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Elevated intracranial pressure and brain herniation

Last updated: May 25, 2021

Summarytoggle arrow icon

Intracranial pressure (ICP) is the pressure that exists within the cranium, including its compartments (e.g., the subarachnoid space and the ventricles). ICP varies as the position of the head changes relative to the body and is periodically influenced by normal physiological factors (e.g., cardiac contractions). Adults in the supine position typically have a physiological ICP of ≤ 15 mm Hg; an ICP of ≥ 20 mm Hg indicates pathological intracranial hypertension. ICP may be elevated in a variety of conditions (e.g., intracranial tumors) and can result in a decrease in cerebral perfusion pressure (CPP) and/or herniation of cerebral structures. Symptoms of elevated ICP are generally nonspecific (e.g., impaired consciousness, headache, vomiting); however, more specific symptoms may be present depending on the affected structures (e.g., Cushing triad if the brainstem is compressed). Findings from brain imaging (e.g., a midline shift) and physical examination (e.g., papilledema) can indicate ICP elevation, but may not be able to rule it out. Therefore, ICP monitoring and quantification are vital in at-risk patients. Management usually involves expedited surgery of resectable or drainable lesions, conservative measures (e.g., positioning, sedation, analgesia, and antipyretics), and medical therapy (e.g., hyperosmolar therapy such as mannitol or hypertonic saline, or glucocorticoids). Treatment options for refractory intracranial hypertension include temporary controlled hyperventilation, CSF drainage, and decompressive craniectomy (DC), as well as other advanced medical therapies (e.g., barbiturate coma, therapeutic hypothermia).

Physiology

  • Physiological ICP is ≤ 15 mm Hg in adults (in supine position); children generally have a lower ICP.
  • ICP varies as the position of the head changes relative to the body and is influenced by certain physiological processes (e.g., cardiac contractions, sneezing, coughing, Valsalva maneuver).
  • Expansion of either blood, CSF, or tissue within the skull limited capacity for the intracranial volume to increase within the rigid skull increase in intracranial pressure

Consequences of elevated ICP

  • Decreased cerebral perfusion pressure (CPP)
    • CPP is the effective pressure that delivers blood to the cerebral tissue.
    • CPP = mean arterial pressure - ICP
    • Therefore, if the ICP rises, the CPP diminishes (as long as the arterial pressure remains constant).
  • Brain tissue herniation
    • As a bony structure, the skull is rigid and cannot expand to compensate elevated internal pressure.
    • Increased pressure gradient within the skull in the presence of inflexible brain structures (e.g., tentorium cerebelli) → flexible brain tissue shifts possible brain tissue herniation
    • This may result in direct physical damage or in blocking of cerebral vessels and subsequent ischemia.
  • Cushing triad: also called Cushing reflex or Cushing response and is thought to reflect brainstem compression. This sign indicates a need for urgent treatment.

Cerebral herniation syndromes

The following clinical features should raise suspicion for a cerebral herniation syndrome, which can be fatal if not treated promptly: acutely worsening level of consciousness (e.g., coma), pupillary changes (e.g., ipsilateral mydriasis, fixed dilated pupils), new focal neurological deficits (e.g., hemiparesis, decerebrate posturing), and cardiorespiratory compromise (e.g., bradycardia, apnea).

References:[3][4]

Neuroimaging (CT head/MRI head) [5]


Clinical examination and imaging may indicate elevated ICP, but cannot rule it out. Additionally, neither allow ICP to be quantified, which is necessary to determine CPP.

Invasive ICP monitoring

  • Invasive monitoring is typically required for confirmation and accurate measurement of ICP.
  • ICP should be evaluated in combination with CPP to guide therapeutic interventions and help prevent secondary brain injury and brain herniation. [6]
  • There are no absolute contraindications for invasive ICP monitoring.
  • Consider the risks versus the benefits in consultation with a specialist.

Indications [7][8][9]

Methods to monitor ICP [6][10][11]

Intraventricular catheters; with an external ventricular drain (EVD) and intraparenchymal catheters; (IPC) are most commonly used to monitor ICP, as they have the highest accuracy compared with other monitoring methods.

  • Intraventricular catheter: a monitoring device placed into the ventricles of the brain along with a CSF drainage system (i.e., an EVD) [12]
    • Allows for continuous ICP monitoring and evaluation of intracranial compliance
    • Useful in conditions in which CSF drainage is required for both diagnostic and therapeutic purposes
    • The preferred monitoring method for intracranial lesions associated with hydrocephalus [6]
    • Complications
      • Infections
      • Hemorrhage attributable to the placement of the device
      • Malpositioning and/or accidental removal
      • Blockage with blood or debris
  • Intraparenchymal catheter: a fiberoptic device placed into the brain parenchyma without an accompanying CSF drainage system [13]
    • Allows for continuous ICP monitoring
    • Accuracy and effect on patient outcomes are considered equivalent to intraventricular catheters
    • Lower risk of infection and hemorrhage compared with intraventricular catheters
    • Technical complications: e.g., dislodgement, breakage

Interpretation

  • Generally, ICP > 20 mm Hg indicates intracranial hypertension, which requires treatment. [6]
  • ICP varies in a complex cyclical manner and is influenced by hemodynamic and metabolic factors.
  • Monitor ICP along with MAP to calculate CPP using the formula CPP = MAP − ICP.

Do not use the ICP value in isolation as a prognostic marker or to inform therapeutic decisions. [6]

Approach [5][6][8][14][15][16]

Stepwise ICP management (based on a multifactorial response) [5][14][17][18]
Step Intervention
Initial steps
  • Identify and expedite the treatment of lesions that are amenable to emergency surgical procedures.
Subsequent step
  • Add medical therapy (e.g., hyperosmolar therapy).
Elective temporizing step
  • Consider short-term (< 30 minutes) controlled hyperventilation in patients with signs of imminent brain herniation and refractory elevated ICP in the interim while waiting for:
    • Surgical procedures
    • Onset of action of medical therapy
Advanced steps
  • General therapeutic targets: Base treatment decisions on trends identified using repeat assessments of ICP, CPP, and clinical status. [6][8]
    • Target ICP: < 20 mm Hg
    • Target CPP range: 60–70 mm Hg

Conservative therapy [19]

See also “Neuroprotective measures.”

Medical therapy [19]

Overview of hyperosmolar therapies in ICP management [19][26][27][28]
Mannitol HTS
Pharmacology [5][8]
  • Mannitol 20% is most commonly used.
  • Lowers ICP within minutes of administration
  • Peak efficacy: 20–60 minutes after administration
  • Duration of effect: 4–6 hours
  • Multiple concentrations of HTS exist (e.g., 3–23.4%), with highly variable dosages and pharmacokinetics. [19]
  • 23.4% HTS is commonly used.
Therapeutic targets to consider [14][19][20]
  • Symptom-based dosing is recommended for patients with SAH.
  • Serum osmolarity (e.g., 300–320 mOsm/L) or osmolar gap
  • Serum sodium (e.g., 145–155 mEq/L) [5][29][30]
Adverse effects [5][14][16]
Considerations [5]

Although hyperosmolar therapies can lower ICP, they have not been shown to improve neurological outcomes in patients with underlying TBI, acute ischemic stroke, ICH, SAH, or hepatic encephalopathy. [19]

Surgical therapy

  • Emergency surgery (if possible): e.g., resection of brain tumor, hematoma evacuation [16]
  • CSF drainage
  • Decompressive craniectomy (DC): removal of a portion of the skull, which allows the brain to expand in volume, thereby reducing ICP [32]
    • Primary DC: removal of a skull flap following evacuation or resection of an intracranial lesion (e.g., brain tumor)
    • Secondary DC: removal of a skull flap without additional surgical procedures to treat refractory elevated ICP
      • Recommended for (controversial): [32]
      • Not recommended for patients with early refractory elevated ICP
    • Multiple approaches have been described in the literature (suboccipital, subtemporal, frontotemporoparietal, etc.) depending on the type and location of the brain lesion. [34]
    • Lowers mortality in TBI without improving neurological or functional outcomes [15]

Nonsurgical therapy for refractory intracranial hypertension [19]

Controlled hyperventilation

Hyperventilation is primarily used as a temporizing measure for intracranial hypertension refractory to medical therapy. [17]

Controlled hyperventilation should only be used short-term and is not recommended routinely or for prophylaxis. Avoid excessive hyperventilation (PaCO2 < 30 mm Hg), prolonged hyperventilation, and hypoventilation of any kind, as CBF and perfusion may become compromised.

Advanced therapies

These are primarily reserved for patients with persistently refractory intracranial hypertension.

Cerebral edema

We list the most important complications. The selection is not exhaustive.

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