Neurology · Topic 4 of 22

Aneurysmal Subarachnoid Hemorrhage

Neurology · hemorrhagic stroke

Aneurysmal Subarachnoid Hemorrhage

A ruptured aneurysm: confirm with CT (then LP if late), secure it within 24 hours, give nimodipine, and watch days 3–10 for delayed ischemia.

Key numbers

Negative CT after 6 h: do LPCT ≤ 6 h, else + LP

Secure the aneurysm within 24 hoursSecure ≤ 24 h

Nimodipine 60 mg q4h for 21 days60 mg q4h × 21 d

01 · DoNegative CT after 6 h: do LP

Get a noncontrast head CT. Within 6 hours, a negative high-quality CT in a neurologically intact patient can exclude SAH; after 6 hours or with a new deficit, a negative CT needs LP for xanthochromia.

02 · DoSecure the aneurysm within 24 hours

Find the aneurysm with CTA or catheter angiography and secure it by coiling or clipping as early as feasible, preferably within 24 hours — early rebleeding is common and often fatal.

03 · GiveNimodipine 60 mg q4h for 21 days

Start enteral nimodipine 60 mg every 4 hours for 21 days, within 96 hours of the bleed, to prevent delayed cerebral ischemia; never inject capsule contents IV — fatal cardiovascular collapse has occurred.

Presentation

What you'll see

Thunderclap headache peaking within seconds must knowSuspect aneurysmal SAH with a sudden severe headache that peaks within seconds ("worst headache of my life"), often with brief loss of consciousness and vomiting; meningismus develops over hours.

Diagnosis & monitoring

Work-up

Grade severity with Hunt-Hess or WFNSGrade severity at presentation with the Hunt and Hess or WFNS scale to predict outcome; high-grade aSAH can still be treated after a frank prognosis discussion with the family.

Do right now

In this order

First moves

Negative CT after 6 h: do LPCT ≤ 6 h, else + LP

→

Reverse any anticoagulant immediately

→

Control BP until the aneurysm is secured

→

Nimodipine 60 mg q4h for 21 days60 mg q4h × 21 d

→

Secure the aneurysm within 24 hoursSecure ≤ 24 h

Why each step

Negative CT after 6 h: do LPGet a noncontrast head CT. Within 6 hours, a negative high-quality CT in a neurologically intact patient can exclude SAH; after 6 hours or with a new deficit, a negative CT needs LP for xanthochromia.

Reverse any anticoagulant immediatelyReverse anticoagulation immediately in any patient with aSAH; routine antifibrinolytic therapy (tranexamic acid) does not improve outcome and is not recommended.

Control BP until the aneurysm is securedUntil the aneurysm is secured, treat marked hypertension (commonly SBP > 160 mmHg) with titrated IV nicardipine, avoiding MAP < 65 and BP swings; no specific target is evidence-based.

Nimodipine 60 mg q4h for 21 daysStart enteral nimodipine 60 mg every 4 hours for 21 days, within 96 hours of the bleed, to prevent delayed cerebral ischemia; never inject capsule contents IV — fatal cardiovascular collapse has occurred.

Secure the aneurysm within 24 hoursFind the aneurysm with CTA or catheter angiography and secure it by coiling or clipping as early as feasible, preferably within 24 hours — early rebleeding is common and often fatal.

Management

Orders

Seizures: treat 7 days; avoid phenytoinTreat new seizures after aSAH with antiseizure medication for 7 days; prophylaxis is not routine (consider only in high-risk patients), and phenytoin should be avoided.

Red flags & don'ts

Avoid harm

Delayed cerebral ischemia: days 3–10 complicationA new deficit or falling consciousness 3–10 days after the bleed suggests vasospasm with delayed cerebral ischemia: keep euvolemia and raise BP to limit it — never prophylactic hypervolemia or hypertension.

Acute hydrocephalus: urgent EVD complicationAcute symptomatic hydrocephalus (headache, obtundation) needs urgent CSF diversion with an external ventricular or lumbar drain, managed under an EVD bundle to cut infection.

Hyponatremia: stay euvolemic, consider fludrocortisone complicationNatriuresis with hyponatremia is common after aSAH; maintain euvolemia (hypovolemia may promote delayed ischemia), use mineralocorticoids such as fludrocortisone, and never induce hypervolemia — it is harmful.

No statins or IV magnesium for vasospasm avoidRoutine statins and IV magnesium do not prevent delayed cerebral ischemia and are not recommended.

ECG changes and stunned myocardium complicationaSAH can cause ST changes, QT prolongation, deep symmetric T-wave inversions and neurogenic stunned myocardium that mimic myocardial infarction.

The rules

Know these

Ottawa SAH Rule for alert patientsOttawa SAH Rule (alert, age > 15, new severe headache peaking within 1 hour): investigate if age ≥ 40, neck pain or stiffness, witnessed LOC, onset with exertion, thunderclap onset, or limited neck flexion.

Aneurysmal SAH or traumatic tap?

Commonly confused

RBCs from tube 1 to tube 4	Stay high
Xanthochromia	Present (blood > ~6 h old)
Crenated RBCs on microscopy	Seen

More detail

Reference

Show 7 reference facts

Frequent neurologic checks by trained nurses detect delayed ischemia; transcranial Doppler, CTA and CT perfusion help detect vasospasm, and continuous EEG helps in poor-grade patients.

A traumatic tap shows RBCs falling across successive tubes; in SAH, RBCs crenate and lyse after about 6 hours, giving xanthochromia (spectrophotometry is highly sensitive).

Up to 20% of patients have multiple aneurysms, so image both carotid and both vertebral arteries; CTA has largely replaced catheter angiography for diagnosis.

Ruptured posterior-circulation aneurysms that are amenable to coiling should be coiled rather than clipped.

Once the aneurysm is secured, start pharmacological or mechanical VTE prophylaxis.

About 13% of patients with aSAH die in hospital and up to 26% die before reaching it; lasting neurologic deficits are common in survivors.

For raised ICP or cerebral edema in SAH, the Neurocritical Care Society suggests symptom-based boluses of hypertonic saline rather than sodium-target dosing.

Pearl

Worst headache of life, peaking in seconds: CT, LP if late, then secure the aneurysm within a day.

Sources · Hoh BL et al. 2023 AHA/ASA Guideline for the Management of Patients With Aneurysmal Subarachnoid Hemorrhage. Stroke 2023;54:e314–e370 (full-text PDF copy) · Merck Manual Professional — Subarachnoid Hemorrhage (updated Aug 2026) · Nimodipine capsules prescribing information — DailyMed · Cook AM et al. Guidelines for the Acute Treatment of Cerebral Edema in Neurocritical Care Patients (Neurocritical Care Society). Neurocrit Care 2020 · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).