The only way to get a true reading of the pressure in the dura is to invade the space. So you can have an LP which many of us have had and a you have said many have post puncture leaks when they are done. Then you get the lie flat and drink caffeine and hydrate talk and if that doesnt work then you get a blood patch. During trauma many times when there is bad brain swelling doctors will drill a hole through the skull and “bolt” the area. They slide a catheter under the skull sometimes in a ventricle of the brain and other times just under the skull but within the cranial cavity. This catheter is then hooked up to a transducer which will give you a constant ICP and is a true measurement of the pressure in your head. These can stay in for days and give you a “trend” of the pressures. The “bolt” term comes from the use a screw that screws into the skull to hold the catheter in place. Also some docs think this is easier on a patients that leak a lot post LP puncture as its the very top of the dura and leakage should not be a factor. That being said its still a pretty big deal and i have had one.
Next, there seems to be some misunderstanding of Cerebral Perfusion Pressure ( CPP) on here. Yes folks have the calculation right- CPP= MAP(Mean Arterial Pressure) – ICP ( Intracranial Pressure). CPP is used to asses whether the brain is getting enough oxygen and nutrients when there is severe swelling, usually from trauma or a tumor. You can not estimate any of the numbers. To get a true CPP you need to have a true MAP which is pretty easy (diastolic pressure- 1/3 (systolic-diastolic). So if you took your BP and it was 120/80 then the formula would look like this 80+ 1/3 (120-80). 80 + 13 would give you an MAP of 93. The only way to get the next number (ICP) is to invade the dural space with an LP or a bolt in the head. You cant estimate. The formula is set up to give you a CPP as you cant guesstimate any numers. So in my example if your MAP was 93 and your ICP was 20 then you would have a CPP of 73. The last 15 or so years the trend in trauma and brain injuries has always been to “optimize” the CPP by elevating the blood pressure on very sick patients. CPP Below 60 and most believe you are not “perfusing” your brain and are having irreversible brain damage. If you falsely elevate the BP on these patients with IV medications then you can increase the CPP regardless of how high the ICP is just by manipulating the calculation. All sounds confusing but its not and is very useful with traumatic head injuries. really not so much for us. I dont know if that helps or not