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

Background

A recent meta-analysis 3 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%. 4 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 Intoxication 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. 7 This is what will be reviewed below.

Study

NEXUS Chest Validation of a Decision Instrument for Selective Chest Imaging in Blunt Trauma 7

Study Design

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



Outcome Data

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:

Pneumothorax

Hemothorax

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.

Results

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. 8 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 9 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. 10 In the same study supine CXR was only 50.2% sensitive. Additionally, thoracic US has good diagnostic accuracy for lung contusion. 11 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



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