Validation of the Ottawa Subarachnoid Hemorrhage Rule in patients with acute headache

Abstract

Background: We previously derived the Ottawa Subarachnoid Hemorrhage Rule to identify subarachnoid hemorrhage (SAH) in patients with acute headache. Our objective was to validate the rule in a new cohort of consecutive patients who visited an emergency department.

Methods: We conducted a multicentre prospective cohort study at 6 university-affiliated tertiary-care hospital emergency departments in Canada from January 2010 to January 2014. We included alert, neurologically intact adult patients with a headache peaking within 1 hour of onset. Treating physicians in the emergency department explicitly scored the rule before investigations were started. We defined subarachnoid hemorrhage as detection of any of the following: subarachnoid blood visible upon computed tomography of the head (from the final report by the local radiologist); xanthochromia in the cerebrospinal fluid (by visual inspection); or the presence of erythrocytes (> 1 × 106/L) in the final tube of cerebrospinal fluid, with an aneurysm or arteriovenous malformation visible upon cerebral angiography. We calculated sensitivity and specificity of the Ottawa SAH Rule for detecting or ruling out subarachnoid hemorrhage.

Results: Treating physicians enrolled 1153 of 1743 (66.2%) potentially eligible patients, including 67 with subarachnoid hemorrhage. The Ottawa SAH Rule had 100% sensitivity (95% confidence interval [CI] 94.6%-100%) with a specificity of 13.6% (95% CI 13.1%-15.8%), whereas neuroimaging rates remained similar (about 87%).

Interpretation: We found that the Ottawa SAH Rule was sensitive for identifying subarachnoid hemorrhage in otherwise alert and neurologically intact patients. We believe that the Ottawa SAH Rule can be used to rule out this serious diagnosis, thereby decreasing the number of cases missed while constraining rates of neuroimaging.

Conflict of interest statement

Competing interests: Jeffrey Perry, Marco Sivilotti, Jane Sutherland, Howard Lesiuk, Corinne Hohl, Marcel Émond, Lisa Calder, Christian Vaillancourt, Venkatesh Thirganasambandamoorthy and Ian Stiell received grants from the Canadian Institutes of Health Research during the conduct of the study. Christian Vaillancourt also received a grant from the Heart and Stroke Foundation of Canada during the conduct of the study. No other competing interests were declared.

© 2017 Joule Inc. or its licensors.

Figures

Figure 1:

The Ottawa Subarachnoid Hemorrhage (SAH) Rule. Used in alert patients > 15 yr of age with new acute severe nontraumatic headache that reaches maximum intensity within 1 h of onset. Not to be used in patients with new neurological deficits, previous aneurysms, SAH or brain tumors, or a history of similar headaches (≥ 3 episodes over ≥ 6 mo).

Figure 2:

Participant selection for the study. SAH = subarachnoid hemorrhage.