> Simon is correct that on transition from a stationary position to forward
> motion there is inclination of the nose of a helicopter for a few moments
(
> 5 to 10 seconds) before leveling out, although there is always a small
> (less than 10 degree) residual inclination.
>
> Changing the location of the head of the casualty would also mean the
need
> to move the attendant so that they can attend to and continue to assess
the
> airway / communicate with the patient. The shift in weight in the HEMS
> Dauphin would alter the centre of gravity of the aircraft and create
> aviation problems.
>
> In a Twin Squirrel (Kent / Lancashire / HEMS stand-in aircraft) the head
is
> at the rear, again so that the head can be attended to.
>
> I worry about significant issues such as adequate oxygenation and
cerebral
> perfusion pressure in the critical heads, rather than a degree of "head
> down" for for the relatively short flight times. This is where the
> secondary injury can be minimised. Only in an ITU setting where
inclination
> is maintained for long periods might there be a significant difference in
> ICP.
>
> In an ambulance that goes from stationary point to stationary point the
> acceleration and deceleration forces must be equal - Isaac Newton ;-)
>
> Let's try keep things in perspective and be practical.
>
> DPW
> Yorkshire
Darren is quite right, the major component of preventing secondary injury
is acheiving adequate perfusion and oxygenation. The other factors
discussed are likely to be of lesser importance. I was merely thinking
around the original question (working with the gas board tends to make you
think physics all day!)
In reply to your comments regarding acceleration/deceleration. Overall
change in speed is equal and indeed the forces required to acheive this are
equal. However, accelaration (change in unit speed per unit time) is
different. I know that the acceleration in a Ferrari pelting to 100mph is
considerably higher than that in our Peugeot 106! Same with deceleration.
My point was that road vehicles can create greater deceleration forces than
acceleration forces (brakes better than engine - a good combination). I'll
try to not mention physics again (I hope I am right???).
Does this make a difference to our hypothetical head injured patient? I do
not know. I thought about testing it a while back but could not come up
with a good enough model. Seems a reasonably easy idea for a project if a
suitable model could be found. (change in ICP would be the outcome
measure).
I have heard of a study that showed a persistant change in ICP head injured
patients tilted head down for a very short period. I will try and find this
paper on Medline to see if it is true.
Simon Carley
Anaesthetics / Intensive Care
Stepping Hill Hospital
Stockport
England
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