**Abstract**

Hyperammonemia is not uncommonly encountered in adult critically ill patients in the intensive care unit (ICU). Although it often occurs in patients with underlying liver disease, it may also occur in patients with no evidence of acute or chronic liver disease. Hyperammonemia can cause serious complications, including acute brain injury (sometimes called hyperammonemia-induced encephalopathy). Hyperammonemia-induced encephalopathy often carries a poor prognosis and may even lead to death. Nephrologists may get involved in the management of hyperammonemic patients (with or without acute kidney injury) for consideration of renal replacement therapy (RRT) as an intervention to lower the ammonia level. This chapter will discuss the role of RRT in adult patients with hyperammonemia.

**Keywords:** ammonia, hyperammonemia, hemodialysis, renal replacement therapy, hyperammonemic encephalopathy
