Phosphate depletion is a known issue during CRRT, with an incidence of hypophosphatemia up to 80% when standard CRRT solutions are used. The aim was to evaluate the effects on serum phosphate and phosphorus supplementation needs of a regional citrate anticoagulation (RCA) protocol combining citrate with a phosphate-containing CRRT solution.
In heart surgery patients undergoing CRRT for acute kidney injury, we adopted RCA in CVVH or CVVHDF modality combining a commercially available citrate solution (18 mmol/l) with a phosphate-containing dialysate and/or replacement fluid (HCO3- 30 mmol/l, phosphate 1.2). Prescribed CRRT dose, corrected for pre-dilution, was at least 25 ml/kg/h with about 50-60% of dialysis dose given as phosphate-containing solution. Hypophosphatemia was defined as follows: mild (<0.81 mmol/l), moderate (<0.61 mmol/l) and severe (<0.32 mmol/l).
Forty-eight patients were treated with RCA-CRRT for a total running time of 12502 hours. Two-hundred and nineteen circuits were used (mean filter life 57.1±41.7 hours, median 47, IQR 24-83). Acid-base status was adequately maintained without additional interventions on RCA-CRRT parameters [pH 7.43 (7.40-7.47), bicarbonate 25.3 mmol/l (23.8-26.6), BE 0.9 (-0.7 to 2.4); median (IQR)]. Serum phosphate was steadily maintained in a narrow range throughout RCA-CRRT days [1.2 mmol/l (0.97-1.45)]. At some times during CRRT, only 10 out of 48 patients (20.8%) received a low amount of phosphate supplementation (d-fructose-1,6-diphosphate 1.05±2.04 g/day) for mild (n=7) to moderate (n=3) hypophosphatemia. In particular, only 33 out of 513 serum phosphorus determinations met the criteria for mild (n = 24) to moderate (n = 9) hypophosphatemia. Severe hypophosphatemia was never observed.
The use of a phosphate-containing CRRT solution, accounting for about 50-60% of CRRT dose in the setting of RCA-CVVH or RCA-CVVHDF, allowed to prevent CRRT-induced phosphate depletion in most of the patients, minimizing the need for phosphate supplementation and maintaining phosphorus levels in near normal range throughout CRRT days.
