To investigate the clearance rate of calcium in ultrafiltrate and to determine whether it can be used as a reference indicator for calcium supplementation rate in patients during continuous venous-venous hemofiltration (CVVH) treatment with local sodium citrate anticoagulation.

Fifty-five patients at high risk for bleeding who required continuous renal replacement therapy (CRRT) were included. They underwent CVVH treatment with local anticoagulant sodium citrate, and the rate of 4% sodium citrate was 200 ml/h. In the first stage of the experiment, totally post-dilutional hemodiafiltration was used, and the total concentrations of calcium in blood and ultrafiltrate were tested to observe the calcium clearance rate in the ultrafiltrate. In the second stage, the patients who had normal and low calcium levels were randomly divided into a total post-dilution group, a pre-dilution to post-dilution ratio 1:1 group, and a total pre-dilution group. During CVVH, calcium was supplemented in the same amount according to the calcium clearance ratio obtained in the first stage of the experiment. The concentration of ionized calcium in the body and post-filter solution were monitored routinely every 4 h. The concentrations of total calcium in blood and ultrafiltrate and ionized calcium in the body were tested before CVVH, 6 h and 12 h after CVVH was stabilized.

The average treatment time per person was (21.2±5.6) h, and no patient terminated the CVVH due to extracorporeal circuit coagulation. In the first stage, the ratio of total calcium concentration in ultrafiltrate to the total calcium concentration in blood was 85% in 15 patients, of which the normal group had a calcium clearance rate of 84.5% and the low calcium group had a rate of 85.5%. There was no significant difference between the total calcium clearance rate and the calcium clearance rate in the normal group and low calcium (F=0.8484, P>0.05). In the second stage, for the 30 patients in the normal group, there was no significant difference in the theoretically calculated and actually measured ultra-filtrate calcium concentrations among the total post-dilution group, the pre-dilution to post-dilution ratio 1:1 group, and the total pre-dilution group (t=0.1637, 1.103, 0.04; P>0.05). For the 10 patients in the low-calcium group, there was also no significant difference in the theoretically calculated and actually measured ultra-filtrate calcium concentrations among the total post-dilution group, the pre-dilution to post-dilution ratio 1:1 group, and the total pre-dilution group (t=0.1968, 2.402, 0.1818; P>0.05). In both the normal and low-calcium groups, there was no significant difference in blood total calcium concentration or blood ion calcium concentration between before, 6 h and 12 h after CVVH treatment (normal group: F=2.5690, 2.8930, P>0.05; low-calcium group: F=0.7124, 1.080, P>0.05). During CVVH treatment, the normal group did not have abnormal blood calcium, and the low calcium group did not have clinical manifestation of hypocalcemia and had normal levels of ionized calcium in blood.

During the course of CVVH with regional citrate anticoagulation with calcium free replacement solution, the clearance of calcium can be calculated according to the total calcium in blood and the input method of replacement fluid, which can be used as an important reference for the calcium supplement during CVVH treatment.