Ottawa SAH Rule

Headache is a common presentation to ED and Subarachnoid is the diagnosis we never want to miss. However, working out who needs a scan can be difficult as 50% of patients presenting with a subarachnoid have no neurological deficit.

The Ottawa SAH Rule is a validated tool for deciding who needs as CT scan.   The Ottawa team have also done further work to decide which of the patients you do scan need a follow-up LP/CTA and who we could discharge.

1. Is your patient suitable?

This is the MOST important question, as with all decision tools if you apply it badly your patient will be treated badly! To apply the Ottawa SAH Rule your patient MUST have ALL of the following. Otherwise, you should reconsider your diagnosis or their suitability for LOW risk rule out [Involve Seniors].

2. Clinical Rule-OUT

If your patient has NONE of the following signs or symptoms, multi-centre trials have shown that SAH can ruled out. [Remember: you have ONLY ruled out SAH if you’re concerned about other diagnoses, these will require investigating separately]

3. Not Ruled-OUT Arrange URGENT CT

[Remember: if the CT finds pathology other than SAH, this will require you to arrange appropriate patient management]

4. Can you trust the report?

Even if no bleed is found can you trust the report? Not always, if the scan has been performed after 6hrs from the onset of headache, the blood may have clotted already and this is much more difficult to see on CT (as compared with fresh blood). Also if you have an Ultra High Risk (UHR) patient, even if the scan has been done within 6 hours they should also be admitted for further testing.

5. And Finally!

If your patient has had  a normal CT scan, within 6 hours of onset and has no UHR features, you can allow them to go home. However, ensure that you have explained that the scan has not ruled out small aneurysms, and if the patients symptoms are worsening that they should return for further investigation.

Further reading

  • PDF: Ottawa SAH Rule poster
  • EMOttawa: great further reading on this topic and its application
  • EUSEM slides Dr Perry: presentation from EUSEM 2018 on the application of this pathway
  • CJEM 2018: Multicentre before-after implementation study of the Ottawa subarachnoid hemorrhage strategy
  • BMJ 2016: New clinical decision rule to exclude subarachnoid haemorrhage for acute headache: a prospective multicentre observational study
  • CMAJ 2017: Validation of the Ottawa Subarachnoid Hemorrhage Rule in patients with acute headache
  • Stroke 2016: Sensitivity of Early Brain Computed Tomography to Exclude Aneurysmal Subarachnoid Hemorrhage A Systematic Review and Meta-Analysis
  • Acad. Emerg. Med 2017: Spontaneous Subarachnoid Hemorrhage: A Systematic Review and Meta-analysis Describing the Diagnostic Accuracy of History, Physical Examination, Imaging, and Lumbar Puncture With an Exploration of Test Thresholds



One comment

Leave a Reply

Your email address will not be published.

11 − six =

This site uses Akismet to reduce spam. Learn how your comment data is processed.