creatinine, defined as > 12.5 mL/min, or a glucose absorption > 72%, both reflecting a large vascular surface, a lymphatic absorption rate (LAR) of > 2.14 mL/min, and a decreased dip in D/P sodium of < 0.046 were identified. Most patients had a combination of causes (12 patients), whereas there was only a decreased dip in D/P sodium in 3 patients, only high MTAC creatinine in 1 patient, and only high LAR in 2 patients. We could not identify a cause in 2 patients. Both groups had similar clearances of serum proteins and peritoneal restriction coefficients. However, dialysate cancer antigen 125 concentrations, reflecting mesothelial cell mass, were lower in the UFF patients (2.79 vs 5.38 U/L).

CONCLUSION: The prevalence of UFF is high in long-term PD. It is caused mainly by a large vascular surface area and by impaired channel-mediated water transport. In addition, these patients also had signs of a reduced mesothelial cell mass, indicating damage of the peritoneum on both vascular and mesothelial sites.