Continuous renal replacement in critical illness

Acute renal failure in the intensive care unit is usually part of the multiple organ dysfunction syndrome, and the complexity of illness in patients with this complication has risen in recent years. Continuous renal replacement therapy (CRRT) was introduced in the late 1970s and early 1980s to compensate for the inadequacies of conventional intermittent hemodialysis (IHD) in the treatment of these patients. IHD was considered aggressive and unphysiological, often resulting in hemodynamic intolerance and limited efficiency. Although CRRT has been shown to be physiologically superior with respect to IHD in both observational and randomized studies, it is not clear whether this physiological superiority translates into clinically important gains. A number of recent studies have tried to address this issue, and with these, there is a lack of evidence to suggest improved survival and major clinical outcomes with CRRT. However, these studies are generally underpowered and have certain aspects which may influence the interpretation of their results. In addition, the development of hybrid techniques, such as slow extended daily dialysis, makes this a dynamic area of study where the terms of comparison are constantly changing. This article reviews recent trials comparing CRRT and IHD, and discusses their results and limitations.