raised intracranial pressure (ICP)

see also:

• the comatose patient
• headache
• stroke (CVA)

• raised ICP may cause fatal further cerebral injury, and thus in those patients at risk, it should be considered as a possible complication and actively managed.
• raised ICP may result in decreased blood perfusion of the brain
  • cerebral blood perfusion pressure = mean arterial pressure - ICP

• normal ICP is ≤ 15mmHg in adults and lower in children
• significant raised ICP is said to occur when ICP > 20mmHg, although transient rises do also occur with Valsalva, cough, sneeze, etc.
• the adult skull has a fixed volume of ~1.5L and contains 80% brain tissue, 10% blood and 10% CSF
• ICP is generally maintained at a relatively constant pressure
• CSF is produced at a rate of ~500mL/day and mostly is absorbed via arachnoid granulations to ensure CSF volume remains constant
• cerebral blood flow (CBF) is determined by:
  • (carotid arterial pressure - jugular venous pressure) / cerebrovascular resistance
  • cerebrovascular resistance is reduced and thus CBF is increased if there is hypoxia or hypercapnia
  • CBF is autoregulated to maintain a relatively constant CBF, however, this autoregulation may fail in stroke or intracranial trauma
• any increase in intracranial mass will first displace CSF into the spinal subarachnoid space
• further increase of ICP to 40-50mmHg results in compression of brain capillaries and resultant global cerebral ischaemia
• raised ICP may also result in herniation of brain tissue through the various anatomic compartments

• cerebral oedema
  • hypoxic brain injury
  • acute stroke (CVA)
  • acute brain trauma
  • intracranial infections
    • encephalitis
    • meningitis
    • cerebral abscess
  • neoplasia / cancer / tumours
• neoplasia / cancer / tumours
• cerebral abscess

• intracranial haemorrhage:
  • subdural haematoma
  • subarachnoid haemorrhage (SAH)
  • extradural haematoma
  • intracerebral haemorrhage / stroke

• hydrocephalus
  • increased CSF production:
    • choroid plexus papilloma
  • impaired CSF absorption:
    • arachnoid adhesions
      • post-meningitis
  • obstructive:
    • pressure from neoplasia / cancer / tumours

• hypercapnia
• hypoxia
• head down position
• stroke
• brain trauma
• venous outflow obstruction
  • venous sinus thrombosis
  • jugular vein compression

• benign raised idiopathic intracranial hypertension / pseudotumor cerebri
  • often young, obese females with amenorrhoea or irregular cycles
  • tetracycline antibiotics
  • isotretinoin (Roaccutane)

• headache
• vomiting
• confusion
• papilloedema
• sixth nerve palsy
• spontaneous periorbital bruising
• may cause brain tissue herniations with their respective features:
  • subfalcine herniation
    • displacement of the cingulate gyrus from one hemisphere to the other, under the falx cerebri.
    • can compress the pericallosal arteries, causing an infarct in their distribution (corpus callosum and medial surfaces of cerebral hemispheres) such as callosal disconnection syndromes, and contralateral hemiparesis with a lower limb predominance (more pronounced distally)
  • central transtentorial herniation
    • diencephalon stage: small reactive pupils, may have Cheyne Stokes respiration, may develop decorticate posturing
    • midbrain/upper pons stage: fixed, mid-position pupils, hyperventilation or Cheyne Stokes respiration, impaired or absent vestibulo-ocular reflexes, decerebrate posturing or no movement
    • lower pons/medulla stage: fixed, mid-position pupils, absent vestibulo-ocular reflexes, no movement, ataxic respiration
    • medulla stage: fixed, mid-position pupils, absent vestibulo-ocular reflexes, no movement, irregular or no respiration
  • uncal transtentorial herniation
    • herniation of the medial temporal lobe from the middle into the posterior fossa, across the tentorial opening
    • compresses the ipsilateral oculomotor nerve, causing a fixed and dilated pupil
    • collapses the ipsilateral posterior cerebral artery, causing an infarct in its distribution resulting in cortical blindness
    • displaces the midbrain laterally, compressing the contralateral cerebral peduncle against the edge of the tentorium, causing paralysis on the same side as the primary lesion
    • may displace the brainstem caudally causing brainstem haemorrhages affecting the RAS and also causing focal neurology and coma
  • upward cerebellar herniation
  • cerebellar tonsillar/foramen magnum herniation
    • pressure from above compresses the pons against the clivus and displaces the cerebellar tonsils into the foramen magnum
    • may cause neck stiffness, head tilt
    • pressure on pons and medullary cardioresp. centres may result in cardiorespiratory arrest
  • transcalvarial herniation
• terminal phase presumable due to brainstem compression results in Cushing's triad:
  • bradycardia
  • hypertension
  • respiratory depression

• CT scan brain:
  • suggestive signs include:
    • mass lesions
    • midline shift
    • effacement of basilar cisterns
    • effacement of sulci
  • does not exclude raised ICP nor its subsequent development
• role of the lumbar puncture (LP):
  • in general, LP is C/I in patients with suspected raised ICP as there is risk of herniation
  • it is useful in assisting Dx for those patients with suspected benign raised intracranial hypertension with a normal CT brain
• ICP monitoring:
  • invasive procedure reserved for cases where:
    • at risk of developing raised ICP, and,
    • GCS < 8, and
    • aggressive care warranted

• resuscitate as per usual guidelines to ensure hypercapnia, hypoxia, hypotension, rapid rise in blood pressure, and further rise in ICP is avoided
  • head up position at 30deg is usually advocated
  • avoid restrictive neck taping which may impair venous return
  • adequate sedation and paralytic agents if rapid sequence induction (RSI) for emergency intubation indicated
  • iv fluids as needed (usually no need to restrict fluids other than free water, as aim to maintain serum osmolality in the 295 to 305 mOsm/L range, and watch for hyponatraemia)
  • avoid fever
• ongoing sedation such as propofol
• anticonvulsants if seizure
• urgent CT brain mainly to search for aetiology
• consider hyperventilation to maintain PCO2 26-30mmHg (maybe C/I in brain trauma or stroke except in terminal phases)
• consider osmotic agents such as iv mannitol 1-1.5g/kg
• AVOID corticosteroids in patients with brain trauma, intracranial haemorrhage or stroke BUT consider use in those with brain tumours or CNS infections
• discuss with neurosurgical service ASAP to Rx the cause and consider other invasive measures