EBM Subarachnoid Haemorrhage

Pedagogical disambiguation: Emergency Medicine Lecture Notes and Evidence Based emergency medicine principles from Professor A.F.T Brown and the Life in the Fast Lane team.


  • Life threatening Causes
    • Meningitis
    • Subarachnoid haemorrhage
    • Space occupying lesion
    • Hypertensive encephalopathy
    • Temporal arteritis (age over 50; ESR > 50)
    • Pre-eclampsia

The majority of cases however are:

  • Migraine: common or classical
  • Tension-type headache
  • Post-traumatic headache
  • Disease in other cranial structures eg. glaucoma, iritis, sinusitis, otitis, TMJ dysfunction.

Subarachnoid Haemorrhage

  • 5% of all acute strokes, but 25% of the fatalities, as case fatality rate around 50% overall (10-20% pre-hospital). 20-30% survivors have residual disability, epilepsy in 7-12% and 50% ‘good’ outcomes have neuropsychological and cognitive impairment.
  • Initially misdiagnosed in 20% as ‘migraine’ or ‘tension-headache’ on first encounter, as headache can abate or disappear. Up to 15% re-bleed early, and 40% in next 4 weeks, although risk is highest in those with large aneurysms / in poor condition.

Clinical Features

  • Typical Presentation
    • Sudden, instantaneous onset, maximum within minutes “worst headache ever”; generalised and unrelenting. Associated vomiting, neck pain, meningismus, altered mental status (>60%), and localising neurological signs incl III N with PCA aneurysm.  May collapse (syncopal episode) then recover.
    • Overall one in 100 headache patients seen in ED will have SAH, and up to 10% of those with a severe, abrupt-onset headache
  • Atypical presentations:
    • Low grade fever, neck or back pain, seizures (7%), coma (up to 30%), focal stroke, restlessness, confusion or delirium.

Kowalski R, Claassen J, Kreiter K et al. Initial misdiagnosis and outcome after subarachnoid haemorrhage. JAMA 2004; 291: 866 -9. [Reference]


  • CT scan (thin < 3 mm cuts without contrast)
    • First line investigation. Over 95% – 98% sensitivity in first 12 hrs, 93% by 24 hrs, but drops to 50% by day 7.
    • May indicate site of bleed, early complications eg. hydrocephalus and cerebral oedema, or an alternative diagnosis.
  • Angiography
    • CT angiography (CTA) sensitivity for aneurysm 97.9%.
    • Negative CT followed by negative CTA will give post-test probability of excluding SAH of 99.43%. But note up to 2% population may have an ‘incidental’ small aneurysm.
    • Digital subtraction angiography (DSA) traditional gold standard, but is invasive. Or possibly proceed to MRA particularly for suspected partial thrombosis or spinal cord / brain stem origin.

McCormack R, Hutson A. Can CTA of the brain replace LP in the evaluation of acute-onset headache after a negative noncontrast cranial CT? Acad Emerg Med 2010;17:444-51. [Reference]

  • Lumbar Puncture (LP)
    • If CT is negative, though see CT/CTA combination NPV 99.43% above.
    • Check for xanthochromia by spectrophotometry of spun CSF, shielded from light.
    • Perform LP 12 hours post headache to most reliably differentiate from a traumatic tap (absence of xanthochromia and bilirubin). Minimum 6 hrs.
    • Note complications of LP include failure, equivocal result (15-20%), post-LP headache (up to 40%), low back pain, local infection or traumatic neurology, and traumatic tap with difficulty in interpretation.

Boesiger B, Shiber J. Subarachnoid hemorrhage diagnosis by computed tomography and lumbar puncture: are fifth generation CT scanners better at identifying subarachnoid hemorrhage? J Emerg Med 2005; 29:23-7. [Reference]

Schwartz D. Feedback: Computed tomography and lumbar puncture for the diagnosis of subarachnoid haemorrhage: The importance of accurate interpretation. Ann Emerg Med 2002; 39: 190-2. [Reference]


  • Airway, oxygen, analgesia, hydration, blood pressure control and ICU care including for possible hydrocephalus, pulmonary oedema, arrhythmias, hyponatraemia etc. Newer interest in statins, magnesium and neuroprotective agents.
  • Nimodipine 60 mg po 4-hrly upon confirmation of diagnosis if BP stable. Consider 1 mg/h IV increased to 2 mg/h after 2 hours if comatose.
    • Reduces vasospasm by up to 50% and delayed ischaemic deficit by up to 60%, by vasodilating and protecting against reperfusion injury from calcium influx.
  • Endovascular platinum coils (GDCs) preferred first line management within first 72 hours, espec posterior circulation.
  • Alternative is early surgery clipping if patient presents within 2-3 days of onset, particularly if large neck to aneurysm.  Or may be delayed up to 14 days if spasm and infarction occur.

Ferro J, Canhão P, Peralta R. Update on subarachnoid haemorrhage. J Neurol 2008;255:465-79. [Reference]

Edlow J, Malek A, Ogilvy C. Aneurysmal subarachnoid haemorrhage: update for emergency physicians. J Emerg Med 2008;34:237-51. [Reference]

van Gijn J, Kerr R, Rinkel G. Subarachnoid haemorrhage. Lancet 2007; 369: 306-318. [Reference]

Al-Shahi R, White P, Davenport R et al. Subarachnoid haemorrhage. BMJ 2006; 333:235-40. [Reference]

Suarez J, Tarr R, Selman W. Aneurysmal subarachnoid hemorrhage. N Eng J Med 2006; 354:387-96. [Reference]

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  1. CJ says

    Can I ask the source of the nimodipine dose? The dose that I have been used to is q4h (6 times a day), which appears to be supported by multiple sources I’ve checked. Is there an evidence base for q6h instead?

    • says

      Thank you for pointing out the error in nimodipine dosing. I have changed to q4h

      A few resources of known critical care texts: * Fink, Mitchell et al. Textbook of Critical Care. 5th edition 2005. * Ashley, Caroline and Currie, Aileen. The Renal Drug Handbook. 2nd ed. United Kingdom: Radcliffe Medical Press Ltd, 2004. * Shann, Frank. Drug Doses. 14th ed. Intensive Care Unit. Royal Childrenʼs Hospital, Parkville, Victoria 3052, Australia, 2008. * McClintock, Alan et al. Notes on Injectable Drugs. 5th ed. New Zealand Healthcare Pharmacistsʼ Association, 2004.Will find some of the more recent papers, but here are a few (http://lib.bioinfo.pl/meid:240847)

  2. Steve says

    SAH LP RBC Criteria?

    In residency, I learned cutoffs for RBC that may represent an SAH and to look for signs of a traumatic tap such as decreasing RBC count and the ratio of RBC to WBC compared to serum, but despite much searching I have yet to find articles describing LP interpretations for SAH, particularly RBC counts.

    Does anyone know of any references that specify LP SAH criteria?