Chest imaging is currently recommended in the evaluation of all blunt trauma patients who present with a concerning mechanism of injury. As a consequence, chest x-ray (CXR) imaging has become a reflexive test, often ordered regardless of clinical signs of injury.^1-2 In fact, the CXR is the most common imaging study performed in blunt trauma patients.³

The use of chest computed tomography (CT) has increased in spite of stable injury prevalence rates.^4-6 The push for head-to-pelvis CT (pan-scan) has similarly fueled an increased in utilization of CT in adult blunt trauma diagnostic protocols.^7-10 Such routine ordering, however, may lead to expensive, low-yield, inefficient care and expose patients to unnecessary radiation exposure.^11-17 For example, when performed after a normal CXR, chest CT diagnoses only one major injury for every 67 studies.¹³ This practice generates approximately $220,000 in radiographic charges and may induce as many as one lethal malignancy for every 11 major injury diagnoses.^12-19

Order sets that include indiscriminate imaging have been shown to increase the costs, and in some cases, risk to patients.²⁰ Median charges for chest x-ray in 2013 are $298 per examination, while median charges for chest CT are $3,294 per patient.^13,21 Potential risks include harmful effects from ionizing radiation exposure, as well as potential renal injury and allergic reactions from intravenous contrast.²² While CXR delivers negligible amounts of radiation, chest CT exposes the patient to a considerable effective radiation dose (ERD) and cancer induction risk, especially for women. Chest CT delivers approximately 8.9 mSv, which is estimated to induce one lethal cancer among every 650 exposed 40 year old women.¹² Although newer CT scan protocols may deliver lower ERD (approximately 5 mSv), lethal malignant transformation rates are higher among younger patients who comprise trauma populations.^15,18,19

With these principles of cancer induction risk, expense, and resource utilization in mind, we have examined the issue of blunt trauma chest imaging in 5 prospective studies conducted over the past 12 years.^3,13,23-26 With the ultimate goals of reducing unnecessary imaging and producing more efficient protocols for blunt trauma chest imaging, we prospectively enrolled over 24,000 adult blunt trauma victims at 10 Level 1 trauma centers. The purpose of this review of our previously published work is to synthesize the three resulting decision instruments into a cohesive summary algorithm with practical implementation recommendations to guide selective imaging in adult blunt chest trauma patients.

We began our chest imaging DI work in 2003, when chest CT was less commonly utilized. We therefore initially directed our efforts at reducing unnecessary CXR in a manner similar to the original NEXUS and Canadian cervical spine studies, which looked primarily at patients with plain radiography of the cervical spine.^27,28 While deriving and validating a rule for selective CXR, we recognized the movement toward greater use of chest CT,^7.8.9.10 and later sought to develop a rule for selective use of chest CT.³

Our DIs were developed as one-way directive instruments intended to reduce the reflexive, nearly universal use of chest imaging in blunt trauma patients. Adhering to the principles for clinical decision rule development put forth by Stiell, et al ²⁹, we employed consistent core methodology in all of our pilot, derivation and validation studies.^29,30 After our pilot study at 3 trauma centers, we conducted our 4 primary studies at 10 urban Level 1 trauma centers, prospectively enrolling patients with the following inclusion criteria: 1) age over 14 years, 2) presentation to the ED for blunt trauma that occurred within 6 hours of arrival, and 3) consistent with our objective to derive one-way rules--having chest imaging (either CXR or chest CT) ordered in the ED as part of their trauma evaluation.^3,23,24 We focused our enrollment primarily to daytime hours according to research personnel availability.

We enrolled 24,010 patients in our four cohorts (2,628 for CXR derivation, 9,905 for CXR validation, 6,002 for CT derivation CT, and 5,475 for CT validation) and found similar patient characteristics in each group. See Table 2 for a summary of patient characteristics.^3,23,24

For selective initial chest imaging (CXR), we derived and validated NEXUS Chest, which consists of 1) age > 60; 2) rapid deceleration mechanism (explicitly defined as fall > 20 feet or motorized vehicle accident > 40 miles per hour); 3) chest pain; 4) intoxication; 5) distracting injury; 6) tenderness to chest wall palpation; and 7) abnormal alertness/mental status.^23,24 In the separate validation cohort, NEXUS Chest had a sensitivity for major injury of 99.7% (95% confidence interval [CI] 98.2-100.0%) and for all injuries of 99.0% (95% CI 98.2-99.4%). NEXUS Chest specificity, however, was low at 13.3% (95% CI, 12.6%-14.0%).²⁴

For selective chest CT we considered trauma providers’ varied minor injury diagnosis thresholds and therefore derived and validated two decision instruments.^10,31 For clinicians who believe it is essential to diagnose all (or nearly all) injuries, we developed NEXUS Chest CT-All, which is highly sensitive for all thoracic injury and consists of 1) abnormal CXR, 2) rapid deceleration mechanism, 3) distracting injury, 4) chest wall tenderness, 5) sternal tenderness, 6) thoracic spine tenderness, and 7) scapular tenderness.^3,10 For those who only seek to detect injuries that result in interventions or other significant changes in patient management, we developed NEXUS Chest CT-Major, which has the same criteria minus rapid deceleration mechanism^3,31. NEXUS Chest CT-Major retains the very high sensitivity for injuries of major clinical significance 99.2% (95%CI, 95.4%-100%), with a slightly lower minor injury sensitivity of 90.7% (95%CI, 88.3%-92.8%), and a higher specificity of 37.9% (95%CI, 35.8%-40.1%), allowing clinicians to forego CT in a greater percentage of patients.

Of note, our three DIs would have detected all of the 38 patients with aortic or great vessel injury (sensitivity 100%; 95% CI 90.8-100%). See Table 3 for summary validation screening performance characteristics of our three chest imaging DIs.

In terms of our assistive guidance for chest CT, we found that abnormal CXR was, by far, the best screening criterion for injury seen on subsequent chest CT (sensitivity for major injury 73.7% [95% CI 68.1-78.6%], specificity 83.9% [95% CI 83.6-84.2]).^26,32 Distracting injury (11.5%), rapid deceleration mechanism (9.0%), and abnormal CXR (3.1%) were the criteria that most frequently occurred in isolation. The presence of any single clinical criterion (other than abnormal CXR) was associated with low prevalence of injury 16.8% (95% CI 15.2-18.6) and clinically significant injury 1.1% (95% CI 0.1-1.8). Injury prevalence increased with an increasing number of criteria present. See Table 4 for likelihood of injury with individual and combinations of criteria.^26,32

Although we used convenience (daytime) sampling, non-enrollment hour patient characteristics were similar and nighttime sampling would be unlikely to change our findings.²³ All study sites were Level 1 trauma center teaching hospitals with many resident physician trauma providers. Nonetheless, all of our criteria are very simple elements of physical exam and history that demonstrated high levels of inter-rater reliability and can likely be assessed easily by a broad range of clinicians. Similarly, our algorithms are straightforward with an application mode that is familiar to trauma clinicians and has been successfully implemented with other well-known decision rules.

The low specificity of our original NEXUS Chest rule limits the potential resource savings from its application. When gauging the risk/benefit ratio of missed thoracic injury versus avoidance of the ionizing radiation of one CXR, we sought very high sensitivity, such that practitioners of all specialties would consider the DI acceptable for use. Our NEXUS Chest CT rules have better specificity, thereby allowing more patients to be effectively ruled out for injury.

One of the primary obstacles to broad acceptance and implementation of our DIs (and all trauma imaging decision rules) is the fundamental disagreement regarding the need to diagnose minor injuries. Practitioners commonly disagree about the significance of non-interventional injuries and generally fall into two camps: those who believe that nearly all injuries should be detected, and those who believe that only management-changing injuries are important.^10,31 We attempted to address part of this controversy by convening expert trauma clinician consensus panels (balanced between EM physicians and trauma surgeons), who classified all injuries seen on imaging according to their clinical significance. Understanding that there is no “right” or “wrong” in this debate, we have presented summary algorithms that offer choices to suit the beliefs and preferences of individual practitioners and institutions. Furthermore, addressing this issue from the standpoint of patient-centered practice in one of our satellite studies, we demonstrated that patients wish to discuss risks and costs of CT and are willing to accept a small risk of missed injury in lower risk scenarios.³³

We present our summary algorithm for blunt trauma chest imaging in Figure 1. We wish to emphasize several points from the standpoint of practical implementation. First, it is important to note that although our DIs were derived and validated in broad groups of patients (including severely injured patients), they are generally intended for use in awake, non-intubated, hemodynamically stable blunt trauma patients. In our work we did not address or refute the findings of several groups of investigators, who have reported improved outcomes with pan-scan in severely injured, poly-trauma patients.^7,8,9,34 In order to use our NEXUS rules, clinicians must be able to assess whether patients have particular criteria (e.g. chest wall or sternal tenderness), and therefore they are not useful for unconscious patients.

Second, we recommend the application of NEXUS Chest in tandem with the NEXUS Cervical Spine rule, with which it shares the common criteria of distracting injury, intoxication and altered level of alertness.^3,27 If a patient has one of these three criteria, they cannot be ruled out for either cervical spine or chest injury. Similarly, chest wall tenderness should be considered analogous to the midline cervical spine tenderness criterion of the NEXUS Cervical Spine rule.

Third, when developing our DIs, we were very cognizant about time pressures and the mental overload that can occur with the need to memorize multiple decision rules. All of our criteria are intuitive elements of trauma history and physical exam, requiring little if any extra provider time or effort. The four physical exam criteria of NEXUS Chest CT (chest wall, sternal, thoracic spine and scapular tenderness) are all elements that are evaluated as part of the typical trauma exam, and for ease of remembering, can be grouped together as thoracic wall tenderness.

Fourth, as emphasized in our methods section, we deliberately developed these DIs as one-way rules to identify patients who are at very low risk of injury, and for whom imaging may be safely omitted. These rules are not intended to be used as primary screening tools to determine the need for imaging, but are designed to be used in conjunction with clinical judgment to reduce imaging. In this regard, we recommend that clinicians first decide whether they would order chest imaging according to their clinical impression and initial assessment. If imaging seems appropriate, the DI should be applied to determine whether imaging can be safely omitted. The presence of DI criteria does not mandate chest radiography in patients who would otherwise not be considered for chest imaging -- misapplication of these DIs to other patients who they were not going to image may paradoxically result in increased CXR and chest CT utilization.

Patients who are deemed low risk for injury (all criteria absent) by NEXUS Chest are effectively cleared for all chest imaging – clinicians may safely forego both CXR and chest CT. In our studies we found that CXR was the best screening criterion for injury seen on chest CT and we therefore advocate for the continued use of portable CXR as the most logical initial modality of chest imaging for most blunt trauma patients.³ If injuries are well characterized by CXR and there is not suspicion for other major injury, further imaging is unnecessary.

CXR may miss injuries that are detected by CT, most notably sternal fractures, rib fractures and minor pulmonary contusions, and clinicians may feel the need to obtain the greater anatomic detail provided by chest CT. In such instances, clinicians should then apply the CT-All or CT-Major DI to determine whether advanced imaging is warranted. Ultimately, the decision regarding whether to employ CT-All or CT-Major is based on individual physician preference and risk tolerance. For clinicians who desire very high sensitivity for all injuries, we recommend use of NEXUS CT-All, which should detect nearly all minor and major injuries, but at the cost of increased imaging and its attendant risk and expense.^3,10 Physicians who want to spare a greater percentage of patients from CT, and thereby reduce costs and radiation exposure, may elect to apply NEXUS CT-Major, which retains the same very high sensitivity for major injuries, but exhibits higher specificity and corresponding greater reduction in CT.^3,31

Patients who exhibit none of the risk criteria in either CT-Major, or CT-All have a very low likelihood of having clinically significant injury. Patients who have normal plain chest radiographs and exhibit only one of the other clinical criteria still have a relatively low risk of injury and may be candidates for an imaging strategy that involves shared decision making. We have demonstrated that most patients prefer to discuss the risks and costs of CT whenever possible and that they will often choose to forego CT in scenarios in which there is a low risk of injury.³³ The shared decision model is less suitable for patients who have two or more criteria, and who consequently have an increased risk of injury and greater benefit from diagnostic CT imaging.

Finally, we recommend the incorporation of the NEXUS Chest DIs and algorithm as checklists into chart templates and electronic medical records. Clinicians may thereby state that a “patient meets NEXUS Chest low risk criteria for injury” or “patient ruled out for chest injury by NEXUS Chest Imaging Algorithm”.

Overall, our work provides clinicians with evidence-based mechanisms to use basic physical exam and history findings, instead of routine imaging, to safely and efficiently rule out injury in appropriate patients. We believe that our DIs and algorithm will save provider and patient time by allowing for the safe avoidance of unnecessary imaging.