Brain pressure is a colloquial term for the pressure that prevails inside the skull ( intracranial pressure , common abbreviation ICP for intracranial pressure , also used in German ). The intracranial pressure is crucial for the blood flow and thus for the function of the brain, as it counteracts the pressure with which the blood is pumped into the brain. If the intracranial pressure and mean arterial blood pressure are the same, the brain is no longer supplied with blood and stops functioning within seconds and dies within a short time. Therefore, the measurement of intracranial pressure is an important reference point for therapeutic decisions in the treatment of patients with severe brain damage, e.g. B. after a traumatic brain injury or a stroke.
The intracranial volume consists of three compartments: the brain tissue, the cerebral vessels and the liquor spaces, i. H. the spaces that are filled with cerebrospinal fluid ( liquor cerebrospinalis ). If the volume of a compartment increases, this can be compensated to a certain extent by the decrease in the intracranial blood or liquor volume, so that the intracranial pressure does not initially rise. Only after these so-called "intracranial reserve spaces" have been used up does the intracranial pressure increase, but then suddenly (exponentially). The relationship between intracranial volume and intracranial pressure is called intracranial compliance . The relationship between intracranial volume and intracranial pressure can be read from the graph of compliance. This concept was first described by Monro and Kellie in the early 19th century and is known as the Monro-Kellie Doctrine .
The measurement of the intracranial pressure is carried out by means of a fluid pressure transducer connected to a ventricular catheter or by means of a measuring probe, which can be located epidurally, subdurally, in the brain tissue (parenchyma) or in one of the cerebral chambers (ventricles). Liquid-coupled pressure transducers fail if the catheter is blocked and / or if the ventricles are squeezed out. The problem with the arrangement of the measuring sensor in the patient is that the zero point drifts and cannot be readjusted. This drift is a systematic drift that only lasts for the first few hours, not during the entire measurement period. Epidural measuring probes are afflicted with considerable measuring errors.
Tip probes are available from manufacturers Integra, Codman, Raumedic and Sophysa. A system is available from the manufacturer Spiegelberg in which the pressure is transmitted via a column of air to a measuring sensor located outside the body in a device. As a result, two different types of drift have an effect on the measurement, because in addition to the systematic drift of the measuring device, the physical drift also occurs through the measuring section. The manufacturer tries to minimize this drift by zeroing its system every hour. The measurement of the intracranial pressure provides absolute values for the intracranial pressure and depending on the extent of the intracranial pressure, which is 1.5 - 20 mm Hg in healthy people depending on the age, the pathophysiological process is also reflected in pathological recorded waveforms, the so-called Lundberg waves.
In addition to headache and vomiting, the main symptom for increased intracranial pressure is a congestive papilla ( edema in the tissue of the optic nerve papilla ), which can be diagnosed using an ophthalmoscope . If these symptoms occur together, one speaks of a " brain pressure triad ". Other symptoms that can occur are dizziness, eye muscle paralysis , bradycardia, as well as respiratory and impaired consciousness , which range from increased absence to coma . Initially, however, there may be an uneasy movement. As a result of the Cushing reflex , there may be a general increase in blood pressure and a decrease in heart rate.
Causes of disease
Due to the pathophysiological conditions outlined above, an increase in intracranial pressure can occur due to the increase in one or more craniocerebral compartments: due to a mass of the brain parenchyma, e.g. B. by a brain tumor, or by the swelling of the brain ( cerebral edema ) after a traumatic brain injury, a stroke or an inflammation of the brain, by the increase in the cerebral blood flow or by the increase in the volume of CSF, e.g. B. by a drainage disruption.
Since the increase in intracranial pressure is a general symptom, a wide range of causative diseases can be considered. First and foremost, the increased intracranial pressure should be considered as part of the triad of symptoms vomiting , headache and increased intracerebral pressure. This triad suggests a brain tumor usually in its late stage. Hypertension , uremia , pseudouremia, subdural hematoma , and neurolues also come into question .
An increase in intracranial pressure can lead to mass displacement and entrapment of parts of the brain.
|0-10 mm Hg
|0-14 cm H 2 O
|11-20 mm Hg
|15-27 cm H 2 O
|slightly increased ICP
|21-40 mm Hg
|28-54 cm H 2 O
|greatly increased ICP
|over 40 mm Hg
|over 55 cm H 2 O
|very high ICP
It is not the one-off increase in intracranial pressure, but a permanently high ICP value that leads to secondary brain damage and worsening of the neurological outcome .
Basically, patients with increased intracranial pressure must be monitored and treated in intensive care.
- If possible, an intracranial pressure probe is installed to monitor intracranial pressure.
- The patients are positioned with the upper body raised by 30 ° to 45 ° (head as straight as possible so as not to obstruct the venous outflow).
- Controlled ventilation is generally required for treatment. The ventilation or breathing should be monitored with measurements of the carbon dioxide partial pressure in the blood and / or the exhaled air by means of capnometry or blood gas analysis . Slight hyperventilation ( PaCO 2 35 to 38 mmHg) leads to constriction of the blood vessels, which means that the ICP can be reduced for a short time (with excessive hyperventilation with PaCO 2 values below 30 mmHg, there is a risk of decreased cerebral blood flow).
- Glucocorticoids (e.g. dexamethasone , methylprednisolone ) have a decongestant effect. However, their effectiveness has only been proven in vasogenic brain edema, i.e. a disruption of the blood-brain barrier caused by malignant tumors or bacterial meningitis . Glucocorticoids can while according to the study able TBI even lead to increased mortality and are therefore contraindicated in this case.
- Also diuretics can reduce the edema by increasing fluid secretion by the kidneys.
- Since the auto-regulation of the blood pressure in the brain may fail, the blood pressure in patients with increased intracranial pressure must be closely monitored by an invasive blood pressure measurement and kept within physiological limits.
- Osmotherapeutic agents ( mannitol ) can temporarily lower intracranial pressure when it reaches critical levels.
- A sedation in pain symptoms as sedation , reduces the metabolic demand and thereby the cranial blood flow, the intracranial blood volume and thus the intracranial pressure.
- A hypothermia can protect the affected brain tissue also by reducing energy consumption.
- The lumbar puncture to relieve pressure can be contraindicated if it poses a lethal risk of entrapment of the brain in the posterior skull.
- Depending on the cause, it may be necessary to drain the cerebral fluid using external ventricular drainage or using a ventriculo-peritoneal shunt .
- As a last resort one can Dekompressionskraniektomie be necessary.
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