Wow, am I glad to see this being discussed!
I work in an SICU that has many neuro patients. About a year ago, one of our attending doctors who is an anesthesiologist, did a whole bunch of "teaching" on Rounds about leveling art lines at the tragus for neuro pts. This was based on one article he had and the fact that this was the practice on the OR. Before that, we always leveled at phleboststic axis, nobody ever questioned it.
It had never been the practice in our unit before. Because our hospital policy states to level art line at phlebostatic axis, if the docs want us to level the art line at the tragus, we have to get the doctor to write a specific order for that. (and then d/c that order once the ICP monitor is out - we had an instance where a pt was sent to a non-neuro step-down unit and the nurses were still following the order to level at tragus, with no understanding of what it was all about).
It "went viral". The neuro docs went to the neuro step-down and said "the nurses in ICU are leveling at the tragus for their art lines, why don't you do that?" - all with NO real basis for this practice change. It's all been very upsetting.
We haven't been able to find any concrete evidence as to why the practice of leveling an art line at the tragus would be a good thing. All the "norms" and safe pressures in texts (CPP, etc) are calculated using the central pressure at the aortic root. We are taught to shoot for MAP of a certain level because this has been shown to generally perfuse all organs.
Are the proponents of leveling art lines at tragus suggesting that we my be under-perfusing the brains of our non-neuro patients?
If you move your transducer up, really all you are doing is manipulating your zero point. Yes, it may give you different CPP values, etc. But as we say "treat the patient, not the numbers".... The danger is (as stated in the pdf presentation linked on the first page of this thread) of when you do start to treat the numbers and use fluids inotropes, etc.
I haven't been able to find any real clinical research as to the exact pressures found the the COW, how this relates to artline readings at either level point, and how much of a difference this makes.
I agree, it is potentially huge. There are many centers practicing leveling at tragus on the assumption that it reflects cerebral perfusion pressure - but what if their assumption is not actually correct. My centre is one of those places, and it's gone to all sorts of practice committees and physician committees because to make a practice change unless you have decent evident makes no sense at all.