Neurology

Subarachnoid haemorrhage

Arterial blood bursts into the cerebrospinal fluid around the brain, usually from a ruptured intracranial aneurysm, raising intracranial pressure and irritating the meninges within seconds. Abbreviated SAH.

In a nutshell

Subarachnoid haemorrhage (SAH) is arterial bleeding into the cerebrospinal fluid, usually from a ruptured intracranial aneurysm. Get an urgent non-contrast CT head: its accuracy is highest within 6 hours of symptom onset.

Classic presentation

A 55-year-old woman collapses with a headache that reached maximum intensity within a minute, and now has neck stiffness, photophobia and vomiting.

Key points

Thunderclap means peaking within 1 to 5 minutes. Most thunderclap headaches are not SAH, but rate of onset is the question you must ask.
Nimodipine prevents delayed cerebral ischaemia. It is not an antihypertensive here, and NICE only says 'consider' it, reflecting weak evidence mostly from the 1980s.
Around half of people who survive an aneurysmal SAH have a second bleed within weeks, and mortality from that second bleed can exceed 50%.
NICE endorses no decision rule and no severity score for deciding who is imaged, transferred or treated. A senior clinical decision-maker decides.
SAH causes 5% of all strokes; around 80% are aneurysmal, and the median age at presentation is between 50 and 60.
Xanthochromia is bilirubin measured by spectrophotometry, not red cells. That is what separates a real bleed from a traumatic tap.

First-line investigation

Urgent non-contrast CT head, after urgent review by a senior clinical decision-maker. Diagnostic accuracy is highest within 6 hours of symptom onset.

Management

Recognise and resuscitate

Suspected SAH outside hospital goes to an emergency department immediately. In hospital, urgent review by a senior clinical decision-maker.¹
Give effective analgesia. If an opioid is needed and morphine is chosen, an adult BNF example is 5 mg by slow IV injection, adjusted to response.^1,8

Diagnose by the clock

Urgent non-contrast CT head. Blood in the subarachnoid space is diagnostic. Accuracy is highest within 6 hours of symptom onset.¹
Negative CT within 6 hours, reported by a radiologist: no routine lumbar puncture. Discuss alternatives with a senior decision-maker and seek specialist advice.¹
Negative CT after 6 hours: lumbar puncture, at least 12 hours from onset. Bilirubin (xanthochromia) on spectrophotometry confirms SAH.¹

Transfer and secure the aneurysm

Urgently discuss transfer with a specialist neurosurgical centre. Never use a severity score alone to decide transfer, timing or suitability for treatment.⁷
CT angiography of the head without delay. If it finds no cause and an aneurysm is still suspected, consider digital subtraction angiography, or magnetic resonance angiography if that is contraindicated.²
Endovascular coiling, or neurosurgical clipping if coiling is unsuitable, at the earliest opportunity. Rebleeding risk is highest within 24 hours of symptom onset.^2,7

Prevent secondary brain injury

Consider nimodipine. If used: 60 mg by mouth every 4 hours, started within 4 days and continued for 21 days.^3,4
Intravenous nimodipine is specialist-only when enteral treatment is unsuitable: 1 mg/hour, or up to 0.5 mg/hour under 70 kg, raised to 2 mg/hour after 2 hours via a central catheter.^3,4
Delayed cerebral ischaemia: ensure euvolaemia (normal blood volume) and consider a vasopressor if symptoms persist. Improvement from a vasopressor may be temporary.⁵
Unexplained deterioration: non-contrast CT head first. Consider cerebrospinal fluid drainage or diversion for acute hydrocephalus. Do not use transcranial doppler outside research.⁵
Manage venous thromboembolism risk in line with NICE NG89 (venous thromboembolism in over 16s), both before and after the aneurysm is secured.^3,6

Rehabilitate and safety-net

Written follow-up plan with a named specialist-centre contact, copied into the discharge letter. Offer rehabilitation and manage blood pressure per the NICE hypertension guideline.⁹
Review headache, fatigue, sleep, mood, cognition, seizures, driving, work and sexual activity. Support smoking cessation, which affects the estimated risk of a further bleed.⁹
Do not withhold antiplatelets or anticoagulants solely because of the SAH once the culprit aneurysm has been secured by coiling or clipping.⁹
Testing relatives is usually limited to people with at least two affected first-degree relatives, and has not been shown to save lives.⁹

Exam traps

A negative CT more than 6 hours after onset does not exclude SAH. A negative CT within 6 hours, reported by a radiologist, largely does.
Do not do a lumbar puncture before 12 hours from onset: bilirubin has not yet formed, so the result cannot be interpreted.
NICE recommends opioid analgesia in suspected SAH even though the BNF lists raised intracranial pressure as an opioid contra-indication. Document the dose and read pupils accordingly.
New deterioration is not automatically vasospasm. CT head first, to find rebleeding, hydrocephalus or seizure.
Do not use transcranial doppler to guide management. NICE restricts it to research.
NICE makes no recommendation for tranexamic acid, and says it must never delay securing the aneurysm.
Headache after discharge is usually benign, but with gait disturbance, incontinence or cognitive decline it suggests chronic hydrocephalus.

Illustrations

Thunderclap versus gradual headache onsetPain-intensity-over-time diagram contrasting the instantaneous maximal onset of subarachnoid haemorrhage with gradual headache build-up.PassFinals · original

CT head showing subarachnoid bloodNon-contrast CT image showing hyperdense blood in the basal cisterns and sulci.James Heilman, MD, Wikimedia Commons · CC-BY-SA-3.0

Circle of Willis aneurysm sitesDiagram highlighting common intracranial aneurysm sites at arterial junctions.PassFinals · original

Key sources

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.