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Prolonging Filter Life: CRRT and Anticoagulation

By Suzan Miller-Hoover, DNP, RN, CCNS, CCRN, contributor

The CRRT practitioner should be aware of the indications for and the risks associated with each type of anticoagulant

Management of acute renal failure¹ and acute kidney injury² is essential in caring for critically ill patients. Continuous renal replacement therapy (CRRT) has replaced peritoneal and intermittent hemodialysis as the treatment of choice in the critically ill (Uppalapati & Cullum, 2010).

One crucial component of this therapy is controlling thrombus formation. Within the CRRT circuit are many blood/surface interfaces where thrombi may form. These areas include:
•    Hemofilters
•    Bubble traps
•    Catheters
•    Luer lock connections
•    Stopcocks

In addition, the rate of the blood pump/flow, the blood viscosity, number of alarms, and the patient’s state of coaguability affect the rate of thrombus formation. When all of these factors are combined, the patient’s risk of thrombus formation is high.

Anytime blood touches the non-endothelial surfaces of the tubing and filter, it causes turbulence and high shear rates³; which activates the clotting cascade. Fundamentally, thrombus formation results from the combined mechanisms of coagulation, platelet activation and adhesion.

Although CRRT can be run without anticoagulation, filters may last much longer if some form of anticoagulation is used. Options for anticoagulation include heparin, prostacyclin, citrate, low molecular weight heparin, and saline.

When choosing a method of anticoagulation, it is important to choose the method that will most closely meet the goals of inhibiting platelet formation and thrombotic activity in the circuit, as well as being easily titrated and reversed to minimize bleeding.

The following are rationales for use of each type of anticoagulation:
No anticoagulation: 
•    Patients with well-functioning catheters, high blood flow rates, and only a few alarms that are quickly adjusted, may not need an anticoagulant.
•    Patients with a bleeding disorder or who otherwise have high aPTT values may not need an anticoagulant.
Saline anticoagulation:
•    Saline infusions, prefilter, reduce the hemoconcentration/viscosity at the filter by reducing the hematocrit
•    May or may not increase the filter life
•    Local/regional anticoagulation
Low-molecular weight heparin:
•    Lower incidence of heparin induced thrombocytopenia (HIT)
•    Lower antithrombin affinity
•    Less platelet activation
•    More expensive than heparin
•    Requires a subcutaneous injection
•    Special anticoagulation assay: anti XA, required to monitor levels (usually a send-out lab)
•    May or may not increase the filter life
•    Systemic anticoagulation
Prostacyclin:
•    Potent platelet aggregation inhibitor
•    Vasodilator for arteries and veins
•    Smooth muscle relaxant
•    Inhibits platelet binding in the circuit tubing
•    Causes Hypotension
•    More expensive than other anticoagulants
•    Not approved for this use in the United States (need more randomized clinical studies)
•    May or may not increase the filter life
•    Systemic anticoagulation
Heparin:
•    Potentiates thrombin inhibition
•    Less expensive than other anticoagulants
•    Can be reversed with protamine
•    Higher risk of bleeding than other anticoagulants
•    Higher incidence of HIT
•    Continuous infusion
•    aPPT/ACT monitoring
•    Systemic anticoagulation
•    May or may not increase the filter life
Citrate:
•    Local/regional anticoagulation
•    Inhibits clotting cascade by chelating ionized Calcium
•    Ionized Calcium monitoring
•    Requires Calcium infusion
•    Significantly increases the filter life
•    May not be used in hepatic failure patients
•    Risks for citrate lock (high systemic calcium levels with declining ionized calcium levels
•    Reduced risk of bleeding
•    Off-label use

In summary, all types of anticoagulation run the risk of increased bleeding tendencies. Therefore, the CRRT practitioner should be aware of the indications for and the risks associated with each type of anticoagulant. The two most common therapies are citrate and heparin anticoagulation. Both are inexpensive and meet the goals of anticoagulation. However, multiple studies have shown that citrate is the anticoagulation therapy of choice because it has increases the life of the filter.

Learn more about heparin induced thrombocytopenia, check out this course on RN.com: Heparin Induced Thrombocytopenia.

Definitions:
² Acute Kidney Injury: mild to severe renal dysfunction
¹ Acute Renal Failure: loss of renal function requiring life sustaining intervention
³Shear Rate: the rate of change of velocity at which one layer of fluid passes over an adjacent layer of fluid

References:
Dirkes, S. & Wonnacott, R. (2016). Continuous renal replacement therapy and anticoagulation:
What are the options? Critical Care Nurse, vol. (36)2; pg. 34-41.

Uppalapati, A. & Kellum, J. (2016). The critically ill patient with acute kidney injury. In Handbook of Continuous Renal Replacement Therapy. ed. / John A. Kellum. Second. ed. Oxford University Press. Pittsburg.



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