Methods of Implementation and Applications of Urea Kinetic Modeling for Patients on Continuous Ambulatory Peritoneal Dialysis

Patients on continuous ambulatory peritoneal dialysis (CAPD) are in a steady state and do not have large changes in volume or solute removal compared with patients on hemodialysis. Therefore, urea kinetic modeling (UKM) for CAPD is not as mathematically complicated as it is for hemodialysis and is very similar to UKM for patients not on dialysis. We used a personal computer (PC) with a spreadsheet program to develop the UKM data base for our patients on CAPD. The peritoneal effluent, analyzed as though it were urine, mimics residual renal function and when combined with residual renal function (Kr_u) provides a value for total solute clearance. Patients bring a 24-hour effluent and urine collection to the clinic every 6 months. Fluid aliquots are analyzed for urea nitrogen, creatinine, glucose, and total protein. These data, along with height, sex, weight, and number and type of exchanges as well as serum values for urea nitrogen and creatinine, are entered into the PC for determination of peritoneal urea and creatinine clearance, Kr_u, protein losses, protein catabolic rate, Kt/V, and estimated glucose absorption. We currently have 90 patients in our CAPD program. Reported here are 53 patients who have had serial UKM evaluations for at least 2 years. The mean time on dialysis when UKM was begun was 25 months (range, 1 to 125). Over time, the Kt/V changed from a mean of 1.9 ± 0.0 SEM to 1.7 ± 0.1 (P < .01, analysis of variance), probably related to a decrease in Kru (0.01 ± 0.00 to 0.00 ± 0.00 mL/s [0.8 ± 0.1 mL/min to 0.2 ± 0.2]; P < .01). Estimated caloric supplement from glucose tended to increase (508 ± 30 to 547 ± 33 kcal, not significant), and weight remained stable. Protein loss was unchanged with time as well (6.2 ± 0.3 g/d to 6.4 ± 0.5 [6,200 ± 300 to 6,400 ± 500 mg/d]; P = .7. Development of UKM for CAPD on a PC is easy and can provide ongoing information concerning changes in and nutritional parameters of CAPD dialysis delivery.