The impact of various cycling regimens on phosphorus removal in chronic peritoneal dialysis patients

The National Kidney Foundation Dialysis Outcome Quality Initiative clinical practice guidelines have suggested that serum phosphate levels be maintained at < or =5.5 mg/dL in patients maintained on dialysis. Over 45% of anuric patients maintained on CAPD have serum phosphate levels >5.5 mg/dL. The present study was designed to address the question whether phosphate removal could be enhanced by increasing the dialysate volume during cycler peritoneal dialysis therapy.

Medically stable patients maintained on chronic peritoneal dialysis therapy, who were high or high-average transporters and had serum phosphate levels > or =5.5 mg/dL, were invited to participate in the study. The protocol involved measuring phosphate and creatinine clearances at weekly intervals on three different cycler prescriptions consisting of 7 and 12 full cycles or 24 cycles with 50% tidal PD (TPD) over 9 hours. Ten patients agreed to participate. Those patients (n=7) with a BMI > 22 had 2 liter (L) fill volumes and 14 L of total dialysate (7 cycles of 2 L) or 24 L total dialysate (12 cycles of 2 L or 50% TPD with 24 cycles).The patients (n=3) with a BMI < 20 had 1.2 L fill volumes and 8.4 L total dialysate (7 cycles) or 14.4 L total dialysate (12 cycles of 1.2 L or 50% TPD with 24 cycles).

The mean age (+/- SD) of the study patients was 50.8 (+/- 9.3) years. There were 6 females, 6 Caucasians and 4 African-Americans. The mean weight of the patients was 71.5 (+/- 24.2) kg and mean height 1.65 (+ 7.6) meters. The mean BMI was 18.3 (+/- 1.27) in the < 20 BMI group and 30.3 (+/- 6.6) in the > 22 BMI group. The mean phosphate clearance (L/night/1.73m 2 ) increased from 3.96 (+/- 1.16) with 7 cycles to 4.71 (+ 1.81) with 12 cycles and 4.51 (+/- 1.61) with 50% TPD. Creatinine clearance (L/night/1.73m 2 ) was 4.74 (+/- 1.74) with 7 cycles, 6.06 (+/- 2.04) with 12 cycles and 5.61 (+/- 2.01) with TPD.

The present study indicates that there is a significant, 19% (P < 0.005) rise in phosphate clearance by increasing dialysate volume 71% from 7 cycles to 14 cycles compared to a 27% increase in creatinine clearance. With tidal PD, phosphate clearance increased by 12% (p=NS) and creatinine clearance increased 18 % (p, 0.02). This increase in phosphate clearance translates into <50 mg net phosphate removal in 9 hours, assuming a serum phosphate of 6 mg/%. Thus, increasing dialysis cycles and volume results in only a minimal increase in net phosphate removal.