CVVH Basics

CVVH (continuous venovenous hemodialysis) is the form of CRRT (continuous renal replacement therapy) used in our hospital. Although most studies have not shown a mortality benefit in patients treated with intermittent hemodialysis versus those treated with CVVH, in my opinion there is a subset of patients--I'm talking the sickest of the sick, often patients on multiple pressors, sometimes those who are s/p major cardiac surgery on balloon pumps and/or ventricular assist devices--who require CVVH in order to achieve adequate volume removal.

At our hospital, there are two main types of CVVH replacement solution that we use: bicarbonate-based and citrate-based. Both provide adequate base, as citrate is metabolized to bicarbonate in the liver. Citrate provides superior anticoagulation to bicarbonate alone; it's also advantageous in that it provides extracorporeal anticoagulation while avoiding systemic anticoagulation, as the Ca gluconate drip which is administered simultaneously to the blood as it re-enters the body binds to and neutralizes the citrate. Bicarbonate can be given with heparin but obviously this comes with some cost of internal bleeding. If a patient is already on heparin for something (e.g. MI, valve replacement) I would generally choose bicarbonate. Citrate-based replacement solution should be avoided in patients with severe liver failure or an anion gap metabolic acidosis; these problems predispose to citrate toxicity, which is reflected as an elevated total calcium but a decreased ionized calcium with a subsequent anion gap.