The development of CRRT from simple arteriovenous ultrafiltration with a treatment using 50 liters a day, has necessitated the development of specialized dialysate/replacement solutions. As the volumes used are large, quality control is vitally important not only in terms of electrolyte composition, but also preventing bacterial and endotoxin contamination. Lactate remains the standard anionic base, as this increases fluid storage time and reduces the risk of bacterial contamination. Some centers use citrate anticoagulation, and the citrate load provides an adequate supply of anionic base to control metabolic acidosis. However, patients receiving very high volume exchanges, or those with severe tissue acidosis and/or liver failure, may be unable to convert the lactate, or citrate load effectively, resulting in hyperlactatemia or hypercitratemia and acidosis. In these circumstances, bicarbonate-based fluids are advantageous. The use of bicarbonate-based dialysate/replacement fluid during CRRT does not mask lactate overproduction, and lactate remains a reliable marker of tissue oxygenation in patients treated by CRRT. Bicarbonate CRRT alone does not treat metabolic acidosis, but allows better control of acidosis, thereby allowing time for the institution of other therapies designed to reverse the underlying cause.