Taking care of patients with neurological injury means managing their intracranial pressure, or as it’s commonly called, ICP. And when we say neurological injury, keep in mind that we’re not just talking about people getting bonked on the head with a 2 x 4. We’re talking about space-occupying lesions, hydrocephalus, intracranial hemorrhage, subdural/epidural hematoma, even severe hyponatremia…basically anything that’s a key player in (drum roll please….) the Monro-Kellie doctrine.
What is the Monro-Kellie doctrine?
Soooooo glad you asked! This elegantly simple, yet highly applicable, doctrine tells you pretty much everything you need to know about WHY we must manage ICP. Inside the skull cavity there are three things taking up the space there…the brain, the blood and the CSF. Now, because the skull is a FIXED compartment, it’s not going to expand and contract as the brain, blood or CSF increases in volume. So, the Monro-Kellie doctrine states that the volume of these three things is CONSTANT. So, if one of the three grows in volume, one or both of the other two must decrease in volume. For example, if you’ve got a big ol’ subdural hematoma (blood) taking up a bunch of space, the brain is going to get squished. If the brain is edematous (as often seen in traumas), then the blood and CSF flow is going to be decreased. Your role as the nurse is to try to keep perfusion going to the brain despite whatever else is going on. Remember, blood flow is key!
When we talk about blood flow, what we’re really talking about is cerebral perfusion pressure, or CPP. To calculate your CPP, you’re going to use this super simple formula: CPP = MAP – ICP. So as your ICP goes up, your CPP goes down. We typically like CPP to be above 60, and ICP below 20. Keep this in mind as we discuss techniques for managing ICP, which range from the basic to the uber complex. We’ll start with the easy-peasy stuff and move on to the big guns. Ready?
Basic ICP management interventions
As you are taking care of your neuro patient with ICP issues, you’ll want to ensure you do all the basic ICP management stuff:
- Maintain the neck in neutral alignment: This ensures optimal flow of CSF out of the skull cavity.
- Raise HOB: Studies show that keeping the HOB at 30-degrees helps CSF flow adequately to maintain the desired ICP.
- Avoid severe flexion at the hips: Flexion can cause increased intra-abdominal pressure, which leads to increased intrathoracic pressure which leads to…you guessed it…increased ICP.
- Consider loosening tight C-spine collars (with MD approval): While C-collars are fantastic for keeping the neck in neutral alignment, tight collars can impede CSF flow.
- Maintain a normal temperature: The thermoregulation center in the brain gets thrown all out of whack when the brain is unhappy. Plus, any kind of penetrating trauma to the brain OR surgery is going to increase the risk of infection and the corresponding fever that comes with it. Tylenol is the go-to, with ice-packs placed at groin and axilla a close second. Cooling blankets are also used, but I’m pretty sure that requires an MD order. Note that shivering increases ICP, so be watchful! In super-sick patients with difficult-to-control temperatures, you may have to paralyze the patient to eliminate shivering. More on that later.
- Hyperventilation: Though not as commonly used as in the past, hyperventilation can be used short-term to get a critically high ICP down stat! Recall that CO2 is a potent vasodilator. By blowing off CO2 through hyperventilation, we lower CO2 leading to arterial vasoconstriction…this lowers cerebral blood flow, cerebral blood volume and ICP. I recently took care of a patient with a pretty severe bleed. We performed a sedation holiday (meaning we turned of all sedation in order to assess true neuro response) and the patient’s natural breathing pattern was one of severe hyperventilation. This was the body’s physiologic response to elevated ICP…it was trying to get the pressures down any way it could. The respiratory rate climbed to 40-50 per minute with extreme accessory muscle use. We had to abort the holiday, put the patient back on sedation…and even considered paralytics because it took so long for the breathing to normalize. And yes, it was a bit tense.
Taking it to the next level
- Sedation: Drugs like propofol are often used for sedation to reduce ICP. The issue you will encounter as that these drugs also reduce MAP. Remember your CPP calculation? CPP = MAP – ICP? Yep…your CPP can go down with sedation because the MAP went down…but ICP also goes down…so it’s a bit of a tightrope to walk.
- Mannitol: Mannitol decreases ICP through osmotic diuresis. It’s hyper-osmolar, so it’s going to pull fluid from the cellular space and place it in the vascular space where it is excreted in urine. When your patient is receiving Mannitol (either q 4 or q 6 hours), you’ll need to check a serum osmolality before every dose. Typically surgeons will write orders to hold mannitol if serum osmolality is greater than 320.
- Hypertonic Saline: The most common hypertonic saline solution used is 3%NaCl at 30ml/hr. This is a HIGH ALERT medication so be extra careful! You will be monitoring serum sodiums to ensure it doesn’t get too high. You’ll also want to label the heck out of this line…you do NOT want anyone bolusing hypertonic saline. If sodium levels rise too quickly, this can lead to locked-in syndrome…not a good thing at all. Hypertonic saline works much the same way as mannitol…it is hyperosmolar, so it will pull fluid into the vascular space, thereby decreasing cerebral edema and ICP.
- Barbituates: The big-daddy of sedatives are the barbituates, which is essentially referred to as a “barbituate coma.” This is a medically-induced comatose state in which brain activity is significantly decreased as a way to manage ICP. Typically, barbituates are only used in patients for whom all other medical and nursing interventions have failed. Common ones you’ll see are pentobarbital and phenobarbital.
- Paralytics: Another method for decreasing ICP is to paralyze the patient using something like vecuronium. Note that patients who are paralyzed MUST be sedated…can you imaging being paralyzed and being aware of it? You will also use paralytics for a patient you are aggressively cooling in order to prevent shivering. Paralyzed patients on my unit have to have their sedation level monitored via a Sedline Monitor, and you must measure Train-of-Four every hour…this measures their twitch response to a small electrical stimuli. You place the device against the trigeminal nerve and turn it on…what you’re watching for is how many times the muscle around the nerve twitches. The device bursts four times…your goal (for an adequately paralyzed patient) is to see two twitches out of four bursts. You will titrate your vecuronium gtt to get a “train of four” that is 2/4. Paralytics are super serious meds and you only want to use the minimal amount needed to get to your 2/4 response…and you want to get the patient off of them asap.
- Vasopressors: Sometimes you’ll need to add vasopressors in order to keep MAP high enough to maintain an adequate CPP. I once had a patient with a MAP goal of 100…so he was on three different vasopressors. This can come in handy when you’re having to use a lot of sedation to keep ICP down, but need to combat the hypotension that it causes. Again, you’ll feel like you’re walking a hemodynamic tightrope much of the time when you’re taking care of these patients.
Is there a neurosurgeon in the house?
Sometimes, despite all your best efforts to keep CPP and ICP within range, the patient just needs MORE. That’s where neurosurgery comes in. If your patient needs surgical intervention, here’s what you could expect:
- Decompressive craniotomy: In a craniotomy, a portion of the skull is removed so that the surgeon can get to whatever is causing the problem…usually blood, but could also be a tumor, bullet, AVM, aneurysm or abscess. There’s a great description of it here.
- Decompressive craniectomy: If the surgeon anticipates swelling problems, the bone flap that is removed from the skull is NOT replaced. In the not-so-distant past, these were imbedded in the patient’s abdomen as a way to maintain blood supply to the bone…nowadays they’re typically just put in the freezer and replaced once the swelling subsides. Be very careful when repositioning these patients! Never turn them onto the side with the missing bone and touch gingerly! There’s a brain RIGHT UNDER THE SKIN!!!
- Burr hole: This procedure is sometimes done to remove a big ol’ blood clot from a subdural hematoma. It’s less invasive than a craniotomy, but the purpose is the same…to evacuate blood and give the brain some room to swell.
- Placement of EVD: If your patient has an extra-ventricular drain, then do a happy dance! Not only are they super cool, but they actually give you a little extra control over managing pesky ICPs! Yay! They are, however, high-risk devices so much care must be taken! Though EVDs warrant a post all their own, the down-and-dirty takeaway is to NEVER let an EVD hang or drop below the ordered height as this can over drain the ventricles and lead to ventricular collapse….very bad! An EVD will enable you to not only monitor ICP but drain CSF in order to decrease ICP as needed. Super cool, huh?
So there you have it…an intro to managing ICP in your neuro patient.