Carbon Dioxide and ICP

Jackfackmasta, ASN, RN · May 17, 2012

I know that CO2 is a vasodilator at a high level which can increase ICP from the increased blood flow as the body tries to compensate and perfuse the area with more oxygenated blood. In neuro patients lower CO2 causes more vasoconstriction and prevents increased ICP. An elevated CO2 often means a low O2 also.

If they have a high CO2 they are probably in respiratory acidosis and the increased metabolism and work to correct the ph can also increase ICP.

But then I am a new graduate starting STICU in a month..... This is what I am thinking :idea:

Correct me experienced nurses if im wrong

Esme12, ASN, BSN, RN · May 17, 2012

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.

"Modulation of Paco₂ has been used for > 40 years,¹ first in neuroanesthesia and subsequently also in neuro-intensive care. Preliminary work has shown that the volume of the swollen brain could be decreased by lowering Paco₂. With the realization that raised intracranial pressure (ICP) is a significant, treatable problem in patients with traumatic brain injury (TBI), hyperventilation became a cornerstone in the management of TBI and has remained so for decades. Hyperventilation lowers ICP by the induction of cerebral vasoconstriction with a subsequent decrease in cerebral blood volume."

^{Hyperventilation in Head Injury*}

Verbatim · May 18, 2012

Nice! I appreciate the explanation.

Please explain triple H therapy! Or does this have nothing to do w/ increased ICP?

Esme12, ASN, BSN, RN · May 18, 2012

Triple H therapy in reference to what........in the ED/med-surg world triple H theray meant an enema and stood for

"High, Hot, and a helluva lot".

In the neuroworld......Triple H therapy is part of the standard care for patient's that have had a subarachnoid hemmorhage from an aneurysm rupture and then had a repair....either clipping or coiling.

The H's are: Hypertension, Hypervolemia and Hemodilution. So, essentially what they are attempting to do is to keep the vessels in the brain open so that they can't go into vasospasm, which is a HUGE, HUGE risk in these patients. Also used to prevent spasm is Nimodipine (a calcium channel blocker).

Where I worked we would at times keep MAPs (mean arterial pressure) as high as 110, assuming the aneurysm is well secured. The stroke that you're trying to prevent is an ischemic stroke due to the vasospasm clamping down the arteries. So you're willing to risk a high blood pressure for a short period to prevent that.

Think of it this way:

if you're trying to push more liquid (blood) through a tube (a cerebral artery) there are three things that you can do.

You can load up the tube with more liquid, pump up the volume- that's hypervolemia.

You can make the liquid less viscous so it slides through more easily, thinned out - that's hemodilution.

And finally, you can push harder - that's hypertension.

All three have their risks. Hypervolemia risks wet lungs - up to and including pulmonary edema. Hemodilution risks depriving tissue of oxygen, if the H/H is low enough. And, hypertension risks hemorrhagic stroke. It's always a trade-off on the risk/reward graph.

Vasospasm After Aneurysmal Subarachnoid Hemorrhage

I hope this helps.

Verbatim · May 21, 2012

Triple H therapy in reference to what........in the ED/med-surg world triple H theray meant an enema and stood for
"High, Hot, and a helluva lot".
In the neuroworld......Triple H therapy is part of the standard care for patient's that have had a subarachnoid hemmorhage from an aneurysm rupture and then had a repair....either clipping or coiling.
The H's are: Hypertension, Hypervolemia and Hemodilution. So, essentially what they are attempting to do is to keep the vessels in the brain open so that they can't go into vasospasm, which is a HUGE, HUGE risk in these patients. Also used to prevent spasm is Nimodipine (a calcium channel blocker).
Where I worked we would at times keep MAPs (mean arterial pressure) as high as 110, assuming the aneurysm is well secured. The stroke that you're trying to prevent is an ischemic stroke due to the vasospasm clamping down the arteries. So you're willing to risk a high blood pressure for a short period to prevent that.
Think of it this way:
if you're trying to push more liquid (blood) through a tube (a cerebral artery) there are three things that you can do.
You can load up the tube with more liquid, pump up the volume- that's hypervolemia.
You can make the liquid less viscous so it slides through more easily, thinned out - that's hemodilution.
And finally, you can push harder - that's hypertension.
All three have their risks. Hypervolemia risks wet lungs - up to and including pulmonary edema. Hemodilution risks depriving tissue of oxygen, if the H/H is low enough. And, hypertension risks hemorrhagic stroke. It's always a trade-off on the risk/reward graph.
Vasospasm After Aneurysmal Subarachnoid Hemorrhage
I hope this helps.

Excellent! Thank you.

Esme12, ASN, BSN, RN · May 21, 2012

You're welcome.

jkr2020788 · Jun 8, 2012

Hyperventing a pt ( lowering CO2) decreases ICP by means of that already explained by Esme12. In my experience though, hyperventing a pt only works for a alittle while and ICP slowly goes back up.I usually see it being used when a pt has an acute increased ICP. This gives you a little bit of time to figure out WHY the ICP went up though. Again just my exp, I could be wrong.

MeTheRN, BSN, MSN, RN · Jun 21, 2012

Hyperventing a pt ( lowering CO2) decreases ICP by means of that already explained by Esme12. In my experience though, hyperventing a pt only works for a alittle while and ICP slowly goes back up.I usually see it being used when a pt has an acute increased ICP. This gives you a little bit of time to figure out WHY the ICP went up though. Again just my exp, I could be wrong.

You're right. The brain auto-regulates in about 6 hours.