131 Intracranial pressure (ICP)

Intracranial pressure: normal range, cerebral perfusion pressure, treatment thresholds and causes of raised ICP.

Intracranial pressure (ICP) is the pressure inside the skull, in the brain tissue and cerebrospinal fluid. The skull is rigid, and its contents (brain about 80%, blood and CSF about 10% each) can change volume only slightly. When one component increases (swelling, bleeding, tumour, blocked CSF), the others are displaced at first, but once these reserves are exhausted, ICP rises steeply. Raised ICP reduces cerebral perfusion pressure and can push brain tissue through openings in the skull (herniation), which is life-threatening.

BrainNeurocritical careHead injury

Normal (supine adult)≈ 7–15 mmHg

Treatment threshold (TBI)> 22 mmHg

Perfusion pressureCPP = MAP − ICP

CPP target (TBI)60–70 mmHg

Figure 1. ICP zones. In severe traumatic brain injury, treatment is recommended when ICP exceeds 22 mmHg (Brain Trauma Foundation, 4th edition).

How ICP is measured

The reference method is invasive: a catheter in a brain ventricle (external ventricular drain, which also allows CSF drainage) or a pressure sensor in the brain tissue. Lumbar CSF pressure reflects ICP only when the CSF pathways are open and no mass lesion is present. Non-invasive signs include papilloedema, optic nerve sheath diameter on ultrasound and imaging findings.

Cerebral perfusion pressure (CPP) = mean arterial pressure (MAP) − ICP

Causes of raised ICP

Head injury with brain swelling or haematoma
Stroke (large infarction, intracerebral or subarachnoid haemorrhage)
Brain tumours and abscesses, meningitis, encephalitis
Hydrocephalus, cerebral venous sinus thrombosis, idiopathic intracranial hypertension
Hepatic encephalopathy in acute liver failure, severe hyponatraemia

Typical signs are headache that is worse in the morning or on straining, vomiting, blurred or double vision, papilloedema, drowsiness and, late, slow pulse with high blood pressure and irregular breathing (Cushing response).

Seek emergency care

for headache with vomiting and increasing drowsiness, confusion, seizures, unequal pupils or weakness, especially after a head injury.

References

Carney N, Totten AM, O’Reilly C, et al. Guidelines for the management of severe traumatic brain injury, fourth edition. Neurosurgery. 2017;80(1):6–15. doi:10.1227/NEU.0000000000001432
Sakka L, Coll G, Chazal J. Anatomy and physiology of cerebrospinal fluid. Eur Ann Otorhinolaryngol Head Neck Dis. 2011;128(6):309–316. doi:10.1016/j.anorl.2011.03.002

This article is for general information and does not replace a consultation with a doctor. Measurements must be interpreted by a physician together with symptoms and other tests.

Published on 12 May 2024