Evaluation of a Simplified Protocol for Regional Citrate Anticoagulation in Continuous Venovenous Hemodiafiltration

Acute renal failure is common among the critically ill [1-3] , and is an independent contributor to morbidity and mortality [4,5]. Continuous renal replacement therapy (CRRT) is commonly used for renal replacement in this group. This requires an extracorporeal circuit, the maintenance of which requires anticoagulation. Heparin has been the most common anticoagulant used with CRRT. However, heparin exposure for CRRT is major risk after surgery or trauma. Citrate has been used as a regional anticoagulant for plasmapheresis and chronic dialysis for many years [12,13], and is increasingly being used for CRRT. Regional anticoagulation refers to the provision of anticoagulation within the extracorporeal circuit without any alteration in coagulation in the patient's systemic circulation. Calcium is a co-factor in coagulation. Citrate reduces levels of ionized calcium in blood of the extracorporeal circuit to levels where coagulation cannot occur. Once the blood is returned to the patient's systemic circulation, the calcium levels are restored and coagulation can occur again. Renal replacement solutions for CRRT using citrate anticoagulation, should be calcium-free. [14-19] Despite a reduced risk of bleeding, widespread adoption of citrate regional anticoagulation has been limited by a lack of commercially available calcium-free solutions and the complexity of many protocols. Part of this complexity is the requirement for a separate citrate infusion into the extracorporeal circuit to achieve regional anticoagulation. This simplified protocol provides citrate in the replacement fluid infused prefilter as both anticoagulant and as buffer.

To predict appropriate replacement rates, Hospal Gambro scientific laboratories have developed a calculation model to predict the physiological interactions between the components of the administered replacement- and hemodialysis fluids and the patient's complex metabolic system. These interactions are influenced, in large part, by systemic parameters such as blood-flow and ultrafiltration rates, and patient parameters, such as acid base-status and liver function. This calculation model needs clinical validation in respect to its ability to predict the outcome and narrow the margin of metabolic disturbances caused by the administration of citrate anticoagulation. A previous study of a similar replacement fluid using citrate 8 mmol/L and citric acid 4 mmol/L resulted in mild metabolic acidosis of minimal clinical significance in some subjects and so this study will evaluate a modified version of fluid containing citrate 10 mmol/L and citric acid 2 mmol/L which has been calculated to provide optimal metabolic balance.

Subjects:

Twenty patients in the General Systems ICU at the University of Alberta Hospital treated with CVVHDF using a Prisma-CFM machine will be studied.

Inclusion criteria: