Prospective Implementation of the Ottawa Subarachnoid Hemorrhage Rule and 6-Hour Computed Tomography Rule

Abstract

Background and Purpose— The Ottawa subarachnoid hemorrhage (SAH) rule identifies patients with headache requiring no testing for SAH, while the 6-hour computed tomography (CT) rule guides when to forgo a lumbar puncture. Our objectives were to: (1) estimate the clinical impact of the Ottawa SAH rule and the 6-hour-CT rule on testing rates (ie, CT, lumbar puncture, CT angiography); (2) validate the 6-hour-CT rule for SAH when applied prospectively in a new cohort of patients. Methods— We conducted a multicenter prospective before/after implementation study from 2011 to 2016 with 6 months follow-up at 6 tertiary-care Canadian Academic Emergency Departments. Consecutive alert, neurologically intact adults with headache were included. For intervention period, physicians were given a 1-hour lecture, pocket cards, posters were installed, and physicians indicated Ottawa SAH rule criteria when ordering CTs. SAH was defined by blood on CT, xanthochromia in cerebrospinal fluid, or >1×10 6 /L red blood cells in cerebrospinal fluid with aneurysm. Results— We enrolled 3672 patients, 1743 before and 1929 after implementation, including 188 with SAH. Proportions undergoing CT was unchanged (88.0% versus 87.5%; P =0.643). Lumbar puncture use decreased (38.9% versus 25.9%; P <0.0001). Additional testing following CT (ie, lumbar puncture or CT angiography) decreased (51.3% versus 42.2%; P <0.0001). Admissions declined (9.8% versus 7.4%; P =0.011). Mean emergency department stay was unchanged (6.3±4.0 versus 6.4±4.2 hours; P =0.685). The Ottawa SAH rule was 100% (95% CI, 98.1%–100%) sensitive, and the 6-hour-CT rule was 95.5% (95% CI, 89.8–98.5) sensitive for SAH. The 6-hour-CT rule missed 5 SAHs: 1 radiology misread, 2 incidental aneurysms, 1 nonaneurysmal cause, and 1 profoundly anemic patient. Conclusions— The Ottawa SAH rule and the 6-hour-CT rule are highly sensitive and can be used routinely when SAH is considered in patients with headache. Implementing both rules was associated with a meaningful decrease in testing and admissions to hospital.

Subarachnoid haemorrhage rules in the decision for acute CT of the head: external validation in a UK cohort

“…External validation has taken place in over 4,000 patients and, with the exception of one study, has demonstrated a sensitivity of 100%. [8][9][10][11][17][18][19] Specificity has been lower and has ranged from 7.6% to 44%. These external validation studies, together with the results from our present study, represent a robust external validation of the Ottawa rule and provide an evidence base for its introduction into clinical practice to aid in the decision for CT of the head in cases of suspected SAH.…”

“…However, in a prospective study from Perry et al, there was no increase in rate of neuroimaging following the introduction of the Ottawa rule to clinical practice. 19 Taken together, although the Ottawa rule is limited by its specificity, it does not necessarily lead to increased rates of neuroimaging. Indeed, given the consistent demonstration of the rule's sensitivity across several studies, its role in reducing neuroimaging and subsequent investigation rates for low-risk patients may be more apparent in larger cohorts.…”

“…Only Perry et al have utilised the Ottawa SAH rule in a prospective fashion. 10,19 All other external validation studies are merely applying the rule retrospectively. The present study is also limited in that patients with a headache peaking in intensity within 1 hour may not have been recorded accurately and so this subgroup may be incomplete.…”

Management of thunderclap headache in the emergency room: A retrospective cohort study

“…Some researchers argue that CT might be sufficient to rule out subarachnoid bleeding if the scan is normal and is done within 6 h of the TCH onset (19,20,27,34). However, other secondary headache disorders can be responsible for the TCH, and even in those studies, 4.0% (19) to 9.3% (27) of patients showed a cause of TCH different from SAH, half of them diagnosed only by LP (25). The 6-h CT rule showed a 95.5% sensitivity rate in a prospective multicenter study in the diagnosis of SAH, reporting 188 cases of SAH out of 3672 patients with TCH (20).…”

“…We also reported the percentage of patients that were evaluated by a neurologist, the percentage of patients that were admitted, and the percentage of patients that were discharged without further examination. As an exploratory endpoint, we assessed if the CT was requested within 6 h of arrival to the ER, if it was completed within 6 h of arrival (19), and whether or not CT detected the presence of SAH in patients with SAH as a final diagnosis (20).…”