October 24, 2018

Background: Headache is a common presentation to the emergency department  (ED) accounting for 2% of all visits [1].  Of the patients that present with headache,1 – 3% will be due to a subarachnoid hemorrhage (SAH) [1]. SAH is a true diagnostic dilemma as delays in diagnosis can lead to significant morbidity and mortality. Further complicating matters, almost half of patients will be alert and neurologically intact at first presentation [3].  Non-Contrast Head CT (NCHCT) is very sensitive when performed soon after headache. However, we don’t want to order unnecessary NCHCTs as that increase cost and radiation exposure. Invasive testing such as lumbar puncture, which in itself can be a painful procedure, can also cause headache.  The Ottawa SAH Clinical Decision Rule was designed to help facilitate the identification of SAH in alert, neurologically intact adults presenting to the ED with acute, non-traumatic headache, while minimizing expensive and invasive over testing.  This post will serve as a review of the current literature in the derivation and validation of the Ottawa SAH Clinical Decision Rule.