USMLE Forums banner

1 - 15 of 15 Posts

·
Registered
Joined
·
216 Posts
Discussion Starter · #1 ·
A 33-year-old man has suffered severe head trauma in a motor vehicle accident. Which of the following precautionary treatments would be most appropriate?

A) Hypoventilation
B) IV Hypotonic Saline Solution
C) IV Thiamine
D) Hyperventilation
E) Lumbar puncture


The Answer is not as important as the underlying mechanism.
Again this is mostly for those who have just started out their Prep for Step 1. Good luck!
 

·
Registered
Joined
·
752 Posts
I think a CT scan would be the best answer to rule out bleeding. But it's not there, so I'll pick LP to rule out SAH at least. This is more Pathology, so I guess it's not the right answer since you say it's a basic physio Q!
 

·
Registered
Joined
·
373 Posts
I think a CT scan would be the best answer to rule out bleeding. But it's not there, so I'll pick LP to rule out SAH at least. This is more Pathology, so I guess it's not the right answer since you say it's a basic physio Q!
The pt suffered a severe head trauma & question asks about the most appropriate precautionary treatment. So doing LP to rule out SAH would be a diagnostic step only....
 

·
Registered
Joined
·
752 Posts
The pt suffered a severe head trauma & question asks about the most appropriate precautionary treatment. So doing LP to rule out SAH would be a daignostic step only....
You're right.

But what about your choice?
 

·
Registered
Joined
·
373 Posts
well the correct answer should be

D) Hyperventilation

Severe head injury lead to inflamation leading to cerebral edema & inc. ICP. Increased ICP would compromise the blood supply to the brain further complicating the injury. So preventing increase in ICP is the key issue immediately following a head injury.

Inc. PCO2 causes dilatation of the cerebral blood vessels, increasing the volume of blood in the intracranial vault and therefore increasing ICP.
So, by hyperventilating the pt cerebral blood flow can be decreased preventing the inc. in ICP.

Hypoventilation would cause the opposite effect, so its not recommended.

Hypotonic fluids are contraindicated in head injury for fear of worsening the cerebral edema.

And as discussed before LP is not a preventive measure in Head injury.
 

·
Registered
Joined
·
216 Posts
Discussion Starter · #6 ·
Excellent Step1an! like I said the explanation is more imp than the answer itself! you nailed it!

you're looking to dec Cerebral edema and Inc intracranial pressure as a precautionary measure!
Hyperventilation is often used to produce a respiratory alkalosis, which in turn produces vasoconstriction and reduces the permeability of cerebral vasculature. This helps to mitigate the formation of cerebral edema.

Hypoventilation would produce a respiratory acidosis and result in vasodilation and increased permeability, exacerbating any potential edema.

IV hypotonic saline would likely worsen cerebral edema.

IV thiamine is used to treat Korsakoff’s syndrome, which results from a thiamine deficiency often associated with long-term alcoholism.

Lumbar puncture is contraindicated in patients with head trauma, as a sudden decrease in pressure within the spinal canal may cause uncal herniation.
 

·
Registered
Joined
·
625 Posts
So in real life - if we have a patient that fell down and hit their head and they have no other symptoms we ask them to hyperventilate just in case to decrease the possibility of cerebral edema?

Since we are talking about mechanisms - again, in real life - wouldn't we put the patient on IV Mannitol?

Thats what I would have picked as an answer if it was an option....
 

·
Registered
Joined
·
216 Posts
Discussion Starter · #8 ·
Since we are talking about mechanisms - again, in real life - wouldn't we put the patient on IV Mannitol?
good Question! sorry I didn't see it here earlier!

There is evidence that excessive administration of mannitol may be harmful, by mannitol passing from the bloodstream into the brain, where it increases pressure within the skull and worsens brain swelling. The research also found that treatment with mannitol may increase the likelihood of death when compared to treatment with hypertonic saline.

Ok well the reason I believe you cannot give Mannitol or any hyperpertonic saline solution is because even in hemorrhage that would create a dramatic Inc (too quickly) in Osmolality and thus according to Dr. Fischer from Kaplan physio as well, that would lead to seizures in the short term....and I guess thats the last thing you want when you have a patient with suspected head injury.

Does anyone else have something they want to add on this subject?
 

·
Registered
Joined
·
373 Posts
hmm its going to be a long post!!!!

When strictly taking about real life or actual clinical practice we cannot make generalizations. In actual practice we follow standard practice guidelines which are evidence based.
So in real life - if we have a patient that fell down and hit their head and they have no other symptoms we ask them to hyperventilate just in case to decrease the possibility of cerebral edema?
Well in order to hyperventilate a patient u would have to intubate & paralyse the pt and put him on a ventilator. So we cann't just hyperventilate a pt which has no other symptoms, to ensure his ICP is not rising.
Since we are talking about mechanisms - again, in real life - wouldn't we put the patient on IV Mannitol?
Mannitol can be used to dec. ICP. But again we cannot put every pt of suspected head injury on Mannitol. Because as mentioned by

There is evidence that excessive administration of mannitol may be harmful, by mannitol passing from the bloodstream into the brain, where it increases pressure within the skull and worsens brain swelling. The research also found that treatment with mannitol may increase the likelihood of death when compared to treatment with hypertonic saline.
For this reason Mannitol is given as a short IV Bolus only instead of continuous infusion.
Also keep in mind that, the key factor determining the outcome of is the Cerebral perfusion pressure

Cerebral Perfusion Pressure= Mean Arterial Pressure - Intra cranial Pressure

Mannitol administration also results in dec. B.P which is dangerous in trauma patients especially with Head injury.

SO the use of Mannitol & Hyperventilation are reserved for those patients who have overt signs & symptoms of Increased ICP.

I hope this clarifies it....:)
 

·
Registered
Joined
·
625 Posts
Thanks so much for explaining guys - I'm a little confused now, I was under the impression that mannitol causes a decrease in ICP because it pulls water out of the CNS as it doesn't cross the BBB. I guess I was way off...

Could you please explain exactly how using an IV bolus instead of continuous drip makes a difference? I guess I don't really understand the entire ICP process and the perfusion equation that you put up.

As far as the intubation is concerned - I know this sounds silly too - but couldn't you just ask the patient to breathe faster instead of intubating them? How fast are we talking in terms of hyperventilation - like over 25?
That does seem excessive if they're walking and talking and all that.

The concept just seems a little strange to me...
 

·
Registered
Joined
·
373 Posts
@ashishkabir

Well your concept still holds true but u have to add a few things...

Regarding Mannitol,

It is an osmotic diuretic and can have significant beneficial effects on ICP, cerebral blood flow and brain metabolism. Mannitol has two main mechanisms of action. Immediately after bolus administration it expands circulating volume, decreases blood viscosity and therefore increases cerebral blood flow and cerebral oxygen delivery.
Its osmotic properties take effect in 15-30 minutes when it sets up an osmotic gradient and draws water out of neurons. However after prolonged administration (continuous infusion) mannitol molecules move across into the cerebral interstitial space and may exacerbate cerebral oedema and raise ICP. Mannitol itself directly contributes to this breakdown of the blood brain barrier.​
Mannitol is therefore best used by bolus administration where an acute reduction in ICP is necessary.

Regarding the equation,
Cerebral Perfusion Pressure= Mean Arterial Pressure - Intra cranial Pressure
I think its quite simple to follow, as brain is enclosed in the bony skull....the cerebral perfusion is determined by both Mean Arterial pressure and the intra-cranial pressure.

Regarding Hyperventilation,

Lets suppose if a pt of head injury has increased ICP, he would not be conscious & cooperative to follow your instruction. He would also have altered consciousness & low GCS.
Also the the conscious awareness of ones respiratory effort is a painful thing (see Ondine's Curse, you can recreate the felling by hyperventilating urself).

I think this explains it....:)

 

·
Registered
Joined
·
24 Posts
but hyperventilation will depress respiratory centre.. Pt of severe head injury has already depressed ventilation.... so hypoventilation can worsen it.... Isnt it??/ plz explain... Im confused....
 

·
Registered
Joined
·
373 Posts
but hyperventilation will depress respiratory centre.. Pt of severe head injury has already depressed ventilation.... so hypoventilation can worsen it.... Isnt it??/ plz explain... Im confused....
Plz explain ur question.. i could not follow which point is confusing you....
 

·
Registered
Joined
·
625 Posts
Thanks so much for that explanation Step1an... it really helps a lot. I agree that hyperventilation without intubation wouldn't work at all :)

@vagp86 - I think if you intubate the patient you control the rate of respiration so your question of depressing the respiratory centre doesnt' come up
 
1 - 15 of 15 Posts
Top