CT scanning in blunt chest trauma: validation of decision instruments

Objective: to perform an external validation of two clinical decision instruments (DIs) – Chest CT-All and Chest CT-Major – in a cohort of patients with blunt chest trauma undergoing chest CT scanning at a trauma referral center, and determine if these DIs are safe options for selective ordering of chest CT scans in patients with blunt chest trauma admitted to emergency units. Methods: cross-sectional study of patients with blunt chest trauma undergoing chest CT scanning over a period of 11 months. Chest CT reports were cross-checked with the patients’ electronic medical record data. The sensitivity and specificity of both instruments were calculated. Results: the study included 764 patients. The Chest CT-All DI showed 100% sensitivity for all injuries and specificity values of 33.6% for injuries of major clinical significance and 40.4% for any lesion. The Chest CT-Major DI had sensitivity of 100% for injuries of major clinical significance, which decreased to 98.6% for any lesions, and specificity values of 37.4% for injuries of major clinical significance and 44.6% for all lesions. Conclusion: both clinical DIs validated in this study showed adequate sensitivity to detect chest injuries on CT and can be safely used to forego chest CT evaluation in patients without any of the criteria that define each DI. Had the Chest CT-All and Chest CT-Major DIs been applied in this cohort, the number of CT scans performed would have decreased by 23.1% and 24.6%, respectively, resulting in cost reduction and avoiding unnecessary radiation exposure.


INTRODUCTION
T he use of computed tomography (CT) imaging in blunt trauma has increased exponentially in trauma centers around the world, particularly over the past two decades 1,2 . The high accuracy of this method in identifying lesions undetected on clinical examination has allowed for faster and more efficient management of the patients [3][4][5][6] to the point that secondary investigation based on whole-body CT (pan scan) has become common in the evaluation of hemodynamically stable patients with blunt trauma 7,8 . However, several studies have indicated that the increased use of CT scanning is directly related to real and quantifiable risks to the patient due to exposure to ionizing radiation [9][10][11] , in addition to increasing hospital costs and prolonging patient stay in emergency units 10 .
A single chest CT scan exposes the patient to an amount of radiation similar to that of 117 chest X-rays 9 . Estimates suggest that the practice of ordering chest CT after a normal chest X-ray may induce a new case of cancer for every 108 chest injuries diagnosed in women and every 231 chest injuries diagnosed in men 10 . Also, 1.5-2.0% of all cases of cancer in the United States are estimated to be related to radiation from CT scanning 11 . Therefore, judicious use of CT scanning is crucial.
In a recent study published in PLOS Medicine, a group of researchers developed and validated two clinical decision instruments (DIs) -NEXUS Chest CT-All and NEXUS Chest CT-Major -which rules out, with high sensitivity, the presence of clinically significant chest injuries in patients with blunt chest trauma. These instruments are based on a list of clinical criteria that must be evaluated during the initial assessment of a The aim of the present study was to perform an external validation of both NEXUS Chest CT DIs, estimating the accuracy of the instruments in a cohort of patients at a trauma referral center. Confirmation of the external validity and high sensitivity of these instruments will broaden their evidence-based applicability in emergency centers worldwide, contributing to a substantial reduction in requests for CT scans in patients who do not benefit from this evaluation.

This cross-sectional study was conducted at
Hospital do Trabalhador, a referral center for trauma care in the city and metropolitan region of Curitiba (Parana).
The protocol of the study was approved by the Ethics The absence of these criteria altogether indicated a likely absence of injury on chest CT.
Rapid deceleration was defined as any highenergy trauma involving a deceleration mechanism, for example, a motor vehicle accident against a partition at speed above 60 km/h, or a fall from an elevation greater than six meters. In the absence of accurate information, deceleration mechanisms described in the medical record with terms like "high energy" and "high impact" were considered to be associated with rapid deceleration.
Distracting injuries included any extrathoracic injury The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the DIs were then calculated based on these data.

Statistical analysis
The data are represented as percentages and medians (± standard deviations). The relationship between the presence of chest injury and each of the clinical criteria that make up the DIs was evaluated.
As a measure of effect, the odds ratio (OR) with a 95% confidence interval (CI) was used. The statistical significance was evaluated using Pearson's chi-square test to control for possible confounding variables, considering p values < 0.05 as significant.

RESULTS
The study included 764 patients, of whom 77.2% (n=590) were males. The age of the patients ranged from 18 to 97 years (mean 43.9±17.9 years) ( Table   1). The most prevalent mechanisms of trauma were truck and car accidents (21.7%, n=166), motorcycle accidents (20%, n=153), and elevated falls (17.7%, n=135) ( Table   2).   In this cohort, the number of chest CT scans requested would have reduced by 23.1% with the Chest CT-All DI and by 24.6%, with the Chest CT-Major DI, which had greater specificity ( Table 5).
Each of the seven criteria that compose the DIs was also analyzed against the presence of the evaluated chest injuries (Table 6). Statistically significant (p<0.05) associations were identified for abnormal chest X-ray and tenderness on palpation of the chest wall, sternum, and scapula. The odds of chest injury were, respectively, 144, 6, 2, and 15 times higher in patients meeting these criteria compared with those not meeting these criteria.

DISCUSSION
The relevance of CT scanning in the diagnosis of trauma injuries is well established 3-6 . However, the high radiation levels associated with this imaging method divide opinions about the need to recommend CT for all victims of blunt trauma [9][10][11] .
DIs are important tools in clinical practice 13,1 4.
Based on objective and easily assessable clinical criteria, DIs help decide the best therapeutic approach. A wellknown example is the CURB-65 score, which recommends hospitalization for patients with community-acquired pneumonia based on five criteria 15 .
In order to predict the absence of chest injury on chest CT imaging based on clinical criteria, Rodriguez et al. 12

developed and validated the DIs Chest CT-All and
Chest CT-Major. These decision instruments identify, with high sensitivity, patients with blunt chest trauma without clinically relevant chest injury, thus safely foregoing chest CT scanning in these patients 12 .
In the present study, we performed an external validation of these two DIs, applying them retrospectively to patients admitted to a referral trauma hospital in a    Patients not meeting any of these DIs clinical criteria but presenting chest injury on CT imaging were considered to have a false-negative screening result. The main concern with the application of these DIs lies with these patients since their injuries would not have been diagnosed based on these instruments alone. However, we found only two false-negative results in our study. The first was a 44-year-old man with pulmonary contusion without chest tenderness who was released on the first day after receiving initial care. The second was a 50-year-old man, also with pulmonary contusion, who was hospitalized for observation as a result of worsening clinical condition with pain on inspiration. This patient was released two days later without intervention. The detection of pulmonary contusion by CT scan did not change the management or prognosis of these patients, so CT scanning could have been foregone in these cases.
The Chest CT-All DI had a high sensitivity for all lesions, while the Chest CT-Major DI had higher specificity, further reducing the use of CT at the cost of a small rate of false-negative results (0.3%). Since the management of both patients with false-negative results was unaffected by the imaging test, we considered the Chest CT-Major DI to be preferable since its ability to reduce ordering of chest CT is considerably higher.
Rapid deceleration is known to be associated with thoracic aortic rupture 16 . A possible concern when choosing Chest CT-Major over Chest CT-All is that the criterion of the deceleration mechanism is absent in the former. The present study had three cases of aortic rupture, one of which was not associated with a deceleration mechanism. In all three cases, the patients presented another criterion -one had an abnormal chest X-ray, another had tenderness on thoracic spine palpation, and the third had a femoral fracture.
Therefore, the absence of the criterion deceleration mechanism did not affect the DI results. The seven criteria that make up these decision tools are simple, objective, and greatly relevant in the initial assessment of trauma patients. The estimated OR showed that patients with an abnormal chest X-ray are 144 times more likely to have chest injuries compared with those with a normal chest X-ray. Tenderness on palpation of the chest wall, sternum, and scapula also showed a significant relationship with the presence of chest injury on CT, and patients with palpation tenderness on one of these sites are 2 to 15 times more likely to have chest injury on CT. The remaining criteria had no significant relationship with the presence of chest injury on CT.
The initial clinical examination is crucial for the prognosis of trauma victims 17