Intracranial Pressure (ICP) is a very important way of monitoring the health and outcome of the brain after injury. The brain is encased in a non-flexible cover - the skull. Therefore, if there are changes which result in increased pressure, the fluid that surrounds the brain has nowhere to go.
Doctors in the emergency room and in acute care facilities in hospitals are constantly interested in whether or not this pressure has been raised. In a healthy adult, the ICP is usually in the range of 0 to 10 mmHg, and any pressure greater than 20mmHg is abnormal. When ICP is greater than 40mmHg, there is almost always some neurological dysfunction (impairment of consciousness, problems breathing, pupil dilation, compression of brain found on MRI) as well as impairment of the brain's electrical activity (an abnormal EEG). A pressure above 60mmHg is fatal, while pressures between 20 and 40mmHg indicate a much poorer outcome. Methods of monitoring the ICP include:
- Intra-ventricular catheter;
- Intra-parenchymal monitor;
- Sub-arachnoid bolt (less accurate);
- Subdural and epidural monitors (less accurate);
- Jugular venous monitoring (necessary during chemically induced coma only).
The problem with increased ICP is that the fluid under pressure tends to deform the brain and pushes tissue in such a way as to cause injury to the brain itself. A MRI or CT taken at the emergency room or during follow-up care can often show shifting of the tissue because of the pressure. This is called midline shift. That is a way doctors can tell there is increased pressure, and they can also directly monitor the pressure through the skull.
There are several strategies used to decrease the ICP and attempt to avoid further brain injury:
MANNITOL
A medication which is often given to attempt to decrease the pressure.
COMA
Persons can be put into a barbiturate coma, (also known as a chemically induced coma), to help alleviate the pressure as well. This can last from days to weeks.
HYPOTHERMIA
This treatment is increasingly used - the body's core temperature is lowered to 95 degrees or lower to slow the flow of blood and other fluids to the brain. Studies have shown a better outcome with this type of treatment.
SHUNT
Installing a "shunt," which is a valve, allows the escape of fluid through the skull (like a small faucet). This method is used on patients who have long term increased pressure and is used to keep the pressure, hopefully within normal levels. A shunt can stay in for days or months
DECOMPRESSIVE CRANIECOTOMY
This is the final method of treatment if others have failed. In this surgical procedure, a portion of the skull is removed in order to expose the brain and allow the fluid under pressure to escape.
The results of increased pressure can often be seen in cases of a "slow bleed." In cases like this, often involving either children who are unable to respond or older patients, a fall or other type of injury will occur, sometimes without even loss of consciousness. In older patients, the veins in the brain are more delicate and they can often tear. This results in a slow bleed which may accumulate pressure over many hours. Persons suffering from this will gradually deteriorate. This is one of the main reasons CT scans of the brain are routinely done on persons who have suffered a blow to the head. The elderly who have received a blow to the head should be routinely given a CT to check for the presence of blood to verify this problem.
The brain damage done when the brain is subjected to increased pressure over a sufficient amount of time is wide spread and can be severe. Often, the results of the subjection to pressure on the brain are not able to be visualized on MRI for several weeks following the pressure. Depending on where the deformation of the brain occurred, there could be small UBO's (white spots on MRI indicating dead tissue) or more focal injury on the outer surface of the brain from where the brain was pressed up against the skull during the period of high pressure. Occasionally, the white cell's damage is unable to be visualized but can be determined through neuropsychological testing.
Overall, it is essential to take steps to reduce the ICP if it is in the abnormal range. Family members and the relatives who act quickly when requested by the emergency personnel or treating physicians are often blessed with better outcomes. Delays can result in additional damage.