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An Intensive Care Unit (ICU), also known as a Critical Care Unit (CCU), Intensive Therapy Unit or Intensive Treatment Unit (ITU) is a special department of a hospital or health care facility that provides intensive-care medicine.
Intensive Care Units cater to patients with the most severe and life-threatening illnesses and injuries; that require constant, close monitoring and support from specialist equipment and medication in order to maintain normal bodily functions. They are staffed by highly trained doctors and critical care nurses who specialise in caring for seriously ill patients. Common conditions that are treated within ICU's include those such as trauma, multiple organ failure and sepsis.
Patients may be transferred directly to an Intensive Care Unit from an Emergency Department if required, or from a ward if they rapidly deteriorate; or immediately after surgery if the surgery is majorly invasive and the patient is at high risk of complications.
In 1854, Florence Nightingale left for the Crimean War, where triage, used to separate seriously wounded soldiers from the less-seriously wounded, was observed. Until recently, it was reported that Nightingale 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 Support of Life", 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 in Copenhagen in 1953. The first application of this idea in the United States was in 1955 by Dr. 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.
Hospitals may have ICUs that cater to a specific medical speciality or patient, such as those listed below:
- Neonatal Intensive Care Unit (NICU)
- Pediatric Intensive Care Unit (PICU)
- Psychiatric Intensive Care Unit (PICU)
- Coronary Care Unit (CCU): Also known as Cardiac Intensive Care Unit (CICU)
- Post Anesthesia Care Unit (PACU): Also known as the Post-Operative Recovery Unit, or Recovery Room, the PACU provides immediate post-op observation and stabilisation of patients following surgical operations and anesthesia. Patients are usually held in such facilities for a limited amount of time, and must meet a set physiological criteria before transfer back to a ward with a qualified nurse escort takes place. Due to high patient flow in Recovery Units, and owing to the bed management cycle, if a patient breaches a time frame and is too unstable to be transferred back to a ward, they are normally transferred to a High Dependency Unit (HDU) or Post-Operative Critical Care Unit (POCCU) for closer observation.
- High Dependency Unit (HDU): Many hospitals have a transitional High Dependency Unit (HDU) for patients who require close observation, treatment and nursing care that cannot be provided on a general ward, but whose care is not at a critical enough level to warrant an ICU bed. These units are also called step-down, progressive and intensive recovery units and are utilised until a patient's conditions stabilises enough to qualify them for discharge to a general ward.
Equipment and systems 
Common equipment in an ICU includes mechanical ventilators to assist breathing through an endotracheal tube or a tracheotomy; cardiac monitors including those with telemetry; external pacemakers; defibrillators; dialysis equipment for renal problems; equipment for the constant monitoring of bodily functions; a web of intravenous lines, feeding tubes, nasogastric tubes, suction pumps, drains, and catheters; and a wide array of drugs to treat the primary condition(s) of hospitalization. Medically induced comas, analgesics, and induced sedation are common ICU tools needed and used to reduce pain and prevent secondary infections.
Quality of care 
The available data suggests a relation between ICU volume and quality of care for mechanically ventilated patients. After adjustment for severity of illnesses, demographic variables, and characteristics of different ICUs (including staffing by intensivists), higher ICU staffing was significantly associated with lower ICU and hospital mortality rates. A ratio of 2 patients to 1 nurse is recommended for a medical ICU, which contrasts to the ratio of 4:1 or 5:1 typically seen on medical floors. This varies from country to country, though; e.g., in Australia and the United Kingdom most ICUs are staffed on a 2:1 basis (for High-Dependency patients who require closer monitoring or more intensive treatment than a hospital ward can offer) or on a 1:1 basis for patients requiring very intensive support and monitoring; for example, a patient on a mechanical ventilator with associated anaesthetics or sedation such as propofol, Midazolam and use of strong analgesics such as morphine, fentanyl and/or remifentanil.
See also 
- ICU quality and management tools
- Intensive Care Foundation, a charity in Australia and New Zealand
- Geriatric Intensive care unit
- "Intensive Care Unit". wiseGEEK. Retrieved 2012-06-15.
- "Intensive Care Unit". Internet Journal of Health. Retrieved 2007-08-25.
- "The Danish anaesthesiologist Björn Ibsen a pioneer of long-term ventilation on the upper airways, Louise Reisner-Sénélar, 2009".
- "Remembering Dr. William Mosenthal: A simple idea from a special surgeon". Dartmouth Medicine. Retrieved 2007-04-10.
- ICU History Video
- Kahn JM, Goss CH, Heagerty PJ, Kramer AA, O'Brien CR, Rubenfeld GD., JM; Goss, CH; Heagerty, PJ; Kramer, AA; O'Brien, CR; Rubenfeld, GD (2006). "Hospital volume and the outcomes of mechanical ventilation". New England Journal of Medicine 355 (1): 41–50. doi:10.1056/NEJMsa053993. PMID 16822995.
|Wikimedia Commons has media related to: Intensive care units|
- Society of Critical Care Medicine
- ICUsteps - Intensive-care patient support charity
- Organisation for Critical Care Transportation
- A Working Lexicon for the Tele-Intensive Care Unit: We Need to Define Tele-Intensive Care Unit to Grow and Understand It