**6.3 Regional citrate anticoagulation**

RCA is a method of anticoagulation involving the infusion of citrate into the extracorporeal circuit. Citrate's mechanism of action is binding to ionized calcium, which is necessary for the activation of coagulation factors. By chelating ionized calcium, citrate inhibits coagulation within the circuit. RCA also requires careful monitoring of the patient's acid–base and electrolyte status, as citrate metabolism can lead to metabolic alkalosis, hypocalcemia, and hypernatremia. However, these effects can be diminished by infusing calcium into the circuit and using a low bicarbonate dialysate or chloride based intravenous fluids. Using a higher chloride citrate solution can also blunt the alkalotic effect. Hypernatremia can be prevented by using lower sodium dialysate or appropriate replacement fluids.

A recent meta-analysis published in 2022 compared the efficacy of citrate vs. heparin anticoagulation in critically ill patients on undergoing CRRT [10]. The study


#### **Table 3.**

*Comparing major types of anticoagulation in CRRT [10].*

noted no significant difference in mortality, metabolic alkalosis, and circuit loss between the two groups. It did note that the citrate group had the advantage of an overall longer filter life and significantly lower risk of bleeding and heparin-induced thrombocytopenia. As such, RCA was deemed to have priority for CRRT in critically ill patients (**Table 3**).

#### **6.4 Monitoring clotting function and dosing**

It is essential to monitor the clotting function of the blood during CRRT and adjust the anticoagulant dosing accordingly.

During CRRT, the clotting function of the blood is monitored using either the aPTT or the ACT. The aPTT measures the time it takes for clotting to occur in a blood sample after the addition of an activator, while the ACT measures the time it takes for clotting to occur in a blood sample after the addition of an activator and a contact activator. Both tests are used to monitor the effectiveness of UFH anticoagulation.

The dose of UFH for CRRT is typically titrated to achieve a target aPTT or ACT. The initial dose is usually 500–1000 units per hour, with adjustments made every 4–6 hours based on the patient's clotting function. LMWH dosing is based on the patient's weight, with dalteparin typically given as a subcutaneous injection at a dose of 5000 units every 12 hours. There is insufficient data to currently recommend for the use of LMWH in CRRT circuit.

RCA dosing is based on the infusion rate of citrate, which is typically started at a rate of 4–6 mmol/min and adjusted based on the patient's ionized calcium levels (iCa). Goal is to maintain iCa between 1 and 1.4 mg/dl (0.25–0.35 mmol/l).

#### **6.5 Complications**

Despite appropriate anticoagulant dosing and monitoring, complications can still occur during CRRT. One of the main complications of CRRT is circuit clotting, which can lead to decreased filter life and increased risk of bleeding. Other complications include bleeding from anticoagulation, metabolic derangements from RCA, and hypotension from the fluid removal during CRRT.

### **6.6 Conclusion**

The choice of anticoagulant for CRRT is a complex one that should be made on a case-by-case basis. There is no single "best" anticoagulant, and the best choice will vary depending on the patient's individual circumstances.
