START: Suspected SAH
Sudden severe headache (thunderclap)
All Pathways
Emergency MedicineEmergency
Subarachnoid Hemorrhage Evaluation (ACEP 2019 + AHA 2023)
Subarachnoid Hemorrhage Evaluation (ACEP 2019 + AHA 2023): START: Suspected SAH → Clinical Assessment → Ottawa SAH Rule → Non-Contrast CT Head → CT Resu...
Pathway Overview
14 steps
Algorithm Steps
14 total
01Start 02Action Clinical Assessment
High-risk features
- Thunderclap headache (max intensity <1 min)
- Worst headache of life
- Neck stiffness/meningismus
- Loss of consciousness, syncope
- Focal neurologic deficit
- Seizure at onset
- Age >40 increases risk
03Action Ottawa SAH Rule
Clinical decision tool
- Consider SAH investigation if ANY present:
- - Age ≥40
- - Neck pain or stiffness
- - Witnessed LOC
- - Onset with exertion
- - Thunderclap headache
- - Limited neck flexion
- 100% sensitive (validation ongoing)
04Action Non-Contrast CT Head
First-line imaging
- Sensitivity 95-100% within 6 hours
- Decreases to 85% at 24h, 50% at 1 week
- Modern CT scanners highly sensitive if interpreted by expert
- Look for: Blood in cisterns, sulci, ventricles
05Decision CT Result?
Interpret findings
06Warning CT Positive for SAH
Blood identified on CT
- Confirm SAH
- Neurosurgery consult immediately
- CTA to identify aneurysm source
- Admit to ICU
07Action CT Angiography
Identify aneurysm
- 95-98% sensitivity for aneurysms >3mm
- Identifies aneurysm location and morphology
- May miss small aneurysms (<3mm)
- DSA if CTA negative but high suspicion
08Action SAH Management
Immediate interventions
- ICU admission
- BP control (SBP <160 before aneurysm secured)
- Nimodipine 60mg PO q4h x 21 days (reduces vasospasm)
- Secure aneurysm: Coiling vs clipping (within 24-72h)
- Monitor for vasospasm, hydrocephalus, rebleeding
09Decision CT Negative - LP Needed?
Depends on timing and clinical suspicion
- CT <6h + low suspicion: Some evidence LP may be deferred
- CT >6h or high suspicion: LP recommended
- Institutional protocols vary
10Action Lumbar Puncture
CSF analysis
- Collect 4 tubes
- RBC count Tube 1 vs Tube 4 (traumatic tap clears)
- Xanthochromia (visual or spectrophotometry)
- Xanthochromia takes 12 hours to develop
- Send for cell count, protein, glucose
11Decision LP Result?
Interpret CSF
- POSITIVE: RBCs not clearing + xanthochromia
- NEGATIVE: No RBCs, no xanthochromia
- EQUIVOCAL: RBCs clearing, no xanthochromia (may need CTA)
12Warning LP Positive for SAH
SAH confirmed
- Path rejoins step 07Shared downstream outcome
13Action LP Negative
SAH unlikely
- No RBCs, no xanthochromia
- Consider alternative diagnoses
- Migraine, tension headache
- Cervical artery dissection (consider CTA if suspicious)
14Outcome Discharge with Precautions
SAH ruled out
- Headache treatment
- Strict return precautions
- Return if: Worse headache, fever, neuro symptoms
- Primary care follow-up
- Path rejoins step 14Shared downstream outcome
Guideline Source
ACEP Clinical Policy: Evaluation of Adult Patients with Suspected SAH + AHA/ASA SAH Guidelines 2023
Clinical Safety Information
Clinical Decision Support — Not a Substitute for Clinical Judgment
Individual patient factors may require deviation from these recommendations.
Known Limitations
- Ottawa SAH Rule requires validation
- LP timing after CT varies by practice
- CTA sensitivity depends on aneurysm size
- Does not cover traumatic SAH management
Contraindicated Populations
pediatric
Applicable Regions
USEUGlobal
US: ACEP 2019 + AHA 2023 combined
Version 1Next review: 2027-01-01
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: Evaluation of Adult Patients with Suspected SAH + AHA/ASA SAH Guidelines 2023.
What guideline is the Subarachnoid Hemorrhage Evaluation (ACEP 2019 + AHA 2023) based on?
This algorithm is based on ACEP Clinical Policy: Evaluation of Adult Patients with Suspected SAH + AHA/ASA SAH Guidelines 2023 (DOI: 10.1016/j.annemergmed.2019.02.001).
What are the limitations of the Subarachnoid Hemorrhage Evaluation (ACEP 2019 + AHA 2023)?
Known limitations include: Ottawa SAH Rule requires validation; LP timing after CT varies by practice; CTA sensitivity depends on aneurysm size; Does not cover traumatic SAH management. Individual patient factors may require deviation from these recommendations.
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