We commonly see patients who have some form of blunt chest trauma. This is the result of motor vehicle collisions, falls, and a myriad of other traumatic events. The decision to perform thoracic imaging can be difficult. Chest xray (CXR) and/or chest CT? In fact, studies have shown that emergency and trauma physicians often disagree 28-40.9% of the time about which patients require a chest CT following blunt trauma [1, 2].
A recent meta-analysis  concluded that patients undergoing whole-body CT (head, neck, chest, abdomen, and pelvis) had a lower overall mortality than trauma patients undergoing selective CT. It is important to note that the results were based on mostly retrospective studies. Also, indiscriminate CTs in low-risk patients have the potential to cause harm from radiation exposure. A 45-year-old who undergoes a whole-body CT has a lifetime attributable risk of cancer mortality of 0.08% . This means that the number needed to harm from a single trauma whole-body CT is approximately 1,250.
The lack of consensus in determining the need for a whole-body CT demonstrates the need for a decision instrument. To address the need for at least chest imaging, Rodriguez et al. have done several studies to develop the NEXUS Chest rule to aid in the decision making process.
The 7 clinical variables in the NEXUS Chest decision instrument are:
- Age > 60 years
- Rapid deceleration mechanism (fall > 20 ft or MVC > 40 mph)
- Chest pain
- Abnormal mental status
- Distracting painful injury
- Tenderness to chest wall palpation
The NEXUS Chest rule was derived in two separate studies [5, 6]. Most recently in 2013, Rodriguez et al. published a validation study of this NEXUS Chest rule . This is what will be reviewed below.
NEXUS Chest Validation of a Decision Instrument for Selective Chest Imaging in Blunt Trauma 
- Prospective, observational, diagnostic decision instrument study
- 9 U.S. Level 1 trauma centers
- Patients enrolled during 7 am -11 pm via systematic sampling method
- Inclusion criteria
- > 14 years old
- Blunt trauma within 24 hours of Emergency department (ED) presentation
- Underwent chest imaging (CXR or chest CT) in the ED as part of their evaluation
The presence or absence of Thoracic Injury seen on Chest Imaging (TICI) was determined on CXRs and Chest CTs, as interpreted by board certified radiologists. Prior to the derivation studies, an expert panel of emergency and trauma physicians defined TICI as any of the following:
- Aortic or great vessel injury
- ≥2 rib fractures
- Ruptured diaphragm
- Sternal fracture
- Pulmonary contusion or laceration
Pericardial tamponade and cardiac contusion were excluded. As part of the NEXUS Chest validation study, an expert panel of 10 physicians classified injuries according to associated clinical interventions.
- 9,905 patients enrolled prospectively
- Mean age: 46 years
- Imaging practices:
- 43.1% patients had a CXR
- 42.0% patients had a CXR and chest CT
- 6.7% patients had a CXR and abdominal CT
- 5.5% patients had multiple CXRs without CT
- 2.6% patients had a chest CT without CXR
- TICI was seen in 1,478 (14.9%) of patients:
- 363/1478 (24.6%) had MAJOR clinical significance
- 1079/1478 (73.0%) had MINOR clinical significance
- 36/1478 (2.4%) had NO clinical significance
- Operating characteristics of NEXUS Chest Decision Instrument for all TICI:
- Sensitivity 98.8% (95% CI, 98.1% – 99.3%)
- Specificity 13.3% (95% CI, 12.6%-14.1%)
- Negative Predictive Value 98.5% (95% CI, 97.6-99.1%)
- Positive Predictive Value 16.7% (95% CI, 15.9-17.5%)
- Negative Likelihood Ratio 0.09 (95% CI, 0.05-0.14)
- Decision instrument missed 17 TICI (false-negatives).
- 1/17 of those TICI was clinically significant (pneumothorax which required a chest tube).
- Therefore, the negative likelihood ratio for TICI with MAJOR clinical significance is 0.02 (95% CI, 0-0.16).
Conclusions and Future Directions
- Patients who do not have any of the 7 NEXUS Chest rule clinical variables (score = 0) do not need chest imaging.
- This decision instrument is nonspecific and, therefore, would likely not lead to a dramatic decrease in imaging. Future research should focus on delineating the need for a chest CT versus only a CXR. The major concern with only a CXR is the fear of missing aortic and major vessel injuries, which are identifiable on chest CT. However, in the NEXUS study reviewed above, only 15/9905 (0.15%) patients had injuries to the aorta or major vessels. This extremely low rate of aortic injury may NOT justify liberal use of chest CT in low-risk stable patients. Instead, a CXR may be a reasonable screening tool for traumatic aortic injury (TAI), as supported by a decision instrument derived in 2006 . In that study, the following CXR criteria of (1) a displaced left paraspinous line, (2) an abnormal aortic knob, and (3) a widened mediastinum comprised a decision instrument with a negative likelihood ratio of 0.18.
- Thoracic ultrasound (US) should be considered in developing future decision rules. In this study, pneumothorax and pulmonary contusion comprised 10/17 of the TICI missed by the decision rule. This included the one missed major injury. A 2010 systematic review  concluded that thoracic US has a higher sensitivity (86-98%) versus a supine AP CXR (28-75%) in the setting of blunt trauma. Another systemic review found thoracic US to have a sensitivity of 90.9% when compared to CT . In the same study supine CXR was only 50.2% sensitive. Additionally, thoracic US has good diagnostic accuracy for lung contusion . Ultimately, US may pick up small contusions and pneumothoraces while obviating the need for CT in most stable patients.
Suggested algorithm for thoracic imaging in trauma
- NEXUS Chest score = 0
- No thoracic imaging required
- NEXUS Chest score ≥ 1
- In well-appearing patient with no evidence of multiorgan injury –> CXR only without chest CT
- In ill-appearing patients and/or those who will receive workup for other serious injury –> chest CT
- Tillou A, Gupta M. Baraff LJ, Schriger DL, Hoffman JR, Hiatt JR, Cryer HM. Is the use of pan-computed tomography for blunt trauma justified? A prospective evaluation. J Trauma. 2009 Oct;67(4):779-87. PMID: 19820586.
- Gupta M, Schriger DL, Hiatt JR, Cryer HG, Tillou A, Hoffman JR, Baraff LJ. Selective use of computed tomography compared with routine whole body imaging in patients with blunt trauma. Ann Emerg Med. 2011 Nov;58(5):407-16.e15. PMID: 21890237
- Caputo ND, Stahmer C, Lim G, Shah K. Whole-body computed tomographic scanning leads to better survival as opposed to selective scanning in trauma patients: A systematic review and meta-analysis. J Trauma Acute Care Surg. 2014 Oct;77(4):534-9. PMID: 25250591
- Brenner DJ, Elliston CD. Estimated radiation risks associated with full-body CT screening. Radiology. 2004 Sep;232(3):735-8. PMID: 15273333
- Rodriguez RM, Hendey GW, Marek G, Dery RA, Bjoring A. A pilot study to derive clinical variables for selective chest radiography in blunt trauma patients. Ann Emerg Med. 2006 May;47(5):415-8. PMID 16631976.
- Rodriguez RM, Hendey GW, Mower W, Kea B, Fortman J, Merchant G, Hoffman JR. Derivation of a decision instrument for selective chest radiography in blunt trauma. J Trauma. 2011 Sep;7(3):549-53. PMID: 21045745
- NEXUS chest: validation of a decision instrument for selective chest imaging in blunt trauma. Rodriguez RM, Anglin D, Langdorf MI, Baumann BM, Hendey GW, Bradley RN, Medak AJ, Raja AS, Juhn P, Fortman J, Mulkerin W, Mower WR. JAMA Surg. 2013 Oct;148(10):940-6. PMID: 23925583. Free article PDF
- Ungar TC, Wolf SJ, Haukoos JS, Dyer DS, Moore EE. Derivation of a clinical decision rule to exclude thoracic aortic imaging in patients with blunt chest trauma after motor vehicle collisions. J Trauma. 2006. Nov;61(5):1150-5. PMID: 17099521
- Wilkerson RG, Stone MB. Sensitivity of bedside ultrasound and supine anteroposterior chest radiographs for the identification of pneumothorax after blunt trauma. Acad Emerg Med. 2010. Jan;17(1):11-7. PMID: 20078434.
- Alrajhi K, Woo MY, Vaillancourt C. Test characteristics of ultrasonography for the detection of pneumothorax: a systematic review and meta-analysis. Chest. 2012. Mar;141(3):703-8. PMID: 21868468
- Hyacincthe AC, Broux C, Francony G, Genty C, Bouzat P, Jacquot C, Albaladejo P, Ferretti GR, Bosson JL, Payen JF. Diagnostic accuracy of ultrasonography in the acute assessment of common thoracic lesions after trauma. Chest. 2012. May;141(5):1177-83. PMID: 22016490.
Expert Peer Review: Dr. Robert Rodriguez (lead author)
October 8, 2014
While the rate of traumatic injuries has remained steady, the use of diagnostic imaging for blunt trauma evaluation (especially head to pelvis CT, or “Pan-Scan”) has increased substantially. Indiscriminate use of imaging leads to higher costs, emergency department time, and perhaps most importantly—increased patient radiation exposure. One important measure to quell this explosion in use of imaging, is the development and use of decision instruments (DIs), such as the NEXUS Cervical Spine rule, to safely guide selective imaging.
Our work is directed at decreasing unnecessary thoracic imaging in blunt trauma evaluation. As Dr. Morley summarizes well, we have derived and validated the NEXUS Chest DI that safely guides selective chest/thoracic imaging. It is true that with its relatively low specificity, NEXUS Chest will be able to rule out intra-thoracic injury and spare imaging in a minority of patients (approximately 13%). Our rationale behind developing this low specificity rule is a product of the need to adhere to the overriding principle of maximizing safety, or sensitivity, of the DI. Our expert trauma panel consisting of emergency medicine physicians and trauma surgeons strongly believed that in order to be widely accepted and implemented, a selective chest trauma imaging DI must have near-perfect ability to detect (and rule out) clinically significant injury. Our rule meets that critically important criterion of safety: The sensitivity and negative predictive value of NEXUS Chest for clinically major injury were 99.7% (95%CI, 98.2%-100.0%) and 99.9% (95%CI, 99.4%-100.0%), respectively .
It is important to note that NEXUS Chest (and essentially all other directive rule out injury DIs) only tell clinicians when it is safe to forego imaging—they do not mandate imaging in those patients who happen to have one or more of the 7 criteria. Misuse of DIs in this manner can paradoxically lead to increased imaging. For example, when evaluating a geriatric patient who had a minor fall, the fact that the patient is older than 60 years (one of our criteria) does not mean that you have to get a CXR or other chest imaging. NEXUS Chest should not be applied to all adult blunt trauma patients—it should be used in those patients in whom you were already planning to image.
NEXUS Chest will eliminate the need for chest imaging (mostly CXR) upfront in certain blunt trauma patients but where do we go from there in terms of reducing unnecessary diagnostic imaging of the thorax in blunt trauma? The next goal is to reduce chest CT in blunt trauma. We have demonstrated that although chest CT has much higher sensitivity for diagnosing intra-thoracic injury, its indiscriminate use is associated with very high cost and patient radiation exposure. Chest CT in the blunt trauma patient who has a normal or near-normal CXR may be associated with over $200,000 in charges and 593 millisievert effective radiation dose per major injury identified .
We are currently in the final stages of developing a DI for selective chest CT in trauma, which we will incorporate into a comprehensive selective chest imaging algorithm.
- Rodriguez RM, Anglin D, Langdorf MI, et al. NEXUS Chest: Validation of a decision instrument for selective chest imaging in blunt trauma. JAMA Surg. 2013 Oct;148(10):940-6. PMID: 23925583.
- Rodriguez RM, Baumann BM, Raja AS, et al. Diagnostic yields, charges, and radiation dose of chest imaging in blunt trauma evaluation. Acad Emer Med. 2014;6:644-650. PMID: 25039548Robert Rodriguez, MD, Professor of Clinical Emergency Medicine, UC San Francisco (UCSF)
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