Intracranial pressure monitoring

Intracranial pressure monitoring
Intracranial pressure monitoring
ICD-9-CM	01.10
MedlinePlus	003411

Last updated December 03, 2022

The monitoring of intracranial pressure (ICP) is used in the treatment of a number of neurological conditions ranging from severe traumatic brain injury to stroke and brain bleeds.^[1] This process is called intracranial pressure monitoring. Monitoring is important as persistent increases in ICP is associated with worse prognosis in brain injuries due to decreased oxygen delivery to the injured area and risk of brain herniation.

Most current clinically available measurement methods are invasive, requiring surgery to place the monitor in the brain itself. Of these, external ventricular drainage (EVD) is the current gold standard as it allows physicians to both monitor ICP and treat if necessary. Some non-invasive intracranial pressure measurement methods are currently being studied, however none are currently able to deliver the same accuracy and reliability of invasive methods.

Intracranial pressure monitoring is just one tool to manage ICP. It is used in conjunction with other techniques such as ventilator settings to manage levels of carbon dioxide in the blood, head and neck position, and other therapies such as hyperosmolar therapy, medications, and core temperature.^[2] However, there is no current consensus on the clinical benefit of ICP monitoring in overall ICP management, with evidence both supporting its use and finding no benefit in reducing mortality.^[3]

Pathophysiology

Injury to the brain will often result in brain swelling. As the brain is encased in the skull, limited swelling can be accommodated until the brain is no longer able to maintain normal function. There are two potential negative consequences from this swelling: ischemia due to compression of the brain tissue resulting in lack of blood and oxygen, and herniation of the brain.^[4]

The three main components in determining ICP is the blood circulation in the brain, cerebrospinal fluid (CSF), and the brain tissue itself. This relationship is dictated by the Monro-Kellie doctrine, which states that as the brain swells, intracranial pressure (ICP) rises and cerebral perfusion decreases. As the brain swelling exceeds a certain point called the critical closing pressure (CrCP), the arterioles feeding the brain oxygen-rich blood will collapse, and the brain becomes deprived of blood.^[1] This secondary injury can cause permanent brain damage from lack of oxygen.

Herniation of the brain can occur when the pressure inside the skull exceeds the pressure of the spinal canal. This is dangerous as it can result in the compression of important areas like the brainstem that regulate breathing leading to significant neurological impairment or death.

Methods

Under normal conditions, regular movements such as leaning forward, normal heartbeat and breathing can cause changes to the ICP. Intracranial monitoring accounts for this by averaging measurements over 30 minutes in non-comatose patients. Readings between 7-15mmHg are considered normal in an adult, 3-7mmHg in children, and 1.4-6mmHg in infants.^[4]

Invasive

External ventricular drainage

The external ventricular drainage (EVD) method of intracranial pressure monitoring is the current gold standard. The placement of an EVD requires a catheter placed into one of the lateral ventricles from a burr hole made into the skull. Benefits of an EVD include its ability to not only measure changes in pressure but also drain CSF as needed, thus making it both diagnostic and therapeutic.^[2] Significantly, an EVD can also be re-calibrated after placement which is particularly useful clinically to manage measurement drift. Risks in the operation to place the EVD are minimal but include infection and brain bleeds. Drawbacks to EVDs are the difficulty to place in comparison to other methods -- especially in the setting of brain swelling or anatomical variation in ventricle size – and once placed, are at increased risk of blockage from blood, air bubbles, or other debris.

Intraparenchymal pressure monitor

There are three types of intraparenchymal pressure monitors (IPM), also called bolts: fiber optic, strain gauge, and pneumatic sensors.^[1] Fiber optic monitors use changes in light reflected back from a mirror at the end of the cable to reflect changes in the ICP. Strain gauge monitors use a diaphragm that is bent by surrounding pressure, which is then converted into electrical signals used to calculate changes in ICP. Pneumatic sensors are fitted with a balloon which measures the surrounding pressure, thereby measuring the ICP.^[4] IPMs are as equally accurate as EVDs, but cannot be recalibrated after placement, which is a major clinical limitation of this method of intracranial pressure monitoring. Risks of IPMs are similar to risks of EVDs as both require a surgical procedure. However, placement of IPMs is still considered less invasive than placement of EVDs. Additionally, placement of IPMs do not require the precision needed for EVD placement, and they are less affected by structural changes to the brain such as brain swelling or midline shift.^[2] IPMs can be placed not only in the parenchyma but also in the ventricular, subarachnoid, subdural, or epidural spaces. Generally, IPMs are chosen when EVD placement is unsuccessful or if CSF drainage is determined to likely not be necessary.^[4]

Continuous brain tissue oxygen tension (PbO2)

This method of intracranial pressure monitoring requires placement of an oxygen probe into the penumbra, the area surrounding the injury that is most at risk of secondary injury from hypoxia. The probe measures levels of oxygen in the area, with levels under 15mmHg treated with increasing oxygen levels in the body.^[2]

Non-invasive

There are many noninvasive methods for intracranial pressure monitoring such as transcranial doppler (TCD), and optic nerve sheath diameter (ONSD). While none of these methods have been able to have the accuracy, reliability, and independent validation of invasive methods, they may eventually be used in determining the severity of injury and if there is a need for more invasive measures.^[1]

Related Research Articles

Cerebrospinal fluid (CSF) is a clear, colorless body fluid found within the tissue that surrounds the brain and spinal cord of all vertebrates.

<span class="mw-page-title-main">Idiopathic intracranial hypertension</span> Medical condition

Idiopathic intracranial hypertension (IIH), previously known as pseudotumor cerebri and benign intracranial hypertension, is a condition characterized by increased intracranial pressure without a detectable cause. The main symptoms are headache, vision problems, ringing in the ears, and shoulder pain. Complications may include vision loss.

<span class="mw-page-title-main">Papilledema</span> Eye disorder

Papilledema or papilloedema is optic disc swelling that is caused by increased intracranial pressure due to any cause. The swelling is usually bilateral and can occur over a period of hours to weeks. Unilateral presentation is extremely rare.

Hydrocephalus is a condition in which an accumulation of cerebrospinal fluid (CSF) occurs within the brain. This typically causes increased pressure inside the skull. Older people may have headaches, double vision, poor balance, urinary incontinence, personality changes, or mental impairment. In babies, it may be seen as a rapid increase in head size. Other symptoms may include vomiting, sleepiness, seizures, and downward pointing of the eyes.

<span class="mw-page-title-main">Cerebral edema</span> Excess accumulation of fluid (edema) in the intracellular or extracellular spaces of the brain

Cerebral edema is excess accumulation of fluid (edema) in the intracellular or extracellular spaces of the brain. This typically causes impaired nerve function, increased pressure within the skull, and can eventually lead to direct compression of brain tissue and blood vessels. Symptoms vary based on the location and extent of edema and generally include headaches, nausea, vomiting, seizures, drowsiness, visual disturbances, dizziness, and in severe cases, coma and death.

Intracranial pressure (ICP) is the pressure exerted by fluids such as cerebrospinal fluid (CSF) inside the skull and on the brain tissue. ICP is measured in millimeters of mercury (mmHg) and at rest, is normally 7–15 mmHg for a supine adult. The body has various mechanisms by which it keeps the ICP stable, with CSF pressures varying by about 1 mmHg in normal adults through shifts in production and absorption of CSF.

Intracranial hemorrhage (ICH), also known as intracranial bleed, is bleeding within the skull. Subtypes are intracerebral bleeds, subarachnoid bleeds, epidural bleeds, and subdural bleeds. More often than not it ends in a lethal outcome.

Normal-pressure hydrocephalus (NPH), also called malresorptive hydrocephalus, is a form of communicating hydrocephalus in which excess cerebrospinal fluid (CSF) occurs in the ventricles, and with normal or slightly elevated cerebrospinal fluid pressure. As the fluid builds up, it causes the ventricles to enlarge and the pressure inside the head to increase, compressing surrounding brain tissue and leading to neurological complications. The disease presents in a classic triad of symptoms, which are memory impairment, urinary frequency, and balance problems/gait deviations. The disease was first described by Salomón Hakim and Adams in 1965.

Cushing reflex is a physiological nervous system response to increased intracranial pressure (ICP) that results in Cushing's triad of increased blood pressure, irregular breathing, and bradycardia. It is usually seen in the terminal stages of acute head injury and may indicate imminent brain herniation. It can also be seen after the intravenous administration of epinephrine and similar drugs. It was first described in detail by American neurosurgeon Harvey Cushing in 1901.

A hypertensive emergency is very high blood pressure with potentially life-threatening symptoms and signs of acute damage to one or more organ systems. It is different from a hypertensive urgency by this additional evidence for impending irreversible hypertension-mediated organ damage (HMOD). Blood pressure is often above 200/120 mmHg, however there are no universally accepted cutoff values. Signs of organ damage are discussed below.

Cerebral perfusion pressure, or CPP, is the net pressure gradient causing cerebral blood flow to the brain. It must be maintained within narrow limits because too little pressure could cause brain tissue to become ischemic, and too much could raise intracranial pressure (ICP).

Osmotherapy is the use of osmotically active substances to reduce the volume of intracranial contents. Osmotherapy serves as the primary medical treatment for cerebral edema. The primary purpose of osmotherapy is to improve elasticity and decrease intracranial volume by removing free water, accumulated as a result of cerebral edema, from brain's extracellular and intracellular space into vascular compartment by creating an osmotic gradient between the blood and brain. Normal serum osmolality ranges from 280 to 290 mOsm/kg and serum osmolality to cause water removal from brain without much side effects ranges from 300 to 320 mOsm/kg. Usually, 90 mL of space is created in the intracranial vault by 1.6% reduction in brain water content. Osmotherapy has cerebral dehydrating effects. The main goal of osmotherapy is to decrease intracranial pressure (ICP) by shifting excess fluid from brain. This is accomplished by intravenous administration of osmotic agents which increase serum osmolality in order to shift excess fluid from intracellular or extracellular space of the brain to intravascular compartment. The resulting brain shrinkage effectively reduces intracranial volume and decreases ICP.

A cerebral shunt is a device permanently implanted inside the head and body to drain excess fluid away from the brain. They are commonly used to treat hydrocephalus, the swelling of the brain due to excess buildup of cerebrospinal fluid (CSF). If left unchecked, the excess CSF can lead to an increase in intracranial pressure (ICP), which can cause intracranial hematoma, cerebral edema, crushed brain tissue or herniation. The drainage provided by a shunt can alleviate or prevent these problems in patients with hydrocephalus or related diseases.

Intraventricular hemorrhage (IVH), also known as intraventricular bleeding, is a bleeding into the brain's ventricular system, where the cerebrospinal fluid is produced and circulates through towards the subarachnoid space. It can result from physical trauma or from hemorrhagic stroke.

Neurocritical care is a medical field that treats life-threatening diseases of the nervous system and identifies, prevents, and treats secondary brain injury.

<span class="mw-page-title-main">External ventricular drain</span> Medical device

An external ventricular drain (EVD), also known as a ventriculostomy or extraventricular drain, is a device used in neurosurgery to treat hydrocephalus and relieve elevated intracranial pressure when the normal flow of cerebrospinal fluid (CSF) inside the brain is obstructed. An EVD is a flexible plastic catheter placed by a neurosurgeon or neurointensivist and managed by intensive care unit (ICU) physicians and nurses. The purpose of external ventricular drainage is to divert fluid from the ventricles of the brain and allow for monitoring of intracranial pressure. An EVD must be placed in a center with full neurosurgical capabilities, because immediate neurosurgical intervention can be needed if a complication of EVD placement, such as bleeding, is encountered.

<span class="mw-page-title-main">Cerebrospinal fluid leak</span> Medical condition

A cerebrospinal fluid leak is a medical condition where the cerebrospinal fluid (CSF) surrounding the brain or spinal cord leaks out of one or more holes or tears in the dura mater. A cerebrospinal fluid leak can be either cranial or spinal, and these are two different disorders. A spinal CSF leak can be caused by one or more meningeal diverticula or CSF-venous fistulas not associated with an epidural leak.

Low-pressure hydrocephalus (LPH) is a condition whereby ventricles are enlarged and the individual experiences severe dementia, inability to walk, and incontinence – despite very low intracranial pressure (ICP).

Increased intracranial pressure (ICP) is one of the major causes of secondary brain ischemia that accompanies a variety of pathological conditions, most notably traumatic brain injury (TBI), strokes, and intracranial hemorrhages. It can cause complications such as vision impairment due to intracranial pressure (VIIP), permanent neurological problems, reversible neurological problems, seizures, stroke, and death. However, aside from a few Level I trauma centers, ICP monitoring is rarely a part of the clinical management of patients with these conditions. The infrequency of ICP can be attributed to the invasive nature of the standard monitoring methods. Additional risks presented to patients can include high costs associated with an ICP sensor's implantation procedure, and the limited access to trained personnel, e.g. a neurosurgeon. Alternative, non-invasive measurement of intracranial pressure, non-invasive methods for estimating ICP have, as a result, been sought.

Spaceflight-associated neuro-ocular syndrome (SANS), previously known as Spaceflight-induced visual impairment, is hypothesized to be a result of increased intracranial pressure. The study of visual changes and intracranial pressure (ICP) in astronauts on long-duration flights is a relatively recent topic of interest to Space Medicine professionals. Although reported signs and symptoms have not appeared to be severe enough to cause blindness in the near term, long term consequences of chronically elevated intracranial pressure is unknown.

References

1 2 3 4 Canac N, Jalaleddini K, Thorpe SG, Thibeault CM, Hamilton RB (June 2020). "Review: pathophysiology of intracranial hypertension and noninvasive intracranial pressure monitoring". Fluids and Barriers of the CNS. 17 (1): 40. doi:10.1186/s12987-020-00201-8. PMC 7310456 . PMID 32576216.
1 2 3 4 Ramirez C, Stein D (2020). Current surgical therapy. Elsevier. pp. 1142–1146. ISBN 978-0-323-64059-6.
↑ Feng J, Yang C, Jiang J (July 2021). "Real-world appraisal of intracranial pressure monitoring". The Lancet. Neurology. 20 (7): 502–503. doi:10.1016/S1474-4422(21)00164-2. PMID 34146500. S2CID 235456638.
1 2 3 4 Harary M, Dolmans RG, Gormley WB (February 2018). "Intracranial Pressure Monitoring-Review and Avenues for Development". Sensors. 18 (2): 465. Bibcode:2018Senso..18..465H. doi: 10.3390/s18020465 . PMC 5855101 . PMID 29401746.

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[Canac_2020-1] 1 2 3 4 Canac N, Jalaleddini K, Thorpe SG, Thibeault CM, Hamilton RB (June 2020). "Review: pathophysiology of intracranial hypertension and noninvasive intracranial pressure monitoring". Fluids and Barriers of the CNS. 17 (1): 40. doi:10.1186/s12987-020-00201-8. PMC 7310456 . PMID 32576216.

[Ramirez_2020-2] 1 2 3 4 Ramirez C, Stein D (2020). Current surgical therapy. Elsevier. pp. 1142–1146. ISBN 978-0-323-64059-6.

[3] Feng J, Yang C, Jiang J (July 2021). "Real-world appraisal of intracranial pressure monitoring". The Lancet. Neurology. 20 (7): 502–503. doi:10.1016/S1474-4422(21)00164-2. PMID 34146500. S2CID 235456638.

[Harary_2018-4] 1 2 3 4 Harary M, Dolmans RG, Gormley WB (February 2018). "Intracranial Pressure Monitoring-Review and Avenues for Development". Sensors. 18 (2): 465. Bibcode:2018Senso..18..465H. doi: 10.3390/s18020465 . PMC 5855101 . PMID 29401746.

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