Raised Intracranial Pressure (ICP)

Emergency Neurological Life Support Intracranial Hypertension and Herniation Protocol Version 4.0. Last updated: Mar 2020.

Article Last Updated:12/06/2026

Raised Intracranial Pressure (ICP)

Raised intracranial pressure (ICP) is an elevation of pressure within the cranial vault, usually defined as sustained ICP above 20–22 mmHg.

This updated UKMLA guide to raised intracranial pressure is based on Emergency Neurological Life Support guidelines, which cover relevant physiology, causes, symptoms, diagnosis, and management.

Relevant Physiology

The cranium is a rigid, non-expandable structure containing 3 main intracranial volume components:

Brain tissue
CSF
Blood

Monro-Kellie principle:

The Monro-Kellie principle states that the total intracranial volume must remain constant because the skull cannot expand
Therefore, if the volume of one component increases, e.g. due to haemorrhage, cerebral oedema, tumour, this must be offset by a compensatory reduction in another component
Early compensatory mechanisms include
- Displacement of CSF into the spinal canal
- Reduction in intracranial venous blood volume

Once the early compensatory mechanisms are exhausted, even a small further increase in intracranial volume can cause a rapid rise in ICP.

Why raised ICP is dangerous

The main danger of raised ICP is reduced cerebral perfusion pressure (CPP), meaning reduced blood flow to the brain.

CPP = pressure gradient driving cerebral blood flow
CPP = mean arterial pressure (MAP) – intracranial pressure (ICP)
As ICP rises, CPP falls. If CPP falls too low, cerebral blood flow becomes inadequate, causing cerebral ischaemia

Causes and Risk Factors

Structural causes (most important): ^[Ref]

Category	Causes
Increase in brain tissue	Space-occupying lesion (mass effect) Tumour Abscess Haematoma
Increase in brain tissue	Cerebral oedema (increase in brain volume) Encephalitis / meningitis Trauma Hypoxic ischaemic injury Hypertensive encephalopathy Metabolic / toxins (e.g. hyponatraemia, DKA, hepatic encephalopathy)
Increase in blood volume	Intracranial haemorrhage (EDH, SDH, SAH, ICH) ↑ Cerebral blood flow Hypercapnia Aneurysms AVMs Venous obstruction (technically considered a secondary cause) Cerebral venous sinus thrombosis Jugular vein thrombosis SVC syndrome ↑ Central venous pressure (e.g. heart failure)
Increase in CSF	Obstructive hydrocephalus (→ reduced CSF absorption) Choroid plexus tumour (→ increased production)

Other causes: ^[Ref]

Idiopathic intracranial hypertension (IIH)
Secondary causes of ↑ ICP ^[Ref1]^[Ref2]
- Medications
  - Antibiotics: tetracyclines, fluoroquinolones
  - Retinoids / vitamin A derivatives
  - Hormones and steroids: corticosteroid withdrawal, anabolic steroids, growth hormone, oral contraceptives
  - Growth hormone
  - Lithium
- Systemic and medical disorders
  - CKD, uraemia, OSA, COPD
  - SLE
  - Infections: HIV, Lyme disease, varicella, psittacosis, CNS infections, otitis media, mastoiditis
- Endocrine disorder
  - Addison’s disease, adrenal insufficiency
  - Thyroid and parathyroid disorders
  - Cushing’s syndrome
- Haematological disorders
  - Anaemia (including severe iron deficiency)
  - Thrombophilia
  - Polycythaemia vera
- Syndromic / genetic conditions
  - Down syndrome
  - Turner syndrome
  - Craniosynostosis

Clinical Features

^[Ref1]^[Ref2]^[Ref3]

Investigation and Diagnosis

Clinical assessment: ^[Ref]

Comprehensive clinical history
Medication review (e.g. steroids, retinoids, tetracyclines, COCPs)
Ophthalmic and neurological examination
Measure blood pressure to assess for malignant hypertension / hypertensive emergency

Investigations: ^[Ref]

Investigation	Description
1st line investigation: neuroimaging	Non-contrast CT head is often performed initially to identify underlying causes of raised ICP MRI may also be useful
Lumbar puncture	Lumbar puncture should ONLY be performed after neuroimaging Opening pressure >20 cm H₂O is suggestive of raised ICP However, this is only supportive, not definitive confirmation of raised ICP
Definitive: invasive ICP monitoring	Provides continuous, real-time measurements Raised ICP is defined as a sustained (> 5 min) elevation of ICP to >22 mmHg Raised ICP is often broadly defined as ICP >20 mmHg. However, modern guidelines commonly use sustained ICP >22 mmHg as a treatment threshold when invasive ICP monitoring is in place.

Investigation

Description

1st line investigation: neuroimaging

Non-contrast CT head is often performed initially to identify underlying causes of raised ICP

MRI may also be useful

Lumbar puncture

Lumbar puncture should ONLY be performed after neuroimaging

Opening pressure >20 cm H₂O is suggestive of raised ICP
However, this is only supportive, not definitive confirmation of raised ICP

Definitive: invasive ICP monitoring

Provides continuous, real-time measurements

Raised ICP is defined as a sustained (> 5 min) elevation of ICP to >22 mmHg

Raised ICP is often broadly defined as ICP >20 mmHg. However, modern guidelines commonly use sustained ICP >22 mmHg as a treatment threshold when invasive ICP monitoring is in place.

Do not perform lumbar puncture before neuroimaging if raised ICP is suspected, due to the risk of brain herniation if there is a space-occupying lesion.

If raised ICP is due to a space-occupying lesion, removing CSF from the spinal canal during lumbar puncture can create a pressure gradient between the skull and spinal canal. This can pull brain tissue downwards and cause brain herniation, especially tonsillar herniation, which can compress the brainstem and become rapidly fatal.

Management

Temporary Acute Management

There are different tiers of raised ICP management, aiming to reduce ICP and prevent brain herniation. If raised ICP or impending herniation is clinically suspected, acute ICP-lowering measures should not be delayed while awaiting investigations.

All ICP-lowering interventions should be viewed as temporising measures to prevent or reverse herniation while the underlying cause is identified and treated.

Management tier	Component / description
Tier 0 – standard preventive measures	The following should be performed in those who are at risk of raised ICP Assess ABC, intubate if GCS ≤8 Elevate the head of the bed to >30° Supportive care Provide appropriate analgesia and/or sedation Maintain normothermia (aggressively manage fever) Avoid and correct hyponatraemia High-dose corticosteroid should only be given in raised ICP due to vasogenic oedema, most commonly caused by brain tumours or abscess Apart from brain tumour and abscess, corticosteroids are contraindicated in TBI and most other causes of raised ICP. ^[Ref]
Tier 1	Hyperosmolar therapy (both have equivalent efficacy) Hypertonic saline (IV 2-23.4%), or Mannitol (IV bolus) Temporary controlled hyperventilation (for <2 hours)
Tier 2	Increase serum sodium goals for hyperosmolar therapy Optimise sedation and analgesia (e.g. propofol) Consider rescue decompressive surgery
Tier 3	For patients who are NOT a surgical candidate: Sedation with pentobarbital (guided by ICP goal or until burst suppression on continuous EEG) Hyperventilation Moderate hypothermia (target core temperature 32–34°C)

Definitive Management

ICP-lowering measures (mentioned above) buy time, but definitive management is treatment of the underlying cause.

Some high-yield cause-specific management:

Cause of raised ICP	Management
Intracranial tumour / metastasis	Definitive tumour treatment options include neurosurgical resection, radiotherapy, chemotherapy See the Brain Tumours in Adults article for more information
Brain abscess	Aspiration + IV antibiotics See the Brain Abscess article for more information
Hydrocephalus	EVD in the acute setting
Extradural or subdural haematoma	Urgent neurosurgical evacuation See the Extradural Haemorrhage (EDH) and Subdural Haemorrhage (SDH) article for more information
Subarachnoid haemorrhage	Neurosurgical clipping or endovascular coiling (if secondary to aneurysm) See the Subarachnoid haemorrhage (SAH) article for more information
Intracerebral haemorrhage	BP control, reverse anticoagulation if appropriate See the Haemorrhagic Stroke article for more information
Cavernous venous sinus thrombosis	Anticoagulation with heparin See the Cerebral Venous Sinus Thrombosis (CVST) article for more information
Encephalitis / meningitis	IV antimicrobials depending on the suspected cause. See the Encephalitis and Meningitis article for more information