The National Nosocomial Infections Surveillance (NNIS) System developed a classification of patients in the intensive care unit (ICU) based on the severity of illness. This can be used to evaluate outcomes and risks for patients. The authors are from the Hospital Infections Programs at the Centers for Disease Control and Prevention (CDC).


Clinical Stability



physiologically stable

postoperative, requiring observation but not intensive care; usually discharged from the ICU within 48 hours; some could have been managed in a recovery room


physiologically stable

require overnight observation and monitoring without intensive care; low risk of significant deterioration


physiologically stable

requires monitoring and intensive nursing care, fairly constant course


physiologically unstable

requires monitoring and intensive care, with frequent reassessment and adjustment of therapy


physiologically unstable, life-threatening

requires monitoring and intensive care, with near constant reassessment and adjustment of therapy; may require cardiopulmonary resuscitation or vasopressor therapy



A person may undergo a change in classification depending on complications or resolution of underlying conditions.


To read more or access our algorithms and calculators, please log in or register.