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Intracranial pressure monitoring
Definition
Intracranial pressure monitoring uses a device, placed inside the head, which senses the pressure inside the skull and sends its measurements to a recording device.
Alternative Names
ICP monitoring; CSF pressure monitoring
How the Test is Performed
There are three ways to monitor pressure in the skull (intracranial pressure).
INTRAVENTRICULAR CATHETER
The intraventricular catheter is thought to be the most accurate method.
To insert an intraventricular catheter, a burr hole is drilled through the skull. The catheter is inserted through the brain into the lateral ventricle. This area usually contains liquid (cerebrospinal fluid or CSF) that protects the brain and spinal cord.
The intracranial pressure (ICP) can be monitored this way. The ICP also can be lowered by draining cerebral spinal fluid (CSF) out through the catheter.
The catheter may be hard to get into place when the intracranial pressure is high.
SUBDURAL SCREW
This method is used if the patient needs to be monitored right away. A subdural screw or bolt is a hollow screw that is inserted through a hole drilled in the skull. It is placed through the membrane that protects the brain and spinal cord (dura mater). This allows the sensor to record from inside the subdural space.
EPIDURAL SENSOR
If an epidural sensor is used, it is inserted between the skull and dural tissue. The epidural sensor is placed through a burr hole drilled in the skull. This procedure is less invasive than other methods, but it cannot remove excess CSF.
Lidocaine or another local anesthetic will be injected at the site where the cut will be made. You will most likely get a sedative to help you relax.
- First the area is shaved and cleansed with antiseptic.
- After the area is dry, a surgical cut is made. The skin is pulled back until the skull is seen.
- A drill is then used to cut through the bone.
How to Prepare for the Test
If you need this procedure done, you will be in the hospital and most likely in an intensive care unit. If you are conscious, your health care provider will explain the procedure and the risks, and (as with any surgery) you will have to sign a consent form.
How the Test Will Feel
If the procedure is done while you are under general anesthesia, you will feel nothing until you wake from the anesthesia. At that time you will feel the normal side effects of anesthesia, plus the discomfort of the cut made in your skull.
If the procedure is done under local anesthesia, you will feel a prick on your scalp like a bee sting as the local anesthetic is injected. You may feel a tugging sensation as the skin is cut and pulled back. You will hear a drill sound as it cuts through the skull. The amount of time this takes will depend on the type of drill that is used. You will also feel a tugging as the surgeon sutures the skin back together after the procedure.
Your health care provider may prescribe mild pain medications for relief. You will not get strong pain medications, so that your doctor can check for signs of brain function.
Why the Test is Performed
This test is usually done to measure intracranial pressure. It is usually done when there is a severe head injury or brain/nervous system disease. It also may be done after surgery to remove a tumor or fix damage to a blood vessel if the surgeon is worried about brain swelling.
High intracranial pressure can be treated by draining CSF through the catheter. It can also be treated by changing the ventilator settings for people who are on a respirator, or by giving certain medicines through a vein (intravenously).
Normal Results
Normally, the ICP ranges from 1 to 20 mm Hg.
Note: mm Hg = millimeters of mercury
Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
What Abnormal Results Mean
High intracranial pressure means that both nervous system and blood vessel tissues are under pressure. If not treated, this can lead to permanent damage. In some cases, it can be life threatening.
Risks
- Bleeding
- Brain herniation or injury from the increased pressure
- Damage to the brain tissue
- Inability to find the ventricle and place catheter
- Infection
- Risks of general anesthesia
References
Rabinstein AA. Principles of neurointensive care. In: Bradley WG, Daroff RB, Fenichel GM, Jankovic J, eds. Bradley: Neurology in Clinical Practice. 5th ed. Philadelphia, Pa:Butterworth-Heinemann Elsevier; 2008:chap 49.
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
