Urea Peritoneal Transfer Evaluated Using Plasma Water Urea Concentrations

Objective To quantify differences in evaluation of urea peritoneal transport parameters according to the expression of urea concentration in whole plasma and plasma water.Design Prospective study in which the dialysate samples for urea determinations were taken at short dwell times (2.5 45 minutes) during three consecutive exchanges of intermittent peritoneal dialysis (IPD). Blood samples were drawn at the beginning and at the end of the study period. Urea peritoneal transport parameters were calculated using urea concentration in whole plasma and plasma water. The results were then compared.Setting Peritoneal dialysis unit of a nephrology de partment.Patients Ten stable patients on IPD.Interventions Dialysateand blood sample collections.. Main Outcome Measures: Dialysate-to-plasma ratios (DIP), peritoneal clearances (Cp)’ and diffusive mass transport coefficients (KBD) of urea.Results At short dwell times, uncorrected (whole plasma) DIP and Cp of urea values were higher than the corrected (plasma water) values by 5.7% -5.9%. Uncorrected urea KBD’ calculated using the simplified two sample model of Garred et al., yielded an overestimation that significantly increased with prolongation of dwell (8.5±0.5% at 2.5 minutes vs 13.0±0.8% at 45 minutes). Urea KBD’ assessed by the linear regression model of Garred and Spencer, was 9.4±0.3% higher for uncorrected values.Conclusions The expression of urea concentration in whole plasma instead of plasma water overestimates urea peritoneal transfer parameters. The percent overestimation (y) of urea KBD’ calculated using the simplified model of Garred et al., can be predicted with the equation y = 0.131x+ 7.563, wherex is the dwell time (in minutes).