“The Ottawa Subarachnoid Hemorrhage Rule” From EMC’s “Ep 194 Subarachnoid Hemorrhage – Recognition, Workup and Diagnosis Deep Dive”

Today, I review, and excerpt The Ottawa Subarachnoid Hemorrhage Rule from Emergency Medicine CasesEp 194 Subarachnoid Hemorrhage – Recognition, Workup and Diagnosis Deep Dive.*

*Helman, A. Lin, K. Perry, J. Episode 194 Subarachnoid Hemorrhage Recognition, Workup and Diagnosis. Emergency Medicine Cases. May, 2024. https://emergencymedicinecases.com/subarachnoid-hemorrhage-recognition-workup-diagnosisAccessed June 12, 2024

All that follows is from the above resource.

Clinical decision rules for subarachnoid hemorrhage

The Ottawa SAH clinical decision rule can help decide which patients with headache require a work-up for SAH. The rule has a sensitivity of 100% and a specificity of 15%. It is important to carefully assess for inclusion and exclusion criteria for your patient.

The Ottawa Subarachnoid Hemorrhage Rule

Inclusion: Apply the rule for alert, GCS 15 patients ≥ 15 years old who present with severe nontraumatic headache reaching maximum intensity within 1 hour. Headache onset within the last 14 days.

Exclusion: Do NOT apply the rule for patients with new neurological deficits, previous aneurysms, previous SAH (subarachnoid hemorrhage), known brain tumors, or chronic recurrent headaches (≥3 headaches of the same character and intensity for >6 months).

Investigate for SAH if 1 or more high-risk variables present:

  1. Age ≥40
  2. Neck pain or stiffness
  3. Witnessed loss of consciousness
  4. Onset during exertion
  5. Thunderclap headache (ie. instantly peaking pain)
  6. Limited neck flexion on examination

Some considerations for using the Ottawa Subarachnoid Hemorrhage rule:

  • Critiques of the rule include its low specificity and that this would lead to increasing usage of CT/ LP. Low specificity is the trade-off for a rule that is highly sensitive.
  • Subsequent implementation study demonstrated that applying the rule does not increase CT use or LPs, and it may actually decrease CT utilization while increasing SAH pick-up rate.
  • Interobserver assessments for the rule indicate moderate to substantial interobserver agreement in general for the rule; however, “worst headache of life” has poor interobserver agreement (kappa 0.45).
  • The rule would suggest that, if applied correctly, SAH can be ruled out in patients who have no high-risk variables present.
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