Of the intracranial pressure is colloquially called Intracranial pressure designated. It plays an important role in blood circulation and the functioning of the brain.
What is intracranial pressure?
In English, the intracranial pressure is called intracranial pressure or short as ICP known. The abbreviation ICP is also used in German-speaking countries. The intracranial pressure is the pressure that exists in the cranial cavity.
The brain skull consists of seven individual bones that enclose and protect the brain. In addition to the brain, the skull contains blood and liquor. The cerebrospinal fluid is a body fluid that is formed by the choroid plexus. It circulates throughout the entire CSF space. The liquor space is a system of cavities in the brain and spinal cord. Since the brain skull already ossifies completely in the first years of life, the total volume of brain, blood and liquor in the head must always remain the same.
In addition to the brain, there is space for around 70 milliliters of liquor and 100 milliliters of blood in adults. The distribution follows the Monro-Kellie doctrine. Accordingly, the distribution is always 80 percent brain tissue, 12 percent blood and 8 percent liquor. The intracranial pressure can only be kept constant if these conditions are observed. In adults, the available intracranial volume is around 1,600 milliliters. The physiological intracranial pressure in healthy people is 5 to 15 mmHg. Converted, this corresponds to a water column of 5 to 20 cm. In children, the intracranial pressure should be between 0 and 10 mmHg.
Function & task
The intracranial pressure plays a crucial role in the blood flow to the brain. Without adequate intracranial pressure, brain function is at risk. The intracranial pressure contrasts with the pressure of the blood in the brain. The brain needs a constant supply of nutrient-rich and oxygen-rich blood. It has a very high basal metabolic rate and takes up around a fifth of the body's total oxygen supply even when it is at rest. In contrast to other body cells, nerve cells are not able to meet their energy requirements without oxygen (anaerobically).
When the cerebral blood flow is reduced, the brain is damaged. Nerve cells die. The intracranial pressure influences the blood flow to the brain and thus also the supply of oxygen and nutrients.
Under physiological conditions, the intracranial pressure is lower than the pressure at which the blood is pumped to the brain. The cerebral blood flow is therefore not influenced by the intracranial pressure. But as soon as the intracranial pressure and the blood pressure in the brain are the same, the brain is no longer properly supplied with blood. There is a lack of nutrients and oxygen.
The brain tissue, the cerebral vessels and the liquor spaces are in constant exchange in order to compensate for fluctuations in volume. For example, if the volume of brain tissue increases, it can be compensated for by decreasing the volume of liquor or blood. The intracranial pressure then does not rise despite an increase in the volume of the brain tissue. The intracranial pressure is therefore a dynamic variable that must be constantly adapted to the current conditions.
If compensation is no longer possible, the intracranial pressure increases. The slower the intracranial pressure increases, the better the pressure increase can be processed. A volume increase of 5 to 10 milliliters can be compensated in this way. In an emergency, increased resorption of the CSF can also absorb larger, slowly progressing increases in volume. Coughing, sneezing or pressing can also briefly increase intracranial pressure to up to 50 mmHg by reducing the venous return flow to the heart. Such short-term pressure peaks can, however, be tolerated well.
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An increase in intracranial pressure can be caused by an increase in volume of one or more compartments. An increase in functional brain tissue can result, for example, from a brain tumor or from brain edema after an accident. A stroke or inflammation of the brain (encephalitis) can also cause an increase in volume and thus an increase in intracranial pressure.
The intracranial pressure also increases with obstructions to the drainage. The outflow of the CSF can be blocked by a tumor. Since the structures continue to produce cerebrospinal fluid despite the blockage, there is a congestion and thus an increase in intracranial pressure. An abscess can also prevent the brain water from draining. Another cause of obstruction to drainage is cerebral haemorrhage. In addition, an increase in fluid in the skull leads to an increase in intracranial pressure. Such an increase in fluid can be metabolic or toxic. Another reason for brain edema is hypoxia. When there is a lack of oxygen, the brain reacts with edema. The most common cause of cerebral edema due to hypoxia is a cerebral infarction. A cerebral infarction is also known as an ischemic insult or a stroke. If a venous vessel is blocked by a thrombosis, the venous blood builds up in the skull. This also increases the intracranial pressure.
The main symptom of a pathological increase in intracranial pressure is a severe headache. Nausea or vomiting can also occur. The so-called papillae is noticeable. It is a swelling of the exit point of the optic nerve. This can lead to impaired vision. The congestive papilla is diagnosed with the help of an ophthalmoscope. The combination of headache, vomiting and congestive papilla is called the intracranial pressure triad. Other symptoms of increased intracranial pressure are dizziness, a slow heartbeat, paralysis of the eye muscles, and mental absence. The Cushing reflex causes an increase in blood pressure with a simultaneous decrease in heart rate. This phenomenon is called pressure pulse.
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