The influence of automated peritoneal dialysis on the decrease in residual renal function

Background. Automated peritoneal dialysis (APD) has been increasingly used in recent years. Our purpose was to investigate whether the good preservation of residual renal function (RRF) that has been reported in patients on continuous ambulatory peritoneal dialysis (CAPD) is also observed in APD. Methods. RRF was determined and compared prospectively over 1 year in two groups of peritoneal dialysis (PD) patients: 18 consecutive new patients starting on APD (12 continuous cyclic peritoneal dialysis (CCPD) patients and six nightly intermittent peritoneal dialysis (NIPD) patients) and 18 selected patients who had started on CAPD at the same time and were matched for baseline characteristics. RRF was assessed on normalized creatinine clearance (ml/min/1.73 m(2)) measured before the start of PD, at 6 months, and at 1 year. Wilcoxon's rank sum test was used to compare differences between the two groups. Results. Creatinine clearance (Cl-Cr) was 6.1 ml/min in the APD group and 6 ml/min in the CAPD group at the start of PD. The monthly rate of Cl-Cr decrease was significantly higher in the APD group: -0.28 ml/min vs -0.1 ml/min (P = 0.04) at 6 months and -0.26 ml/min vs -0.13 ml/min (P = 0.005) at 1 year. RRF decreased at the same rate in patients treated with NIPD or CCPD. The daily instilled volume of 3.86% glucose dialysis solution (1/day) was higher in APD patients than in CAPD patients: 2.5 vs 0 at 6 months and 1 year but there was no significant difference in ultrafiltration rate (1/day) between APD and CAPD patients at these timepoints: 0.53 vs 0.6 and 0.88 vs 0.7 respectively. There was no difference between the two groups in body weight and blood pressure, which remained stable in both groups throughout the study period. Conclusions. RRF declined rapidly in APD patients whereas it was well preserved in CAPD patients. This may be explained by the less stable fluid and osmotic load together with the intermittent nature of APD and the larger use of hypertonic dialysate. RRF should be closely monitored in APD patients in order to adjust PD prescriptions and maintain adequacy.