Ottawa subarachnoid haemorrhage rule

Ottawa subarachnoid haemorrhage (SAH) rule

• is for alert patients >15 years old with new severe non-traumatic headache reaching maximum intensity within one hour
• is not appropriate for patients with new neurological deficits, history of previous aneurysms, or history of similar headaches (≥3 episodes over ≥6 months)
• it takes into account clinical features that were deemed a high risk for SAH, including:
  • age ≥40 years,
  • neck pain/stiffness,
  • witnessed loss of consciousness,
  • onset during exertion,
  • thunderclap headache
  • limited neck flexion on examination

• patients require investigation if one or more finding is present

• a validation study concluded that "..in patients presenting to the ED (emergency department) with an acute non-traumatic headache, the Ottawa rule can be used to safely exclude patients with SAH and can thereby inform decisions for further investigations.."

Reference:

1. Foley RW et al. Subarachnoid haemorrhage rules in the decision for acute CT of the head: external validation in a UK cohort. Clin Med (Lond). 2021 Mar;21(2):96-100.