before infusing it directly into the blood line. In the United States, regulatory agencies have not yet approved on-line creation of substitution fluid because of concerns about its purity. For this reason, hemodiafiltration, had historically never been used in an outpatient setting in the United States. Continuous hemofiltration or hemodiafiltration (CHDF) Continuous hemofiltration (CHF) was first described in a 1977 paper by Kramer et al. as a treatment for fluid overload. Hemofiltration is most commonly used in an intensive care unit setting, where it is either given as 8- to 12-hour treatments, so called SLEF (slow extended hemofiltration), or as CHF (continuous hemofiltration), also sometimes called continuous veno-venous hemofiltration (CVVH) or continuous renal replacement therapy (CRRT). Hemodiafiltration (SLED-F or CHDF or CVVHDF) also is widely used in this fashion. In the United States, the substitution fluid used in CHF or CHDF is commercially prepared, prepackaged, and sterile (or sometimes is prepared in the local hospital pharmacy), avoiding regulatory issues of on-line creation of replacement fluid from dialysis solution. With slow continuous therapies, the blood flow rates are usually in the range of 100-200 ml/min, and access is usually achieved through a central venous catheter placed in one of the large central veins. In such cases a blood pump is used to drive blood flow through the filter. Native access for hemodialysis (e.g. AV fistulas or grafts) are unsuitable for CHF because the prolonged residence of the access needles required might damage such accesses. The length of time before the circuit clots and becomes unusable, often referred to as circuit life, can vary depending on the medication used to keep blood from clotting. Heparin and regional citrate are often used, though heparin carries a higher risk of bleeding. However, a comprehensive analysis of audit data from intensive care units in the UK revealed that, compared with heparin, citrate-based drugs were not associated with fewer deaths among patients with acute kidney injury after 90 days of treatment. Citrate-based drugs were, however, associated with a substantially higher cost of treatment. See also Hemodialysis Renal replacement therapy Extracorporeal therapy Dialytrauma References Membrane technology Nephrology procedures