Principles of observation medicine.

The defining characteristic of emergency medicine is "time," or the acuity of disease presentation. Observation, like resuscitation, involves the management of time-sensitive conditions. In the ED there is a continuum of time-sensitive conditions. This continuum extends from resuscitation on one end to observation on the other. When performed well, observation services have been shown to improve diagnostic accuracy, improve treatment outcomes, decrease costs, and improve patient satisfaction. For the subset of ED patients who would have been inappropriately discharged or unnecessarily admitted, the OU has become a safety net of the ED itself. Like EDs, OUs have progressed from being poorly managed areas of the hospital to the cutting edge of acute health care. The principles developed through past experience and research provide a framework for future developments in emergency medicine.