INTRACRANIAL HYPERTENSION

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-sustained ICP > 15 mmHg
May results from:
-expanding tissue mass or fluid volume
-interference of the normal CSF absorption
-excessive CBF
-systemic derangement leading to cerebral edema

ICP > 30 mmHg
-leads to progressive decrease in CBF
-viscous cycle occurs due to ischemia secondary to decreased CBF
-resultant cerebral ischemia causes cerebral edema which again leads to inc ICP
-viscous cycle continues: ↑ICP:↓CBF:↑cerebral ischemia:↑cerebral edema:↑ICP …brain herniation

SYMPTOMS
-headache
-nausea and vomiting
-papilledema
-focal neurological deficits
-altered mental status
Cushings response: abrupt increase in ICP ( ≅ 1 – 15 mins) with bradycardia

Cerebral Edema
-increase in water content within the brain
-due to disruption in the integrity of the blood brain barrier
possible causes of cerebral edema include:
-mechanical trauma
-inflammatory lesions
-brain tumors
-hypertension
-infarction

TREATMENT goal: temporarily decrease brain edema and lower the ICP
-correct underlying disorders
-corticosteroids (ex dexamethasone) help promote repair of the blood brain barrier
-fluid restriction reduce the amount of free water content within the brain
-osmotic agents rapidly lowers ICP by affecting the serum osmolality
-loop diuretics slowly decreases ICP and may decrease CSF production
-hyperventilation (mild) relationship: ↓ PaC02: cerebral vasoconstriction: ↓CBF and ↓ICP

osmotic diuresis
ex. mannitol 0.25g- 0.5 g/kg
-effective in rapidly reducing ICP
-main effect on serum osmolality
-desired serum osmolality 300 – 315 mOsm/L
-weak vasodilation may cause a transient decrease in MAP
disadvantages of mannitol:
-possible transient increase in intravascular volume
-may lead to pulmonary edema in cardiac and/or renal patients
-may allow a hematoma to expand due to decreased volume of brain around the hematoma secondary to diuresis and dec ICP
-rapid decrease in ICP in the elderly may lead to SDH due to rupture of the fragile bridging veins of the sagittal sinus

loop diuretic
ex. furosemide
-less effective than osmotic diuresis (mannitol)
-requires more time compased to osmotic diuresis (upto 30 minutes)
-benefit may include directly decreasing the CSF production

loop diuretic + osmotic diuretic synergistic use:
-synergistic effect may be beneficial
-closely monitor [K+]