Trauma patient scoring

4 Trauma patient scoring HOWARD

R. CHAMPION

Patient scoring mechanisms serve a dual purpose in emergency medicine. They are used at the scene of an accident or sudden illness as factors in the triage decision, and later they become essential elements of patient outcome evaluation and quality assurance. This chapter will describe the various scoring methods and how they are used in patient assessment and to improve the quality of trauma patient care.

Scoring aids in triage The term triage has shed its battlefield connotation and has come to refer to a system of patient assessment that aids in determining the appropriate course of treatment. Triage techniques can be applied in the field to assess injury severity; to determine whether transfer to a specialized facility, such as a trauma centre, is necessary and during mass casualty or disaster situations (ACSCOT, 1990). Emergency medical personnel at the scene must make triage decisions that determine whether the injuries are severe enough to warrant trauma centre care. In the past, many such decisions were based on investigative modalities that consisted mainly of a physical examination and measurement of vital signs, which provided only cursory information on patient condition and therapeutic need. The need for accurate field indicators of injury severity prompted the development of quantifiable patient assessment methods that could be used by physicians and non-physicians alike during this critical stage of emergency medical care (Champion et al, 1980). PATIENT ASSESSMENT AND OUTCOME EVALUATION At the scene, use of physiological indices facilitates accurate patient assessment by non-physician emergency personnel because such indicators reflect the body's response to the injury sustained (Champion et al, 1980). These scores thus provide an indication of injury severity and are correlated with mortality. Anatomical measures are also used to classify injury severity and have been shown to be predictive of patient mortality; this enables injury severity to be quantified for epidemiological studies, comparisons among patient cohorts and quality assurance (Champion and Sacco, 1986). Many Bailli~re's Clinical Anaesthesiology-Vol. 6, No. 1, March 1992 ISBN 0-7020-1616-0

47 Copyright 9 1992, by Bailli6re Tindall All rights of reproduction in any form reserved

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H. R. CHAMPION

anatomical indices require complete and accurate diagnosis, however, which limits their use for field triage because a complete diagnosis for anatomical scoring purposes is generally unavailable until definitive diagnosis or autopsy. Physiological scores

The patient's response to injury, reflected in the vital signs (blood pressure and respiratory rate) and the level of consciousness, and the extent and type of injury are key factors in determining the appropriate treatment and transport strategy. Physiological scores using these elements have been routinely used in trauma triage for many years. The Trauma Index was an early method of quantifying injury severity that assigned numerical ratings based on the patient's cardiovascular, central nervous system and respiratory status, as well as the site and type of injury (Kirkpatrick and Youmans, 1971). Subsequently, the Illness Injury Severity Index was developed for non-physician emergency medicine practitioners (Bever and Veenker, 1979). This index assigned numerical scales to blood pressure, respiratory condition, skin colour, level of consciousness, bleeding, pulse, and site and type of injury. Although simple to use in the field, neither of these methods proved to be a reliable predictor of patient outcome and both had dubious misclassification rates (Champion et al, 1980). They are important to mention, however, because they laid the foundation for the development of current physiological scoring systems, which include the Revised Trauma Score, the Glasgow Coma Scale, the Shock Score, the CRAMS Scale and the Acute Physiology and Chronic Health Evaluation classification system.

Glasgow Coma Scale The Glasgow Coma Scale (GCS) is a universally accepted method for grading the severity of coma in injured patients and has been validated as a prognostic tool in the study of head injury. Since its introduction in 1974 by Teasdale and Jennett, the GCS has been widely used by prehospital care personnel to aid in trauma triage (Champion et al, 1981; ACSCOT, 1990). The GCS correlates with survival and disability scales, and its inter-rater reliability is such that prehospital personnel can quickly measure coma with a high degree of accuracy and reproducibility (Moreau et al, 1985). The ability of the GCS to allow personnel from a wide variety of health care disciplines to precisely measure and communicate coma levels has made obsolete terms such as 'lethargic' and 'semi-comatose' to describe the conscious state following injury. Ranging from 3 (no response) to 15 (normal), the GCS score is the sum of the best scores for eye opening, verbal and motor responses to verbal or painful stimuli (Figure 1). GCS scores of 3-8, 9-12 and 13-15 denote severe, moderate and mild head injury, respectively. When obtained within 24 h of injury, the GCS helps to predict outcome and, especially in the moderate range, serves as a guide in triage and initial patient management (Jennett and Bond, 1975; Geisler and

49

TRAUMA PATIENT SCORING

1.

Eye opening: Spontaneous To voice To pain None

2. Verbal response: Oriented Confused inappropriate words IncomprehensibLe sounds None 3.

Motor response: Obeys commands Localizes pain Withdraws (pain) Flexion (pain) Extension (pain) None

Total GCS points (1 + 2 + 3) Total GCS points

Score

14-15 11-13 8-10 5-7 3-4

5 4 3 2 1

Figure 1. GlasgowComa Scale. From Championet al (1991b) with permission. Salcman, 1986). Because incrementally lower GCS scores relate directly to the risk of death and morbidity (the latter being defined by the Glasgow Outcome Scale, which measures the level of ultimate brain function), the GCS is a reliable predictive measure (Jennett et al, 1976; Geisler and Salcman, 1986). Studies in many countries by Miller et al (1981), Salcman et al (1981), Young et al (1981) and Levati et al (1982) have confirmed its value. The GCS is also a crucial element in trauma research. No outcome assessment study of head-injured patients would be complete without a description of case mix in terms of admission GCS. Commonly used to describe and control for case mix differences in cohorts of injured patients, the GCS facilitates evaluation and comparison of treatment in different facilities over time. Pooling data of this type is essential to evaluating the outcomes of head-injured patients because few individual trauma centres treat large numbers of patients with severe head injuries. Revised Trauma Score

Prehospital personnel arriving on the scene immediately assess the extent of the trauma victim's injuries and initiate the necessary medical interventions.

50

H. R. CHAMPION

The first steps in this process are to evaluate the airway, breathing and circulation (the 'ABCs') and to check the patient's vital signs (Champion et al, 1988a). The results of this initial evaluation of the patient are quantified by use of the Revised Trauma Score (RTS), a physiological measure of injury severity that assigns numerical values to the patient's respiratory rate (RR), systolic blood pressure (SBP) and responsiveness with regard to the GCS (Champion et al, 1981). The RTS (based on a descending severity scale of 0 to approximately 8) determines the level of care and immediacy of treatment required by the patient. The probability of survival (Ps) for each RTS value is given in Table 1. Table 1. The probability of survival (Ps) for RTS values. From Champion et al (1989) with permission. RTS

P~

8 7 6 5 4 3 2 1

0.988 0.969 0.919 0.807 0.605 0.361 0.071 0.027

The development of the RTS was based on both the Triage Index (Champion et al, 1980) and the Trauma Score (Champion et al, 1981). The Trauma Score contains the GCS and assessments of cardiovascular and respiratory status. Weighted values of the indicators are summed to obtain the score, which ranges from i (worst prognosis) to 16 (best prognosis). The Triage Index, an interval ranking scale, was a precursor to the Trauma Score and was devised by using multivariate statistical techniques on biochemical and physiological variables post-injury (Champion, 1991). Before its revision in 1989, the Trauma Score had shown a high degree of inter-rater reliability and was the most widely accepted physiological scoring system used in field triage. However, field use of the Trauma Score revealed difficultiesin assessing respiratory expansion and capillary refill under certain circumstances. Further, there was a concern that the Trauma Score underestimated the severity of some types of head injuries (Champion et al, 1989). As a result, the RTS was developed to be simpler than its predecessors, i.e. respiratory expansion and capillary refill are no longer included as variables. RTS, therefore, is highly suited to field triage (see Table 2). A patient with any below-normal value (i.e. GCS < 13, SBP <90 or RR < 10 or >29) should immediately be taken to a trauma centre because such values indicate a survival rate of less than 90% (CEMS, 1981). Use of these RTS variables in the field allows rapid characterization of neurological, circulatory and respiratory distress and better assessment of the severity of serious head injuries (Smith et al, 1990; Champion and Sacco, 1991).

51

TRAUMA PATIENT SCORING Table 2. RTS variables. From C h a m p i o n et al (1990a) with permission. GCS 13-15 9-12 6- 8 4- 5 3

SBP ( m m H g )

R R (per minute)

Coded value

> 89 76-89 50-75 1-49 0

10-29 > 29 6- 9 1- 5 0

4 3 2 1 0

In addition, the RTS as a summary value has important applications in patient outcome evaluation and quality assurance. The RTS is computed from coded values of the GCS (G), SBP (S) and RR (R). These values are multiplied by weights determined by logistic regression of a baseline data set, as follows: RTS = 0.9368(G) + 0.7326(S) + 0.2908(R) Expressed as the unweighted sum of the coded variables, the RTS is a better predictor of patient outcome than the Trauma Score and is, therefore, a useful tool for quality assurance (Champion et al, 1990a). Shock Score Unlike the RTS, the Shock Score is derived on admission from the following variables: SBP, haematocrit and arterial pH. Although sometimes used to predict Ps, it is not universally used for this purpose because its applicability to certain subsets of trauma victims is limited (Champion et al, 1991b). CRAMS Scale The ll-point CRAMS (circulation, respiration, abdomen, motor, speech) Scale is a scoring system that aids in identifying thresholds of severity (Gormican, 1982). CRAMS was developed in an attempt to simplify the Trauma Score for field use. It replaced eye opening and respiratory effort with thoracic and abdominal assessments. Because its accuracy and precision have yet to be validated and its numerical scores are not consistent throughout the range of severity, the CRAMS Scale has not been widely accepted (Champion, 1990). Acute Physiology and Chronic Health Evaluation The Acute Physiology and Chronic Health Evaluation (APACHE) classification system was designed to be used in the intensive care unit (ICU) environment and was not intended for use solely on emergency/trauma patients. The APACHE system was developed to create a better methodology for measuring case mix among ICU patients (Knaus et al, 1989). The updated APACHE II score combines 12 physiological measurements, representing disturbances in the body's seven major organ systems, to give the Acute Physiology Score (APS) (Knaus et al, 1985). Measurement of all

52

H . R. C H A M P I O N

12 values is required and the worst results within 24 h of admission are scored. The APS is then combined with the patient's age and chronic health status (i.e. the presence of chronic disease of the cardiovascular, respiratory, hepatic, renal and immunological systems). Assigned weights are totalled to obtain the APACHE II score, which ranges from 0 to 71 on an ascending scale of severity. According to its authors, APACHE II has been used to help surgeons risk-stratify patients so that the benefits of different drugs or varying surgical approaches can be evaluated, to triage patients not only for interhospital transfer but also for various treatment regimens, and to research the utilization and quality of ICUs (Knaus et al, 1989). In general, however, trauma patients are considered coarsely in APACHE II: trauma is classified into postoperative and non-operative groups, then as 'multiple trauma' or 'head trauma', and regression weights for survival probability predictions are derived from limited samples. Further, a scale that measures the severity of illness or injury at ICU admission without subsequent measurements is not well suited to the trauma patient, whose pathology and physiological response to injury often does not peak for 48 to 96 h following the injury. For example, even among a general ICU population, APACHE II's predictive power was shown to improve if daily scores, as opposed to a single score, were taken (Chang et al, 1988). While APACHE II requires further testing specific to trauma patients in the ICU environment, its shortcomings relative to trauma mandate that simpler scales be developed and validated. Other physiological scores, such as the Revised Trauma Index (a triage tool that considers type and region of injury, respiratory effort, cardiovascular response and neurological status) and the Rapid Acute Physiology Score (an abbreviated version of APACHE II that considers pulse, blood pressure, RR, and a weighted GCS score), are also used periodically in patient assessment (Rhee et al, 1990; Smith and Bartholomew, 1990). Regardless of type, all physiological scores are used to supplement the judgement and experience of emergency medical personnel in the field and are not intended to be the sole factors in the triage decision. Indeed, extensive physiological assessment can cause delay and have a detrimental effect on patient outcome. In addition, the full extent of thepatient's injuries is often not apparent at the scene. For example, a head-injured patient initially may have a low GCS score but may subsequently develop intracranial haemorrhage, or a gunshot victim with abdominal wounds and marked vascular injury may initially have a normal blood pressure (Champion and Sacco, 1986). All physiological scores are valuable triage tools if they assess the status of the respiratory, cardiovascular and central nervous systems. Despite the need for continued development and improvement, correctly used physiological assessments identify patients in need of trauma centre or other tertiary care. However, all patients should be periodically re-evaluated for any changes in status or evidence of additional injury. Physiological scores are an important element of the triage algorithm

TRAUMA PATIENT SCORING

53

(Figure 2), which also incorporates site, type and mechanism of injury. This algorithm provides prehospital personnel with a decision logic for determining the appropriate triage strategy. Anatomical scores

Injury severity measures based on the patient's anatomical injuries provide a method for assessing and classifying the damage associated with these injuries. Subsequently, a complete description of anatomical injury obtained from surgery, computed tomography (CT) scan or post-mortem examination is essential to the use of anatomical severity scores. The post-mortem examination is especially critical because it often reveals previously undetected injuries. For example, in a recent study, post-mortem examinations identified anatomical injuries that resulted in a change in the Injury Severity Score (discussed below) in trauma patients who died within 24 h of admission (Harviel et al, 1989). The American College of Surgeons has recommended that a post-mortem examination be performed for all trauma deaths (ACSCOT, 1986). To varying degrees, anatomical scoring systems are predictive of patient outcome; this enables injury severity to be quantified for epidemiological studies, comparisons among patient cohorts and quality assurance (Champion and Sacco, 1986). Anatomical diagnoses are coded into the International Classification of Diseases, 9th Revision, Clinical Modification (CPHA, 1977) and scored for severity using the Abbreviated Injury Scale taxonomies. The data are used to establish national normative outcome standards against which hospitals can compare their own patients' outcomes. Such comparisons introduce objective criteria to care evaluation and support peer review quality of care assessment.

International Classification of Diseases The International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM) is the accepted nomenclature of diseases throughout the world (CPHA, 1977; Champion and Sacco, 1986). All diagnoses of anatomical injury are coded (between ICD 800.00 and 959.9) using this taxonomy. For example, intracranial injuries, haematomas and skull fractures carry ICD-9-CM codes 800, 801,803,851,852, 853 and 854. At present, the ICD system does not include characterizations of severity and, therefore, is not an anatomical severity scoring system. However, ICD-10CM, an update due to be issued in 1995, is expected to minimize the variations in injury severity within categories (Champion and Sacco, 1986; Champion et al, 1991a).

Abbreviated Injury Scale The Abbreviated Injury Scale (AIS) is a list of hundreds of types of injuries, each graded on an ascending severity scale from 1 (minor) to 6 (fatal). The AIS is not an interval scale, i.e. the increase in injury severity from AIS 1 to 2

54

H.R.

I

STEPI

Measure vital signs and level of consciousness

Glasgow Coma Score Systolic blood pressure Respiratory rate Revised Trauma Score Pediatric Trauma Score

CHAMPION

I

<13 or <90 or <10 or > 29 or <11 <9

+ Assess anatomy of injury

Take to trauma center

STEP II

All penetrating injuries to head, neck, torso, and extremities proximal to elbow and knee Flail chest Combination trauma with burns of 10% or inhalation injuries Two or more proximal long bone fractures Pelvic fractures Limb paralysis Amputation proximal to wrist and ankle

I Take to trauma center

+ Evaluate for evidence of mechanism of injury and highenergy impact

continued

55

TRAUMA PATIENT SCORING

STEP III

Ejection from automobile Death in same passenger compartment Extrication time > 20 minutes Falls > 20 feet Roll-over High speed auto crash Initial speed > 40 mph Velocity change > 20 mph Major auto deformity > 20" Passenger intrusion > 12"

Auto-pedestrian injury with significant (> 5 mph) impact Pedestrian thrown or run over Motorcycle crash > 20 mph or with separation of rider and bike

+ Take to trauma center

STEP IV

Age < 5 or > 55 Known cardiac disease, respiratory disease, or psychotic patient on medication Diabetics on insulin, cirrhosis, malignancy, obesity, or coagulopathy

Contact medical control and consider transport to trauma center

I

+ Re-evaluate with medical control

WHEN IN DOUBT, TAKE PATIENT TO A TRAUMA CENTER

I

Figure 2. Triage algorithm. From Champion et al (1991a) with permission.

56

n.R. CHAMPION

is much less than the increase from AIS 3 to 4 or 4 to 5 (Copes et al, 1988a). This is best illustrated by the results of a 1990 study that showed the Ps for each severity level, summarized for all body regions: for AIS 1 and 2, P s = 9 9 . 8 % for AIS 3, Ps=94.7%; for AIS 4, P s = 7 7 . 6 % ; for AIS 5, P~ = 54.1% and for AIS 6, Ps = 10.7% (Copes et al, 1990). In addition, each injury description carries a unique, five-digit code similar to those used in the ICD-9-CM coding system described above (Champion, 1991). The AIS was developed in 1971 to categorize and compare anatomical injuries from automobile accidents (AMA, 1971). Major revisions were made in 1974, 1975, 1976, 1980 and 1985 under the auspices of the American Association of Automotive Engineers. Because of its emphasis on motorvehicle related injuries, these early versions of the AIS focused exclusively on blunt trauma (Copes et al, 1988a). The 1985 version, however, contains the important additions of scores for penetrating injury and a more extensive listing of vascular, thoracic and abdominal injuries (Copes et al, 1988a; Champion et al, 1990b). The 1990 version (AIS-90), which is in the last stages of revision, contains more detail on head, chest and abdominal injuries than previously, and includes vascular head/brain injuries for the first time (Copes et al, 1988a; Champion, 1991).

Injury Severity Score Because the AIS does not account for multiple injuries, the Injury Severity Score (ISS) was developed in 1974 as a summary measure of anatomical injury severity (Baker et al, 1974; Baker and O'Neill, 1976). The ISS, which is based on an ascending severity scale of i to 75, is computed from the AIS scores for individual injuries ( A A A M , 1985). To compute the ISS, injuries are grouped into six body regions as follows: (1) head and neck, (2) face, (3) thorax, (4) abdomen and pelvis, (5) extremities and (6) external. The highest AIS score in each body region is identified and the three largest of these values are squared and summed to obtain the ISS (Harviel et al, 1989). If a patient has an AIS 6 injury, an ISS of 75 is assigned. Patients with an ISS in the 1-25 range are considered to have an excellent chance of survival if they are treated at a regional trauma centre (Champion et al, 1988b). It has been proposed that an ISS as low as 15 should trigger triage to a trauma centre, because many patients in this range will die if they do not receive expert trauma care (Champion et al, 1988b). Widely used in trauma research, the ISS is an important tool in assessing, comparing and categorizing injury severity among patient populations (Kraus et al, 1985; Mucha et al, 1986; Copes et al, 1988b). The ISS has been correlated with age and blunt-injured patient mortality (Baker et al, 1974; Bull, 1975; Baker and O'Neill, 1976). Problems with the ISS include its reliance on the non-interval AIS, which makes direct comparisons of patient mortality among institutions difficult, its consideration of injuries with equal AIS scores to be of equal severity, regardless of body region, and its exclusion of all but the most serious injury to any one body region (e.g. patients with one or several AIS 5 thoracic injuries are included in the same ISS cohort) (Copes et al, 1988b; Champion, 1991). Lack of homogeneity

57

TRAUMA PATIENT SCORING

within ISS intervals prevents accurate categorization of injury severity. An ISS of 25, for example, could be based on a patient's severe (AIS 5) head injury (52 = 25) or on a patient's AIS 4 abdominal injury combined with an AIS 3 extremity fracture (42+32=25). Despite an identical ISS, these patients have very different probabilities of survival (Copes et al, 1990). In order to mitigate this heterogeneity within ISS interval cohorts for the multiply-injured trauma patient population, it has been proposed that ISS values be based on combination AIS scores; for example, an ISS in the 50-66 range would be based on two AIS 5 and one AIS 4 injury (Copes et al, 1988b) (see Table 3). Table 3. Proposed ISS value intervals. From Copes et al (1988b) with permission.

ISS interval

Most severe injury or combination

i- 8 9-15 16-24 25-40 41-49 50-66 75

AIS 2 AIS 3 AIS 4 AIS 5 but not AIS 5 and AIS 4 * AIS 4 and AIS 5 * Two AIS 5s and one AIS 4 * A t least one AIS 6 or three AIS 5 injuries

* In different body regions.

Anatomic Profile Limitations in the ISS such as those described above prompted the development in 1990 by Copes et al of The Anatomic Profile (AP) that more accurately accounts for the multiple injuries sustained by a large proportion of trauma patients. In the AP, A is a summary score of all serious (defined as AIS > 2) head, brain or spinal cord injuries; B considers serious injuries to the thorax, abdomen and pelvis; C covers serious injuries to all other body regions; and D is a summary score for all injuries that are considered non-serious (AIS < 2 ) (Sacco et al, 1988; Copes et al, 1990) (see Table 4). Whereas the ISS uses only the highest AIS score in each body region, the AP takes into account less severe injuries as well. The relative weight of additional injuries is measured by taking the square root of the sum of the squares of all AIS scores to yield a component value. For example, a patient with an AIS 5, an AIS 4 and an AIS 3 injury to various parts of the digestive system would have a component value of 7.07 for category C (the square root of 52 + 42 + 32), whereas the square root of the AIS 5 injury alone is 5. Component values of the AIS scores for each of these categories are added to produce the AP. Weighting the values in this manner makes the AP more precise than the ISS in describing anatomical injury. For example, regression analysis reveals that patients with the same ISS but different AP values have markedly different survival probabilities, revealing that the AP more precisely describes anatomical injury than the ISS (Copes et al, 1990) (see Table 5).

58

H.R. CHAMPION

Table 4. Injury assignments to AP components. From Copes et al (1990) with permission.

AIS severity

ISS body region

Head/brain Spinal cord Thoracic

3-5 3-5 3-5

1 1, 3, 4 3

Front of neck

3-5

1

Abdomen/pelvis Spine without cord Pelvic fracture Femoral artery Crush above knee Amputation above knee Popliteal artery Face All others

3-5 3 4-5 4-5 4-5 4-5 4 1-4 1-2

4 1, 3, 4 5 5 5 5 5 2 1-6

Component

Injury

A B

C

D

ICD-9-CM codes 800, 801,803,850-854 806, 950, 952, 953 807,839.61/.71, 860-862, 901 807.5/.6,874, 900 863-868,902 805,839 808,839.42/.52/.69/.79 904.0/. 1 928.00/.01,928.8 897.2/.3/.6/.7

904.41 802, 830 --

Table 5. Comparison of AP and ISS for four patients. From Copes et al (1990) with permission. Patient

ISS

A

B

C

AP Ps

1 2 3 4

25 25 25 25

5.0 7.07 0 0

0 0 5.0 4.0

0 0 0 5.2

0.84 0.65 0.93 0.89

E V A L U A T I O N AND Q U A L I T Y A S S U R A N C E Diversity in m e c h a n i s m and type of injury, p r e m o r b i d conditions and delivery of care m a k e patient categorizations and systematic and effective quality assurance m o r e difficult for e m e r g e n c y medicine than for m a n y o t h e r medical and surgical specialties. M o s t t r a u m a quality assurance p r o g r a m m e s focus heavily on patient o u t c o m e as an indicator of quality of care ( C h a m p i o n et al, 1983, 1990a,b). T h e ability to determine the appropriateness of patient o u t c o m e , h o w e v e r , is d e p e n d e n t u p o n quantitative comparisons of actual patient o u t c o m e against a standard or expected o u t c o m e . Until recently, insufficiently large patient samples seriously limited this type of comparison. The severity of this p r o b l e m p r o m p t e d the (US) National R e s e a r c h Council to state that, until corrected, 'effective p r o g r a m m e s of injury p r e v e n t i o n and care evaluation c a n n o t be accomplished' ( N R C , 1985). The M a j o r T r a u m a O u t c o m e Study

In the early 1980s, t r a u m a surgeons across the U n i t e d States initiated a systematic data collection effort for trauma. T h e goal of this effort was to d e v e l o p and test Ps n o r m s based on t h e n - c u r r e n t injury severity indices

59

T R A U M A PATIENT S C O R I N G

(Champion et al, 1990a). Coordinated by the American College of Surgeons' Committee on Trauma, this effort was known as the Major Trauma Outcome Study (MTOS). During the 1982-1989 study period, demographic, cause of injury, injury severity and outcome data on more than 170 000 patients were submitted to the MTOS from 160 hospitals in the United States, Canada, the United Kingdom and Australia (Champion et al, 1990a). All MTOS participants received yearly confidential analyses of patient outcomes to support their institutional evaluation and quality assurance programmes. Because of the diversity of the institutions submitting data, four level I trauma centres (accredited by the American College of Surgeons) served as control centres to adhere rigidly to study data collection procedures and other stringent requirements (e.g. 100% autopsy rate). A central objective of the MTOS was the identification of patients whose unexpected outcomes suggested that their cases would be good candidates for peer review. Many participating trauma centres used MTOS data to support quality assurance activities by identifying patients with statistically unexpected outcomes (Champion et al, 1990a). MTOS outcome norms were derived using the TRISS index (described below), which combines both physiological and anatomical indices and is used to characterize the severity of injury and estimate the Ps. C o m b i n a t i o n scores used in t r a u m a research

Used together, physiological and anatomical indices are invaluable tools for quality assurance, as well as for epidemiological studies of injury, trauma programme evaluation and patient outcome evaluation. The combination scores used today include TRISS and A Severity Characterization of Trauma.

TRISS The TRISS methodology was introduced in 1981 to quantify Ps as a function of injury severity (Champion et al, 1983; Harviel et al, 1989). These Ps estimates are derived from anatomical and physiological indices combined in a mathematical formula with patient age (Champion et al, 1990b). TRISS is widely used in retrospective P~ analyses and is an accepted element in most trauma registries.

Logistic model. TRISS' physiological index is the RTS as assessed at emergency department/trauma centre admission, and the anatomical index is the ISS (Baker et al, 1974; Champion et at, 1989). TRISS employs the following logistic model to estimate patient survival probability: Ps = 1/(1 + e -b) where e = 2.7182 (base of Napierian logarithms), and b = b0 + bx(RTS) + b2(ISS) + b3(age). The b values are regression weights that differ for blunt and penetrating injury (Champion et al, 1983; Boyd et al, 1987), and age is 0 for ages less than 55 years and 1 for ages of 55 years or more.

60

H. R. CHAMPION

TRISS, utilized in the preliminary and definitive outcome-based evaluation methodologies (described below) for the MTOS, identifies patients whose unexpected outcomes make their cases worthy of peer review by a quality assurance committee.

Preliminary outcome-based evaluation. TRISS-generated probabilities of survival are utilized in the preliminary outcome-based evaluation (PRE) to support quality assurance activities (Champion et al, 1989). Patients are characterized by their physiological status upon admission (coded by RTS), definitive anatomical diagnosis (based on surgery, CT scan and/or autopsy, and classified according to the AIS and ISS taxonomies) and age. The RTS and ISS are plotted on a graph known as a PRE chart (see Figure 3).

0L

D

D D D D

2-

D

D L

~

3-

4.

REVISED TRAUMA 8CORE

L

LD

L

5" L

L

L

LD

~

PS 50 ISOBAR

6" L

L

7L

L ILL

L L

L L

LL

LL

L

L L

L

L

L

L

8" 0

10

20

30

40

60

80

70

INJURY S E V E R I T Y S C O R E

Figure 3. Example PRE chart. From Champion et al (1990a) with permission.

Separate PRE charts are developed for specific age and aetiology (blunt or penetrating) cohorts. An 'unexpected survivor' (plotted as L) is a patient discharged from the acute care facility whose TRISS-estimated P~ was less than 0.50. An 'unexpected death' (plotted as D) is a non-survivor whose P~ exceeded 0.50. The diagonal line across the chart, known as the Ps50 isobar, marks a 50% Ps for the particular age cohort. Survival probability is determined by the position of each value in relation to the Ps50 isobar, i.e. survivors above the line and non-survivors below it are classified as having unexpected outcomes. The cases of all patients with unexpected outcomes are identified for peer review. Example case summaries for a TRISSidentified and peer-review-supported unexpected death and unexpected survivor are given below (Karmy-Jones et al, 1992).

61

T R A U M A P A T I E N T SCORING

Unexpected death Age: 27 Blunt injury; ISS = 33; RTS = 7.84; TRISS Ps = 0.990 Peer review committee estimated P~: 95% The patient fell four stories and sustained an L1 burst fracture without deficit, a right femur fracture and an open left Colles' fracture. On his tenth day in the hospital, during surgery for the lumbar fracture, the patient arrested and died a few hours later. The post-mortem examination confirmed the presence of a large saddle embolism. It was subsequently determined that deep venous thrombosis prophylaxis had not been started, although it had been ordered. This death was deemed to have been unexpected and preventable.

Unexpected survivor Age: 33 Penetrating injury; ISS = 25; RTS = 3.830; TRISS P~= 0.488 Peer review committee estimated Ps: 5-50% The patient had a stab wound to the chest and was taken to the trauma centre within 20rain post-injury. The patient arrested soon after admission and an emergency thoracotomy was performed. The patient's specificinjuries included a laceration of the left ventricle and of the (non-dominant) left anterior descending coronary artery. After 11 days, the patient was discharged home. This patient was determined to have survived because she was transported so quickly that her physiology deteriorated only after arrival at the trauma centre, where her injuries could be effectively managed. A s shown, P R E can be used to p r o v i d e the basis for a t r a u m a c e n t r e ' s i n t e r n a l p e e r review. H o w e v e r , P R E does n o t allow a t r a u m a c e n t r e to j u d g e h o w well its o u t c o m e s c o m p a r e against a n o r m a t i v e o u t c o m e . T h e definitive o u t c o m e - b a s e d e v a l u a t i o n was c r e a t e d for this p u r p o s e .

Definitive outcome-based evaluation. T h e definitive o u t c o m e - b a s e d evaluation ( D E F ) is used by t r a u m a centres to c o m p a r e their overall p e r f o r m a n c e against a n o r m . If assessed periodically, D E F can p r o v i d e an i n d i c a t i o n of the effectiveness of n e w protocols or facilities in t e r m s of p a t i e n t o u t c o m e . T h r e e statistics are used in D E F : z, W a n d M. T h e z statistic c o m p a r e s the actual n u m b e r s of survivors in a t r a u m a c e n t r e (A) with the n u m b e r e x p e c t e d b a s e d o n c u r r e n t n o r m s (E). T h e z statistic is expressed as:

(A - E)/S w h e r e S = ~ / ~ Pi ( I - P i ) . T h e W statistic provides perspective o n the practical or clinical significance of statistically significant z scores a n d indicates v a r i a n c e f r o m the expected n o r m of survivors p e r 100 p a t i e n t s ( C h a m p i o n , 1991):

W = (A - E)/(N/IO0) where N is the n u m b e r of p a t i e n t s in the study p o p u l a t i o n . T o mitigate the effects of differences in severity mix b e t w e e n a facility's p a t i e n t set a n d the n o r m , the M statistic was i n t r o d u c e d . E x p r e s s e d o n a scale of 0 ( p o o r i n j u r y severity c o r r e l a t i o n ) to 1 (best c o r r e l a t i o n ) , M provides an i n d i c a t i o n of the relative bias of the z statistic. This p r e v e n t s , for e x a m p l e , a facility that treats a high p r o p o r t i o n of severely i n j u r e d p a t i e n t s from b e i n g falsely b r a n d e d as

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a worse care provider than a facility with less severely injured patients (Champion and Sacco, 1986).

Peer review. Quality assurance can be greatly strengthened by basing care review on statistically derived outcome norms. In this regard, TRISS provides a basis for reliable and consistent case review. TRISS has limitations, however, due largely to certain shortcomings of its component severity scores. For this reason, TRISS is most effective when used in combination with traditional quality assurance tools such as peer review (Karmy-Jones et al, 1992). Peer review keeps the human element in quality assurance and compensates for identified weaknesses in the various statistical methods. TRISS combined with peer review by qualified physicians provides a reliable, quantifiable base for development and improvement of trauma centre quality assurance programmes (Karmy-Jones et al, 1992). A Severity Characterization of Trauma A Severity Characterization of Trauma (ASCOT) was developed by Champion et al in 1990(b) as a more statistically reliable predictor of Ps than TRISS. Although TRISS is almost universally used in trauma registries and is often used in injury research, its classification of the deaths of patients with serious injuries such as multiple head wounds as statistically unexpected may frequently be contradicted by peer review (Champion et al, 1990b). Concurrently, AIS underscoring of the severity of certain injuries (e.g. shear injury of the midbrain) limits the predictive ability of TRISS (KarmyJones et al, 1992). ASCOT attempts to improve on these limitations by incorporating the number, location and severity of all anatomical injuries into a TRISS-like method for estimating patient survival probability (Copes et al, 1988b, 1990; Sacco et al, 1988; Champion et al, 1990b). ASCOT is computed as follows: Ps = 1/(1 + e -k) where k = kl + k2G + k3S + k4R + ksA + k6B + k7C + ks (age) and G, S and R are the coded values of the RTS variables. Like TRISS, ASCOT includes physiological and anatomical indices, type of injury and patient age. While TRISS uses the RTS and the ISS, ASCOT uses weighted values of the RTS plus the three elements of the AP (A, B, C) that relate to patient mortality. In addition, patient age is modelled more precisely, using not a binary classification of patient age as in TRISS (age = 0 for age < 55 years and age = 1 for age i> 55 years) but a five-point scale that further breaks down the 54-85 age group (Champion et al, 1990b) (see Table 6). ASCOT's reliance on the AP rather than the ISS to quantify injury severity more comprehensively by incorporating the number and location of injuries and its weighting of the RTS variables (GCS, SBP and RR) according to the aetiology of the injury facilitate better physiological characterization. The Hosme~Lemeshow goodness of fit statistics indicate that ASCOT is a reliable predictor of outcome for patients with penetrating

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Table 6. ASCOT patient age characterization. From Champion et al (1990b) with permission. ASCOT age characterization

Patient age in years

0 1 2 3 4

0-54 55-64 65-74 75-84 -----85

injuries and a reliable (although slightly less so) outcome predictor for blunt-injured patients (Champion et al, 1990b). ASCOT has the additional advantage of being applicable to patient morbidity as well as mortality and may be used in studies relating to the length of hospital stay and the effectiveness of resource utilization (Champion et al, 1990b). CONCLUSION Changes in injury coding, trauma care delivery and clinical management mandate the continual updating of relationships between severity measures and mortality. This is crucial because conclusions regarding patient management or health care policy issues are based, to a large degree, on these data. As illustrated in this chapter, severity scoring is a continually improving process. The perfect numerical characterization, one that unfailingly predicts patient survival probability, will probably never be achieved. The combination of severity scores and clinical expertise, however, greatly influences individual patient outcomes and permits critical evaluation and continual refinement of trauma programmes. SUMMARY

The wide variety of mechanisms and types of injury, premorbid conditions and delivery of care make basic patient categorizations and systematic and effective quality assurance more difficult for emergency medicine than for many other medical and surgical specialties. To properly evaluate the severity and nature of injuries at the scene of an accident or sudden illness, an assessment of the resultant anatomical damage and an evaluation of the physiological status of the patient must be performed. Because precise determination of anatomical damage generally is not possible at the scene, evaluative methods based on the patient's physiological status and the anatomy of the injury to determine the extent of the damage must be applied. In addition, systems for classifying injury severity are widely used for comparing patient samples, for quantifying changes in individual patient status, and for evaluating physicians and treatment programmes. Most trauma quality assurance programmes use patient outcome data to evaluate

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the quality of care. The ability to determine the appropriateness of patient o u t c o m e , h o w e v e r , is d e p e n d e n t u p o n q u a n t i t a t i v e c o m p a r i s o n s o f a c t u a l patient outcome against a standard or expected outcome.

Acknowledgements We thank Ellen Shair for her assistance in the preparation of this manuscript.

REFERENCES A A A M (American Association for Automotive Medicine) (1985) The Abbreviated Injury Scale (A1S)--1985 Revision. Morton Grove, Illinois: AAAM. ACSCOT (American College of Surgeons' Committee on Trauma) Subcommittee on Emergency Services (1986) Position papers on trauma autopsies. ACS Bulletin 17: 37. ACSCOT (American College of Surgeons' Committee on Trauma) (1990) Resources for Optimal Care of the Injured Patient, 79 pp. Chicago: ACS. AMA (American Medical Association) Committee on the Medical Aspects of Automotive Safety (1971) Rating the severity of tissue damage: The abbreviated scale. Journal of the American Medical Association 215: 277. Baker SP & O'Neill B (1976) The Injury Severity Score: An update. Journal of Trauma 16: 882-885. Baker SP, O'Neill B, Haddon W e t al (1974) The Injury Severity Score: A method for describing patients with multiple injuries and evaluating emergency care. Journal of Trauma 14: 187-196. Bever DG & Veenker CH (1979) An illness-injury severity index for non-physician emergency medical personnel. Emergency Medical Technician Journal 3: 45. Boyd CR, Tolson MA & Copes WS (1987) Trauma care: The TRISS method. Journal of Trauma 27: 370-378. Bull JP (1975) The Injury Severity Score of road traffic casualties in relation to mortality, time of death, hospital treatment time and disability. Accident Analysis and Prevention 7: 249-255. CEMS (Commission on Emergency Medical Services) (1981) Air Ambulance Guidelines. Washington, DC: US Department of Transportation. Champion H R (1991) Trauma systems and trauma scoring. In Critical Care: State of the Art, vol. 12. Fullerton, CA: Society of Critical Care Medicine. Champion HR & Sacco WJ (1984) The trauma scores applied to penetrating injury. Annals of Emergency Medicine 13: 6. Champion HR & Sacco WJ (1986) Trauma Severity Scales. In Maull, Cleveland, Strauch & Wolfertfi (eds) Advances in Trauma Care, vol. 1. St Louis: Mosby Year-Book. Champion HR & Sacco WJ (1991) Triage of trauma victims. In Trunkey DD & Lewis FR Jr (eds) Current Therapy of Trauma, vol. 3. Philadelphia: BC Decker. Champion HR, Sacco W J, Hannan DS et al (1980) Assessment of injury severity: The Triage Index. Critical Care Medicine 8: 201-208. Champion HR, Sacco WJ, Carnazzo AJ et al (1981) The Trauma Score. Critical Care Medicine 9: 672-676. Champion HR, Sacco WJ & Hunt TK (1983) Trauma severity scoring to predict mortality. Worm Journal of Surgery 7:4-11. Champion HR, Moreau MM & Gainer PS (1988a) Assessment and triage. In Baskett P & Weller R (eds) Medicine for Disasters, pp 19-35. Kent: Butterworths. Champion HR, Sacco WJ, Gainer PS & Patow SM (1988b) The effect of medical direction on trauma triage. Journal of Trauma 28: 235-239. Champion HR, Sacco WJ, Copes WS et al (1989) A revision of the Trauma Score. Journal of Trauma 20: 623. Champion HR, Copes WS, Sacco WJ et al (1990a) The major trauma outcome study: Establishing national norms for trauma care. Journal of Trauma 30: 1356-1365.

TRAUMA PATIENT SCORING

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Champion HR, Copes WS, Sacco WJ et al (1990b) A new characterization of injury severity. Journal of Trauma 30: 53%546. Champion HR, Copes W & Sacco WJ (1991a) Injury severity scoring. In Trunkey DD & Lewis FR Jr (eds) Current Therapy of Trauma, vol. 3. Philadelphia: BC Decker. Champion HR, Sacco WJ & Copes W (1991b) Trauma scoring. In Moore E, Mattox K & Feliciano D (eds) Trauma, vol. 2. East Norwalk, Connecticut: Appleton & Lang. Chang RWS, Jacobs S, Lee B e t al (1988) Predicting deaths among intensive care unit patients. Critical Care Medicine 16: 34-42. Copes WS, Lawnick MM, Champion HR & Sacco WJ (1988a) A comparison of Abbreviated Injury Scale 1980 and 1985 versions. Journal of Trauma 28: 78-86. Copes WS, Champion HR, Sacco WJ et al (1988b) The Injury Severity Score revisited. Journal of Trauma 28: 6%77. Copes WS, Champion HR, Lawnick MM et al (1990) Progress in characterizing anatomic injury. Journal of Trauma 30: 1200-1207. CPHA (Commission on Professional Hospital Activities) (1977) International Classification of Diseases, 9th Revision, Clinical Modification. Ann Arbor, Michigan: Edwards Brothers. Flora J (1978) A method for comparing survival of burn patients to a standard survival curve. Journal of Trauma 18: 701. Geisler FH & Salcman M (1986) Initial neurotrauma scoring of head injury. Trauma Quarterly 3: 51-62. Gormican SP (1982) CRAMS scale: Field triage of trauma victims. Annals of Emergency Medicine 11: 132. Harviel JD, Landsman I, Greenberg A et al (1989) The effect of autopsy on injury severity and survival probability calculations. Journal of Trauma 29: 766-773. Jennett B, Bond M (1975) Assessment of outcome after severe brain damage. Lancet i: 480-484. Jennett B, Teasdale G, Braakman R et al (1979) Prognosis of patients with severe head injury. Neurosurgery 4: 283-289. Karmy-Jones R, Copes WS, Champion HR et al (1992) Results of a multiinstitutional outcome assessment: Results of a structured peer review of TRISS-designated unexpected outcomes. Journal of Trauma (in press). Kirkpatrick JR & Youmans RL (1971) Trauma index: An aid in the evaluation of injury victims. Journal of Trauma 11: 711. Knaus WA, Draper EA, Wagner DP et al (1985) APACHE II: A severity of disease classification system. Critical Care Medicine 13: 818--829. Knaus WA, Wagner DP & Draper EA (1989) Development of APACHE. Critical Care Medicine 17: $181-S185. Kraus J, Conroy C, Cox P e t al (1985) Survival times and case fatality rates of brain-injured persons. Journal of Neurosurgery 63: 53%543. Levati A, Farina ML, Vecchi G e t al (1982) Prognosis of severe head injuries. Journal of Neurosurgery 57: 779-783. Miller JD, Butterworth JF, Gudeman SK et al (1981) Further experience in the management of severe head injury. Journal of Neurosurgery 54: 28%299. Moreau M, Gainer PS, Champion HR et al (1985) Application of the Trauma Score in the prehospital setting. Annals of Emergency Medicine 14: 1049-1054. Mucha P Jr, Daly RC & Farnell MB (1986) Selective management of blunt splenic trauma. Journal of Trauma 26: 970-979. NRC (National Research Council) & The Institute of Medicine (1985) Injury in America: A Continuing Public Health Problem, 164 pp. Washington, DC: National Academy Press. Rhee KJ, Mackenzie JR, Burney RE et al (1990) Rapid acute physiology scoring in transport systems. Critical Care Medicine 18:1119-1123. Sacco WJ, Jameson JW, Copes WS et al (1988) Progress toward a new injury severity characterization: Injury profiles. Computers in Biology and Medicine 18: 419429. Salcman M, Schepp RS & Ducker TB (1981) Calculated recovery rates in severe head trauma. Neurosurgery 8: 301-308. Smith JS Jr & Bartholomew MJ (1990) Trauma Index revisited: A better triage tool. Critical Care Medicine 18: 174-180. Smith EJ, Ward AJ & Smith D (1990) Trauma scoring methods. British Journal of Hospital Medicine 44(2): 114-118.

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Teasdale G & Jennett B (1974) Assessment of coma and impaired consciousness: A practical scale. Lancet ii: 81. Young B, Rapp RP, Nortona JA et al (1981) Early prediction of outcome in head injured patients. Journal of Neurosurgery 54: 300-303.