Measuring Injury Severity

A brief introduction

Thomas Songer, PhDUniversity of Pittsburgh

tjs@pitt.edu

Degrees of Injury Severity

Households

Emergency Dept.

Hospitalization

Injury Deaths

Physician Visit

Injury

Police

Hospital

Self-Treat

Robertson, 1992

doctor

EMS

Rehab CenterTrauma Center

Morgue

Emergency Dept.

Major Areas of Application on Injury Severity Indices

Triage Prognostic Evaluation Research and Evaluation

Is there potential for Is there potential for improvement in the care of improvement in the care of

injured patients?injured patients?

Improvements in outcomes related Improvements in outcomes related to injury may be achieved by:to injury may be achieved by:

• Enhancing pre-hospital care

• Adopting ATLS principles

• Integrating trauma care within and between hospitals

• Investing in rehabilitation services

Measuring the Burden of Injuries

• Fatal– Counts and rates– Years of

Potential Life Lost

• Non-fatal– Short term

• Health care use– Hospitalization rates

• Functional limitations• Severity

– AIS– RTS, etc

• Pathology

Segui-Gomez

Injury Severity Scales

Impact of the Injury will depend on...

Extent of tissue damage Physiological response to the injury Host factors that mediate the

response

Aspects of Injury Severity

Anatomical Injury

Physiological Measurements

AgeBlunt/Penetrating

Probability of survival of individual patientsProbability of survival of individual patients

Comparisons between groupsComparisons between groups

INJURY SEVERITYINJURY SEVERITY

Alphabet SoupAlphabet Soup

Abbreviated Injury Scale (AIS)

Anatomical measure that addresses the extent of tissue damage

ICD-based classifications

AIS Severity Component

MINORMINORMODERATEMODERATESERIOUSSERIOUSSEVERESEVERECRITICALCRITICALMAXIMUM INJURY,MAXIMUM INJURY,VIRTUALLY VIRTUALLY UNSURVIVABLEUNSURVIVABLE

1 1 22 33 44 5 5 66

Severity scores are subjective assessments assigned by experts

Implicitly based on four criteria:

Threat to life Permanent Impairment Treatment Period Energy Dissipation

Addressing Multiple Injuries

for predicting survival

Injury Severity Score (ISS)The New Injury Severity Score (NISS)The Anatomic Profile (AP)

The Injury Severity Score (ISS)

Sum of squares of the highest AIS in each

of 3 most severely injured body regions

ISS Body Regions:– Head or neck - Face

– Abdominal - Chest

– Extremities - External

INJURY SEVERITY SCORE Example

AIS Score

Small subdural haematoma 4

Parietal lobe swelling 3

Major liver laceration 4

Upper tibial fracture (displaced) 3

ISS = 42 + 42 + 32 = 41

Criticisms of the ISS

Does not take into account multiple injuries within a body system

Equal weights across body regions; underscores severe head injuries

The New Injury Severity Score (NISS)

Sums of squares of the 3 highest AIS scores regardless of body region

ISS vs. NISS - an Example

Multiple abrasionsDeep laceration tongueSubarachnoid hemorrhageMajor kidney lacerationMajor liver laceration

1 2344

External Face Head/Neck Abdomen Abdomen

ISS = (4)ISS = (4)22 + (3) + (3)22 + (2) + (2)22 = 29 = 29NISS = (4)NISS = (4)22 + (4) + (4)22 + (3) + (3)22 = 41 = 41

AIS Score Region

Anatomic Profile

Anatomic ProfileDefinition of Components

AIS Region AIS Region

AIS SeverityAIS SeverityAA

BB

CCDD

Head/BrainHead/BrainSpinal cordSpinal cordThoraxThoraxFront of NeckFront of NeckAll other body regionsAll other body regionsAll othersAll others

3-63-63-63-63-63-63-63-63-63-61-21-2

The square root of the sum of squares of AIS scores The square root of the sum of squares of AIS scores is used to summarize a component’s injuriesis used to summarize a component’s injuries

Component Component

ICD to AIS Conversion(ICDMAP)

Converts ICD-9CM coded discharge diagnoses into AIS scores and computes ISS, NISS, APS

Conservative measure of injury severity - refer to as ICD/AIS scores

Injury Severity Scales

In Use

Evaluating System Performance

Using hospital discharge data, classify patients according to where they should have been treated (based on AIS severity)

Compare where they should have been treated to where they actually were treated

Percent of ISS > = 16 Patients Getting to Trauma Centers:

Metro Area A 55%Metro Area B59%Metro Area C66%Metro Area D 68%Metro Area E73%Metro Area F78%Metro Area G 85%

Physiologic Response

Glasgow Coma Score Revised Trauma Score

Glasgow Coma Scale

• Head injuries vary as to severity ranging from mild, moderate, to severe

• The Glasgow Coma Scale is a measure of this severity

• The GCS is assessed immediately following the injury and during the initial recovery

Glasgow Coma Scale

Parameter Response ScoreNil 1To pain 2To speech 3

Eye opening

Spontaneously 4Nil 1Extensor 2Flexor 3Withdrawal 4Localising 5

Motor response

Obeys command 6Nil 1Groans 2Words 3Confused 4

Verbal response

Orientated 5

Revised Trauma ScoreRevised Trauma Score

- a physiological measurement

- based on data at arrival to hospital

considers: Respiratory rate

Systolic blood pressure

Glasgow Coma Scale

Revised Trauma Score

Clinical Parameter Category Score x weight10-29 4>29 36-9 21-5 1

Respiratory rate(Breaths per minute)

0 0

0.2908

>89 476-89 350-75 21-49 1

Systolic bloodPressure

0 0

0.7326

13-15 49-12 36-8 24-5 1

Glasgow ComaScale

3 0

0.9368

Assessing RTS may be problematic

Accurate GCS and RR difficult when the patient is intubated, chemically paralyzed or under the influence of drugs or alcohol

Host Factors

Age Pre-existing conditions Other

Combining information on …

Tissue damage

Physiologic response

Host factors

Probability of Survival Models

TRISS ASCOT

Further Improvements

Refining the State of the Art

1. Further refine the AIS and RTS

2. Revisit Probability of Survival Models -- especially for population based data

3. Better delineate role of host factors

AIS BASED MEASURES of IMPAIRMENT

Injury Impairment Scale (IIS) Functional Capacity Score (FCI)