Evaluation of the impact of the Canadian subarachnoid haemorrhage clinical decision rules on British practice.

Introduction: Acute headache is among the commonest presenting complaints to emergency departments. While it is estimated that only 1-3% result from subarachnoid haemorrhage (SAH), because the disease carries such significant morbidity and mortality if missed, most clinicians have a low threshold for investigation. A recent prospective cohort study in Canada determined a number of high-risk clinical characteristics for SAH in patients with acute headache.