Factors affecting peritoneal phosphate removal. Therapeutic options

Impaired phosphate excretion resulting in hyperphosphatemia is one of the e arliest consequences of chronic renal failure. To control serum phosphate l evels, we can use the following therapies: 1) Restriction of dietary phosph ate (but on CAPD, obligatory protein losses via peritoneal fluid makes impr actical any reduction of phosphate diet 2) Reduction of phosphate absorptio n, using phosphate binders. 3) Peritoneal phosphate removal. Object: 1) To evaluate the factors affecting peritoneal phosphate removal s uch as plasma phosphate, peritoneal membrane transport type, peritoneal dia lysis modality prescription (CAPD or APD) and daily dialysate volume. 2) To test the best calcium concentration in the peritoneal dialysis fluid (5, 6 or 7 mg/dl) in order to permit the use of calcium carbonate or acetate wit hout the risk of hypercalcemia or hyperparathyroidism. Method: Phosphate was measured in seventy 24-hour dialysate collections, 33 from patients on CARD and 37 from patients on APD. 24-hour peritoneal phos phate removal (mg/24 hours) and weekly peritoneal phosphate clearance was c alculated (L/week). The peritoneal membrane was studied by the peritoneal e quilibrium test (PET), using a 2.27% glucose. We calculated also the perito neal calcium balance in 25 daily peritoneal fluid collections from patients using a calcium dialysate concentration of 5 6 or 7 mg/dl each one. IPTH l evels and doses of vitamin D were compared at 6 months in patients using a calcium concentration of 5 6 or 7 mg/dl from the beginning of peritoneal di alysis (5 patients of each calcium dialysate concentration). Results: Weekly peritoneal phosphate clearance (WPC) were higher or APD tha n on CARD (57 +/- 21 vs 47 +/- 14, p < 0.005). Daily dialysate volume was a lso higher on APD (14 +/- 4 vs 7.8 +/- 7.8 L/day, p < 0.001). WPC was highe r on APD when a mild-day exchange was done (61 +/- 23 vs 45 +/- 15, p < 0.0 05). instead an equal total daily volume of the dialysate. Peritoneal calci um balance was significantly more negative in patients using a calcium in t he dialysis fluid of 5 than 6 or 7 mg/dl (-125 +/- 7 vs -18 47 vs -11 +/- 4 9, p < 0.001). At 6 months, patients using a calcium fluid concentration of 5 mg/dl increased iPTH levels (from 160 +/- 101 to 332 +/- 153, p < 0.001) and vitamin D needs (from 0 to 1.87 +/- 0.37 mcg/week, p < 0.001). In summary, peritoneal phosphate clearance depends on plasma phosphate leve ls, daily volume of dialysate prescribed and peritoneal membrane transport characteristics. It can be improved by increasing the total peritoneal flui d. On APD, a mild-day exchange may improve phosphate clearance, without tot al volume increase. The risk of secondary hyperparathyroidism can be decrea sed with a calcium fluid concentration of 6 mg/dl, which was shown to be be tter than 5 mg/dl when calcium phosphate binders are not correctly taken.