Delayed cerebral ischaemia (DCI) affects more than one quarter of patients between 3 and 14 days after the onset of their aneurysmal subarachnoid haemorrhage, and accounts for about one third of patients who are dead or dependent as a result of the haemorrhage. Despite the importance of DCI, little can be done to prevent it: only calcium antagonists are supported by good evidence, and the effectiveness of nimodipine is modest (20 patients need to be treated to prevent one poor outcome).¹ Future hope is offered only by the window of opportunity between subarachnoid haemorrhage and DCI onset, and sufficient clinical research …