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Objective: The recent increase in the use of automated peritoneal dialysis (APD) has led to concerns about the adequacy of clearances delivered by this modality. Few clinical studies looking at the effects of varying the individual components of the APD prescription on delivered clearance have been done, and most published data are derived from computer modeling. Most controversial is the optimal frequency of exchanges per APD session. Many centers prescribe 4 to 6 cycles per night but it is unclear if this is optimal. The purpose of this study was to address at what point the beneficial effect of more frequent cycles is outweighed by the concomitant increase in the proportion of the total cycling time spent draining and filling., Methods: A comparison was made between the urea and creatinine clearances (CCrs) achieved by 4 different APD prescriptions, used for 7 days each, in 18 patients. The prescriptions were for 9 hours each and were all based on 2-L dwell volumes, but differed in the frequency of exchanges. They were 5 x 2 L, 7 x 2 L, and 9 x 2 L, as well as a 50% tidal peritoneal dialysis (TPD) prescription using 14 L. Ultrafiltration, dwell time, glucose absorption, sodium and potassium removal, protein excretion, and relative cost were also compared. Clearances due to day dwells and residual renal function were not included in the calculation., Results: Mean urea clearances were 7.5, 8.6, 9.1, and 8.3 L/night for the four prescriptions respectively. Urea clearance with 9 x 2 L was significantly greater than with the other three prescriptions (p < 0 0.05). Urea clearance with 7 x 2 L and TPD were superior to 5 x 2 L (p < 0.05). Mean CCr was 5.1, 6.1, 6.4, and 5.6 L/night, respectively. Compared to 5 x 2-L, the 7 x 2-L, 9 x 2-L, and TPD prescriptions achieved greater CCr (p < 0.05). Taking both urea and CCr into account, 9 x 2 L was the optimal prescription in 12 of the 18 patients. Ultrafiltration and sodium and potassium removals were all significantly greater with the higher frequency prescriptions., Conclusion: The 5 x 2-L prescription significantly underutilizes the potential of APD to deliver high clearances, and 7 x 2 L is a consistently superior prescription if 2-L dwells are being used. Although more costly, 9 x 2 L should be considered if higher clearances are required.

Objective: To clinically validate the use of a computer-based kinetic model for peritoneal dialysis (PD) by assessing the level of agreement between measured and modeled values of urea and creatinine clearances and ultrafiltration (UF)., Design: An open multicenter observational study., Patients: There were 111 adult continuous ambulatory peritoneal dialysis (CAPD) patients (47 female, 64 male) in four centers. All patients underwent a four-hour peritoneal equilibration test (PET) using 2.5% dextrose but with variable fill volumes (range: 1-3 L). Patients with a residual renal function greater than 10 mL/min were excluded., Main Outcome Measures: Correlations and limits of agreement between measured and modeled values of total weekly urea KT/V, total weekly normalized creatinine clearance (L/week/1.73 m2), daily drain volume (L), net ultrafiltration (L), daily peritoneal urea clearance (L/day), and daily peritoneal creatinine clearance (L/day). Measured values were obtained from 24-hour urine and dialysate collections while modeled values were based on results from the PET in combination with the PD ADEQUEST kinetic program., Results: The results show there is excellent agreement between measured and modeled urea KT/V and creatinine clearances, with concordance correlations of 0.94 and 0.92, respectively. Given the excessive variation and limited range in ultrafiltration values, the concordance correlation between measured and modeled UF was only 0.50. In terms of daily peritoneal clearances and ultrafiltration, the level of precision (i.e., standard deviation) in the differences between modeled and measured values is +/- 1.05 L/day for urea clearance +/- 1.03 L/day for creatinine clearance, and +/- 0.919 L/day for ultrafiltration. By contrast, the level of precision (i.e., standard deviation) in the differences between two measured values is estimated to be +/- 0.979 L/day for urea clearance, +/- 0.802 L/day for creatinine clearance, and +/- 0.707 L/day for ultrafiltration. Defining the limits of clinical agreement to be +/- 2 standard deviations of the differences between two clinically measured 24-hour clearances (or ultrafiltration), we find that 94% of the modeled urea clearances, 87% of the modeled creatinine clearances, and 86% of the modeled ultrafiltration values fall within the limits of clinical agreement., Conclusion: Data for a carefully performed PET and overnight exchange can, in combination with a scientifically validated kinetic model, provide clinicians with a powerful mathematical tool for use in CAPD dialysis prescription management. Although not intended to replace actual measurements, kinetic modeling can prove useful as a means for predicting clearances for various alternative prescriptions and perhaps also as a means for checking certain types of noncompliance.

Objective: To evaluate the use of the ratio of measured to predicted creatinine excretion as an index of compliance in peritoneal dialysis (PD) patients., Design: A prospective analysis., Setting: Academic teaching hospital dialysis unit., Patients: Forty-three patients on PD., Measurements: Creatinine excretion in daily dialysate and urine collections was measured on one occasion in 10 patients and on two occasions in 33 patients, and, after adding an estimate for extrarenal creatinine degradation, was divided by predicted creatinine excretion to give a creatinine excretion ratio, which has been proposed as an index of compliance with exchanges in PD patients. Values above 1.24 have been suggested to indicate noncompliance. Lean body mass was also estimated from creatinine excretion., Results: The mean creatinine excretion ratio was 1.12, and 30% of patients had a value above 1.3. Only one patient admitted noncompliance. Studies on four consecutive days of guaranteed compliance in 7 patients with high ratios showed that creatinine excretion remained constant, suggesting that the patients were high creatinine producers rather than noncompliant. Creatinine excretion was stable when measured at intervals of days, but over months it tended to change markedly in many patients. Lean body mass estimations using creatinine excretion were low in most patients., Conclusion: Comparison of measured and predicted creatinine excretion is not a reliable indicator of noncompliance because many compliant patients consistently excrete more creatinine than predicted. The standard formulas were not validated in dialysis patients and underestimate creatinine excretion significantly in many PD patients. Existing estimates in the literature of noncompliance, using this methodology, may not be accurate. Better methods of detecting this problem are required.