Choice of replacement solution and anticoagulant in continuous venovenous hemofiltration.

BACKGROUND: Several types of replacement fluid and methods of anticoagulation have been employed for continuous renal replacement therapy, but there is no consensus on a preferred approach. We evaluated the indications for the selection of replacement fluid and anticoagulant among critically ill patients receiving continuous venovenous hemofiltration (CVVH) and assessed the effect of the selection on the efficacy of anticoagulation and complications.
METHODS: We retrospectively studied 29 consecutive patients who received CVVH in the Medical Intensive Care Unit at Massachusetts General Hospital. There were 3 types of replacement solution available, an isotonic citrate solution which was also used for regional anticoagulation of the extracorporeal circuit, and bicarbonate and lactate solutions which were used with low-dose heparin or no anticoagulant. Blood flow rate was set at 120 ml/min when citrate replacement fluid was used and at 200 ml/min with bicarbonate or lactate. The replacement fluid was administered proximal to the hemofilter at a constant rate of 1,600 ml/h.
RESULTS: There were 22 patients who received citrate replacement fluid which was mainly chosen for the purpose of anticoagulation in the setting of contraindications to heparin. 12 patients received bicarbonate, predominantly when citrate was considered contraindicated due to liver failure or high-anion gap metabolic acidosis, and 2 received lactate; 8 of these 14 patients were anticoagulated with heparin and 6 were managed without anticoagulation. There were 44 filters used in the patients receiving citrate with a median filter life of 42.0 (interquartile range 22.2 - 70.7) hours. Only 8 of the 44 filters were lost due to clotting. Heparin was used for anticoagulation of 17 filters and no anticoagulation was used in the case of 15 filters, resulting in a median filter life of 43.0 (13.5 - 75.0) and 12.0 (4.0 - 33.0) hours, respectively. Clinically significant bleeding occurred in 2 patients, 1 receiving citrate and another receiving heparin. No patient had evidence for citrate toxicity, metabolic alkalosis or hypernatremia. 14 (48.3%) patients survived.
CONCLUSIONS: The use of regional citrate anticoagulation of the CVVH circuit appears advantageous in patients with increased risk of bleeding and bicarbonate-based replacement fluid seems desirable in patients with lactic acidosis due to shock and/or severe liver failure. Tailoring the type of replacement fluid and method of anticoagulation to the individual patient leads to long filter lives, excellent metabolic control and minimal complications.