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Encyclopedia > Intracranial pressure

Intracranial pressure, (ICP), is the pressure exerted by the cranium on the brain tissue, cerebrospinal fluid (CSF), and the brain's circulating blood volume. ICP is a dynamic phenomenon constantly fluctuating in response to activities such as exercise, coughing, straining, arterial pulsation, and respiratory cycle. ICP is measured in millimeters of mercury (mmHg) and, at rest, is normally less than 10–15 mmHg. Changes in ICP are attributed to volume changes in one or more of the constituents contained in the cranium. Cranium can mean: The brain and surrounding skull, a part of the body. ... The human brain In animals, the brain (enkephalos) (Greek for in the skull), is the control center of the central nervous system, responsible for behavior. ... Cerebrospinal fluid (CSF), Liquor cerebrospinalis, is a clear bodily fluid that occupies the subarachnoid space in the brain (the space between the skull and the cerebral cortex—more specifically, between the arachnoid and pia layers of the meninges). ... Human blood smear: a - erythrocytes; b - neutrophil; c - eosinophil; d - lymphocyte. ... The word dynamics can refer to: a branch of mechanics; see dynamics (mechanics) the volume of music; see dynamics (music) When used referring to mechanics, it is referring to the study of the motion of both rigid bodies and particles. ... For other uses, see Phenomena (disambiguation). ... One way of defining pressure is in terms of the height of a column of fluid that may be supported by that pressure; or the height of a column of fluid that exerts that pressure at its base. ...

Contents

The Monro-Kellie Hypothesis

The pressure-volume relationship between ICP, volume of CSF, blood, and brain tissue, and cerebral perfusion pressure (CPP) is known as the Monro-Kellie doctrine or the Monro-Kellie hypothesis. Cerebral perfusion pressure, or CPP, is the net pressure of blood flow to the brain. ...


The Monro-Kellie hypothesis states that the cranial compartment is incompressible, and the volume inside the cranium is a fixed volume. 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.


The principal buffers for increased volumes include both 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. These compensatory mechanisms are able to maintain a normal ICP for any change in volume less than approximately 100–120 mL.


Increased ICP

One of the most damaging aspects of brain trauma and other conditions, directly correlated with poor outcome, is an elevated intracranial pressure.[1] ICP is very likely to cause severe harm if it rises beyond 40 mmHg in an adult.[2] Even intracranial pressures between 25 and 30 mm Hg are usually fatal if prolonged, except in children, who can tolerate higher pressures for longer periods.[3] An increase in pressure, most commonly due to head injury leading to intracranial hematoma or cerebral edema can crush brain tissue, shift brain structures, contribute to hydrocephalus, cause the brain to herniate, and restrict blood supply to the brain, leading to an ischemic cascade.[4] This article needs to be cleaned up to conform to a higher standard of quality. ... This article needs to be cleaned up to conform to a higher standard of quality. ... Cerebral edema (cerebral oedema in British English) is an excess accumulation of water in the intra- and/or extracellular spaces of the brain. ... Herniation, a deadly side effect of very high intracranial pressure, occurs when the brain shifts across structures within the skull. ... The ischemic cascade is a series of biochemical reactions that take place in the brain after seconds to minutes of ischemia (inadequate blood supply) (Arnold, 2003). ...


Pathophysiology

The cranium and the vertebral body, along with the relatively inelastic dura, form a rigid container, such that the increase in any of its contents --- brain, blood, or CSF --- will increase the ICP. In addition, any increase in one of the components must be at the expense of the other two -- a relationship known as the Monro-Kellie doctrine. Small increases in brain volume do not lead to immediate increase in ICP because of the ability of the CSF to be displaced into the spinal canal, as well as the slight ability to stretch the falx cerebri between the hemispheres and the tentorium between the hemispheres and the cerebellum. However, once the ICP has reached around 25 mmHg, small increases in brain volume can lead to marked elevations in ICP. A diagram of a thoracic vertebra. ...


Traumatic brain injury is a devastating problem with both high mortality and high subsequent morbidity. Injury to the brain occurs both at the time of the initial trauma (the primary injury) and subsequently due to ongoing cerebral ischemia (the secondary injury). Cerebral edema, hypotension, and axonal hypoxic conditions are well recognized causes of this secondary injury. In the intensive care unit, raised intracranial pressure (intracranial hypertension) is seen frequently after a severe diffuse brain injury and leads to cerebral ischemia by compromising cerebral perfusion.


The difference between the ICP and the mean arterial pressure within the cerebral vessels is termed the cerebral perfusion pressure (CPP)(cerebral perfusion pressure is calculated by subtracting the intracranial pressure from the mean arterial pressure CPP=MAP-ICP), the amount of blood able to reach the brain. One of the main dangers of increased ICP is that it can cause ischemia by decreasing cerebral perfusion pressure. Once the ICP approaches the level of the mean systemic pressure, it becomes more and more difficult to squeeze blood into the intracranial space. The body’s response to a decrease in CPP is to raise blood pressure and dilate blood vessels in the brain. This results in increased cerebral blood volume, which increases ICP, lowering CPP further and causing a vicious cycle. This results in widespread reduction in cerebral flow and perfusion, eventually leading to ischemia and brain infarction. Increased blood pressure can also make intracranial hemorrhages bleed faster, also increasing ICP. In medicine, ischemia (Greek ισχαιμία, isch- is restriction, hema or haema is blood) is a restriction in blood supply, generally due to factors in the blood vessels, with resultant damage or dysfunction of tissue. ... Cerebral perfusion pressure, or CPP, is the net pressure of blood flow to the brain. ... A sphygmomanometer, a device used for measuring arterial pressure. ... f you all The blood vessels are part of the circulatory system and function to transport blood throughout the body. ... This article needs cleanup. ...


Highly increased ICP, if caused by a one-sided space-occupying process (eg. an haematoma) can result in midline shift, a dangerous condition in which the brain moves toward one side as the result of massive swelling in a cerebral hemisphere. Midline shift can compress the ventricles and lead to buildup of CSF.[5] Prognosis is much worse in patients with midline shift than in those without it. Another dire consequence of increased ICP combined with a space-occupying process is brain herniation (usually uncal or cerebellar), in which the brain is squeezed past structures within the skull, severely compressing it. If brainstem compression is involved, it may lead to decreased respiratory drive and is potentially fatal. This herniation is often referred to as "coning". The human brain as viewed from above, showing the cerebral hemispheres. ... The ventricular system is a set of structures in the brain continuous with the central canal of the spinal cord. ... Herniation, a deadly side effect of very high intracranial pressure, occurs when the brain shifts across structures within the skull. ...


Major causes of morbidity due to increased intracranial pressure are due to global brain infarction as well as decreased respiratory drive due to brain herniation.


Intracranial Hypertension

Minimal increases in ICP due to compensatory mechanisms is known as stage 1 of intracranial hypertension. When the lesion volume continues to increase beyond the point of compensation, the ICP has no other resource, but to increase. Any change in volume greater than 100–120 mL would mean a drastic increase in ICP. This is stage 2 of intracranial hypertension. Characteristics of stage 2 of intracranial hypertension include compromise of neuronal oxygenation and systemic arteriolar vasoconstriction to increace MAP and CPP. Stage 3 intracranial hypertension is characterised by a sustained increased ICP, with dramatic changes in ICP with small changes in volume. In stage 3, as the ICP approaches the MAP, it becomes more and more difficult to squeeze blood into the intracranial space. The body’s response to a decrease in CPP is to raise blood pressure and dilate blood vessels in the brain. This results in increased cerebral blood volume, which increases ICP, lowering CPP further and causing a vicious cycle. This results in widespread reduction in cerebral flow and perfusion, eventually leading to ischemia and brain infarction. Neurologic changes seen in increased ICP are mostly due to hypoxia and hypercapnea and are as follows: decreased LOC, Cheyne-Stokes respirations, hyperventilation, sluggish dilated pupils and widened pulse pressure. Cheyne-Stokes respiration is an abnormal pattern of breathing characterized by periods of breathing with gradually increasing and decreasing tidal volume interspersed with periods of apnea. ...


Causes of increased ICP

Causes of increased intracranial pressure can be classified by the mechanism in which ICP is increased:

  • mass effect such as brain tumor, infarction with edema, contusions, subdural or epidural hematoma, or abscess all tend to deform the adjacent brain.
  • generalized brain swelling can occur in ischemic-anoxia states, acute liver failure, hypertensive encephalopathy, pseudotumor cerebri, hypercarbia, and Reye hepatocerebral syndrome. These conditions tend to decrease the cerebral perfusion pressure but with minimal tissue shifts.
  • increase in venous pressure can be due to venous sinus thrombosis, heart failure, or obstruction of superior mediastinal or jugular veins.
  • obstruction to CSF flow and/or absorption can occur in hydrocephalus (blockage in ventricles or subarachnoid space at base of brain, e.g., by Arnold-Chiari malformation), extensive meningeal disease (e.g., infectious, carcinomatous, granulomatous, or hemorrhagic), or obstruction in cerebral convexities and superior sagittal sinus (decreased absorption).
Main article: hydrocephalus
  • increased CSF production can occur in meningitis, subarachnoid hemorrhage, or choroid plexus tumor.

Signs and symptoms of increased ICP

In general, symptoms and signs that suggest a rise in ICP including headache, nausea, vomiting, ocular palsies, altered level of consciousness, and papilledema. If papilledema is protracted, it may lead to visual disturbances, optic atrophy, and eventually blindness. A headache (cephalgia in medical terminology) is a condition of pain in the head; sometimes neck or upper back pain may also be interpreted as a headache. ... For other uses, see Nausea (disambiguation). ... Emesis redirects here. ... Papilledema is optic disc swelling that is caused by increased intracranial pressure. ...


In addition to the above, if mass effect is present with resulting displacement of brain tissue, additional signs may include pupillary dilatation, abducens (CrN VI) palsies, and the Cushing's triad. Cushing's triad involves an increased systolic blood pressure, a widened pulse pressure, bradycardia, and an abnormal respiratory pattern.[6] In children, a slow heart rate is especially suggestive of high ICP. Mydriasis is an excessive dilation of the pupil due to disease or drugs. ... Cushings triad is the triad of hypertension, bradycardia, and Cheyne-Stokes respiration (irregular breathing) in patients with head injuries. ... Blood pressure is the pressure exerted by the blood on the walls of the blood vessels. ... Pulse pressure is the change in blood pressure seen during a contraction of the heart. ... Bradycardia, as applied to adult medicine, is defined as a resting heart rate of under 60 beats per minute, though it is seldom symptomatic until the rate drops below 50 beat/min. ...


Irregular respirations occur when injury to parts of the brain interfere with the respiratory drive. Cheyne-Stokes respiration, in which breathing is rapid for a period and then absent for a period, occurs because of injury to the cerebral hemispheres or diencephalon.[7] Hyperventilation can occur when the brain stem or tegmentum is damaged.[7] Cheyne-Stokes respiration is an abnormality of the pattern of breathing. ... The human brain as viewed from above, showing the cerebral hemispheres. ... The diencephalon is the region of the brain that includes the epithalamus, thalamus, and hypothalamus. ... In medicine, hyperventilation (or hyperpnea) is the state of breathing faster or deeper (hyper) than necessary, and thereby reducing the carbon dioxide concentration of the blood below normal. ... The brain stem is the lower part of the brain, adjoining and structurally continuous with the spinal cord. ... The midbrain tegmentum is part of the midbrain extending from the substantia nigra to the cerebral aqueduct. ...


As a rule, patients with normal blood pressure retain normal alertness with ICP of 25 to 40 mmHg (unless there's concurrent tissue shift). Only when ICP exceeds 40 to 50 mmHg do CPP and cerebral perfusion decrease to a level that results in loss of consciousness. Any further elevations will lead to brain infarction and brain death.


In infants and small children, the effects of ICP differ due to the fact that their cranial sutures have not closed. In infants, the fontanels, or soft spots on the head where the skull bones have not yet fused, bulge when ICP gets too high. In human anatomy, a fontanelle (or fontanel) is one of two soft spots on a newborn humans skull. ...


Treatment of increased ICP

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.


One of the most important treatments for high ICP is to ensure adequate airway, breathing, and oxygenation, since inadequate oxygen levels or excess carbon dioxide cause cerebral blood vessels to dilate and ICP to rise.[8] Inadequate oxygen also forces brain cells to produce energy using anaerobic metabolism, which produces lactic acid and lowers pH, which dilates blood vessels.[1] On the other hand, blood vessels constrict when carbon dioxide levels are below normal, so hyperventilating a patient with a ventilator or bag valve mask can temporarily reduce ICP but limits blood flow to the brain in a time when the brain may already be ischemic. Artificially ventilating a patient at a fast rate used to be a standard part of head trauma treatment because of its ability to rapidly lower ICP, but the chance of developing ischemia was later recognized to be too much of a risk.[9] Furthermore, the brain adjusts to the new level of carbon dioxide after 48 to 72 hours of hyperventilation, which could cause the vessels to rapidly dilate if carbon dioxide levels were returned to normal too quickly.[9] Now hyperventilation is used when signs of brain herniation are apparent because the damage herniation can cause is so severe that it may be worthwhile to constrict blood vessels even if doing so reduces blood flow. Another way to lower ICP is to raise the head of the bed, allowing for venous drainage. A side effect of this is that it could lower pressure of blood to the head, resulting in inadequate blood supply to the brain. Another simple method used to lower ICP (particularly in trauma cases) is to loosen neck collars and clothing. This method is more useful is the patient is sedated and thus movement is minimal. Sandbags may be used to further limit neck movement. The airways are those parts of the respiratory system through which air flows, to get from the external environment to the alveoli. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ... For other uses, see Fermentation. ... For the production of milk by mammals, see Lactation. ... For other uses, see PH (disambiguation). ... In medicine, hyperventilation is the state of breathing faster or deeper than necessary, and thereby reducing the carbon dioxide concentration of the blood below normal. ... A medical ventilator is a device designed to provide mechanical ventilation to a patient. ... A disposable BVM Resuscitator A bag valve mask (also known as a BVM or Ambu bag) is a hand-held device used to provide ventilation to a patient who is not breathing or who is breathing inadequately. ... In medicine, ischemia (Greek ισχαιμία, isch- is restriction, hema or haema is blood) is a restriction in blood supply, generally due to factors in the blood vessels, with resultant damage or dysfunction of tissue. ... Herniation, a deadly side effect of very high intracranial pressure, occurs when the brain shifts across structures within the skull. ...


In the hospital, blood pressure can be artificially raised in order to increase CPP, increase perfusion, oxygenate tissues, remove wastes and thereby lessen swelling.[9] Since hypertension is the body's way of forcing blood into the brain, medical professionals do not normally interfere with it when it is found in a head injured patient.[7] When it is necessary to decrease cerebral blood flow, MAP can be lowered using common antihypertensive agents such as calcium channel blockers.[1] For other forms of hypertension, see Hypertension (disambiguation). ... Antihypertensives are a class of drugs that are used in medicine and pharmacology to treat hypertension (high blood pressure). ... Calcium channel blockers are a class of drugs and natural substances with effects on many excitable cells of the body, like the muscle of the heart, smooth muscles of the vessels or neuron cells. ...


Struggling can increase metabolic demands and oxygen consumption, as well as increasing blood pressure.[10][8] Thus children may be paralyzed with drugs if other methods for reducing ICP fail. Paralysis allows the cerebral veins to drain more easily, but can mask signs of seizures, and the drugs can have other harmful effects.[8] Structure of the coenzyme adenosine triphosphate, a central intermediate in energy metabolism. ... Paralysed redirects here. ... This article is about epileptic seizures. ...


Pain is also treated to reduce agitation and metabolic needs of the brain, but some pain medications may cause low blood pressure and other side effects.[1]


Intracranial pressure can be measured continuously with intracranial transducers (only used in neurosurgical intensive care). A catheter can be surgically inserted into one of the brain's lateral ventricles and can be used to drain CSF (cerebrospinal fluid) in order to decrease ICP's. This type of drain is known as an EVD (extraventricular drain).[1] In rare situations when only small amounts of CSF are to be drained to reduce ICP's, drainage of CSF via lumbar puncture can be used as a treatment. The ventricular system is a set of structures in the brain continuous with the central canal of the spinal cord. ...


Craniotomies are holes drilled in the skull to remove intracranial hematomas or relieve pressure from parts of the brain.[1] As raised ICP's may be caused by the presence of a mass, removal of this via craniotomy will decrease raised ICP's. A craniotomy is a surgical operation in which part of the skull (part of the cranium) is removed in order to access the brain. ... This article needs to be cleaned up to conform to a higher standard of quality. ...


A drastic treatment for increased ICP is decompressive craniectomy, in which a part of the skull is removed and the dura mater is expanded to allow the brain to swell without crushing it or causing herniation.[9] The section of bone removed, known as a bone flap, can be stored in the patient's abdomen and resited back to complete the skull once the acute cause of raised ICP's has resolved. Decompressive craniectomy is a surgical procedure in which part of the skull is removed to allow a swelling brain room to expand without being squeezed. ... The dura mater (from the Latin hard mother), or pachymeninx, is the tough and inflexible outermost of the three layers of the meninges surrounding the brain. ... A hernia is the protrusion of an organ or tissue out of the body cavity in which it normally lies. ...


Low ICP

It is also possible for the intracranial pressure to drop below normal levels, though increased intracranial pressure is a far more common (and far more serious) sign. The symptoms for both conditions are often the same, leading many medical experts to believe that it is the change in pressure rather than the pressure itself causing the above symptoms.


External links

Reduced intracranial pressure affects the monre kei constant The University of Adelaide (colloquially Adelaide University or Adelaide Uni) is a public university located in Adelaide. ...


References

  1. ^ a b c d e f Orlando Regional Healthcare, Education and Development. 2004. "Overview of Adult Traumatic Brain Injuries." Accessed September 6, 2007.
  2. ^ Dawodu S. 2005. "Traumatic Brain Injury: Definition, Epidemiology, Pathophysiology" Emedicine.com.Accessed January 4, 2007.
  3. ^ Tolias C and Sgouros S. 2006. "Initial Evaluation and Management of CNS Injury." Emedicine.com. Accessed January 4, 2007.
  4. ^ Graham DI and Gennareli TA. Chapter 5, "Pathology of Brain Damage After Head Injury" In, Cooper P and Golfinos G. 2000. Head Injury, 4th Ed. Morgan Hill, New York.
  5. ^ Downie A. 2001. "Tutorial: CT in Head Trauma" Accessed January 4, 2007.
  6. ^ Sanders MJ and McKenna K. 2001. Mosby’s Paramedic Textbook, 2nd revised Ed. Chapter 22, "Head and Facial Trauma." Mosby.
  7. ^ a b c Singh J and Stock A. 2006. "Head Trauma." Emedicine.com. Accessed January 4, 2007.
  8. ^ a b c Su F and Huh J. 2006. "Neurointensive Care for Traumatic Brain Injury in Children." Emedicine.com. Accessed January 4, 2007.
  9. ^ a b c d Shepherd S. 2004. "Head Trauma." Emedicine.com. Accessed January 4, 2007.
  10. ^ Bechtel K. 2004. "Pediatric Controversies: Diagnosis and Management of Traumatic Brain Injuries." Trauma Report. Supplement to Emergency Medicine Reports, Pediatric Emergency Medicine Reports, ED Management, and Emergency Medicine Alert. Volume 5, Number 3. Thomsom American Health Consultants.
  • Monroe A. Observations on the structure and function of the nervous system, Edinburgh: Creech & Johnson; 1783.
  • Kelly G. An account of the appearances observed in the dikssection of two of three individuals presumed to have perished in the storm of the 3rd, and whose bodies were deiscovered in the vicinity of the Leith on the morning of the 4th of November 1821, with some reflections on the pathology of the brain, Trans Med Chir Sci Edinb 1824;1:84–169.

is the 249th day of the year (250th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 4th day of the year in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 4th day of the year in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 4th day of the year in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 4th day of the year in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 4th day of the year in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 4th day of the year in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ...

External links

  1. Gruen P. 2002. "Monro-Kellie Model" Neurosurgery Infonet. USC Neurosurgery. Accessed January 4, 2007.
  2. National Guideline Clearinghouse. 2005. Guidelines for the management of severe traumatic brain injury. Firstgov. Accessed January 4, 2007.

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