Intracranial Pressure ICP

In this lesson, we’re going to talk about Intracranial Pressure - what it is and why it is SO important that we keep it within normal range.

So Intracranial pressure or ICP is the pressure inside the cranium - or the skull. The normal pressure is 5-15 mmHg. Once you hit 20 or more mmHg, the patient needs intervention immediately. Now - the basis for understanding ICP and why this creates problems for the patient is the Monro-Kellie Hypothesis. If you can understand this, all of the issues and treatments will make sense. Monro-Kellie says that the skull is a fixed box - it doesn’t expand or contract, therefore the total volume inside the box is fixed. It also says that there are three things within that box: brain tissue, blood, and cerebrospinal fluid, or CSF. These all exist in certain proportions and volumes within the skull. If one of those things increases in volume, the others HAVE to decrease - because there is NO room.

You can see here that there is extra blood here. This is taking up space and it puts pressure on the brain tissue. You can see it has shifted the brain tissue over and it has collapsed the ventricles. There was no more room for that CSF so it has been moved out of the skull. The more this blood increases, the more and more pressure will build up because there’s nowhere for it to go! Eventually this can cut off blood supply to the brain or even cause herniation.

Now, herniation is when part of the brain tissue is pushed or squeeze through another structure in the skull. The most common example is when the brain tissue is compressed so much that it ends up squeezing through the foramen magnum here at the bottom. This will cause devastating damage to the brainstem. Remember we talked about how the brainstem controls the most primitive reflexes we have, like breathing. So if the brain herniates through this hole, it will destroy and cut off the brainstem, and this will cause Brain Death. So ultimately we want to monitor and control ICP before it has these devastating consequences.

So what will we see if our patient has an increased ICP? Well first and foremost you will see an altered LOC. Refer back to the LOC lesson for details, but one thing we want you to be aware of is that sometimes these changes are very subtle. I may even ask the family “Is she acting like herself?”. We’ll also look at pupils as well as look for posturing or babinski reflexes - be sure to review the neuro assessments lessons for a refresher on those. And as ICP increases, we may also see seizures. Now, remember the big risk is herniation if ICP gets too high. The classic sign of impending herniation is Cushing’s Triad. The 3 things here are abnormal respirations, remember the brainstem is under pressure so our breathing response is affected. We will see pulse pressure widening. They may start with a blood pressure of 120/80, then you look up and it’s 220/60. That difference between systolic and diastolic is much larger because that systolic pressure is going up and up and up, trying to perfuse the brain. And then you’ll also see reflexive bradycardia. They also will struggle to regulate their temperature because of the pressure on the hypothalamus - these patients may have a super high temp, like 104 or higher.

So the main goals of our medical interventions are to decrease the total volume in the cranium. We have 3 things we can work to decrease: brain tissue (as in swelling), blood volume, and CSF volume. One of the things we can do is intentionally hyperventilate the patient - this blows off more CO2 and allows for what we call permission hypocapnia - usually a pCO2 around 30 mmHg. This will cause cerebral vasoconstriction - so that will decrease the total circulating blood volume within the brain and allowing a bit of pressure relief. We will also give osmotic diuretics like mannitol or hypertonic solutions like 1.5% or 3% saline. The goal with these is to pull fluid out of the tissues so that it can be circulated and excreted through the kidneys. That will help to decrease the swelling and fluid in the brain. Then, finally, we’ll give corticosteroids to help decrease any swelling or inflammation in the brain.

Now, we know that if you sprained your ankle - it would swell up and expand, right? The same thing happens with damage to the brain, except it doesn’t have room to swell. So when we do see a lot of bleeding or swelling, we have some surgical options we can use to give the brain more room to expand. First is a craniectomy, also known as a bone flap. The surgeon will actually remove a piece of bone from the skull and save it. That gives the brain a place to expand out while it swells. Then, when the swelling goes down, we will replace the flap and secure it back in place. The other option we have is great for patients with head bleeds or hydrocephalus. It’s called an external ventricular drain. It may also be called an EVD or a Bolt. So what happens is the surgeon will drill a hole in the skull and insert a catheter into the ventricles. Then we’ll connect it to a pressure monitor and a drain like this one. The doctor will order us to level it at a certain point. Usually between 10 and 15 cmH2O. If you can see here, 10 cmH2O correlates to between 7-8 mmHg. So, anytime the patient’s ICP goes above 7 or 8 mmHg, their CSF will drain out. Now, you don’t need to know much about this as a new grad, but the MOST important thing is that you NEVER clamp this except while you’re zeroing it or if the doctor specifically says to. If the CSF can’t drain, the ICP will keep going up and the patient could herniate.

So when we’re caring for a patient with increased ICP, we of course need to monitor and assess pupils and LOC - those are our staples. In fact, we will likely be doing neuro checks every 1-2 hours. An important note here is that we will avoid sedatives or CNS depressants as much as possible so that we can get accurate neuro checks. We will also monitor their temperature as well as their electrolytes - especially if they’re on mannitol or hypertonic saline because this can affect sodium levels. Our other nursing interventions will be aimed at minimizing their ICP. First, we want to keep their head of bed between 30-45 degrees. Any lower and blood flow to the brain increases, any higher and the intrathoracic pressure increases so much that the blood can’t flow OUT of the brain as easily. We will also decrease stimuli and decrease any valsalva actions. This would be bearing down or coughing - so we give stool softeners and minimize how often we suction intubated patients, and we make sure they stay calm. Then, of course, if they have an EVD we need to make sure it’s leveled at the right place and open to drain.

Let’s recap quickly - intracranial pressure is the pressure within the skull. The Monro-Kellie Hypothesis tells us that the skull is a fixed box filled with brain, blood, and CSF and that if one of those increases in volume, the others must decrease or the pressure will go up. We will do frequent neuro checks including pupils and LOC and assessing for signs of Cushing’s Triad. We provide interventions to decrease the volume in the skull, such as permissive hypocapnia, osmotic diuretics like mannitol, and corticosteroids to decrease inflammation. And we have surgical options like a craniectomy or EVD to provide more room within the skull. Ultimately we want to keep ICP low and prevent devastating herniation.

So those are the most important things you need to know about increased intracranial pressure. Make sure you check out the lesson on Cerebral Perfusion Pressure to understand more about how this impacts our care of these patients. Go out and be your best selves today. Happy nursing!