In this prospective study, we derived a set of variables that predict whether CT of the chest including the thoracic spine is likely to reveal relevant injuries in high-energy blunt trauma patients. These clinically intuitive predictors were derived from data that are available at initial presentation in the emergency department, including age, physical examination, laboratory analyses, CR and abdominal ultrasonography. If CTs were obtained in patients with one or more positive predictors (high-risk patients) only, CT investigations would have been avoided in 18% of patients in this study’s population, thereby decreasing ionising radiation exposure and health-care expenditure.
However, our study data also suggested that if our positive predictors were implemented as scanning indications, 5% (24/508) of all patients with chest injuries on CT would not be identified. This implies that the chance of missing injuries of the chest remains 13% (24/192) in the low-risk patient group if these patients do not undergo chest CT. This risk is substantially lower compared with chest injury risk in the entire blunt trauma population, which was 49% in our study; it is even relatively low compared with previously described “low-risk” populations. Omert et al. reported a prevalence of 39% (95% CI, 27–51%) of chest injuries in patients with normal CR and normal physical examination [17
], and Salim et al. reported a prevalence of 20% (95% CI, 16–23%) of pulmonary, mediastinal and rib injuries in patients who were clinically evaluable and had both a normal physical examination and CR [2
One may pose the question of whether an injury probability of 13% is acceptable for a low-risk patient group. We argue that this risk can be considered acceptable, mainly because these chest injuries had no clinically relevance in most cases. The small pulmonary contusions, pneumothoraces and rib fractures rarely had an impact on patient management (in only 2% of all low-risk patients) and were, perhaps with the exception of the missed thoracic spine fracture, unlikely to affect patient morbidity if left unmanaged. Although cost-effectiveness studies have established acceptable risks for cost-effective injury detection by using CT [18
], these, unfortunately, do not pertain to injuries of the entire chest including the thoracic spine.
Predicting variables that were evaluated in this study were, in part, based on previous studies on appropriate patient selection for chest CT. However, these studies only investigated distinct chest or thoracic injuries and used a case-control design [20
], or did not use CT as a standard of reference [14
To our knowledge, this was one of the first prospective studies to identify selection criteria to facilitate a more appropriate use of CT of the entire chest in adult blunt trauma patients. We used CT as the standard of reference in all included patients. We investigated and described strong criteria that predict presence of any type of relevant chest injuries on CT. Our results might not be surprising as they indicate that chest CT is warranted with abnormal PE or CR. However, this study adds to previous knowledge by defining not only in which patients chest CT is warranted, but also by defining in which patients chest CT could be safely omitted. With further validation, incorporation of these criteria into a diagnostic algorithm for patient selection for chest CT could be an important step towards optimising resource use in trauma imaging.
We are aware that several centres do not use CR of the spine because it is not as sensitive as CT in injury detection [25
] or do not have laboratory analyses available in the emergency department. However, omission of these tests from our prediction model substantially decreased predictive capacity. As long as no techniques other than CR of the spine and laboratory analyses are used to provide indications for CT imaging, these investigations seem indispensible for selective chest CT algorithms in patients who do not have other positive predictors.
Our study has a number of limitations. According to the Oxford levels of evidence grading [26
], good diagnostic research incorporates index tests and reference tests that are applied blindly and objectively. However, the standard of reference (CT) was not interpreted independently from other clinical information because in our practice, radiologists and surgeons work closely together in trauma patient care. However, we do not consider this a major source of incorporation bias because chest CT rarely misses injuries that are visualised on CR [27
A second limitation is that we abstracted information on potential predictors or index tests from medical records. Although we used objective predictor definitions and instructed trauma team members to record all data on potential predictors prospectively (blinded to CT outcomes), this introduced a retrospective component in this study. However, we minimised hindsight bias on presence of predictors by dictating which data on potential predictors had to be present in all medical records and by personally monitoring patient evaluations. Researchers, therefore, only rarely had to ask trauma team members for additional information on potential predictors in retrospect.
Third, the findings of our study have not been externally validated in different trauma populations and settings. External validation is needed for three reasons:
- The performance of our model is likely to be over-optimistic: The model was created in the same sample of patients in which the performance was determined and should therefore be evaluated in a new sample of trauma patients in our centre.
- External validation should furthermore be carried out to evaluate our model in other centres: The definition of some clinically relevant injuries (such as occult injuries for which the care level was upgraded or additional diagnostic work-up was needed) is institution- and clinician-dependent.
- The costs, effectiveness and impact on patient quality of life of CT in chest injury diagnosis should be further investigated.