Pannu and Gibney bleeding complications, reported to occur in 5%–26% of treatments (Webb et al 1995). Unfractionated heparin is the mainstay of anti- coagulation for IHD and CRRT (Favre et al 1996). Heparin is generally administered as a bolus, followed by a continuous infusion into the arterial limb of the dialysis circuit, to maintain a partial thromboplastin time (PTT) of 1.5–2 × normal. Low molecular weight heparin is excreted renally and should not be used without careful monitoring of factor Xa levels in patients with ARF (Schrader et al 1990). Systemic anticoagulation is relatively contraindicated in patients at high risk of bleeding, although the heparin dose can be modified in these circumstances. Its use, however, is associated with a high incidence of bleeding and in some instances heparin-induced thrombocytopenia (Mehta et al 1992). Because of the shorter duration and high blood flow used, it is often possible to perform IHD without anticoagulation, particularly when the patient is coagulo- pathic. In heparin-free dialysis, blood flows are kept between 250–500 mL/min and saline flushes are administered every 15–30 min into the arterial limb of the dialysis circuit to minimize hemoconcentration and to wash fibrin strands from the kidney into the bubble trap. The volume of saline administered with such frequent flushing must be removed during the dialysis to prevent hypervolemia. This technique is associated with only a 2% clotting rate (Schwab et al 1987). In newly postoperative patients and others with a contraindication to systemic anticoagulation, regional anticoagulation of the circuit is preferred. Regional heparinization, with pre-filter administration of heparin, and a post-filter protamine infusion has been used (Swartz and Port 1979; Abramson and Niles 1999), but regional citrate anticoagulation has become increasingly popular. Citrate anticoagulation may be used with both continuous and intermittent therapies. Regional citrate anticoagulation is achieved using a continuous citrate infusion through the arterial limb of the circuit, which chelates free calcium and inhibits the coagulation cascade. The citrate-calcium complex is removed by a combination of dialysis clearance against calcium-free dialysate and endogenous processes. In patients with normal liver function, levels of citrate and ionized calcium return to normal values within 30 min of discontinuing a citrate infusion (Mehta et al 1990). Plasma calcium levels are restored with the use of a continuous calcium infusion at the site of blood return to the patient. 146 The infusion rate of citrate is adjusted to keep the activated clotting time (ACT) above 160 s. Regional citrate anticoagulation requires the use of a specialized dialysis solution and frequent monitoring of ionized calcium (Kutsogiannis et al 2000). Potential complications arising from this technique include metabolic alkalosis, hypo- natremia, hypocalcaemia, and citrate toxicity in patients with liver dysfunction. If properly monitored, the complication rate associated with this technique is quite low (Flanigan et al 1987). When used with CRRT techniques, filter longevity in excess of 96 h is fairly common with citrate anticoagulation, while 36–48 h patency is usually the norm with heparin (Bellomo 1993). Low molecular weight heparin (Hory et al 1985; Wynckel et al 1991), prostacyclin analogues (Davenport et al 1994), and other anticoagulants such as danaparoid (Chong and Magnani 1992) and high molecular weight dextran (Palevsky et al 1995) have been used with both continuous and intermittent renal replacement therapies (Campbell 1999). See Table 2 for a comparison of anticoagulation strategies. At the current time none of these methods is ideal, and selection is usually influenced by patient factors. Technical factors and experience with anticoagulants are important determinants of the success of any anticoagulation regimen. Does CRRT confer an advantage over IHD in the management of acute renal failure? CRRT has several theoretical advantages over intermittent blood purification techniques, including better hemodynamic tolerability, more efficient solute clearance, better control of intravascular volume, and better clearance of middle and large molecular weight substances. Hypotension is one of the most common complications associated with intermittent hemodialysis, occurring in approximately 20%–30% of all treatments. Some of the causes are dialysis specific, such as excessive or rapid volume removal, changes in plasma osmolality, and autonomic dysfunction. In critically ill patients who may be hemodynamically unstable, it would be desirable to minimize this complication, as it may lead to further organ ischemia and injury. Several prospective and retrospective studies have demonstrated better hemodynamic stability associated with CRRT (Paganini et al 1984; Davenport et al 1993); however, this observation has not been validated in a randomized controlled trial. Therapeutics and Clinical Risk Management 2005:1(2)