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

Clinical Decision Rules to Rule Out Subarachnoid Hemorrhage for Acute Headache

 

Attachments

• 1311191832_ottawa_editorial.pdf (109 Kb)