Seems like the UK has noticed these discrepancies. They did a survey in 2006 and found that 6 out of 20 leveled at the tragus. But all used the same calculations to monitor CPP. This seemed to spark debate about the wide variation in practice.
In 2009 they did a lit review to establish a standard of practice. They found conflicting data and no agreement on where the transducer should be placed.
The Brain Trauma Foundation Guidelines 2007 has no recommendations on placement.
It seems that everyone agrees that only one way is correct. But there does not seem that there is agreement. I have been unable to find a standard of practice on this. Either the aortic root is overestimating CPP or the tragus is underestimating it. It can not be both.
CRNAs and Anesthesiologist are taught to level at the tragus as law, but as I said before, I have never seen this performed on a unit.
Here is a very detailed letter about CPP. I have not read it all to varify the math or rational behind it.
Anyone have any literature to back up one practice vs another? Anyone seen any SOP of a major nursing organization?