Intracranial Pressure: Function, Role & Diseases

Intracranial pressure is colloquially known as intracranial pressure. It plays an important role in blood flow and brain function.

What is intracranial pressure?

Intracranial pressure is colloquially referred to as intracranial pressure. It plays an important role in blood flow and brain function. In English, intracranial pressure is known as intracranial pressure or ICP for short. The abbreviation ICP is also commonly used in German. Intracranial pressure is the pressure that exists in the cranial cavity. The cerebral skull consists of seven individual bones that enclose and protect the brain. In addition to the brain, the cerebral skull contains blood and cerebrospinal fluid. The cerebrospinal fluid is a bodily fluid formed by the choroid plexus. It circulates throughout the cerebrospinal fluid space. The CSF space is a system of cavities in the brain and spinal cord. Since the cranium ossifies completely in the first years of life, the total volume of brain, blood and CSF in the head must always remain the same. In addition to the brain, there is room for about 70 milliliters of cerebrospinal fluid and for 100 milliliters of blood in adult humans. The distribution follows the Monro-Kellie doctrine. According to this, the distribution is always 80 percent brain tissue, 12 percent blood and 8 percent CSF. Only if these ratios are maintained can intracranial pressure be kept constant. In adults, the available intracranial volume is about 1600 milliliters. The physiological intracranial pressure in a healthy person is 5 to 15 mmHg. Converted, this corresponds to 5 to 20 cm of water column. In children, intracranial pressure should be between 0 and 10 mmHg.

Function and purpose

Intracranial pressure plays a critical role in blood flow to the brain. Without adequate intracranial pressure, brain function is compromised. Intracranial pressure is opposite to the pressure of blood in the brain. The brain needs a constant supply of nutrient- and oxygen-rich blood. It has a very high basal metabolic rate and uses about one-fifth of the body’s total oxygen supply even at rest. Nerve cells, unlike other cells in the body, are also unable to meet their energy needs without oxygen (anaerobically). When cerebral blood flow is reduced, damage to the brain occurs. Nerve cells die. Intracranial pressure affects blood flow to the brain and thus oxygen and nutrient supply. Under physiological conditions, intracranial pressure is lower than the pressure at which blood is pumped into the brain. Thus, cerebral blood flow is not affected by intracranial pressure. However, as soon as the intracranial pressure and the blood pressure in the brain are equal, the brain is no longer supplied with blood properly. There is a lack of nutrients and oxygen. The brain tissue, cerebral vessels and cerebrospinal fluid spaces are in constant exchange to compensate for volume fluctuations. For example, if the volume of brain tissue increases, it may be balanced by a decrease in CSF or blood volume. Intracranial pressure then does not increase despite an increase in volume of brain tissue. Thus, intracranial pressure is a dynamic variable that must be constantly adjusted to current conditions. If compensation is no longer possible, the intracranial pressure increases. The slower the intracranial pressure rises, the better the pressure increase can be processed. 5 to 10 milliliters of volume increase can be compensated in this way. In an emergency, increased resorption of the cerebrospinal fluid can also absorb larger, slowly progressing increases in volume. Coughing, sneezing or pressing also briefly increase intracranial pressure up to 50 mmHg by reducing venous return to the heart. However, such short-term pressure spikes can be well tolerated.

Diseases and complaints

An increase in intracranial pressure may be caused by an increase in volume of one or more compartments. For example, an increase in brain functional tissue may result from a brain tumor or from cerebral 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. Intracranial pressure also increases with outflow obstruction. The outflow of cerebrospinal fluid may be blocked by a tumor.Since the structures continue to produce cerebrospinal fluid despite the blockage, congestion occurs, resulting in an increase in intracranial pressure. An abscess can also prevent cerebrospinal fluid from draining. Another cause of drainage obstruction is cerebral hemorrhage. In addition, increases in fluid in the skull lead to an increase in intracranial pressure. Such fluid increases can be metabolic or toxic. Another cause of cerebral edema is hypoxia. The brain responds to a lack of oxygen with edema. The most common cause of cerebral edema due to hypoxia is cerebral infarction. Cerebral infarction is also known as ischemic insult or stroke. When a venous vessel is occluded by thrombosis, venous blood backs up in the skull. This also increases intracranial pressure. The leading symptom of a pathological increase in intracranial pressure is severe headache. Nausea or vomiting may also occur. The so-called congestion papilla is conspicuous. This is a swelling of the exit site of the optic nerve. This can lead to visual disturbances. The congestion papilla is diagnosed with the aid of ophthalmoscopy. The combination of headache, vomiting, and congestive papilla is called intracranial pressure triad. Other symptoms of intracranial pressure increase include dizziness, a slowed heartbeat, paralysis of the eye muscles, and mental absence. Due to the Cushing’s reflex, there is an increase in blood pressure with a simultaneous decrease in heart rate. This phenomenon is called a pressure pulse.