Injury severity score

The Injury Severity Score (ISS) is an internationally recognized anatomical scoring system to assess trauma severity that provides an overall score for patients with multiple injuries ¹. Each injury is assigned an Abbreviated Injury Scale (AIS) score and is allocated to one of six body regions. The highest Abbreviated Injury Scale (AIS) score in each body region is used. The three most severely injured body regions have their score squared and added together to produce the Injury Severity Score (ISS) score ².. The Injury Severity Score (ISS) correlates with mortality, morbidity and hospitalization time after trauma.

To calculate an Injury Severity Score (ISS), take the highest Abbreviated Injury Scale (AIS) severity code in each of the three most severely injured Injury Severity Score (ISS) body regions, square each Abbreviated Injury Scale (AIS) code and add the three squared numbers for an Injury Severity Score (ISS):

• Injury Severity Score (ISS) = A² + B² + C²

where A, B, C are the Abbreviated Injury Scale (AIS) scores of the three most injured Injury Severity Score (ISS) body regions.

The Injury Severity Score (ISS) assesses the combined effects of the multiply-injured patients and is based on an anatomical injury severity classification, the Abbreviated Injury Scale (AIS) (see below). To calculate an Injury Severity Score (ISS) for an injured person, the body is divided into 6 Injury Severity Score (ISS) Body Regions to which injuries can be assigned, although the bbreviated Injury Scale (AIS) 2005 – Update 2008 dictionary is divided into 9 anatomical chapters.

The following may assist with assigning the body regions:

1. Head or neck: Head or neck injuries include injury to the brain or cervical spine, skull or cervical spine fractures and asphyxia/suffocation.
2. Face: Facial injuries include those involving mouth, ears, nose, eyes and facial bones.
3. Chest: Chest injuries include all lesions to internal organs, drowning and inhalation injury. Chest injuries also include those to the diaphragm, rib cage, and thoracic spine.
4. Abdomen or pelvic contents: Abdominal or pelvic contents injuries include all lesions to internal organs. Lumbar spine lesions are included in the abdominal or pelvic region.
5. Extremities or pelvic girdle: Extremities or pelvic girdle injuries include sprains, fractures, dislocations and amputations.
6. External: External and other trauma injuries include lacerations, contusions, abrasions, and burns, independent of their location on the body surface, except amputation burns that are assigned to the appropriate body region.
   1.  Other traumatic events assigned to this Injury Severity Score (ISS) body region are: electrical injury, frostbite, hypothermia and whole body (explosion-type) injury.

The Injury Severity Score (ISS) scores ranges from 0 to 75 (i.e. Abbreviated Injury Scale (AIS) scores of 6 for each injury in every body region according to its relative severity). If an injury is assigned an Abbreviated Injury Scale (AIS) of 6 (identified currently as untreatable injury or unsurvivable injury), the ISS score is automatically assigned 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.

If any of the three Abbreviated Injury Scale (AIS) scores is a 6, the score is automatically set at 75.

A major trauma or polytrauma is defined as the Injury Severity Score (ISS) being greater than 15 (ISS> 15).

Bolorunduro etal. categorised and validated the Injury Severity Score (ISS) as follows ³:

• ISS <9 = Mild
• ISS 9 – 15 =Moderate
• ISS 16–24 = Severe
• ISS >/=25 = Profound

The most important drawback of the ISS is that it only considers one injury in each body region. This leads to injuries being overlooked and to less severe injuries occurring in other body regions being included in the calculation over more serious ones in the same body region ³.

The ISS score is virtually the only anatomical scoring system in use and correlates linearly with mortality, morbidity, hospital stay and other measures of severity (Figure 1).

The Injury Severity Score (ISS) scoring rules

The Injury Severity Score (ISS) is the sum of the squares of the highest Abbreviated Injury Scale (AIS) code in each of the three most severely injured ISS Body Regions.

The following example demonstrates an Injury Severity Score (ISS) calculation:

ISS Body Region*	Injury	AIS Code	Abbreviated Injury Scale (AIS)	Abbreviated Injury Scale (AIS)²
HEAD/NECK	Cerebral contusion NFS Internal carotid artery transection (neck)	140602.3 320212.4	4	16
FACE	Closed fractured nose	251000.1	1
CHEST	Rib fractures left side, ribs 3 – 4	450202.2	2
ABDOMEN	Retroperitoneal Haematoma	543800.2	2	4
EXTREMITIES	Fractured femur (NFS)	853000.3	3	9
EXTERNAL	Abrasions (NFS)	910200.1	1
				ISS = 29

Footnote: * Note that these ISS Body Regions do not necessarily coincide with the chapters used in the AIS 2005 – Update 2008 dictionary.

Figure 1. ISS score in predicting trauma outcome

Footnote: ROC curve showing validity of ISS score in predicting outcome (i.e. mortality).

[Source ¹ ]

Abbreviated Injury Scale (AIS)

The Abbreviated Injury Scale (AIS) is an anatomically based consensus-derived global severity scoring system that classifies each injury in every body region according to its relative severity on a six-point ordinal scale:

1. AIS 1 = Minor;
2. AIS 2 = Moderate
3. AIS 3 = Serious
4. AIS 4= Severe
5. AIS  5= Critical
6. AIS 6 = Maximal (currently untreatable).

Information about updates and changes to the Abbreviated Injury Scale (AIS) versions are available at the Association for Advancement of Automotive Medicine (AAAM) – AIS update information page (https://www.aaam.org/abbreviated-injury-scale-ais).

There are 6 Abbreviated Injury Scale (AIS) corresponding to 6 body regions:

1. Head or neck injuries
   1. AIS 1 = Minor;
   2. AIS 2 = Moderate
   3. AIS 3 = Serious
   4. AIS 4= Severe
   5. AIS  5= Critical
   6. AIS 6 = Maximal (currently untreatable).
2. Facial injuries
   1. AIS 1 = Minor;
   2. AIS 2 = Moderate
   3. AIS 3 = Serious
   4. AIS 4= Severe
   5. AIS  5= Critical
   6. AIS 6 = Maximal (currently untreatable).
3. Chest injuries
   1. AIS 1 = Minor;
   2. AIS 2 = Moderate
   3. AIS 3 = Serious
   4. AIS 4= Severe
   5. AIS  5= Critical
   6. AIS 6 = Maximal (currently untreatable).
4. Abdominal or pelvic contents injuries
   1. AIS 1 = Minor;
   2. AIS 2 = Moderate
   3. AIS 3 = Serious
   4. AIS 4= Severe
   5. AIS  5= Critical
   6. AIS 6 = Maximal (currently untreatable).
5. Extremities or pelvic girdle injuries
   1. AIS 1 = Minor;
   2. AIS 2 = Moderate
   3. AIS 3 = Serious
   4. AIS 4= Severe
   5. AIS  5= Critical
   6. AIS 6 = Maximal (currently untreatable).
6. External and other trauma injuries
   1. AIS 1 = Minor;
   2. AIS 2 = Moderate
   3. AIS 3 = Serious
   4. AIS 4= Severe
   5. AIS  5= Critical
   6. AIS 6 = Maximal (currently untreatable).

Injury Severity Score (ISS) = A² + B² + C²

where A, B, C are the Abbreviated Injury Scale (AIS) scores of the three most injured Injury Severity Score (ISS) body regions.

References

1. Javali RH, Krishnamoorthy, Patil A, Srinivasarangan M, Suraj, Sriharsha. Comparison of Injury Severity Score, New Injury Severity Score, Revised Trauma Score and Trauma and Injury Severity Score for Mortality Prediction in Elderly Trauma Patients. Indian J Crit Care Med. 2019;23(2):73–77. doi:10.5005/jp-journals-10071-23120 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6487611
2. Baker SP,, O’Neill B,, et al. The injury severity score: a method for describing patients with multiple injuries and evaluating emergency care. J Trauma. 1974;;14::187–196.
3. Bolorunduro OB,, Villegas C,, et al. Validating the Injury Severity Score (ISS) in different populations: ISS predicts mortality better among Hispanics and females. J Surg Res. 2011 Mar; 166((1):):40-–44.