It is unclear whether different modes of continuous renal replacement therapy (CRRT) impact post-filter ionized calcium concentrations during regional citrate anticoagulation (RCA) when using calcium-containing replacement fluid.

This prospective, single-center, observational cohort study will screen all patients receiving CRRT for eligibility. General clinical information will be collected before commencing CRRT treatment. Patients will be randomly assigned to either the veno-venous hemofiltration (CVVH) or continuous veno-venous hemodialysis (CVVHD) group and switch to the alternative mode in the subsequent treatment session. Pre-filter and post-filter ionized calcium, systemic total and ionized calcium, and effluent total and ionized calcium will be measured 2 hours after the initiation of CRRT. Electrolyte levels, arterial blood gases, hourly citrate dose, and total citrate dose will be recorded every 6 hours until the end of CRRT. The primary outcome is the difference in ionized calcium concentrations at each site over time between the two modes.

Inclusion Criteria:

1. Age ≥ 18 years old;
2. Receiving citrate anticoagulation;
3. Obtain Informed consent from patients or next of kin.

Exclusion Criteria:

1. Pregnant or lactating women;
2. Allergic to citrate anticoagulants;
3. Severe liver dysfunction (total bilirubin levels exceeding two times the normal range);
4. Hypoxemia (PaO2 < 60 mmHg);
5. Inadequate tissue perfusion (blood pressure < 90/60 mmHg despite high doses of vasoactive agents);
6. Hyperlactatemia (lactate> 4 mmol/L);
7. Hypernatremia;
8. Estimated length of hospital stay < 48h;
9. Participated in other studies.

All patients admitted to the ICU who need RCA-CRRT will be screened for study eligibility.