A new clinical decision rule may have a sensitivity and a specificity of nearly 100% for ruling out subarachnoid hemorrhage (SAH), according to a validation study published September 25 in JAMA. The study examined patients who presented to 10 Canadian emergency departments with acute headache.
The Ottawa SAH Rule requires the clinician to answer six questions regarding the patient’s presentation. The tool has the potential to reduce the number of costly and invasive procedures that are required to distinguish SAH from other pathologies, said Jeffrey J. Perry, MD, Assistant Professor of Emergency Medicine at the University of Ottawa.
It can be difficult to determine which patients who present to the emergency department with acute severe headache but are neurologically healthy require further investigation. About half of all patients with SAH present in this way, and approximately 5% of patients with confirmed SAH are misdiagnosed during an initial evaluation in the emergency department.
Standard practice for patients with this presentation is to perform an unenhanced head CT and, if the results are negative, a lumbar puncture. But lumbar puncture entails a degree of risk and can produce a headache that may make diagnosis more difficult.
The Ottawa SAH Rule
Dr. Perry and his colleagues devised three clinical decision rules to help clinicians rule out SAH. The group assessed the three rules’ accuracy, reliability, and acceptability to clinicians in a validation cohort of consecutive patients age 16 or older who presented to an emergency department with a nontraumatic headache that reached maximal intensity within one hour.
The investigators examined data for 2,131 participants, and the population’s mean age was 44. Approximately 61% of patients were women, and 26% of patients arrived at the emergency department by ambulance. All participants were treated by attending physicians certified in emergency medicine or by supervised residents at 10 university-affiliated, urban, tertiary care teaching hospitals during a four-year period. All patients were alert and oriented and had no neurologic deficits. A total of 132 patients (6.2%) had SAH.
After comparing the performance of the three candidate decision rules, the investigators refined the decision tool to combine the six factors that were most predictive of SAH: age 40 or older, neck pain or stiffness, witnessed loss of consciousness, onset of headache during exertion, thunderclap headache (defined as instantly peaking pain), and limited neck flexion (defined as the inability to touch chin to chest when upright or to raise the head 8 cm above the bed when supine). The presence of any one of these six factors indicates that SAH is possible, and further investigation is required using CT and, perhaps, lumbar puncture, said Dr. Perry.
The Ottawa SAH rule had an overall sensitivity of 99.2% and a specificity of 99.6% in identifying SAHs when the derivation cohort and the validation cohort were combined. Of 262 patients with SAH in both cohorts, this rule would identify 260, Dr. Perry and his associates reported.
Decision Rule Could Reduce Unnecessary Assessments
Emergency physicians likely will deem these levels of sensitivity and specificity clinically acceptable. “Following this rule would decrease the investigation rate [ie, the rate of further assessment using CT and lumbar puncture] to 74.0% from the current investigation rate of 84.1%,” said the investigators.
The Ottawa SAH rule must be evaluated further before it can be adopted into clinical practice. “An implementation study is the next step required to determine how the Ottawa SAH rule performs in clinical practice, to assess the actual effects on patient care and patient outcomes, and to conduct a formal health economic analysis,” said Dr. Perry.
Ultimately, the rule “may help to standardize which patients with acute headache require investigations, and may provide evidence for physicians to use in deciding which patients require imaging to decrease the relatively high rate of missed SAH.”
—Mary Ann Moon
IMNG Medical News