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Injury Severity Principles
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Objectives
• Introduction to key injury severity scores / scales
• Overview of key elements that affect these scores
• Provide reference material
• Introduction to the principles of “mapping” for severity
• Introduction to key bench marking principles
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Types of Physiologic Scores
• Glasgow Coma Scale (GCS)
• Trauma Score (TS)
• Revised Trauma Score (RTS)Triage (RTS/T)Evaluation (RTS/E)
• Survival Probability (Ps)
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Glasgow Coma Scale (GCS)
• Ranges: 3-15
• Composed of 3 parametersBest Eye, Verbal, & Motor (EVM)Response
• What is the purpose of the GCS?• Purpose: Determination of Brain Injury
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GCS Important Hints
• Use specifically for Head Injuries and not Spinal Cord Injuries
• Give each component of the GCS
• It does no good to just tell GCS total
• First Recorded GCS*
• GCS Assessment Qualifier*• 1. Patient Chemically Sedated or
Paralyzed• 2. Obstruction to the Patient Eye• 3. Patient Intubated• 4. Valid GCS: Patient was not
sedated, not intubated, and did not have an obstruction to the eye
*Per National Trauma Data Standard, Data Dictionary, 2014 Admissions
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GCS Important Hints
Brain Injury Severity:
13-15 – mild
9 - 12 – moderate
3 – 8 - severe
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Trauma Score (TS)
• Ranges: 1-16
• Composed of 5 components:Objective Data: Systolic, Respirations, GCSSubjective Data: Capillary Refill, Respiratory Effort
• Purpose – • scoring multiple trauma
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Revised Trauma Score (RTS)
• Due to limitations with the subjective data of the TS
• Divided into 2 Categories:1. Triage – Prehospital, unweighted system2. Evaluation – Emergency Department, weighted system
*RTS-E is installed in trauma registry software for the Emergency Department phase of care.
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Revised Trauma Score (RTS)
• High inter-rater reliability
• Scored from the first set of data obtained on the patient.
• Range: 0.0000 – 7.8408
• Normal: 7.8408 (weighted formula)
Formula: RTS = 0.9368 (GCS) + 0.7326 (SBP) + 0.2908 (RR)
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Injury Severity Score Calculations
• Calculation to reflect the level of severity of the patient’s injuries
• Key Component of the Probability of Survival
• The sum of the squares of the highest AIS from the three most severely injured body regions.
• A² + B² + C² = ISS
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ISS ExampleRegion Injury AIS Square
Description Top Three Head &
Neck Cere. Cont. 4 16
Face Mandible Fx 2Chest Flail Chest 4 16
Abdomen Liver Cont. 2 Grade 5 Spleen
injury5 25
Extremity Humerus fx. 3 External Knee Abrasion 1
Injury Severity Score: 57
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ISS
• AIS 6 severity is an automatically an ISS of 75 (un-survivable injury)
• example: massive crush destruction of both cranium and brain
• Correlates mortality, morbidity, hospital stay and other measures of severity
• Coding Errors lead to AIS severity errors
• ISS in not weighted and thus many different injury patterns can yield the same score.
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New Injury Severity Score (NISS) or Revised ISS
• Drawback of ISS is it does not account for single system injuries
• Purpose: • to reflect severity of multi-organ injury in the same body region
• Has not been validated or accepted as the national norm
• The sum of squares of the highest AIS from the three most severely injured body organs.
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NISS ExampleRegion Injury AIS Square
Description Top Three Head & Neck SAH
Open Skull Fx, LOC WRTBL
55
2525
Face No Injury 0 Chest No Injury 0
Abdomen No Injury 0Extremity No Injury 0External No Injury 0 Injury Severity Score = 25 NISS = 50
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“MAPPING FOR SEVERITY”
• A computerized conversion table using the ICD-9-CM system into AIS-85 system including body region and severity but not the entire 7 digit AIS number
• This computerized conversion allowed abstractors to enter an ICD-9-CM code which then mapped or linked to an AIS severity score for that injury
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“MAPPING FOR SEVERITY”
• These individual ICD-9-CM codes follow the same rules for calculating ISS (most severe injury in 3 different body regions squared)
• This procedure was redone with AIS 90 was released
• Not aware of a validated, published system for AIS 05.
• Mapping for severity is included in most if not all Trauma Registry Software.
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“MAPPING FOR SEVERITY”
• Many hospitals in the US use AIS, however some use AIS 85, AIS 90, AIS 90 with 98 updates, AIS 05, and now AIS 05 with 09 updates.
• What version do you use?
• Because of this vast difference in methodology, and version, the National Trauma Data Bank requires all hospitals to report ICD-9-CM codes and then applies a single mapping to all records to ensure the same rules (good / bad / ugly) apply to every hospital.
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MAPPING EXAMPLE
• Patient with pneumothorax
ICD-9-CM 860.0 Body Region = 4Severity = 3
“Behind the Scenes”
ISS = most severe injury in 3 different body regionhowever this is an isolate injury
ISS = 9
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Survival Probability (Ps)
• Also know as TRISS
• Coefficients b0 - b3 are derived the Major Trauma Outcome Study (MTOS) database 1987.
• Ranges: 0.000 – 1.000 (% Survival)
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Ps Components• Age
• Mechanism (Blunt vs. Penetrating)
• RTS (Evaluation)
• ISS
• Formula: Ps = 1 / (1 + E –b)
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Ps Key Factors
•Age 0-54 or 55 and greater
•Different coefficients for blunt verses penetrating trauma.
• If the patient is less than 15, the blunt coefficients are used regardless of mechanism.
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Survival Probability Calculator
• Trauma.org• http://www.trauma.org/index.php/main/article/387
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Benchmarking Scores
• TRISS Chart
• M & Z
• W Score
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TRISS Chart
• PRE Chart
• Utilizes a Scatter plot
• Used to demonstrate expected and unexpected outcomes
• Threshold is 0.50 or 50%
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TRISS Chart
0 15 30 45 60 75
0
2
4
6
8
ISS
RTS
L
L L
L
D L
L
DD
= Outliers
L = LivedD = Died
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M Score
• Characterizes case mix
• Based on ISS compared to the MTOS
• Score Ranges:0.0 – 0.87 = Dissimilarity to MTOS.88 – 1.0 = Similarity to MTOS
* First step in benchmarking: is your patient population Similar or Dissimilar. If Similar – continue on with Z score, if Dissimilar – you can not use Z score as a benchmark
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Z Score
• Describes provider’s performance
• Values between -1.96 to + 1.96 allow national comparison
• Score Ranges:Values exceeding +1.96 are significantly betterValues exceeding -1.96 are significantly worse
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W Score
• Describes the # of unexpected survivors (+) or deaths (-) per 100 patients
• Formula:W = A – B ÷ C/100
A = Total # of pts with Ps – those that diedB = Sum of the PsC = Total # of pts with Ps
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RIPPLE EFFECT
• If any one component is incorrect this causes a ripple effect in the data
• This can be anything from GCS to initial vital signs to under or over coding an injury
Inaccurate mapping for Blunt
VS Penetrating
InaccurateProbabilityOf Survival
PotentialInaccurate
M & ZStatistic
Potential InaccurateW Score
Invalid E-code
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Examples:
• A 47 year old male was assaulted to head and back with fists and then slammed into a wall. Found unresponsive in a jail cell.
Initial vital signs HR 76, R 14, BP 127, GCS 8. Injuries: EDH with LOC--AIS=5; eyelid contusion--AIS 1.
ISS 26, RTS 5.967
IF YOU CHOOSE THE WRONG COEFFICIENT FOR BLUNT / PENETRATING• PS (Blunt) = 90.1%• PS (Penetrating) = 84.5%
Inaccurate Injury
Severity Score (ISS)
Inaccurate Probability
Of Survival (PoS)
InaccurateM & Z
Statistic
InaccurateTRISSChart
Incomplete or Inaccurate
Injury Coding
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EXAMPLES:
• 65 year old male, fall from ladder, CHI, multiple rib fxs and femur fx.
Initial VS: SBP 110, RR 20, GCS 13 (RTS 7.841)
BASED on this documentationCHI AIS 2Rib Fxs unspecified AIS 2Femur Fx unspecified AIS 3
ISS = 17
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EXAMPLE: Clear, detailed documentation
• 65 year old male, fall 12 feet from ladder landing on concrete, positive LOS continuing for 2.5 hours. Initial VS: SBP 110, RR 20, GCS 13 (RTS 7.841)
Injury List includes:Flail chest with unstable chest wall AIS 4Cerebral Contusion (LOC 2.5 hours) AIS 4Intertrochanteric Femur Fx AIS 3
ISS 41
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ADVERSE EFFECT
• Based on this example
Age 65RTS 7.841Mechanism BLUNT
ISS 17 = Ps 93.9%ISS 41 = Ps 67.3%
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Injury Severity Principles Summary
• Know the Rules:a) GCSb) Initial Vital Signs = RTSc) Accurate ICD-9-CM coding guidelines to ensure
accurate ISSd) ISS and other valid data elements ensures
accurate Ps, M, Z, W scores
• Recite Principles / Components of different scores
• Make no assumptions
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