Bicarbonate buffered dialysate and replacement solutions for CRRT: effect of crystallization on the measured levels of electrolytes and buffer

The aim of this study was to investigate the impact of the addition of calcium to bicarbonate solutions for CRRT. We tested single bag (SB; bicarbonate and calcium mixed 24 h before testing) and double bag (DB) solutions (mixed immediately before), with and without the addition of 4 mEq/l acetate. Prescribed calcium varied from 0-5 mEq/l. In all test solutions prepared with calcium 5 mEq/l there was a decrease in the measured calcium concentration. SB solutions presented lower concentrations of calcium, compared with DB solutions. When the prescribed calcium concentration was increased, there was a parallel increase in calcium deficit (prescribed-measured). The prescribed calcium showed a negative correlation with sodium and potassium and a positive correlation with pCO₂. We also found a positive correlation between calcium deficit and pCO₂ (r = +0.59; P < 0.001). The crystallization, as measured by the weight of the crystals, was greater in the SB solutions when compared to the DB solutions (17.7 ± 7.0 mg versus 9.1 ± 1.8 mg, n = 14; P = 0.01). The crystallization correlated with the measured concentration of calcium (r = -0.62; P = 0.02), and pCO₂ (r = +0.75; P = 0.002). We also observed a negative correlation between the pH, and the pCO₂ (r = -0.82; P < 0.001). Our results suggest that the use of bicarbonate solutions containing calcium as replacement fluids for CRRT is a potentially unsafe procedure.