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Why it may not be helpful to describe RTC mechanism as a combined speed of impact....
If you hear this handover, what does it tell you about the mechanism of injury and the forces applied to the patient? Can you predict their severity of injury based on this information?
If you hear this handover, what does it tell you about the mechanism of injury and the forces applied to the patient? Can you predict their severity of injury based on this information?
Let’s start by comparing the two examples below:
Two identical cars travel at 50mph in opposite directions and have a head-on collision “combined speed 100mph” OR
One car travelling at 50mph hits a stationary car.
(All cars = same size and mass)
Two identical cars travel at 50mph in opposite directions and have a head-on collision “combined speed 100mph” OR
One car travelling at 50mph hits a stationary car.
(All cars = same size and mass)
All vehicles had a momentum equivalent to speed x mass.
The occupant has decelerated from 50mph to 0mph, & the forces are equivalent. Both drivers have had a 50mph crash.
Have a look at this Youtube video where the G forces & damage were the same:
The occupant has decelerated from 50mph to 0mph, & the forces are equivalent. Both drivers have had a 50mph crash.
Have a look at this Youtube video where the G forces & damage were the same:
Now some would argue that in the head on collision, the total 100mph of kinetic energy was shared between two vehicles, where as in the moving v stationary car there was 50mph shared. However, no one driver sustained all the forces of a 100mph crash.
Now imagine there are two identical cars (the same size and mass) travelling at different speeds when they have a head on collision.
Which patient would you expect to have more severe injuries?
The patient who has decelerated from 30-0mph or 70-0mph? Or are they the same?
Which patient would you expect to have more severe injuries?
The patient who has decelerated from 30-0mph or 70-0mph? Or are they the same?
Next: Force = mass x change in velocity.
If a heavy HGV lorry impacts with a small car at the same speed, the driver of the car will experience greater forces and be more likely to have severe injuries (but this was described as a 100mph combined speed for both drivers!).
If a heavy HGV lorry impacts with a small car at the same speed, the driver of the car will experience greater forces and be more likely to have severe injuries (but this was described as a 100mph combined speed for both drivers!).
Next think about the time to stop. Force = mass x change in velocity divided by time. If the vehicle hits something that crumples/moves, the force will be less as it takes longer to decelerate. Did the driver start braking before impact? Do they have airbags and crumple zones?
How reliable do we think the drivers reported speed is? (mmm)
Does it matter - do I change what I do as a trauma team leader if the est speed is 60mph or 90mph? (no)
So twitter: should we stop using the term "combined speed"?
Let me know what you think!
Does it matter - do I change what I do as a trauma team leader if the est speed is 60mph or 90mph? (no)
So twitter: should we stop using the term "combined speed"?
Let me know what you think!
