Ottawa SAH Clinical Decision Rule Revisited
The Article: The Ottawa Subarachnoid Hemorrhage Clinical Decision Rule for Classifying Emergency Department Headache Patients, AJEM 2019
The Idea: This was another study created to evaluate the Ottawa SAH (OSAH) clinical decision rule which was derived from an initial 2010 Perry paper. Since the derivation, this rule has been evaluated with very high sensitivity in several papers (2013 JAMA, 2015 AJEM).
The Study: Single-center Taiwanese retrospective cohort study from Jan 2016-March 2017 Looked at patients with the primary complaint of an atraumatic headache 2 objectives: assess the OSAH rule’s performance and to evaluate the impact of the rule for ICH and other intracranial pathology
Results: – 913 patient included in the study (>17 years, no trauma, HA less than 14 days, no neurologic deficit) – Incidence of SAH was 1.6% – OSAH rule had a 100% sensitivity for SAH (95% CI, 78.2-100), sensitivity also100% (84.6-100) for all ICH – Specificity similar to prior at ~37% – 33.1% of all patients in the group got a head CT. If the OSAH was validated, it would raise the imaging rate of these patients to 63.6%
The Takeaway: It is good to have another study in support of a clinical decision rule that MAY help us safely decide to avoid CT scanning. A limitation of the study is a lower incidence of SAH (1.6% in this cohort versus the 5.8% reported in the Perry validation study), lacking the power for a narrow CI (Perry study reported 100% sensitivity with a 95% CI between 94.5-100%). This cohort was also specific to a single center in Taiwan which may have contributed to the low incidence. Lastly, the paper discussed that the rate of ordering CT scans would increase should the OSAH rule be applied to all patients in this cohort which is concerning for a rule that should be helping us to safely avoid CT scans. I still believe this rule has a place in clinical practice, however, and this study is yet another data point to add towards its validation.