Ottawa Rules for Subarachnoid Hemmorhage (SAH)

Background

• Headache is a common reason for ER visits
• 1-3% of headaches are SAH
• Misdiagnosis of SAH can be fatal
• Lumbar puncture can be a painful/time-consuming procedure
• Goal is to design a decision rule to help guide the clinician

Design

• Multi-center study at ten Canadian emergency departments.
• 2131 adults with a headache peaking within 1 hour and no neurologic deficits
• Non-traumatic headaches only; GCS of 15 required
• SAH defined as: 1. CT evidence of SAH; 2. Xanthochromia in CSF; or 3. RBCs in the final tube of CSF, WITH positive angiography findings.

Results

132 (6.2%) had SAH

Decision rule including any:

1. age 40 years or older
2. neck pain or stiffness
3. witnessed LOC
4. onset during exertion

Had 98.5% sensitivity (95% CI, 94.6%-99.6%) and 27.5% specificity (95% CI, 25.6%-29.5%)

Adding “thunder-clap” headache and “limited neck flexion on examination” (inability to touch chin to chest or raise the head 8cm off the bed if supine) resulted in 100% (95% CI, 97.2%-100%) sensitivity.

The rule was then evaluated using a bootstrap analysis on old cohort data to validate the rule.

Conclusion/Limitations

• Exciting new rule for SAH that needs to be validated in a new, independent cohort
• The rule may not decrease the rate of investigation (CT, LP, or both)
• It may decrease the amount of SAH that are missed on first visit to the ER
• Limited by narrow criteria for inclusion in the rule/not meant for other causes of headache
• See the JAMA editorial with the article for a nice discussion of the difficulties with decision making rules.
• The rule:
  The Ottawa SAH Rule

  • For alert patients older than 15 y with new severe nontraumatic headache reaching maximum intensity within 1 h

  • Not for patients with new neurologic deficits, previous aneurysms, SAH, brain tumors, or history of recurrent headaches (≥3 episodes over the course of ≥6 mo)

  • Investigate if ≥1 high-risk variables present:

  1. Age ≥40 y

  2. Neck pain or stiffness

  3. Witnessed loss of consciousness

  4. Onset during exertion

  5. Thunderclap headache (instantly peaking pain)

  6. Limited neck flexion on examination

   

 

References

Attachments

1311191832_ottawa_editorial.pdf (109 Kb)