Intensive Care Medicine or critical care medicine is a branch of medicine concerned with the provision of life support or organ support systems in patients who are critically ill and who usually require intensive monitoring.

Patients requiring intensive care usually require support for hemodynamic instability (hypertension/hypotension), airway or respiratory compromise (such as ventilator support), acute renal failure, potentially lethal cardiac dysrhythmias, and frequently the cumulative affects of multiple organ system failure. Patients admitted to the intensive care unit not requiring support for the above are usually admitted for intensive/invasive monitoring, such as the crucial hours after major surgery when deemed too unstable to transfer to a less intensively monitored unit.

Ideally, intensive care is usually only offered to those whose condition is potentially reversible and who have a good chance of surviving with intensive care support. Since the critically ill are close to dying the outcome of this intervention is difficult to predict. Many patients therefore still die in the Intensive Care Unit. A prime requisite for admission to an Intensive Care Unit is that the underlying condition can be overcome. Therefore treatment is merely meant to win time in which the acute affliction can be resolved.

Medical studies suggest a relation between intensive care unit(ICU) volume and quality of care for mechanically ventilated patients.[1] After adjustment for severity of illness, demographic variables, and characteristics of the ICUs (including staffing by intensivists), higher ICU volume was significantly associated with lower ICU and hospital mortality rates. For example, adjusted ICU mortality (for a patient at average predicted risk for ICU death) was 21.2% in hospitals with 87 to 150 mechanically ventilated patients annually, and 14.5% in hospitals with 401 to 617 mechanically ventilated patients annually. Hospitals with intermediate numbers of patients had outcomes between these extremes.

It is generally the most expensive, high technology and resource intensive area of medical care. In the United States estimates of the 2000 expenditure for critical care medicine ranged from US$15-55 billion accounting for about 0.5% of GDP and about 13% of national health care expenditure (Halpern, 2004).