START: Suspected SAH (adult)
Sudden severe non-traumatic headache peaking within 1 h (thunderclap: peak within 1 min)
All Pathways
Emergency MedicineEmergency
Subarachnoid Hemorrhage Evaluation (ACEP 2019 + AHA 2023)
Subarachnoid Hemorrhage Evaluation (ACEP 2019 + AHA 2023): START: Suspected SAH (adult) → Assess time of onset, GCS and neuro exam → No rule-out tools i...
Pathway Overview
17 steps
Algorithm Steps
17 total
01Start 02Action Assess time of onset, GCS and neuro exam
Record the exact time of headache onset and the time to peak pain
- Thunderclap: peak within 1 min; rule-out tools cover peak within 1 h
- Neck pain or stiffness, LOC or syncope, seizure, vomiting
- GCS, pupils, focal deficit, papilloedema
- Anticoagulant or antiplatelet use: check FBC and coagulation now
- History: prior aneurysm or SAH, brain tumour, shunt, similar past headaches
03Warning No rule-out tools if GCS below 15, new focal deficit or papilloedema
Also not for: age 15 or under; prior aneurysm, SAH, brain tumour, shunt or hydrocephalus; presentation mainly with seizure, syncope or neck pain. Go straight to CT.
- GCS below 15 or new deficit: resuscitate, CT now, call neurosurgery
- If CT normal: LP or CTA; the 6-hour CT rule does not apply
- Children: seek paediatric advice; these rules are adult-only
04Decision Ottawa SAH Rule applies?
Yes only if ALL: alert (GCS 15), age over 15, new severe non-traumatic headache peaking within 1 h, normal neuro exam, none of the exclusions above, and not 3 or more similar headaches over more than 6 months.
- If Yes
- Rule applies
05Decision Any Ottawa SAH Rule criterion present?
Age 40 or over; neck pain or stiffness; witnessed LOC; onset during exertion; thunderclap (instant peak) onset; limited neck flexion on exam.
- If Yes
- Any criterion
06Action Rule not applicable or any criterion: non-contrast CT head now
Modern CT (third generation or later) reported by an experienced radiologist
- Record the time from headache onset to CT
- Look for blood in basal cisterns, fissures, sulci and ventricles
- Sensitivity about 99% within 6 h of onset (pooled 98.7%); 86% after 6 h
- Hb below 100 g/L can reduce CT sensitivity
07Decision SAH on CT?
Blood in the subarachnoid space on non-contrast CT
- If Yes
- Positive
08Warning CT shows SAH: call neurosurgery now
Treat as aneurysmal SAH until proven otherwise
- Urgent neurosurgical referral; transfer to an aSAH centre
- Reverse anticoagulants now
- Next: CTA to find the aneurysm
09Action SAH confirmed or possible: CT angiography
Find the aneurysm and plan treatment with neurosurgery and neurointervention
- CTA pooled sensitivity about 97% against DSA
- Diffuse SAH with a normal CTA: DSA is still needed
- DSA is the reference standard and guides the choice of treatment
10Action SAH confirmed: neurocritical care and early aneurysm repair
Reverse anticoagulants now. Nimodipine: 30 mg (not 60 mg) every 4 h in cirrhosis; caution if SBP below 100 mmHg; do not give with rifampicin.
- Transfer to a centre with neurosurgery, neurointervention and neuro-ICU
- Secure the aneurysm early, preferably within 24 h
- Adult: nimodipine 60 mg orally or by NG every 4 h for 21 days; start within 96 h
- BP: if SBP above 180-200 mmHg, lower gradually; avoid MAP below 65 mmHg and large swings
- Never inject tablet or capsule contents; IV nimodipine infusion only in ICU with specialist advice
- Hypotension on nimodipine: treat BP; stop only if BP cannot be controlled
- Acute hydrocephalus: urgent CSF diversion; neurosurgery chooses EVD or lumbar drain
- Keep euvolaemia; no prophylactic hypervolaemia; no routine tranexamic acid
- Seizure: treat for 7 days; no routine prophylaxis; avoid phenytoin
11Outcome Neurosurgical ICU admission
Frequent neuro checks for rebleeding, hydrocephalus and delayed cerebral ischaemia
If No- Negative
12Decision CT normal: does the 6-hour rule exclude SAH?
Yes only if ALL: CT within 6 h of headache ONSET (not arrival), normal neuro exam, headache peaked within 1 h, modern CT read by an experienced radiologist, and presentation was not mainly neck pain, syncope or seizure.
- If Yes
- 6-hour rule met
13Action SAH excluded: consider other causes of thunderclap headache
A negative SAH work-up does not exclude other serious causes. Pregnant or postpartum: also consider eclampsia, PRES, CVST and RCVS.
- RCVS, cerebral venous sinus thrombosis, cervical artery dissection
- Pituitary apoplexy, intracerebral haemorrhage, ischaemic stroke, intracranial hypotension
- Pregnant or postpartum: check BP and urine protein; MRI or CTV before discharge
- If suspected: CTA or CTV, or MRI, before discharge; discuss with neurology
- Fever, meningism or raised CSF white cells: treat as possible meningitis
14Outcome SAH and other serious causes excluded: discharge with safety-net
Return now if headache returns or worsens, fever, neck stiffness, weakness, confusion or seizure. GP follow-up.
- Treat pain: non-opioid analgesia first
- Give the return advice in writing
- GP follow-up
If No- 6-hour rule not met
15Action 6-hour rule not met: LP (at least 12 h after onset) or CTA
Do LP at least 12 h after headache onset. Anticoagulated, coagulopathy or low platelets: use CTA, not LP.
- LP: record opening pressure; RBC count in first and final tube
- Xanthochromia by spectrophotometry where the lab offers it
- LP done before 12 h and negative: not reliable; confirm with CTA
- Also send cell count, protein, glucose, Gram stain and culture
- CTA: may find an incidental aneurysm; misses CSF causes such as meningitis
16Decision LP or CTA positive or indeterminate?
Yes: xanthochromia, OR final-tube RBC 2000 x10^6/L or more, OR aneurysm on CTA. No: no xanthochromia AND final-tube RBC below 2000 x10^6/L, OR normal CTA. Falling RBC counts between tubes do not exclude SAH.
- If Yes
- Positive or indeterminate
17Warning LP or CTA positive or indeterminate: treat as possible SAH
Urgent neurosurgical referral
- Xanthochromia or final-tube RBC 2000 x10^6/L or more: CTA next
- Aneurysm on CTA with no CSF blood may be incidental: neurosurgery decides
- Reverse anticoagulants if SAH is confirmed
- Path rejoins step 09Shared downstream outcome
If No- Negative
- Path rejoins step 13Shared downstream outcome
If No- No criterion
- Path rejoins step 13Shared downstream outcome
If No- Rule does not apply
- Path rejoins step 06Shared downstream outcome
Guideline Source
ACEP Clinical Policy: Adult ED Patients With Acute Headache (Ann Emerg Med 2019;74:e41-e74) + AHA/ASA 2023 Guideline for Aneurysmal SAH (Stroke 2023;54:e314-e370, doi 10.1161/STR.0000000000000436)
Clinical Safety Information
Clinical Decision Support — Not a Substitute for Clinical Judgment
Individual patient factors may require deviation from these recommendations.
Known Limitations
- Rule-out steps (Ottawa SAH Rule, 6-hour CT) apply only to alert adults with normal neuro exam and headache peaking within 1 h
- 6-hour CT rule needs modern CT, an experienced reader and an accurate onset time
- CTA can miss small aneurysms and finds incidental ones
- Does not cover traumatic SAH or detailed ICU care
Contraindicated Populations
children (15 years or under)head traumaGCS below 15 or new focal neurological deficit (rule-out steps do not apply)known aneurysm or prior SAH (rule-out steps do not apply)
Applicable Regions
AUUSEUGlobal
AU: Nimotop 30 mg tablets and Nimotop 0.2 mg/mL IV infusion are on the ARTG. The AU PI oral-only course is 10-14 days; the 21-day course follows the US label and AHA/ASA practice. Haemoglobin in g/L (100 g/L = 10 g/dL). Emergency: 000.
US: ACEP 2019 clinical policy + AHA/ASA 2023 aSAH guideline
Version 2Next review: 2027-09-30
Next steps
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Related Resources
Frequently Asked Questions
What is the Subarachnoid Hemorrhage Evaluation (ACEP 2019 + AHA 2023)?
The Subarachnoid Hemorrhage Evaluation (ACEP 2019 + AHA 2023) is a emergency clinical algorithm for Emergency Medicine. It provides a structured decision tree to guide clinical decision-making, based on ACEP Clinical Policy: Adult ED Patients With Acute Headache (Ann Emerg Med 2019;74:e41-e74) + AHA/ASA 2023 Guideline for Aneurysmal SAH (Stroke 2023;54:e314-e370, doi 10.1161/STR.0000000000000436).
What guideline is the Subarachnoid Hemorrhage Evaluation (ACEP 2019 + AHA 2023) based on?
This algorithm is based on ACEP Clinical Policy: Adult ED Patients With Acute Headache (Ann Emerg Med 2019;74:e41-e74) + AHA/ASA 2023 Guideline for Aneurysmal SAH (Stroke 2023;54:e314-e370, doi 10.1161/STR.0000000000000436) (DOI: 10.1016/j.annemergmed.2019.07.009).
What are the limitations of the Subarachnoid Hemorrhage Evaluation (ACEP 2019 + AHA 2023)?
Known limitations include: Rule-out steps (Ottawa SAH Rule, 6-hour CT) apply only to alert adults with normal neuro exam and headache peaking within 1 h; 6-hour CT rule needs modern CT, an experienced reader and an accurate onset time; CTA can miss small aneurysms and finds incidental ones; Does not cover traumatic SAH or detailed ICU care. Individual patient factors may require deviation from these recommendations.
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