Understanding Intracranial Pressure (ICP)

Bleeding, Swelling and Fluid Buildup Lead to High ICP after Head Trauma

Football players hitting heads
Science Picture Co/Getty Images

 Just like you have blood pressure, which is measured when you go to the doctor’s office, the brain also has an ideal pressure range. The pressure in the brain normally runs between 5 and 15 mm/hg. This pressure is called “Intracranial Pressure” or ICP.

There are several things that contribute to intracranial pressure. First, the bony skull provides a framework. In medical terms this bony skull is called the cranium.

Next, brain tissue fills the space inside the cranium. Finally, fluid fills that space. This fluid includes blood, cerebrospinal fluid and other fluids necessary for normal nerve cell activities.

In order to function correctly, the skull, brain tissue and fluids need to exist at a state of balance. Since the skull is made entirely of bone, it can’t expand. That means that any increase in fluid or tissue will increase the pressure. Here's how head trauma affects ICP:


One of the most common causes of increased ICP after trauma is bleeding into the brain. If the brain is subjected to centrifugal forces during an accident, blood vessels can tear. A penetrating injury can directly cut blood vessels. A blow to the side of the head can damage vessels that run over the brain.

The heart doesn’t know when vessels have ruptured inside the brain. Its job is to constantly supply the brain with oxygen rich blood which keeps nerve cells alive.

After an accident, the heart continues to pump blood into the brain, but some of that blood doesn’t complete the circuit and return to the heart. Instead, it leaks out of the broken blood vessels and starts to build up inside the skull.

This immediately affects the delicate pressure balance. The extra fluid causes intracranial pressure to rise.


Even if there isn’t bleeding, swelling after trauma also increases ICP. If nerve cells are torn or damaged by a lack of oxygen, they release a variety of chemicals, including glutamate. These chemicals are toxic to neighboring nerve cells and a chain reaction of cell death begins.

The body’s natural inflammatory responses rush to the rescue, and this brings extra fluid to the injured damaged areas.

Consider what happens after a mosquito bite. After the bite there is swelling and redness around the sting, as the body’s inflammatory response reacts and tries to limit the damage. It can be a pretty large bump. The same mechanisms are at work in the brain.

However, the extra fluid and swelling around the damaged areas in the brain, increase the intracranial pressure since it’s trapped inside the bony skull.

Build-up of Cerebrospinal Fluid

A condition called hydrocephalus can also contribute to increased ICP. Fluid inside the brain, called cerebrospinal fluid, is produced and stored in the brain’s ventricles.

Cerebrospinal fluid bathes and protects both the brain and spinal cord. If this fluid isn’t reabsorbed, or if the flow is blocked due to trauma, then it builds up and exerts pressure.


Treating increased ICP requires addressing what caused the imbalance in the first place. If there is bleeding, surgery may be necessary to remove the built up blood.

When there is swelling due to nerve cell damage or lack of oxygen, the brain is kept as quiet as possible, usually through sedation. Depending on the nature and timing of the swelling, steroids may be used.

When there is hydrocephalus, a shunt may be placed to drain the excess fluid.


Increased ICP is common after serious head trauma. It is important to reduce the ICP quickly so that brain tissues are not further damaged. Outcomes depend on how high the ICP went, and how long the brain was under high pressure.  


MacLaughlin, B. W., Plurad, D. S., Sheppard, W., Bricker, S., Bongard, F., Neville, A., & ... Kim, D. Y. (2015). The impact of intracranial pressure monitoring on mortality after severe traumatic brain injury. The American Journal Of Surgery, doi:10.1016/j.amjsurg.2015.08.007

Roytowski, D., & Figaji, A. (2013). Raised intracranial pressure: What it is and how to recognise it. CME: Continuing Medical Education, 31(3), 85-90.

Continue Reading