Hemodialysis is a treatment used to augment or replace renal excretory function. Most water-soluble substances that are not protein- or tissue-bound in the extracellular fluid can be effectively removed through hemodialysis. In general, the management of acute renal failure consists of supportive care until the kidney recovers from the acute renal insult. Acute renal replacement therapy in the form of intermittent dialysis or continuous renal replacement therapy is indicated when pharmacologic management is insufficient to treat or prevent the following situations: volume overload with pulmonary edema or hypertension, hyperkalemia, metabolic acidosis, uremia, calcium–phosphorus imbalance, or neurologic symptoms secondary to uremia or electrolyte imbalance. Acute hemodialysis also is indicated in certain clinical situations that are not accompanied by renal failure, such as tumor lysis syndrome in patients with newly diagnosed leukemia or lymphoma, hyperammonemia in patients with inborn errors of metabolism and drug intoxications (Table 450.1). In such clinical cases, close attention to and supplementation of the patient’s serum phosphorus and potassium is required, because hemodialysis can lead rapidly to hypophosphatemia and hypokalemia in a patient with normal renal function. Hemodialysis is indicated for the elimination of a toxin if there is a potential clinical benefit to the patient of removing the toxin more quickly than the endogenous clearance rate, a significant amount of the toxin can be removed, and a clear relationship exists between the blood levels of an agent and its toxic effects. Toxins that can be removed successfully through dialysis are distributed in body water, have low molecular weights, and are not bound to plasma or tissue proteins.