Trauma program leaders use trauma scores to monitor and improve quality of care. Three of the most important trauma scores are the Injury Severity Score (ISS), the New Injury Severity Score (NISS) and the Trauma Injury Severity Score (TRISS).
ISS and NISS are very similar, and TRISS is based in part on ISS. All three scores play an important role in trauma performance improvement (PI). However, there are key differences in how these scores are calculated and how they are used in trauma program management.
Most registry software systems automatically calculate the ISS, NISS and TRISS for all trauma patients. However, trauma registrars who understand the underlying formulas will do a better job of managing data quality.
Q. How do you calculate the ISS?
After you have assigned Abbreviated Injury Scale (AIS) codes to a patient’s injuries, identify the three most severely injured ISS body regions. Take the highest AIS severity code in each of these three regions, square each AIS code and then add the three squared numbers.
For example, a patient has a head injury with an AIS severity code of 4, a face injury with an AIS severity code of 1, a chest injury with an AIS severity code of 3, and an abdominal injury with an AIS severity code of 2. The three most severely injured body regions are head (4), chest (3) and abdomen (2). The ISS calculation is:ISS values range from 1 to 75. If any injury is assigned an AIS of 6 (maximal injury), the ISS is automatically the maximum score of 75.
Remember that the ISS body regions are:
- Head or neck (includes cervical spine)
- Chest (includes thoracic spine)
- Abdominal or pelvic contents (includes lumbar spine)
- Extremities or pelvic girdle
Q. How do you calculate the NISS?
The New Injury Severity Score (NISS) is similar to the ISS, except it is calculated using the patient’s three most severe injuries regardless of the body region in which they occur.
For example, a patient with multiple gunshot wounds to the abdomen sustains injuries to their small intestine, liver and kidney, with AIS severity codes of 3, 4 and 5, respectively. Since these three injuries are all to one body region (the abdomen), the ISS calculation would only include the kidney injury. However, the NISS calculation will include all three abdominal injuries.
Q. How do you calculate the TRISS?
The components of the Trauma Injury Severity Score (TRISS) are the patient’s ISS, the patient’s Revised Trauma Score (RTS) and the patient’s age. The components of RTS are Glasgow Coma Scale (points), systolic blood pressure (mmHg) and respiratory rate (breaths per minute).
The TRISS equation is a complex logarithmic regression. As noted above, most registry software systems automatically calculate the TRISS. You can also use an online TRISS calculator to score patients manually.
The main takeaway is that TRISS takes into account both physiologic parameters and information about the patient’s injury to predict probability of survival.
Q. How are ISS, NISS and TRISS used in trauma care?
Since the ISS is based on the patient’s three most severely injured body regions, it is most useful for patients with multiple injuries across multiple body systems — for example, a crash or fall victim with several neurologic and orthopedic injures.
Since the NISS is based on the patient’s three most severe injuries regardless of the body region in which they occur, it is most useful for patients whose injuries are concentrated in one system — for example, a patient with a GSW to the abdomen (as in the above example) or a patient with multiple injuries to the chest. In general, the NISS is an important tool for trauma centers that see a high volume of patients with penetrating injuries or multiple injuries concentrated to one body region.
Since the TRISS determines a patient’s probability of survival (PS), it is useful for evaluating care by comparing actual outcomes to predicted outcomes. (Note: Because TRISS incorporates ISS, it is more useful when evaluating patients with multisystem trauma and less useful when evaluating patients with injuries concentrated in one system.)
All three scores play an important role in a trauma PI program. For example:
Data validation. ISS values also help trauma program leaders and trauma registrars monitor data quality. For example, any record with an ISS of 75 (maximal injury) or no ISS should be checked for accuracy.
Primary review. ISS scores help trauma PI coordinators identify cases requiring further review. For example, any patient with an ISS greater than 9 who was admitted to a nonsurgical service should be reviewed since this represents potential undertriage.
Secondary and tertiary review. Every trauma case presentation should include the patient’s ISS and TRISS. These scores give the trauma medical director or the peer panel a starting point for assessing the condition of the trauma patient and the anticipated outcome. If the patient had a cluster of injuries in one body region, the case presentation should also include the NISS.
Acting on TQIP benchmark reports. When a trauma center has an outlier value on its TQIP risk-adjusted benchmarking reports, trauma program leaders can use the drill-down feature to analyze the specific patient cohort for commonalities. For example, a TQIP report shows that a center is an outlier on “days to withdrawal of care.” The drill-down shows that the common factors are ISS greater than 17 and one or more organs failing. For future trauma patients, these factors could be considered a trigger to consult palliative care.
Q. How can we improve the accuracy of our trauma scores?
All three of these trauma scores depend on AIS codes. Therefore the best way to improve trauma score accuracy is for trauma registrars to develop their AIS coding skills. Here are three effective strategies:
Keep up with data validation. A strong data validation process will help registrars continuously improve their AIS coding skills. Registry leaders can use logic validation registry reports to identify field values that indicate a potential AIS coding mistake. For example, a logic validation report might flag charts that include an ICU days value but an ISS less than 9 — a situation that is possible, but not likely. Reviewing these charts is an opportunity to check the AIS coding and help registrars learn from any mistakes. It is also important to keep up with inter-rater reliability (IRR) checks. An important step in the IRR process is validating the patient’s injuries and verifying that chosen AIS codes reflect all available injury detail.
Code difficult cases as a team. Any time a registrar is having difficulty assigning an AIS code, he or she should feel empowered to call upon other members of the registry team for assistance. Even the most experienced registrar or data manager will sometimes need another set of eyes on a chart and another interpretation on how to code a case. Any learning points gleaned from these interactions should be shared with the entire registry team. If it’s a problem for you, it will be a problem for someone else in the future.
Leverage AAAM resources. Many coding resources are available on the Association for the Advancement of Automotive Medicine (AAAM) website — visit AIS FAQs. Registry professionals can also contact the AAAM directly with any coding questions — email Kathy Cookman at firstname.lastname@example.org.
Commit to professional development. New registrars should sign up for courses required by the American College of Surgeons (ACS) within 12 months of being hired: (a) the American Trauma Society’s Trauma Registrar Course or an equivalent course provided by a state trauma program and (b) the AAAM Injury Scaling Course. Under current ACS requirements, registrars should complete a minimum of 8 hours of registry-specific continuing education per year. In addition, all registrars should be encouraged to earn professional certifications: Certified Abbreviated Injury Scale Specialist (CAISS) and Certified Specialist in Trauma Registries (CSTR).
Amy Brammer, MSN, RN, TCRN, TNS, CEN, CAISS, CSTR
Trauma Program Director, Kaiser Permanente Vacaville Medical Center
Vice Chair of the Abbreviated Injury Scale Certification Board
Faculty for the Abbreviated Injury Scaling Course
Jessica Pemberton, MSN, RN, CEN, TCRN, CAISS, CSTR
Trauma Performance Improvement Coordinator
Kaiser Permanente Vacaville Medical Center
Kathy Cookman, BS, CSTR, CAISS, EMT-P, FMNP
AIS Business Director/International Technical Coordinator – AAAM
CEO – KJ Trauma Consulting, LLC
Resources for Optimal Care of the Injured Patient (2014 ed.). Chicago, IL: American College of Surgeons.
Association for the Advancement of Automotive Medicine. (2008). The Abbreviated Injury Scale Dictionary (2005 – Update 2008 ed.). Barrington, IL: Association for the Advancement of Automotive Medicine.
Association for the Advancement of Automotive Medicine. (2008). Course Training Manual (The Abbreviated Injury Scale 2005-Update 2008). Barrington, IL: Association for the Advancement of Automotive Medicine.