The important RENAL study on dosing of CRRT in ICU patients with AKI has been reported this past week in the New England Journal. The high intensity dosing arm using CVVHDF (40ml/kg/hr) was not superior to the lower intensity arm (25ml/kg/hr) in terms of 90 day mortality. This result was similar to other recently reported studies (Tolwani, 2008 and Palevsky, 2008). There was no significant difference in renal recovery between the two arms and the high intensity arm had a higher rate of hypophosphatemia. Although the higher dose arms have not been associated with improved mortality in these recent studies, it is still clear that delivered dose of dialysis is critical in this patient population (Shiffl, 2002). These studies suggest that a dose of > 20-25 ml/kg/hr does not provide any further benefit on mortality. However, it must be remembered that delivered dose is commonly lower than prescribed dose, especially outside of clinical trials. It would seem reasonable to recommend a target of ~30 ml/kg/hr. If clotting is minimal and system running time is maximized, one should watch for hypophosphatemia. If other electrolytes and acid-base status are acceptable, a reduction in dose to 20-25 ml/kg/hr could be suggested. Many critical elements of CRRT delivery remain to be investigated. These include timing of initiation of therapy, use of hemofiltration vs hemodialysis and impact of volume control on mortality. Further studies to address these issues are eagerly awaited. Benjamin J Freda, DO