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Old 01-09-2009, 02:33 PM
LauraL840 LauraL840 is offline
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Default Intracranial Pressure Measurements

Recently several people have raised excellent points/questions/observations regarding ICP and what's considered 'normal'. I thought I had an intelligent answer (rotflol) or at least something 'of worth' to add because the very same questions bugged me to pieces in the summer of 2007 when DH was at UNC and we kept getting different numbers thrown out at us and none of them came close to making any sense!

That summer I learned that ICP measurements can be taken using three different means (millimeters water, centimeters water, and millimeters mercury - aka - mm H2O, cm H2O, mm Hg). While mm H2O and cm H2O can be quickly interchanged (100 mm H2O = 10 cm H2O), mm Hg and mm (or cm) H20 cannot. They aren't 'equivalent' and I have not yet found a formula to convert one to the other.

Now if that doesn't seem confusing enough, add to it that a patient can be 1) sitting up, 2) in the lateral decubitus position (laying on side), or 3) prone (laying on stomach). AND that each of those positions influences the lumbar opening pressure!

So when the question came up in another post I was going to fire off one of those 'I know the answer, I know the answer' posts and then I went digging some more and found out ... I don't REALLY know the answer and the deeper I dig the deeper the hole gets and the more confusing the answer seems to be!

I think that when a LUMBAR PUNCTURE is performed that the fluid is ALWAYS measured in either cm or mm of WATER. Fluid flows through catheter and into a long glass pipette which is held parallel to the spine.

I also think that when you read measurements taken in mm Mercury that those measurements are taken by more sophisticated equipment (manometers, transducers) and usually through an ICP 'bolt' or access through a shunt, etc.

So I've been mulling it around and googling different terms trying to find out more specifics! And here's what I know (so far):

It's vitally important that you ask the physician taking the pressure what unit of measurement they are using! DO NOT ASSUME that "x" facility measures ICP the same way throughout the facility! What's used in the ER is likely different than what's used in clinic which is likely different than what's used in radiology, etc.
We found that the facility here in NC used both cm water and mm water! And that their documentation was not always clear! DH's record in clinic says his opening pressure (after 3 dry taps) was 15 and low. 15 WHAT? Fortunately I asked her how they were measuring (water or mercury) and she said mm water and that anything below 60 was low ... fast forward to 4 months later when he goes for imaging studies and the neuroradiologist says his pressure is 17 and normal? Huh??? So we go into clarifying and the radiology department measures in CENTIMETERS while the clinic measures in MILLIMETERS ... same facility, two different means of measuring ICP.
Know what circumstances and factors alter ICP and may throw off an accurate pressure reading. The most accurate ICP reading is taken in the lateral decubitus position (with legs in neutral position, not pulled towards abdomen) in a patient who is fully relaxed but not unconscious (some sedation medications also lower ICP). I bet some of you guys are laughing ... how the HECK does anyone with a mind-blowing headache RELAX while someone sticks a 5 inch long needle in their back?

Know that a 'normal' opening pressure does NOT rule out a leak! Persons who leak intermittently or have a very slow leak often present in the 'normal' range. Emphasis on RANGE!
Dr. Gray (Duke neuroradiologist) says that every person their own unique ideal ICP. What is normal for her may be high pressure to 'Jennifer' and low pressure to 'Max'. My husbands highest pressure reading was 17 cm water which is clearly considered normal and possibly on the 'higher' end of normal and FOR HIM it was way too low - he had excruciating symptoms with an opening pressure (in lateral decubitus position) of 17 cm H2O.

With the exception of the 15 mm water reading in clinic, ALL the other LP pressure readings for my husband were NORMAL and he had a leak!
So here's what I've come across so far:

One article says normal opening pressure is 60-200 mm water, which is same as 6-20 cm H2O.

Another (brain injury) site says pressure higher than 60 mm Hg is fatal ... don't know if the site is wrong, because mm Hg don't readily convert to mm H2O ... and I haven't been able to find a conversion for cerebrospinal fluid. And since mm Hg measurements are based on the DENSITY of the fluid, it's important to have either the density of CSF or a conversion factor.

Let's see .... one Mayo study says the mean CSF pressure in 49 patients was 13 +/- 4 mm Hg and that 'normal' was 5-15 mm Hg. Another study of the Mayo study expanded on the comparison between mm Hg and cm H2O and gave the following relative rates:
12.4 cm H20 = 9.1 mm Hg
17.7 cm H2O = 13 mm Hg
and then went on to state that 11-17 cm H20 is considered normal.

Another article showed normal ICP as 8-18 mm Hg and stated that anything over 20 mm Hg was increased ICP.

So, anyone else here seeing a HUGE discrepancy between HOW ICP is measured?
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Old 01-09-2009, 04:25 PM
sadlisa sadlisa is offline
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I suppose this is why one of my doctors stated that not all information on the internet is valid. Which of course I responded with, this is why I need a doctor to help me sort through it.

From what I have heard and read 6-22 cm H2O is normal. The 2 times mine was done the reading was different, but both were normal. I would think it makes a difference if you are a cranial or spinal leaker as well.

I agree there is a HUGE discrepancy. Thanks for looking into it and posting what you found.

Thia
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Old 01-09-2009, 04:25 PM
Sally Girl Sally Girl is offline
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Bless your heart, Laura. I sort of figured you were working on some research.

I dug out what I have on Anna's LP's. I have requested the record of her first LP and her last one (the most important one--that last one)! Neither have come yet in the mail.

The LP report from June 2006 states: "Opening pressure 32 cm, closing pressure 12 cm, after removal of 35 mL of spinal fluid."

This neurosurgeon verbally told me her pressure was 42, but his report said 32. My adult son who was with me remembered him saying the 42 number.

Here is from the Mayo Clinic report of March 2008: "We obtained a spinal tap opening pressure, and it was normal, measuring 8 cm H20."

Thanks, Laura.

Cheryl
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Old 01-09-2009, 05:04 PM
LauraL840 LauraL840 is offline
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I suspect for most people 'normal' is a MUCH narrower pressure range, but because all the 'experts' can't seem to agree, the range is much wider.

For example, Kim was CLEARLY in high pressure and agony at Cedars, but her opening pressure was 22 cm H2O. They told her that was higher than normal, but not alarming. Her brain was alarmed, she was beside herself with pain and moaning in her sleep!

Also, DH had opening pressures of both 12 and 17 cm H2O, both 'normal' and he was leaking both times!

That's what is the most frustrating about what is considered 'normal' and how wide the range seems to be! I know when I spoke with Dr. Schievink in May about this 'range' he mentioned that there really needed to be more than three categories of pressures (more than low, normal and high) and that really the normal category should be subdivided into low-normal, normal, and high-normal. I don't know that everyone in medicine will ever agree on it, that's for sure!
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Old 01-09-2009, 06:59 PM
Sally Girl Sally Girl is offline
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I have read people on the PTC forum say that their pressure gets as high as 50-60.

I wonder what Anna's "sweet spot" is. The best she has ever been (head pain wise) was right after being shunted (while laying flat on her back in the hospital for one week). Hardly any head pain at all. Her shunt was programmed to twelve.

When she had the ICP probe put in her head, the nsg said her opening pressure was ten. Then her pressure dropped down to zero. He said that anesthesia can elevate pressure. So his theory was that when the anesthesia wore off, she dropped to zero.

Then I wonder about IV Ketamine and Lidocaine infusions she has been able to try in Chicago. Her head pain disappears with those infusions. She gets them for pain relief. Do they raise up her pressure for a period of time? Is that why they give her pain relief?

When she had anesthesia for the ICP probe, it was followed by some type of drilling in her head for the placement of the probe. Drilling, pressure on her head would produce head pain. Waking up from that surgery, her head hurt a lot! No pain relief at all--more head pain.

Getting IV Ketamine or IV Lidocaine is one little IV in the arm, and her head is not messed with at all. At some point during the infusion, her head pain goes away completely. Her longest period of pain relief from an infusion was four days.

I'm just rambling here, wondering about things for her.

Cheryl
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Old 01-10-2009, 02:26 PM
vini vini is offline
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Default thanks laura

thank,s laura

very well written less confusing for us now , there are many variables as you explane , also body mass , age ect play a part in whats normal ICP I have heard the term normal pressure hydrocephalus I wonder if leaking can infact cause this state in leakers, when the fluid from my nose is more my ha is less, there are peaks and troughs in production but nausea and balance worse when leak rate high

Cheryl I doubt if shunt setting equate exactly to ICP eg shunt setting 12 may not mean 12 cm h2o

hope anna is feeling a bit better each day
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