Icp

In 1893, Heinrich Quincke was the first to describe the connection between increased intracranial pressure and the disease process of idiopathic intracranial hypertension. At the time, he referred to the disease as "meningitis serosa" (Willenborg 2017).

The possibility of measuring intracranial pressure was first made possible by the Frenchmen Guillaume and Janny and the Swede Lungberg. Lundberg divided the individual types of intracranial pressure into A waves (steep increase in intracranial pressure to values of up to 50 mm Hg, which only lasts for a short time), B waves (short and less pronounced increases in pressure that are dependent on breathing) and C waves (so-called Traube-Herring waves, which are caused by fluctuations in the arterial filling of the cerebral vessels).

The first devices for measuring pressure were developed as early as the 1950s, but it was not until the 1970s that constant pressure measurement became possible (Povacz 2000).

Intracranial pressure (ICP) is the pressure inside the cranial cavity (Antwerpes 2024) or, in other words, the pressure exerted by the contents of the skull on the dural envelope (Huttner 2023).

Numerous neurological diseases can lead to a life-threatening increase in ICP, as the volume of the interior of the skull is constant (Huttner 2023).

Physiologically, the intracranial pressure of a healthy adult in a sitting position is 5 - 15 mm Hg. The Foramen Monroi is declared to be the zero point.

However, there is no established upper limit for intracranial pressure (Huttner 2023). Similarly, a critical lower limit for intracranial pressure has not yet been evaluated (Diener 2008)

The intracranial pressure can rise considerably as a result of simple actions such as sneezing, coughing, pressing, etc., as the venous return flow to the heart is throttled in these cases. Pressure peaks of up to 50 mm Hg can occur, but these are generally well tolerated (Antwerpes 2024).

On the other hand, intracranial pressure can rise to life-threatening levels in the event of brain damage such as after a traumatic brain injury, a subarachnoid hemorrhage or a hemorrhagic apoplexy . Chronic intracranial pressure of over 20 mm Hg already leads to permanent damage and should always be treated accordingly (Antwerpes 2024).

The monitoring of intracranial pressure (ICP) is of utmost importance in the case of life-threatening brain damage, such as after a traumatic brain injury, a subarachnoid hemorrhage and a hemorrhagic apoplexy . In most cases, ICP is measured invasively, but there are now also some newer techniques that show promising results at lower risk (Hawyluk 2023).

According to Povacz (2000), three types of measurement are possible:

- Ventricular by puncture of the respective ventricle: This has the advantage that cerebrospinal fluid can be drained therapeutically. The disadvantage is the risk of infection, which is approx. 10 %.

- Subarachnoid: The advantage here is the lower risk of infection, the disadvantage is the increased incidence of incorrect measurement data.

- Epidural: The method is technically simpler, the risk of infection is low, but there is an increased incidence of incorrect measurement data.

Nowadays, intracranial pressure can be measured using:

- Sensors that continuously measure the pressure and are located in the ventricle, parenchyma, sub- or epidural space, the cisterna magna or in the lumbar subarachnoid space

- Pressure micro-transducers, which consist of an elastic or movable component that deforms or moves when pressure is applied and generates a signal. This signal correlates with the pressure (Pelah 2023).

The average deviation of the measured pressure from the actual ICP can be up to + / - 6 mmHg (Pelah 2023).

The historical gold standard is direct manometry of the lateral ventricles. Alternatively, according to the guideline, similarly precise intraparenchymal pressure measurement systems can be used (Huttner 2023).

In addition to the brain, the skull also contains approx. 70 ml of cerebrospinal fluid and approx. 100 ml of blood. As the skull bone ossifies early (at the age of 2), even a small increase in volume leads to an increase in intracranial pressure. For this reason, the components brain, cerebrospinal fluid and blood must remain constant - in accordance with the so-called "Monro-Kellie doctrine" (Antwerpes 2024).

Brain tissue requires constant blood flow for its functions, which is why it has the ability to maintain systemic blood pressure over a wide range. Cerebral perfusion pressure (CPP) provides the driving force for circulation through the capillaries of the brain. Even when systemic blood pressure drops, cerebral blood flow is maintained through vasodilation in the brain. At high systemic pressures, arteriolar vasoconstriction occurs in order to maintain constant perfusion (Kasper 2015).

However, this process can be unpredictably disrupted by, for example, traumatic brain injury, severe focal ischemia, etc. (Kasper 2015).

Increased intracranial pressure can be treated conservatively or surgically.

Conservative treatment involves elevating the body by approx. 30°, positioning the head in a frame and possibly intubation. Long-term hyperventilation should be avoided in particular, as this can worsen cerebral perfusion. Osmotherapy with e.g. mannitol 50 mg i.v. every 6 h is also recommended (Herold 2018).

Neurosurgical treatment includes a decompression craniotomy in the presence of a large medial infarction or brain stem decompression in the case of a large infarction of the posterior fossa. In the case of a cerebellar infarction with occlusive hydrocephalus, temporary ventricular drainage is recommended (Herold 2018).

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