An intensive care unit (ICU), also known as an intensive therapy unit or intensive treatment unit (ITU) or critical care unit (CCU), is a special department of a hospital or health care facility that provides intensive care medicine. Intensive care units cater to patients with severe or life-threatening illnesses and injuries, which require constant care, close supervision from life support equipment and medication in order to ensure normal bodily functions. They are staffed by highly trained physicians, nurses and respiratory therapists who specialize in caring for critically ill patients. ICUs are also distinguished from general hospital wards by a higher staff-to-patient ratio and access to advanced medical resources and equipment that is not routinely available elsewhere. Common conditions that are treated within ICUs include acute respiratory distress syndrome, septic shock, and other life-threatening conditions. Patients may be referred directly from an emergency department or from a ward if they rapidly deteriorate, or immediately after surgery if the surgery is very invasive and the patient is at high risk of complications. History In 1854, Florence Nightingale left for the Crimean War, where triage was used to separate seriously wounded soldiers from those with non-life-threatening conditions. Until recently, it was reported that Nightingale’s method reduced mortality from 40% to 2% on the battlefield. Although this was not the case, her experiences during the war formed the foundation for her later discovery of the importance of sanitary conditions in hospitals, a critical component of intensive care. In 1950, anesthesiologist Peter Safar established the concept of advanced life support, keeping patients sedated and ventilated in an intensive care environment. Safar is considered to be the first practitioner of intensive care medicine as a speciality. In response to a polio epidemic (where many patients required constant ventilation and surveillance), Bjørn Aage Ibsen established the first intensive care unit globally in Copenhagen in 1953. The first application of this idea in the United States was in 1955 by William Mosenthal, a surgeon at the Dartmouth-Hitchcock Medical Center. In the 1960s, the importance of cardiac arrhythmias as a source of morbidity and mortality in myocardial infarctions (heart attacks) was recognized. This led to the routine use of cardiac monitoring in ICUs, especially after heart attacks. Types Hospitals may have various specialised ICUs that cater to a specific medical requirement or patient: Equipment and systems Common equipment in an ICU includes mechanical ventilators to assist breathing through an