Injury Severity Score

The Injury Severity Score (ISS) is an established medical score to assess trauma severity. It correlates with mortality, morbidity and hospitalization time after trauma. It is used to define the term polytrauma.

Abbreviated Injury Scale AIS
The ISS is based (see below) upon the Abbreviated Injury Scale (AIS). The AIS describes the severity of injury to one body region: 1 Minor, 2 Moderate, 3 Serious, 4 Severe, 5 Critical, 6 Maximal (Currently untreatable).

ISS Definition
To calculate an ISS for an injured person, the body is divided into six regions. These body regions are
 * Head and neck, including cervical spine
 * Face, including the facial skeleton, nose, mouth, eyes and ears
 * Thorax, thoracic spine and diaphragm
 * Abdomen, abdominal organs and lumbar spine
 * Extremities including pelvic skeleton
 * External soft tissue injury

An ISS is then calculated according to ISS = A^2 + B^2 + C^2 where A, B, C are the AIS scores of the three most injured body regions. The ISS takes scores from 0 to 75 (i.e. AIS scores of 5 for each category). If any of the three scores is a 6, the score is automatically set at 75. Since a score of 6 ("unsurvivable") indicates the futility of further medical care in preserving life, this may mean a cessation of further care in triage for a patient with a score of 6 in any category.

Polytrauma
A Polytrauma is defined as ISS >= 16.