Now don't quote me on this, but see if this makes sense to you. I think where they are going with nixing the lumbar puncture on these patients has to do with the pressure within the spinal column. I couldn't find in my notes where she said to never do a lumbar puncture on pts with increased ICP, but here's what a I found in my critical care book:
Reduction of ICP by CSF drainage:
Accomplished only by using intraventricular or ventriculostomy systems. To prevent herniation when draining CSF, drainage collection bags must be maintained at the level of the tragus of the ear or higher, thereby preventing excessive CSF flow caused by higher-to-lower pressure gradient.
I'm pretty sure she mentioned herniation in her lecture when she was on her soapbox about not doing the lumbar puncture. It makes sense to me.
Now, wouldn't the same principal apply with the lumbar puncture? It's well below the ventricle of the brain and if there's a lot of pressure (intracranial bleed for example) on the brain tissue above the ventricle, it could force the cerebral tissue into the space against the mid brain (aka CNS control center)as a result from a vacuumlike suction from the pressure being released from below. This would result in a herniation (central, I want to say).
Sorry, if this wasn't too organized. I was trying to think "aloud" on paper. I definitely think this is where they are going with regard to not wanting to do a lumbar puncture on these patients.
When is your test? I'm actually shadowing on a Neuro floor tomorrow and I definitely want to ask this. I'll have a for sure answer tomorrow. Good luck on your test too!