The cranium and its constituents (blood, CSF, and brain tissue) create a state of volume equilibrium, such that any increase in volume of one of the cranial constituents must be compensated by a decrease in volume of another. *This concept only applies to adults, as the presence of fontanelles and open suture lines in infants that have not yet fused means there is potential for a change in size and intracranial volume. The principal buffers for increased volumes include CSF and, to a lesser extent, blood volume. These buffers respond to increases in volume of the remaining intracranial constituents. For example, an increase in lesion volume (e.g., epidural hematoma) will be compensated by the downward displacement of CSF and venous blood.The Monro–Kellie hypothesis is named after Edinburgh doctors Alexander Monro and George Kellie. Diagnosis
The most definitive way of measuring the intracranial pressure is with transducers placed within the brain. A catheter can be surgically inserted into one of the brains lateral ventricles and can be used to drain CSF (cerebrospinal fluid) in order to decrease ICPs. This type of drain is known as an external ventricular drain (EVD). This is rarely required outside brain injury and brain surgery settings.In situations when only small amounts of CSF are to be drained to reduce ICPs (e.g. in IIH), drainage of CSF via lumbar puncture can be used as a treatment. Non-invasive measurement of intracranial pressure is being studied. Treatment
The treatment for ICP depends on the cause.
In addition to management of the underlying causes, major considerations in acute treatment of increased ICP relates to the management of stroke and cerebral trauma.For long-term or chronic forms of raised ICP, especially idiopathic intracranial hypertension (IIH), a specific type of diuretic medication (acetazolamide) is used. In cases of confirmed brain neoplasm, dexamethasone is given to decrease ICP. Although the exact mechanism is unknown, current research shows that dexamethasone is capable of decreasing peritumoral water content and local tissue pressure to decrease ICP. Ventilation
In people who have high ICP due to an acute injury, it is particularly important to ensure adequate airway, breathing, and oxygenation. Inadequate blood oxygen levels (hypoxia) or excessively high carbon dioxide levels (hypercapnia) cause cerebral blood vessels to dilate, increasing the flow of blood to the brain and causing the ICP to rise. Inadequate oxygenation also forces brain cells to produce energy using anaerobic metabolism, which produces lactic acid and lowers pH, also dilating blood vessels and exacerbating the problem. Conversely, blood vessels constrict when carbon dioxide levels are below normal, so hyperventilating a person with a ventilator or bag valve mask can temporarily reduce ICP. Hyperventilation was formerly a part of the standard treatment of traumatic brain injuries, but the induced constriction of blood vessels limits blood flow to the brain at a time when the brain may already be ischemic—hence it is no longer widely used.