Power and Precision: The study planned to enroll 1,200 patients with 75 cases of SAH to achieve near 100 percent sensitivity with tight confidence intervals. The study included 1,153 patients with 67 SAH cases. Therefore, the study was slightly underpowered, and the lower end of the sensitivity was 94.6 percent. This is less precise than they were hoping to achieve.

Shared Decision Making: One unmeasured obstacle to more efficient uptake of decision aids is the engagement of patients and families in the complex discussions around diagnostic evaluations. The science of developing patient decision aids is distinct from that of validating clinical decision rules and requires both a rigorous implementation strategy and sustainable funding environments.

Bottom Line: The Ottawa SAH Rule needs external validation, a meaningful impact analysis performed, and patient acceptability of incorporating this rule into a shared decision-making instrument before being widely adopted.

Case Resolution

The patient is not high risk by the Ottawa SAH Rule. After his HA resolves with IV metoclopramide, you explain the differential diagnosis of HA, including SAH. Your clinical gestalt is that the HA characteristics aren’t typical for SAH and more consistent with his previous tension headaches. You discuss the Ottawa SAH Rule and the fact that he has none of the high-risk criteria and his risk of SAH would be less than 1 percent. He is reassured and discharged home with instructions for follow-up.

Thank you to Christopher Carpenter, MD, MSc, of Washington University, who is the deputy editor of Academic Emergency Medicine and a faculty member of an emergency medicine and critical care course.

Remember to be skeptical of anything you learn, even if you heard it on the Skeptics’ Guide to Emergency Medicine.

References

1. Vermeulen M, van Gijn J. The diagnosis of subarachnoid haemorrhage. J Neurol Neurosurg Psychiatry. 1990;53(5):365-372.
2. Perry JJ, Stiell I, Wells G, et al. Diagnostic test utilization in the emergency department for alert headache patients with possible subarachnoid hemorrhage. CJEM. 2002;4(5):333-337.
3. Morgenstern LB, Huber JC, Luna-Gonzales H, et al. Headache in the emergency department. Headache. 2001;41(6):537-541.
4. Landtblom AM, Fridriksson S, Boivie J, et al. Sudden onset headache: a prospective study of features, incidence and causes. Cephalalgia. 2002;22(5):354-360.
5. Delasobera BE, Osborn SR, Davis JE. Thunderclap headache with orgasm: a case of basilar artery dissection associated with sexual intercourse. J Emerg Med. 2012;43(1):e43-47.
6. Pascual J, Iglesias F, Oterino A, et al. Cough, exertional, and sexual headaches: an analysis of 72 benign and symptomatic cases. Neurology. 1996;46(6):1520-1524.
7. Dodick DW, Brown RD Jr, Britton JW, et al. Nonaneurysmal thunderclap headache with diffuse, multifocal, segmental, and reversible vasospasm. Cephalalgia. 1999;19(2):118-123.
8. Vermeulen MJ, Schull MJ. Missed diagnosis of subarachnoid hemorrhage in the emergency department. Stroke. 2007;38(4):1216-1221.
9. Weir B. Headaches from aneurysms. Cephalalgia. 1994;14(2):79-87.
10. Schievink WI. Intracranial aneurysms. N Engl J Med. 1997;336(1):28-40.
11. Carpenter CR, Hussain AM, Ward MJ, et al. 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. Acad Emerg Med. 2016;23(9):963-1003.