Subarachnoid hemorrhage (SAH) refers to traumatic as well as nontraumatic bleeding into the subarachnoid space. SAH most often results from head trauma. Nontraumatic SAH is responsible for 5–10% of all strokes and is most commonly caused by the rupture of an aneurysm involving the circle of Willis. SAH typically presents with severe headache, nausea, vomiting, and/or acute loss of consciousness. Acute bleeding in the subarachnoid space appears hyperdense on noncontrast CT scan, which is the initial recommended test in diagnosis. CT angiography and lumbar puncture may be necessary for further evaluation if the initial noncontrast head CT is unremarkable. Treatment consists of carefully lowering blood pressure and preventing cerebral vasospasm. Definitive management typically consists of clipping or coiling the bleeding aneurysm to prevent potentially fatal rebleeding. SAH has a high mortality rate as a result of complications such as rebleeding and secondary ischemic strokes due to vasospasm.
- Subarachnoid hemorrhage: bleeding into the subarachnoid space
- Intracerebral hemorrhage: bleeding within the brain parenchyma
- Intracranial hemorrhage: a broad term used to describe any bleeding within the skull (including intracerebral hemorrhage, subarachnoid hemorrhage, subdural hemorrhage, etc.)
- Hemorrhagic stroke: cerebral infarction due to hemorrhage
- Intraventricular hemorrhage: bleeding within the ventricles
- Head trauma is the most common cause of SAH.
- 40–60% of patients with have subarachnoid bleeding. 
Epidemiological data refers to the US, unless otherwise specified.
- Traumatic SAH: 
Nontraumatic (spontaneous) SAH
- Ruptured intracranial aneurysms
- Ruptured arteriovenous malformations (AVM)
- Others: cortical thrombosis, angioma, neoplasm, infection
- Triggers: most cases unknown, may be triggered by an acute rise in blood pressure; (e.g., caffeine consumption, fits of anger, physical exertion) 
- Risk factors 
- Thunderclap headache
- Meningeal signs :
- Nonspecific signs
- Signs due to mass effect
- Prodromal symptoms due to sentinel leak (a "warning leak")
- Immediate noncontrast head CT
Lumbar puncture (LP)
- Best test if head CT is negative but suspicion for SAH remains high
- Angiography: if CT and lumbar puncture are negative but clinical suspicion for SAH is still high and/or to identify the source of ongoing bleeding (prior to intervention).
- Additional testing to consider
Medical therapy 
- Reverse anticoagulation
- Blood pressure management
- Prevent vasospasm in all patients: administer calcium channel blocker (drug of choice: oral nimodipine)
- Maintain euvolemia
- Avoid/treat hyponatremia
- Maintain normoglycemia
- If patient has elevated ICP:
- Seizure prophylaxis 
Surgical therapy 
- Should be performed as early as possible to prevent rebleeding
Definitive treatment options for aneurysmal SAH
- Surgical clipping
- Endovascular coiling
- The decision on which procedure to perform should be made on an individualized basis.
- If the patient has hydrocephalus: ventricular drain, serial LPs, or permanent may become necessary.
Use of nitrates should be avoided, since they may raise ICP!
- Urgent neurosurgery and neuroradiological consult for consideration of surgical or endovascular aneurysm repair
- Airway management: Consider anesthesiology consult.
- Identify and treat any underlying coagulopathy.
- Vasospasm prophylaxis: Start nimodipine. 
- Blood pressure management
- Consider invasive blood pressure monitoring.
- Target blood pressure: SBP < 160 mm Hg and MAP > 70 mm Hg
- Avoid overly aggressive lowering of blood pressure.
- If SBP > 160 mm Hg, consider one of the following: 
- If MAP < 70 mm Hg, consider hemodynamic support with vasopressors (e.g., phenylephrine ). 
- Identify and treat the underlying cause: Consider further imaging (e.g., CT angiography to evaluate for vascular malformation).
- Treat complications (e.g., seizures). ,
- Euglycemia: Avoid hypoglycemia and hyperglycemia.
- Normothermia: antipyretics for fever
- Normovolemia: IV fluids for hypovolemia
- Close observation, BP monitoring, GCS monitoring
- Admit to neurosurgical ICU.
- VTE prophylaxis
- Occurs in approx. 30% of patients with SAH 
- Transcranial doppler ultrasound study can help identify vasospasm.
- Can lead to ischemic stroke
- Most common in patients with nontraumatic SAH due to a ruptured aneurysm
- Usually occurs between 3–10 days after SAH
- Occurs in 4–14% of patients with SAH in the first 24 hours 
- Risk of rebleeding is highest in the first 2–12 hours after SAH
- The cumulative risk of recurrent bleeding within the first six months is about 50%.
- Other complications 
We list the most important complications. The selection is not exhaustive.
- Approx. 30% mortality rate in the U.S. within the first 30 days 
- Survivors: increased rates of neurologic impairment (e.g., cognitive, mood changes, functional, epilepsy) and increased risk of recurrent SAH