Clinical review: use of renal replacement therapies in special groups of ICU patients.

Acute kidney injury (AKI) in ICU patients is typically associated with other severe conditions that require special attention when renal replacement therapy (RRT) is performed. RRT includes a wide range of techniques, each with specific characteristics and implications for use in ICU patients. In the present review we discuss a wide range of conditions that can occur in ICU patients who have AKI, and the implications this has for RRT. Patients at increased risk for bleeding should be treated without anticoagulation or with regional citrate anticoagulation. In patients who are haemodynamically unstable, continuous therapies are most often employed. These therapies allow slow removal of volume and guarantee a stable blood pH. In patients with cerebral oedema, continuous therapy is recommended in order to prevent decreased cerebral blood flow, which will lead to cerebral ischemia. Continuous therapy will also prevent sudden change in serum osmolality with aggravation of cerebral oedema. Patients with hyponatraemia, as in liver failure or decompensated heart failure, require extra attention because a rapid increase of serum sodium concentration can lead to irreversible brain damage through osmotic myelinolysis. Finally, in patients with severe lactic acidosis, RRT can be used as a bridging therapy, awaiting correction of the underlying cause. Especially in ICU patients who have severe AKI, treatment with RRT requires balancing the pros and cons of different options and modalities. Exact and specific guidelines for RRT in these patients are not available for most clinical situations. In the present article we provide an update on the existing evidence.