Posture effect on ICP

ED Nurse, RN · Dec 31, 2015

Any rapid change in position can cause an increase in ICP bc the fluid can shift from one area to another. The rationale is correct.

combinate · Dec 31, 2015

It seems the "fluid shift" upon sitting upright might cause a pulse (slosh) or two (transient effect), but then, wouldn't gravity have the same old orthostatic effect to pull the fluid down along the spine, causing a decrease in ICP? Another question rationale says "Elevating or lowering the head after lumbar puncture can increase ICP". How come "NCLEX gravity" works different than "Earth gravity"?

Can I take a magic pony to the NCLEX for good luck?

ED Nurse, RN · Dec 31, 2015

It seems the "fluid shift" upon sitting upright might cause a pulse (slosh) or two (transient effect), but then, wouldn't gravity have the same old orthostatic effect to pull the fluid down along the spine, causing a decrease in ICP? Another question rationale says "Elevating or lowering the head after lumbar puncture can increase ICP". How come "NCLEX gravity" works different than "Earth gravity"?
Can I take a magic pony to the NCLEX for good luck?

Fluid does not "drain" down into the spine. This is why people with increased ICP due to increased csf, blood, tumors, swelling, need to have holes drilled in their head or shunts placed to drain the fluid, or worse, part of their skull removed. Any change in position can cause an increase in ICP. This is why people are kept at a strict 30 degrees in bed. Fluid is not "sloshing" around in your head. A shift of the fluid is typically a very small measurement but can cause profound effects. Fluid on one side of the head can cause a midline shift of your brain, a lot of the time this is the point of no return. This isn't "NCLEX Gravity" this is how it actually works.

combinate · Jan 1, 2016

Ok, the increase in ICP is not due to movement dynamics; even without movement, a strict position is prescribed.

The four ventricles are connected to one another and to the space around the brain, and around the spinal cord (one interconnected compartment system). The fluid "circulates", but even if that is very slow (essentially static, as you suggest), the hydrostatic effect of raising the head would increase the pressure going down along the spine and decrease pressure in the head. This is intuitive because we feel the hydrostatic pressure changes on blood and other fluids when we change positions (lying, sitting up, dangling limbs, Trendelenburg ...). There must be an additional mechanism that causes increased ICP in a raised-head posture compared with lying supine or at 30 degrees.

ED Nurse, RN · Jan 2, 2016

Ok, the increase in ICP is not due to movement dynamics; even without movement, a strict position is prescribed.
The four ventricles are connected to one another and to the space around the brain, and around the spinal cord (one interconnected compartment system). The fluid "circulates", but even if that is very slow (essentially static, as you suggest), the hydrostatic effect of raising the head would increase the pressure going down along the spine and decrease pressure in the head. This is intuitive because we feel the hydrostatic pressure changes on blood and other fluids when we change positions (lying, sitting up, dangling limbs, Trendelenburg ...). There must be an additional mechanism that causes increased ICP in a raised-head posture compared with lying supine or at 30 degrees.

You're in nursing school, right? You can believe whatever you would like- I have been in actual practice for almost 8yrs and have seen increased ICP quite regularly throughout my career. Like I said, you believe what you wish- good luck on your NCLEX and in actual practice.

combinate · Jan 2, 2016

I can accept that ICP increases in upright posture compared with lying down.

Now, can someone in the forum please explain the mechanism(s) causing this increase. I tried to explain a couple potential mechanisms, but they don't support the common clinical finding. What does explain the phenomenon?

ED Nurse, RN · Jan 2, 2016

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