A high-dependency unit is an area in a hospital, usually located close to the intensive care unit, where patients can be cared for more extensively than on a normal ward, but not to the point of intensive care. It is appropriate for patients who have had major surgery and for those with single-organ failure. Many of these units were set up in the 1990s when hospitals found that a proportion of patients was requiring a level of care that could not be delivered in a normal ward setting.^[1] This is thought to be associated with a reduction in mortality.^[1] Patients may be admitted to an HDU bed because they are at risk of requiring intensive care admission, or as a step-down between intensive care and ward-based care.^[1]

In 2000 the UK Department of Health issued the Comprehensive Critical Care report, which set out the number of high dependency ("level 2") beds a hospital should have to deliver care appropriately. By this time, two thirds of UK hospitals had beds identified as "high dependency".^[2] The report defines level 2 care as "more detailed observations or intervention including support for a single failing organ system or postoperative care and those 'stepping down' from higher levels of care".^[2]

If positive airway pressure ventilation is used to treat respiratory failure, this may be administered in a high dependency unit or equivalent area.^[1][3]