Dialysis efficacy during acetate-free biofiltration.

BACKGROUND: Acetate-free biofiltration (AFB) is a haemodiafiltration technique based on continuous post-dilution infusion of a sterile isotonic bicarbonate solution. We performed a long-term randomized prospective trial to compare dialysis efficacy and metabolic control of AFB versus bicarbonate haemodialysis (HD).

METHODS: The AFB group consisted of 11 and the HD group of nine patients, matched for age, sex and urea reduction rate. Biochemical parameters were obtained every 3 months for 1 year (haemoglobin, calcium, phosphate, urea, pre- and post-dialysis bicarbonate, and parathormone (PTH)) and medication was updated. Efficacy of dialysis calculated by KT/V using the dialysate sampling method was determined every 3 months. In AFB patients, the infusion rate of bicarbonate solution was adjusted individually to obtain bicarbonate values of > or = 22 mmol/l before dialysis and < or = 32 mmol/l after dialysis. In the HD group, bicarbonate was added as oral medication to match these bicarbonate concentrations. Statistical analysis was performed using ANOVA for repeated measurements.

RESULTS: Pre-dialysis serum bicarbonate levels had risen to the same extent in both groups at the end of the study period (AFB from 21.8 to 26.1 mmol/l, P < 0.001, and HD from 20.8 to 24.9 mmol/l, P < 0.001). Post-dialysis bicarbonate level was higher in the AFB than in the HD group (P < 0.01). Calcium and phosphate levels remained stable in both groups. PTH increased in both groups (AFB from 10.6 to 23.7 pmol/l, and HD from 24.6 to 32.8 pmol/l), with a significant rise only in the AFB patients (P < 0.04). In AFB patients, KT/V increased from 2.73 to 3.17 per week (P < 0.04). In HD patients KT/V did not change (P < 0.38); the difference between the groups was significant at the end of the trial (P < 0.013). Finally, haemoglobin levels and erythropoietin dosage did not change in either group. No significant differences between the two groups were observed.

CONCLUSIONS: Acidosis was better corrected in AFB without the need for oral supplementation of bicarbonate. However, neither serum calcium nor phosphate levels changed. The observed increase in PTH in the AFB group remains to be clarified. Dialysis efficacy, measured as KT/V, improved during AFB.