OBJECTIVES: To compare the small molecule clearances on tidal peritoneal dialysis (TPD) and intermittent peritoneal dialysis (IPD), controlling for dialysate flow rate. DESIGN: Alternating 8-hour treatments on IPD and TPD (2 of each in 6 patients), each treatment separated by 3 or more days [patients returning to continuous ambulatory peritoneal dialysis (CAPD) in the interim] were performed. IPD treatments consisted of 15 exchanges with 2 L/exchange for a total of 30 L/treatment. TPD treatments consisted of 29 exchanges, with an initial fill volume of 2 L, followed by 1 L tidal volume for the subsequent exchanges (reserve volume of 1 L) for a total of 30 L/treatment. PATIENTS: Six patients, with a mean dialysate/plasma (D/P) creatinine as determined by the peritoneal equilibration test (PET) of 0.64 +/- 0.10, were studied. Four had a low-average D/P creatinine, while 2 had a high-average D/P creatinine. MEASUREMENTS: Urea nitrogen, creatinine, phosphate, and potassium clearances on TPD and IPD were compared using the paired t-test. RESULTS: The dialysate flow rates were 3.7 +/- 0.1 L/hour for IPD and 3.8 +/- 0.2 L/hour for TPD. The mean dialysate dextrose was 1.9 +/- 0.5 g/dL for both. The creatinine clearances were 9 +/- 2 versus 10 +/- 3 mL/minute, the urea nitrogen clearances 19 +/- 3 versus 20 +/- 3 mL/minute, and phosphate clearances 10 +/- 3 versus 11 +/- 3 mL/minute for IPD and TPD, respectively (all not different). The ultrafiltration rates were 2.9 +/- 0.9 mL/minute on IPD and 3.3 +/- 1.6 mL/minute on TPD (not different). On both IPD and TPD the clearances of urea nitrogen, creatinine, and phosphate for the 2 patients with high-average D/P creatinine were higher than for the 4 patients with low-average D/P creatinine. CONCLUSIONS: When the dialysate flow rate is controlled and a TPD prescription of 1 L reserve and tidal volumes is used, the small molecule clearances on IPD are similar to those on TPD.

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