The Ottawa Subarachnoid Hemorrhage Rule is a clinical calculator used in the field of emergency medicine to determine the likelihood of a subarachnoid hemorrhage in patients presenting with acute headache. This rule applies specifically to patients who are alert and over 15 years old with a new severe non-traumatic headache reaching maximum intensity within 1 hour.
The clinical utility of this calculator is to help clinicians decide whether a lumbar puncture or computed tomography scan is necessary to rule out a subarachnoid hemorrhage. It is designed to be 100% sensitive for identifying subarachnoid hemorrhage, meaning that if a patient meets none of the criteria, the likelihood of them having a subarachnoid hemorrhage is extremely low.
Exclusion criteria for the use of the Ottawa Subarachnoid Hemorrhage Rule include patients with new neurological deficits, patients with a history of three or more headaches of the same character and intensity as their current headache over a period of six months, and patients with previous diagnoses of brain tumors or subarachnoid hemorrhage.
Reference
Jeffrey J Perry, Ian G Stiell, Marco L A Sivilotti et al. Clinical decision rules to rule out subarachnoid hemorrhage for acute headache. JAMA. 2013 Sep 25;310(12):1248-55.
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