|Traumatic rupture is a rare and lethal injury in patients sustaining blunt chest trauma. The chest radiograph remains a useful means to screen the thorax for aortic injury. A normal chest radiograph virtually excludes aortic rupture. In the past, an abnormal chest radiograph was investigated with an aortogram to exclude rupture. However, the yield was low. CT has been used as a means to better select those requiring angiography. Most recently, spiral CT has been investigated as a means for primary diagnosis, with promising results.
The chest radiograph is important to screen for a variety of injuries which occur in the blunt trauma victim. The ABC's approach is a useful pneumonic to survey for these injuries.
|ABC's Blunt Chest Trauma
- A: Aortic Transection
B: Bronchial Fracture
C: Cord Contusion
D: Diaphragmatic Rupture
E: Esophageal Fracture
F: Flail Chest
G: Gas (subtle pneumothorax, pneumomediastinum)
H: Heart (cardiac injury)
I: Iatrogenic injury (misplaced tubes and catheters)
no vehicle occupant restrain device used, or unknown
Any systolic blood pressure < 90 mm Hg while in emergency department
Rib fracture, pneumothorax, lung contusion, or laceration
lumbar spine fracture, pelvic fracture, or injury requiring laparotomy
Fracture of humerus, radius, ulna, femur, tibia, or fibula
Skull fracture, intracranial or intraparenchymal hemorrhage, or unconsciousness at evaluation
Likelihood ratios are intuitive measures of the diagnostic information provided by a test result or clinical finding. The likelihood ratio varies from zero to infinity, depending on the degree of strength of the test result. A test strongly suggestive of aortic rupture has a likelihood ratio much greater than one, a test that suggests no rupture has a likelihood ratio close to zero, and a test that contains no diagnostic information has a likelihood ratio of one. In the odds-likelihood ratio form of Bayes theorem, the odds that the aorta is ruptured is the product of the likelihood ratios favoring aortic rupture multiplied by the prior odds of aortic rupture.
- Posterior odds = prior odds x likelihood ratios
- = Prob in subjects with aortic rupture / Prob in subjects without aortic rupture
- = Sensitivity / (1 - Specificity)
- = True positive fraction / False positive fraction
- Probability = Odds / (Odds + 1)
- Odds = Prob / (1 - Prob)
When the likelihood of developing disease (or in this case, rupturing the aorta) is low, then the case-control study if often used to study risk factors. The odds ratio is an approximation of relative risk and when the prevalence of the disorder is small. Odds ratio is computed from a 2x2 table as AD/BC.
|Risk Factor present
|Risk Factor absent