Increased Intracranial Pressure (ICP)

Definition/Etiology:

Intracranial pressure is… the pressure in the cranium. I mean that’s a simple way of saying it, but it is the sum of the pressure exerted by the brain, blood and cerebrospinal fluid that is housed in the skull.

An increase in ICP can occur from a non-traumatic event such as a stroke, but more commonly, is due to trauma. Falls, MVC, struck by or against events (Its football season as i create this lecture and there have been some pretty severe injuries over the years), and assaults all can cause head injuries that lead to increased ICP. The CDC estimates that 1.7 million people sustain a TBI annually.

Pathophysiology:

The skull contains 3 things. Blood, Brain and cerebro spinal fluid (CSF). Normally if one of these increases, the others adjust to compensate. When swelling or fluid gets too great, ICP rises. When this happens, this stuff has nowhere to expand to, so it just slides down through the foramen magnum, also known as “herniation”. When ICP exceeds the mean arterial pressure, all blood flow to the brain ceases. Our job is to make sure this doesn’t happen.

Let’s take a second to talk about the Monroe Kellie Doctrine. No this isn’t paperwork that was signed to end WWI. The Monro-Kellie doctrine states that the skull is a rigid compartment and contains three components: brain, blood, and cerebrospinal fluid. If an increase occurs in the volume of one component, the volume of one or more other components must decrease, or ICP will be elevated. When this is prevented, for whatever reason, ICP rises.

Clinical Presentation:

Much like any head injury, symptoms can be varied. First, we want to assess LOC or level of consciousness. From there, being aware of your neuro assessments is very important.

We’re not going to go into signs of a head injury. Firstly, you know most of them (i know you do) and secondly, here we are more concerned about the signs that ICP is rising.

Increased ICP activates the Cushing reflex, a nervous system response resulting in Cushing’s triad.

Cushing’s triad, which is a sign that ICP is rising, is composed of bradycardia, irregular respirations, and a widened pulse pressure (that’s the difference between the systolic and diastolic. For example… 120/80, good. 160/60, not so good.) Some also include an increasing systolic as part of the triad instead of the respirations.

In addition to Cushing’s, some pretty common signs that the ICP is going up would be a change in behavior, or LOC, weakness, (which may actually come before the vitals change), lethargy, a more severe headache, blurred vision and anisocoria. (What is aisocoria, it’s just a cool word for unequal pupils)

Collaborative Management:

So, what do we do? Well, here is where we need some math. When we worry about an increased ICP, we worry that the brain is not perfusing. Not getting what it needs. We need to maintain a good Cerebral Perfusion Pressure. “But Mike, you never mentioned that before!” Well…. I just did. The CPP is just what it sounds like, it’s the amount of pressure needed to perfuse the brain. The normal CPP is between 70-100 mm/Hg. The way we figure this out is pretty simple. Just subtract the IPP from the MAP and you get the CPP.  That also easy…just look at the monitor and it should tell you. Usually, the number in a different color under your systolic and diastolic. If not, stay with me here… double the diastolic, add the systolic and then divide by 3.

OK so there’s some brain math for ya. As far as testing…. I think it goes without saying that we need a CT of the head. If there is an increasing ICP, it might be nice to know why.

To treat the problem:

• We need to increase the MAP. Fluids, pressors, and blood can all do this.
• We need to decrease vasodilation. Easy, elevate the head of the bed. We can also give diuretics like Manitol.
• WE also need to manage their Ph level as acidity can cause vasodilation which we do not want. CO2 is an acid. Respiratory acidosis is real in these patients. We need to manage their O2 and ventilations. But this is tricky. Hyperventilation, which will deliver more O2 and better perfuse the brain….is good. But hyperventilation also can increase intrathoracic pressure which in turn increases ICP… which is bad. There is a fine balance, and it is individual to the patient.

Evaluation | Patient Monitoring | Education:

We need to keep an eye on all the things we talked about. The ICP, the MAP, the CPP, the Co2 level, Oxygen status. These are all vital pieces of information when treating these patients.

One of the best ways to monitor ICP is with an ICP monitor. I’m not going to get in depth, but just know that you drill a hole and place a device in the skill that will monitor the pressure for us. It also helps to drill that hole to let a little of that pressure out. This is something that may or may not be done in the ED as its usually an ICU procedure. But…well i don’t have to tell you guys about ICU in the ED these days.

We want to avoid the “H Bombs” as best we can. Hypoxemia, hypercapnia, and H+ (respiratory acidosis) are all vasodilators. Cerebral vasodilation causes an increase in blood to the brain and a subsequent increase in ICP.

Linchpins: (Key Points)

• Prevent the “H Bombs”
• Maintain CPP
• Prevent vasodilation
• Be aware of changes