Comparison of Injury Severity Score, New Injury Severity Score, Revised Trauma Score and Trauma and Injury Severity Score for Mortality Prediction in Elderly Trauma Patients

1Trauma is one of the leading causes of mortality and morbidity worldwide. Injuries in the elderly are rapidly becoming a major public health concern.

2An appropriate scoring system to predict the mortality and morbidity in elderly is necessary because the elderly population has continued to grow and will continue to represent an increasing proportion of patients in our trauma bays. Additionally, elderly trauma patients have an increased morbidity and mortality for a given severity of injury, a decreased 5-year survival compared to their uninjured counterparts, as well as an increase in intensive care unit (ICU) stays and longer hospital length of stay–.

3Nonetheless, aggressive treatment for elderly trauma patients is paramount, as patients who survive such events often return to independent living.

4Trauma scores were introduced more than 30 years ago for assigning numerical values to anatomical lesions and physiological changes after an injury. Physiological scores describe changes due to a trauma and translated by changes in vital signs and consciousness. Anatomical scores describe all the injuries recorded by clinical examination, imaging, surgery or autopsy. If physiological scores are used at first contact with the patient (for triage) and then repeated to monitor patient progress, anatomical scores are used after the diagnosis is complete, generally after patient discharge or postmortem. They are used to stratify trauma patients and to measure lesion severity. Scores that include both anatomical and physiological criteria (mixed scores) are useful for patient prognosis.

5Abbreviated injury scale (AIS)

6Injury severity score (ISS)

7New injury severity score (NISS)

8Organ injury scale (OIS)

9Anatomic profile

10International Classification of Diseases (ICD-9) Injury Severity Score (ICISS)

11Revised trauma score

12Glasgow coma score

13APACHE scoring (Acute physiology and chronic health evaluation (APACHE I, II, III)

14Trauma and injury severity scores (TRISS)

15A severity characterization of trauma (ASCOT)

16The injury severity score (ISS) is an anatomical scoring system that provides an overall score for patients with multiple injuries. Each injury is assigned an abbreviated injury scale (AIS) score and is allocated to one of six body regions. The highest AIS score in each body region is used. The three most severely injured body regions have their score squared and added together to produce the ISS score.

17The ISS score takes values from 0 to 75. If an injury is assigned an AIS of 6 (Unsurvivable injury), the ISS score is automatically assigned to 75. The ISS score is virtually the only anatomical scoring system in use and correlates linearly with mortality, morbidity, hospital stay and other measures of severity (Graph 1).

18Major trauma is considered when ISS> 15.

19Bolorunduro etal. categorised and validated the ISS as follows:

20<9 = Mild

219 – 15 =Moderate

2216–24 = Severe

23>/=25 = Profound

24The most important drawback of the ISS is that it only considers one injury in each body region. This leads to injuries being overlooked and to less severe injuries occurring in other body regions being included in the calculation over more serious ones in the same body region.

25A simple modification to the ISS, the new injury severity score (NISS), was designed by Osler et al. in 1997 to counter this problem. The NISS is simply the sum of squares of the three most severe injuries, regardless of body region injured. Therefore, the NISS will be equal to or higher than the ISS (Graph 2).

26The revised trauma score is a physiological scoring system, with high interrater reliability and demonstrated accuracy in predicting death. It is scored from the first set of data obtained on the patient and consists of glasgow coma scale, systolic blood pressure and respiratory rate (Graph 3).

27RTS = 0.9368 GCS + 0.7326 SBP + 0.2908 RR

28RTS score coding is shown in Table 1. Values for the RTS are in the range 0-7.8408. The RTS is heavily weighted towards the Glasgow coma scale to compensate for major head injury without multisystem injury or major physiological changes. A threshold of RTS <4 has been proposed to identify those patients who should be treated in a trauma centre, although this value may be somewhat low.

29TRISS determines the probability of survival (Ps) of a patient from the ISS and RTS using the following formulae:

30Ps= 1/ (1 + e-b)

31Where ‘b’ is calculated from:

32b = b0 + b1 (RTS) + b2 (ISS) + b3 (Age Index)

33The coefficients b0 - b3 are derived from multiple regression analysis of the Major Trauma Outcome Study (MTOS) database. Age Index is 0 if the patient is below 54 years of age or 1 if 55 years and over. b0 - b3 are coefficients which are different for blunt and penetrating trauma. If the patient is less aged than 15 years, the blunt coefficients are used regardless of mechanism (Graph 4).

34The TRISS calculator determines the probability of survival from the ISS, RTS and patient's age. ISS and RTS scores can be given independently or calculated from their base parameters.

35TRISS uses combination of both anatomic and physiologic scoring systems and gives a more accurate probability of survival.

36Our study was a prospective observational study carried out over a period of 18 months (December 2016 - June 2018) on elderly victims of trauma presenting to the Department of Emergency Medicine. Patients were selected after taking into account the inclusion and exclusion criteria (Flowchart 1).

37Age more than 60 years.

38History and clinical evidence of trauma.

39Patients discharged against medical advice.

40Patients/ Attendants of patients who were not willing to participate in the study.

41The sensitivity, specificity and correct prediction of outcome for each cutoff point were calculated for ISS, NISS, RTS and TRISS. The best cutoff point in each scoring system is determined when the point yields the best specificity and sensitivity in the two-by-two Table. The best Youden index also determines the best cutoff point. The Youden index was used to compare the proportion of cases correctly classified. The higher the Youden index, the more accurate is the prediction (higher true positive and true negatives and fewer false positive and false negatives) at the cutoff point. Descriptive statistics were expressed as mean ± one standard deviation unless otherwise stated. A receiver operating characteristic (ROC) curve depicts the relation between true-positive and false-positive for each scoring system. This method compares scores without fixing arbitrary cutoff points. The area under ROC curve was calculated and evaluated. AUROC represents that a randomly chosen diseased subject is more correctly rated or ranked than a randomly chosen non-diseased subject.

42A value of 0.5 under the ROC curve indicates that the variable performs no better than chance and a value of 1.0 indicates perfect discrimination. A larger area under the ROC curve represents more reliability and good discrimination of the scoring system.

43Two hundred trauma patients aged more than 60 years were included in our study with a mean age of 66.35 ± 6.865 years. Of the total, 74% were men (n= 148) and 26% were women (n=52). Most common mechanism of trauma was road traffic accident (94%), followed by fall (5.5%). All cases were blunt trauma. 166 patients (83%) recovered after treatment in hospital and 34 patients (17%) died (Table 2).

44Among those who were discharged, mean± SD of ISS, NISS, RTS and TRISS scores were 7.52±5.03, 8.80±6.19, 7.60±0.48 and 95.49±4.41 respectively. Among those who were expired, mean ± SD of ISS, NISS, RTS and TRISS scores were 20.85 ±5.00, 27.65 ±7.49, 5.43±1.29 and 58.48 ±25.58 respectively (Table 3).

45In our study mean trauma scores of ISS and NISS were significantly higher in expired subjects than in Living subjects, RTS and TRISS were significantly lower in expired subjects than in Living subjects.

46The predictive accuracies of the ISS, NISS, RTS and the TRISS were compared using receiver operator characteristic (ROC) curves for the prediction of mortality. Best cutoff points for predicting mortality in elderly trauma patients in ISS, NISS, RTS and TRISS systems were 15, 17, 7.108, 91.6 with sensitivity of 91%, 91%, 97%, 97% and specificity of 89%, 93%, 80%, 87%, respectively.

47The area under ROC curve was 0.963, 0.970, 0.947, 0.972 in the ISS, NISS, RTS and TRISS respectively. The Youden index had best cut-off points at 0.80, 0.84, 0.77 and 0.85 for ISS, NISS, RTS and TRISS respectively (Table 4).

48Most of elderly trauma patients in the present study were men. Some studies have shown similar results,. Mean age of our patients was 66.35 years with age range of 60 to 95 years. This is lesser than other studies,. The present study indicated that the most common mechanisms leading to trauma in the elderly were motor vehicle accidents, followed by falls. A study by Aydin et al. also revealed that most common mechanism leading to trauma was motor vehicle accident. Most frequently injured organ was extremity followed by head and neck. Aydin et al. study also reported that the most common injury sites were head and extremities. In this study, 17% of elderly trauma patients died. Yousefzadeh-Chabok etal. study reported mortality rate of 13.9%.

49In the present study, mean plus standard deviation of ISS for non-survivors was 20.85±5.00 and 7.52±5.03 for survivors; mean plus standard deviation of NISS for non-survivors was 27.65±7.49 and 8.80±6.19 for survivors, mean plus standard deviation of RTS for non-survivors was 5.43±1.29 and 7.60±0.48 for survivors. Mean plus standard deviation of TRISS for non-survivors was 58.48±25.58 and was 95.49± 4.41 for survivors.

50In a study by Orhon et al., mean plus standard deviation of ISS for non-survivors was 24.37 ± 12.85 and 5.78 ± 6.71 for survivors;; mean plus standard deviation of NISS for former was 27.62 ± 12.85 and 6.92 ± 8.13, mean plus standard deviation of RTS for former was 5.62 ± 1.31, and 7.75 ± 0.46 for latter group. Mean plus standard deviation of TRISS for non-survivors was 72.80 ± 19.35 and was 98.34±6.58 for survivors.

51In a study by Yousefzadeh-Chabok et al., mean plus standard deviation of ISS for non-survivors was 15.95±10.46 and 7.31±6.22 for survivors; mean plus standard deviation of RTS for former was 5.65±1.82, and 7.79±0.27 for latter group. Mean plus standard deviation of TRISS for non-survivors was 1.04±1.49 and was 3.49±0.6 for survivors.

52Our results indicated that ISS and NISS value for survivors is significantly lower than for non-survivors. RTS and TRISS value for survivors were higher than non-survivors. This difference was statistically significant.

53In the present study, area under ROC curve using ISS, NISS, RTS, and TRISS for predicting death was 0.963, 0.970, 0.947 and 0.972 respectively; all of these scores were statistically significant in terms of mortality prediction.

54In Aydin et al. study, area under ROC curve using ISS, NISS and TRISS for predicting death was 0.907, 0.914 and 0.934, respectively. In Yousefzadeh-Chabok et al. study, area under ROC curve using ISS, RTS and TRISS for predicting death was 0.76, 0.87 and 0.94, respectively.

55In a study conducted by Mitchell et al. in Canada published in 2007, it was reported that scoring systems including TRISS had a good ability to predict the prognosis of patients with trauma. In a study conducted in India, Hariharan et al. concluded that using TRISS system to predict morbidity and mortality after fall in the elderly can play an important role in treatment planning.

56According to logistic regression model used in our study, NISS and TRISS were strong predictors of mortality in elderly trauma patients.

57The sample size is relatively small.

58This is a single centre study

59Our study findings suggest that utility and applicability of injury severity scoring systems in elderly trauma patients using ISS, NISS, RTS, and TRISS scores can better help the emergency physicians in predicting the prognosis. However, TRISS has maximum prediction in outcome when compared with the other scores.