Critical Care Theory (Neuro)- Help!

Published

I have an exam this Thursday over Neuro. We are discussing tumors and my notes say that when there is a tumor in the brain, vascular volume/CSF increase, and ICP also increases. I'm told this a compensatory mechanism, it's called autoregulation.

OK- I think I may be completely off but here's my shot at understanding this.

For some reason the presence of the tumor activates this mechanism to increase cerebral perfusion. Increased CSF will have to go back into circulation, correct? I found a diagram that said:

> CSF = > Central venous pressure through the Jugular Vein.

So basically it's increasing venous return? increasing CO? increasing cerebral perfusion?

GAH! I refuse to just memorize what the notes say )=

Then my notes say autoregulation can lost due to injury from the tumor itself.

CO2 will relax smooth muscle (vasodilation) basically will increase the CBF.

I scavenged by book and notes for this ... but is there a way we can control CO2 for desired outcomes. Are there circumstances in which patients are at risk for cerebral ischemia in where we can control this? Is it the ventilator settings?

(also does the vasodilation happen only at the cerebral level)? How could vasodilation improve CBF (cerebral blood flow) is vessels were peripherally vasodilated?

I have here that acidosis can cause vasodilation and thusly a decrease in autoregulation, so I imagine this vasodilation is peripheral?

Also, autoregulation can be both bad and good?

I would appreciate your help.

Thank You

Up Vote Up Vote ×
Specializes in Critical Care, ED, Cath lab, CTPAC,Trauma.

I will answer this...but I am on the run....the brain is complicated.

Hyperventilation and decreasing the ICP in by vasodilitation (vasoconstriction) increases (decreases) the (cerebral blood flow) venous return and there by decreasing swelling (flow) and decreasing the ICP....to a point....too much lowering of the CO2 will cause cerebral (anoxia/ischemia from severe vasoconstriction)edema. The cerebral blood flow is increased because the cerebral swelling is decreased......I'll be back. :)

Up Vote Up Vote ×

OKAY! I think I got it. I have continued my research and I actually re-listened to the lecture and I did some search on AN combined with your response I think I am getting closer to getting it.

The tumor causes an increase in ICP and THAT is what causes the autoregulation to kick it. It's going to displace the CSF and it will exit out into the JV.

OK.

Next.

CO2 is acidic and therefore CO2 will cause vasodilation. Vasodilation means decreased CBF.

For this reason we want to "blow off" as much CO2 as we can WITHOT increasing the ICP

because an extreme drop in CO2 will actually cause increased ICP.

So vent setting could include: Increasing respiratory rate and expiatory volume. (this will IMPROVE the CBF but we need to be weary of the ICP)

I hope this is right.

Thanks for your help Esme!

Up Vote Up Vote ×
Specializes in Critical Care, ED, Cath lab, CTPAC,Trauma.
OKAY! I think I got it. I have continued my research and I actually re-listened to the lecture and I did some search on AN combined with your response I think I am getting closer to getting it.

The tumor causes an increase in ICP and THAT is what causes the autoregulation to kick it. It's going to displace the CSF and it will exit out into the JV. :up:

OK.

Next.

CO2 is acidic and therefore CO2 will cause vasodilation. Vasodilation means decreased CBF. (no it means and increase of the CBF/ is you decrease the swelling there is more room got the blood to perfuse the brain...right?)

For this reason we want to "blow off" as much CO2 as we can WITHOUT increasing the ICP

because an extreme drop in CO2 will actually cause increased ICP. (Yes)

So vent setting could include: Increasing respiratory rate and expiatory volume. (this will IMPROVE the CBF but we need to be weary of the ICP) Well.....both the rate and the Tidal volume are considered....the volume you put in you should get back

I hope this is right.

Thanks for your help Esme!

decreasing the CO2 will cause vasodilitation which increases the venous return (outflow) thereby decreasing the swelling of the brain......http://www.trauma.org/archive/neuro/index.html......

If you decrease the swelling you will increase Cerebral blood Flow and CPP (cerebral perfusion pressure MAP-ICP= CPP)....TRAUMA.ORG : Neurotrauma : Cerebral Perfusion Pressure

If you "blow of" to much CO2 you will cause cerebral swelling/edema thereby decreasing venous return and increasing the ICP....TRAUMA.ORG : Neurotrauma

Up Vote Up Vote ×

Decreasing CO2 causes vasodilation?

I thought that CO2 = vasodilation.

If CO2 = vasodilation

Increased CO2 causes an increase in ICP

according to http://trauma.org/archive/neuro/icpcontrol.html

"Carbon dioxide dilates the cerebral blood vessels, increasing the volume of blood in the intracranial vault and therefore increasing ICP."

Hyperventilating a patient will "blow off CO2" so in the premise that CO2 causes vasodilation and increased ICP ... hyperventilating will causes a decrease in ICP? Correct?

Decreasing the ICP will improve the cerebral blood flow?

As evidenced by this mathematical equation, correct?

CPP = MAP - ICP

Example: A) 60(MAP) - ICP (15) = 45(CPP)

Example: B) 60(MAP) - ICP (10) = 50(CPP)

This justifies that a decreased intracranial pressure leads to a higher CPP (cerebral perfusion pressure)

Up Vote Up Vote ×

I'm going to ask my professor what exactly he wants me to know! I'm running in circles! :banghead:

Up Vote Up Vote ×

Hyperventilation, or decreasing the CO2 level, is going to cause a cerebral vasoconstriction, not vasodilation. This is why, in the past, patients with traumatic brain injury were vigorously hyperventilated; however current guidelines no longer recommend routine hyperventilation.

The current Guidelines for the Management of Severe Traumatic Brain Injury are available on the Brain Trauma Foundation's guidelines page.

Up Vote Up Vote ×
Specializes in Critical Care, ED, Cath lab, CTPAC,Trauma.

Jeeze......:banghead: I am such an idiot.....:banghead:

I have been so sick......and way too much on my plate......you are right.

Hyperventilation lowers intracranial pressure (ICP) by the induction of cerebral vasoconstriction with a subsequent decrease in cerebral blood volume. The downside of hyperventilation, however, is that cerebral vasoconstriction may decrease cerebral blood flow to ischemic levels....I am so sorry....SoH.:banghead:

You guys have it correct.....my bad. I am so sorry.....sigh

But the links are good..:shy:

Up Vote Up Vote ×
Specializes in Critical Care, ED, Cath lab, CTPAC,Trauma.
decreasing the CO2 will cause vasodilitation (vasoconstriction) which increases (decreases) the venous return thereby decreasing the (cerebral blood flow allowing a temporary stop gap measure) (to decrease blood flow to the) swelling of the brain......http://www.trauma.org/archive/neuro/index.html......

If you decrease the swelling you will increase Cerebral blood Flow and CPP (cerebral perfusion pressure MAP-ICP= CPP)....TRAUMA.ORG : Neurotrauma : Cerebral Perfusion Pressure (this is OK)

If you "blow of" to much CO2 you will cause (a decrease of cerebral blood flow that will damage the brain) cerebral swelling/edema thereby decreasing venous return and increasing the ICP....TRAUMA.ORG : Neurotrauma

I corrected as best I can my garbage .

This is the exact opposite......I was sleep deprived but the links are good sorry. Back for a nap.

Up Vote Up Vote ×

Ah! Thank you, y'all. I always always appreciate your help. Please DO know that.

Get some shut eye Esme, hope you feel refreshed and well rested.

Up Vote Up Vote ×

Increased ICP will decrease the sizes of the ventricles and decrease the amount of CSF but it doesn't exit the head via the jugular vein. CSF is continually produced and absorbed in the head-- if there is higher ICP it is harder for fluid to turn into CSF, and the ventricles, being compressed by increased intracranial edema or a tumor mass or a bleed mass, won't hold as much CSF.

"> CSF = > Central venous pressure through the Jugular Vein."

This doesn't mean JV pressure increases because somehow it's filling up with CSF. I don't know what it really says, but that's not what goes on.

Or am I missing something you're assuming?

Yes, people with high ICP are managed with lots of things-- we up their serum sodiums by decreasing free water intake and meds to increase water loss, which sucks water out of cells, decreasing cerebral edema (useful after trauma or stroke-related cerebral edema) and also sedate the heck out of them and hyperventilate them to a CO2 in the lowish 20's, the better to decrease the amt of blood in the cerebral vessels.

Up Vote Up Vote ×

I'm assuming that the mechanism you're describing (less csf being produced in response to IICP) is autoregulation?

Because I began to think... if CSF production reduces, why do we use ventriculostomy?

Its because autoregulation mechanism can be damaged by whatever is causing the IICP (trauma

Up Vote Up Vote ×
+ Add a Comment