Urea kinetic analysis of automated peritoneal dialysis allows calculation of a CAPD-equivalent Kt/V-urea

Background Based on evidence of increased mortality with decreasing urea cl earance, the Dialysis Outcomes Quality Initiative (DOQI) recommended a week ly Kt/V-urea of 2.0 or higher for patients receiving continuous ambulatory peritoneal dialysis (CAPD). DOQI recommendations for automated peritoneal d ialysis (APD) are based on efforts to determine the clearance providing ure a mass removal equivalent to CAPD. We have adapted a variable volume direct quantitation urea kinetic model (UKM) in an effort to assess DOQI APD guid elines. Methods. The daily urea mass removed with a weekly Kt/V-urea of 2.0 was cal culated using standardized CAPD patient profiles. Using this value and defi ning the pre-APD plasma urea nitrogen (PUN) as C and equal to the CAPD stea dy-state PUN. the UKM reiteratively calculated the urea clearance from an A PD treatment that provided a urea mass removal equivalent to CAPD. A total weekly Kt/V-urea was calculated for various levels of continuous urea clear ance (defined as K(pr)t/V-urea) and plotted against K(pr)t/V-urea (weekly). The impact of dialytic time (t), drain volume of the daytime dwell (delta) , and ultrafiltration volume (phi) were assessed, and all profiles were per formed with C-0 equal to the corresponding blood urea nitrogen of 60, 70, a nd 80 mg/dL. Results. The relationship between requisite weekly Kt/V-urea and K(pr)t/V-u rea (weekly) was linear. Weekly Kt/V-urea declined with increasing K(pr)t/V -urea, t, delta, and phi. The efErct of phi on the weekly Kt/V-urea was ind ependent of K(pr)t/V-urea, and the magnitude of the effect of t and delta o n the weekly Kt/V-urea, decreased with increasing continuous clearance. Wee kly Kt/V-urea, values were independent of V and C-0. The latter observation allowed extrapolation of CAPD clearance and urea generation relationships to APD: CAPD-equivalent weekly Kt/V-urea = [700 x (U-D + U-r)]/(C-0 x V), w here U-D and U-r are the daily urea mass (mg) in dialysate and urine, respe ctively. Conclusions. The APD urea clearance. which provides urea mass removal equiv alent to CAPD. varies as a function of a combination of patient and treatme nt variables. However. a CAPD-equivalent weekly Kt/V-urea can be calculated by collecting appropriate dialysis and urine samples and estimating patien t V. The results can be evaluated in the context of evidence-based CAPD gui delines, increasing the precision of adjustment and monitoring of the APD p rescription.