Increased intracranial pressure
-normal ICP is 10-15 mmhg (136-204 mmH2O)-primarily contributed by arterial pulsations transmitted to the brain directly & through the choroids plexus
-increased ICP always occurs when there is a disparity between intracranial volume & the intracranial contents
Common causes of increased ICP
Localized masses:heamatomas: epidural-subdural-intracerebral
neoplasms
abscess
focal odema due to trauma infection tumor
Obstruction to CSF pathways hydrocephalus
Obstruction to major venous sinuses depressed skull fracture over major venous sinuses thromboembolic disease from contraceptive pillsDiffuse brain odema or swelling encephalitis, meningitis, diffuse head injury SAH Reyes syndrome lead encephalopathy water intoxication from fluid overload
Idiopathic pseudotumor cerebri
Increased ICP can affect the brain in 2 ways
1-Brain ischemia when cerebral perfusion pressure is reduced to critical levels2-Focal masses can cause distortion & herniation of the brain resulting in compression of critical brain stem structures. The presence of herniation syndromes with occlusion of the tentorial incisura or the aqueduct further elevates ICP by blocking CSF pathway
Symptoms & signs
-headache most common generalized in nature
-nausea vomiting (projectile)
-bluring of vision
-papillodema
-hypertension
-bradycardia
-ataxia
-cranial nerve paralysis
Treatment
Eliminate the causeIf it is due to mass effect blood clot, prompt evacuation of the offending lesion
1-ventricular drainage
2-mannitol osmotic agent
-it is not metabolized
-does not cross the blood brain barrier
-Dose is 0.25 g/kg at 4-6 hours intervals
-decreases CSF production
-increases cerebral blood flow & cerebral oxygen consumption
-decreases blood viscosity
-effective for 48-72 hours
-beyond 72 hours ineffective because slowly leaks out of the blood vessels
3-hypertonic saline
-increasingly used since 2001-experimental & clinical studies suggest that it may be as effective as mannitol
4-hyperventilation
-decreases ICP by reducing blood flow & blood volume through vasoconstriction-for acute management of increased ICP
-not useful for sustained treatment
5-loop diuretics
-furosemide used as adjunct to mannitol because they seem to have synergistic effect-it is thought to reduce CSF production
6-steroids
-dexamethasone used for treating chronic increased ICP
-especially those related to vasogenic odema caused by primary or metastatic tumors
-not effective in vasogenic odema due to head trauma or cerebral infarction
-stabelizes cell membrane & restores the normal permeability of endothelial cells
-loading dose 10 mg I.V.
-4 mg every 6 hours
7-barbiturate coma
-Induction of coma with short acting barbiturates is the last resort in the management of increased ICP when all measures fail-the most commonly used drug is thiopental
-loading dose is 3-10 mg/kg over 10 min.
-maintenance dose of 1-2 mg/kg/hr
Next page; Cerebral odema
Cerebral odemaState of increased brain volume as a result of an increase in water content
Interstitial odemaCytotoxic odema (intracellular)Vasogenic odema (extracellular)TypeIncreased brain water due to impairment of CSF absorptionCellular swelling(neuronal, glial, endothelial)Increase capillary permeabilitypathogenesisPeri-ventricular white matterGrey & white matter Mainly white matterlocationCSFIncrease intracellular water & sodium due to failure of membrane transportPlasma filtrate containing plasma proteinsComposition of fluidincreaseddecreasedincreasedExtracellular fluidObstructive or communicating hydrocephalusEarly stages of infarction, water intoxicationPrimary or metastatic tumor, abscess, late stage of infarction, traumaPathologic lesionWith Greetings; Saif AlDeen Adil