Airbags have had a significant effect on decreasing fatalities in high speed motor vehicle collisions. However they are also responsible for injuries, in most cases minor, in approximately half the cases where they are deployed. Not wearing a seat belt and sitting less than 25cm from the bag, predicts a subgroup of patients that are more likely have severe injuries, including 6-7 times more likely to have cervical fractures. However other injuries such as carotid artery dissection can also occur.
Airbags are deployed by deceleration sensors and inflate with a velocity that averages over 200km/hr. The total inflation takes less than 10ms. The first stage of inflation causes the sternal injuries. The second stage causes the displacement of body parts.
A 50 yo woman presents to the Emergency Department following a high speed deceleration injury, where she crashed her car into a tree. The patient complains of severe sternal chest pain, and is finding it hard to breath. The ambulance have given 20mg of Morphine. No other injuries are obvious.
Clinical examination was essentially normal, apart from severe sternal pain and pain in the surrounding ribs. There was a lower abdominal seatbelt mark, however the abdomen was soft and the FAST scan normal. Log roll was normal. Investigations included a CT chest an aortogram looking for thoracic dissection and Ct angio looking for carotid artery dissection. Labs included a Troponin and an ECG was done. The aortogram was straightforward, deceleration injury and severe chest injury. Why would we want carotids when the patient had no neurology? Read on.
There are 4 types of Airbag injury that can occur:
- Schrapnel injury from the bags themselves. Although there have been recalls, there are still cars with these type of ‘Takata’ airbags
- Injures to the face: Usually involving the eyes and include: Abrasions, contusions, hyphaemas and retinal detachments. patients wearing glasses will have potentially more severe injuries.
- Thoracic Injuries: These include sternal fractures, rib fractures, pneumothoraces, chest wall burns
- Cardiovascular Injuries: Aortic transection, carotid artery dissection, cardiac contusions, delayed right atrial rupture and valve(tricuspid, aortic) injury.
In sternal fractures where there is a suspicion of cardiac contusion, the patient should have an ECG, a troponin and an echo. A normal ECG and Troponin have a negative predictive value for cardiac injury of 100%. Cardiac contusions with an abnormal ECG and troponin can be mistaken for an infarction. Coronary spasms can lead to arrhythmias. These patients need angiograms.
There is also an association with carotid artery dissection. Patients can present with neurological sequel, that includes hemiplegia and Horner’s Syndrome. However some patients are asymptomatic at presentation and can remain so, for up to 10 hours.
Treat these as deceleration injuries. Be aware of those patients that may not have been wearing a seatbelt and think of the carotids.
High speed(> 100km/hr) deceleration injuries, especially with sternal injuries, where airbags have deployed, and even moreso when they have not, should be investigated as deceleration injuries and an aortogram considered. A chest Xray may give enough information to avoid an aortogram. If there is serious suspicion of a cervical injury, also think of potential carotid injury, even if there is no neurology
- Khozan R N. et al., Next Generation Airbags and the Possibility of Negative Outcomes due to Thoracic Injury. Can J Card 30(2014)396-404.
- Wallis LA. Greaves I. Injuries Associated with Airbag Deployment. Emergency Medicine J 2002; 23:490-493
- Mednkour A. Tabbara AK. Airbag Associated with Bilateral Carotid Dissection and Hyperdense Middle carotid Artery Sign: A Case Report. The Internet Journal of Neurosurgery 2011.
- Duncan M A. et al., Traumatic Bilateral Internal Carotid Artery Dissection Following Airbag Deployment in a patient with Fibbromuscular Dysplasia. BJA. 85;3:426-428