Wayne S. Copes

Evaluating trauma care : the TRISS method. Trauma Score and the Injury Severity Score

Evaluation of trauma care must be an integral part of any system designed for care of seriously injured patients. However, outcome review should offer comparability to national standards or norms. The TRISS method offers a standard approach for evaluating outcome of trauma care. Anatomic, physiologic, and age characteristics are used to quantify probability of survival as related to severity of injury. TRISS offers a means of case identification for quality assurance review on a local basis, as well as a means of comparison of outcome for different populations of trauma patients. Methods for calculating statistics associated with TRISS are presented. The Z and M statistics are explained with the nonstatistician in mind. We feel this article is a source for those interested in developing or upgrading trauma care evaluation.

A revision of the Trauma Score.

The Trauma Score (TS) has been revised. The revision includes Glasgow Coma Scale (GCS), systolic blood pressure (SBP), and respiratory rate (RR) and excludes capillary refill and respiratory expansion, which were difficult to assess in the field. Two versions of the revised score have been developed, one for triage (T-RTS) and another for use in outcome evaluations and to control for injury severity (RTS). T-RTS, the sum of coded values of GCS, SBP, and RR, demonstrated increased sensitivity and some loss in specificity when compared with a triage criterion based on TS and GCS values. T-RTS correctly identified more than 97% of nonsurvivors as requiring trauma center care. The T-RTS triage criterion does not require summing of the coded values and is more easily implemented than the TS criterion. RTS is a weighted sum of coded variable values. The RTS demonstrated substantially improved reliability in outcome predictions compared to the TS. The RTS also yielded more accurate outcome predictions for patients with serious head injuries than the TS.

The Injury Severity Score revisited.

The injury severity score (5) (iss) is a scalar (single number) measure of anatomic injury, widely used in and an important contribution to trauma research. The iss is the sum of squares of the highest abbreviated injury scale (1-3) (AIS) grade in each of the three most severely injured body regions. Thus the iss is a summary measure of trauma to single or multiple body regions. Per cent mortality for blunt injured patients has been shown to be related to iss (based on AIS-76) and patient age (4-6). Patients used to establish those relationships were treated in 1961 and 1967-1968. Similar relationships for penetrating injuries have not been prepared because, until the 1985 version, the AIS provided severity grades for blunt injuries only. The iss is frequently used to assess or compare the injury severity of patient populations (7, 10, 13, 16) and as the anatomic component of trauma patient characterizations used in evaluation of care and quality assurance methods (8). The AIS first published in 1971, was developed to classify anatomic injury from motor vehicle-related trauma. It has been revised and broadened in scope in 1976, 1980, and 1985. Changes in injury coding, trauma care delivery, and clinical management mandate the updating of relationships between severity measures and mortality from which conclusions regarding patient management or healthcare policy issues may be drawn. The present study uses the most recent AIS version (AIS-85) to derive relationships between mortality rate and the iss for comtemporary patients with blunt or penetrating injuries and identifies important properties of the iss which should be considered when the measure is used to compare case mix severity in different populations.(Author/TRRL)

A New Characterization of Injury Severity

ASCOT (A Severity Characterization of Trauma) is a physiologic and anatomic characterization of injury severity which combines emergency department admission values of Glasgow Coma Scale, systolic blood pressure, respiratory rate, patient age, and AIS-85 anatomic injury scores in a way that obviates ISS shortcomings. ASCOT values are related to survival probability using the logistic function and regression weights reaffirm the importance of head injury and coma to the prediction of patient outcome. The ability of TRISS and ASCOT to discriminate survivors from non-survivors and the reliability of their predictions, as measured by the Hosmer-Lemeshow statistic, were compared using Major Trauma Outcome Study (MTOS) patient data. ASCOT performance matched or exceeded TRISSs for blunt-injured patients and for penetrating-injured patients. ASCOT performance gains were modest for blunt-injured patients. The Hosmer-Lemeshow statistics suggest that ASCOT reliably predicts patient outcome for penetrating-injured patients and nearly so for blunt-injured patients. Statistically reliable predictions were not achieved by TRISS for either set. ASCOT provides a more precise description of patient physiologic status and injury number, location, and severity than TRISS. The ASCOT patient description may be useful in relating to other important outcomes not highly correlated with TRISS or the Injury Severity Score (ISS) such as disability, length of stay, and resources required for treatment.

Mortality of patients with head injury and extracranial injury treated in trauma centers.

The types and severity of injuries of 49,143 patients from 95 trauma centers were coded according to the 1985 version of the Abbreviated Injury Scale (AIS). This paper analyzes the causes, incidence, and mortality in 16,524 patients (33.6% of the trauma center patients) with injury to the brain or skull and compares them to patients without head injury. Relative to its incidence, patients with head injury composed a disproportionately high percentage (60%) of all the deaths. This was due to the high mortality rate for head-injured patients. Overall mortality of patients with head injury (18.2%) was three times higher than if no head injury occurred (6.1%). This mortality was little influenced by extracranial injuries except when minor and moderate head injuries were accompanied by very severe (AIS levels 4 to 6) injuries elsewhere. The cause of death in head-injured patients was approximated and it was found that 67.8% were due to head injury, 6.6% to extracranial injury, and 25.6% to both. Head injury is thus associated with more deaths (3,010 vs. 1,972) than all other injuries and causes almost as many deaths (2,040 vs. 2,170) as extracranial injuries. Because of its high mortality, head injury is the single largest contributor to trauma center deaths.

Major trauma in geriatric patients.

Contemporary trauma to the elderly, its severity and associated mortality and morbidity in 111 United States and Canadian trauma centers are described. Three-thousand eight-hundred thirty-three (3,833) trauma patients age 65 years or older are compared to 42,944 injured patients under age 65. Although both groups had equivalent measures of injury severity, the older group had higher case fatality and complication rates and longer hospital stays. The results raise important questions regarding the triage, acute care, accurate prediction of outcome, and hospital reimbursement for the elderly injured patient, with implications for care evaluation, quality assurance, and the long-term viability of trauma centers and systems of care.

Assessing contemporary intensive care unit outcome: an updated Mortality Probability Admission Model (MPM0-III).

Objective:To update the Mortality Probability Model at intensive care unit (ICU) admission (MPM0-II) using contemporary data. Design:Retrospective analysis of data from 124,855 patients admitted to 135 ICUs at 98 hospitals participating in Project IMPACT between 2001 and 2004. Independent variables considered were 15 MPM0-II variables, time before ICU admission, and code status. Univariate analysis and multivariate logistic regression were used to identify risk factors associated with hospital mortality. Setting:One hundred thirty-five ICUs at 98 hospitals. Patients:Patients in the Project IMPACT database eligible for MPM0-II scoring. Interventions:None. Measurements and Main Results:Hospital mortality rate in the current data set was 13.8% vs. 20.8% in the MPM0-II cohort. All MPM0-II variables remained associated with mortality. Clinical conditions with high relative risks in MPM0-II also had high relative risks in MPM0-III. Gastrointestinal bleeding is now associated with lower mortality risk. Two factors have been added to MPM0-III: “full code” resuscitation status at ICU admission, and “zero factor” (absence of all MPM0-II risk factors except age). Seven two-way interactions between MPM0-II variables and age were included and reflect the declining marginal contribution of acute and chronic medical conditions to mortality risk with increasing age. Lead time before ICU admission and pre-ICU location influenced individual outcomes but did not improve model discrimination or calibration. MPM0-III calibrates well by graphic comparison of actual vs. expected mortality, overall standardized mortality ratio (1.018; 95% confidence interval, 0.996–1.040) and a low Hosmer-Lemeshow goodness-of-fit statistic (11.62; p = .31). The area under the receiver operating characteristic curve was 0.823. Conclusions:MPM0-II risk factors remain relevant in predicting ICU outcome, but the 1993 model significantly overpredicts mortality in contemporary practice. With the advantage of a much larger sample size and the addition of new variables and interaction effects, MPM0-III provides more accurate comparisons of actual vs. expected ICU outcomes.

Improved predictions from a severity characterization of trauma (ASCOT) over Trauma and Injury Severity Score (TRISS): results of an independent evaluation

OBJECTIVE In 1986, data from 25,000 major trauma outcome study patients were used to relate Trauma and Injury Severity Score (TRISS) values to survival probability. The resulting norms have been widely used. Motivated by TRISS limitations, A Severity Characterization of Trauma (ASCOT) was introduced in 1990. The objective of this study was to evaluate and compare TRISS and ASCOT probability predictions using carefully collected and independently reviewed data not used in the development of those norms. DESIGN This was a prospective data collection for consecutive admissions to four level I trauma centers participating in a major trauma outcome study. MATERIALS AND METHODS Data from 14,296 patients admitted to the four study sites between October 1987 through 1989 were used. The indices were evaluated using measures of discrimination (disparity, sensitivity, specificity, misclassification rate, and area under the receiver-operating characteristic curve) and calibration [Hosmer-Lemeshow goodness-of-fit statistic (H-L)]. MEASUREMENTS AND MAIN RESULTS For blunt-injured adults, ASCOT has higher sensitivity than TRISS (69.3 vs. 64.3) and meets the criterion for model calibration (H-L statistic < 15.5) needed for accurate z and W scores. The TRISS does not meet the calibration criterion (H-L = 30.7). For adults with penetrating injury, ASCOT has a substantially lower H-L value than TRISS (20.3 vs. 138.4), but neither meets the criterion. Areas under TRISS and ASCOT ROC curves are not significantly different and exceed 0.91 for blunt-injured adults and 0.95 for adults with penetrating injury. For pediatric patients, TRISS and ASCOT sensitivities (near 77%) and areas under receiver-operating characteristic curves (both exceed 0.96) are comparable, and both models satisfy the H-L criterion. CONCLUSIONS In this age of health care decisions influenced by outcome evaluations, ASCOTs more precise description of anatomic injury and its improved calibration with actual outcomes argue for its adoption as the standard method for outcome prediction.

Comparison of mortality, morbidity, and severity of 59,713 head injured patients with 114,447 patients with extracranial injuries

An analysis of the completed Major Trauma Outcome Study (MTOS) data set was undertaken to compare the incidence, mortality, morbidity, and injury severity of patients with head injuries (HI) with those of patients with extracranial injuries (ECI). The MTOS was completed recently after data from 174,160 patients submitted from 165 trauma centers from 1982 through 1989 were collated and validated. Data were analyzed with regard to the effect of injury causation for vehicular-related, nonvehicular-related, and penetrating injuries for patients with HI, ECI, or both. Detailed analyses of relationships between AIS-85 and Glasgow Coma Scale score from the entire data base, and between discharge status, functional independence measures (FIM scores), and severity of HI and ECI in a subset of 70,000 surviving patients were performed. Vehicular-related injuries (49.7%) were divided into those to vehicle occupants (36.4%), pedestrians (7.2%), and motorcyclists (6.0%). Nonvehicular-related blunt injuries included falls (18.4%) and assaults (13.2%) and penetrating injuries consisted of gunshots (8.7%), stabbings (8.0%), and other penetrations (1.8%). There were 59,713 patients with HI (34%) and 114,447 with no head injuries (NHI) (66%). Vehicular causes produced more HI (66.6%) than all other causes, despite the preponderance of nonvehicular-related HI in the overall series (50.3%). The overall MTOS mortality rate was 8.3%, but was three times higher in the HI group (14.5%) than in the NHI patients (5.1%). Injury severity measured by AIS-85 had, as expected, a profound influence on mortality of both HI and NHI groups. A similar high correlation was found between Glasgow Coma Scale score and mortality for head injured patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of injury severity : The triage index

Injury severity scales of proven reliability and validity are essential for the appropriate allocation of therapeutic resources, for prediction of outcome, and for evaluation of the quantity and quality of emergency medical care in differing facilities and over time. Quantitation of injury severity in the field is particularly necessary. Existing scales are too imprecise to permit comparisons of management or systems of care. In this paper, the authors present the Triage Index, a measure of injury severity based on five simple variables observed in a design data set of 1084 patients. The Triage Index has been developed with state-of-the-art multivariate statistical techniques, meets the requirements of an interval ranking scale, and has been both validated and assessed for interuser reliability. The Triage Index is proposed as a validated system of early, rapid, noninvasive, accurate patient assessment permitting appropriate matching of trauma victims with available therapeutic resources as a means of reducing mortality and morbidity.