There are a wide number of indications for extracorporeal therapies in the critical care environment. A common indication seen by the acute physician is continuous renal replacement therapy (CRRT) in a proportion of patients with acute kidney injury. It is therefore important that acute physicians have a sound understanding of the principles of CRRT in the acutely unwell patient. This review will outline the indications for its use, commonly used methods and anticoagulation considerations. It will discuss when to start and stop CRRT as well as describing potential treatment complications. This review will also discuss the role of therapeutic plasma exchange in critical care and novel extracorporeal therapies including blood purification in sepsis and carbon dioxide removal in acute respiratory distress syndrome and acute exacerbations of obstructive lung disease. Extracorporeal membrane oxygenation is outside of the scope of this article.