Delayed cerebral ischaemia Vasospasm Vasospasm is the most serious complication following SAH. It occurs in 40-90% of patientsand is usually seen in the most severe cases . defined cerebral vasospasm as ‘a reversible narrowing of the intradural subarachnoid arteries’. Sobey and Faraci (2007) explained that the contraction of arteries that occurs during vasospasm reduces blood flow to the cerebral tissues, causing tissue ischaemia. Vasospasm begins approximately 3 days after SAH, peaks at 7 to 8 days, and then resolves by 14 days . In this respect Mrs S seemed atypical as she had vasospasm on admission. However, the signs of meningeal irritation she had for the 10 days prior to hospital admission suggest she may have had a bleed prior to her presenting bleed, which would place her within the usual timeframe for developing vasospasm. Signs and symptoms of vasospasm include headache and fluctuations in GCS and motor strength, which Mrs S presented with, as well as high white cell count and raised cerebral blood flow velocity . The pathogenesis of vasospasm remains uncertain; several theories have been postulated. It has been proposed that vasospasm is caused by spasmogens released as the erythrocytes of the blood clot haemolyse . Oxyhaemoglobin is the spasminogen most implicated. It causes the production of free radicals, which damage the cerebral blood vessel endothelium. This leads to increased permeability of the vascular cell membrane, which allows an influx of calcium . Calcium is central to the contractility of smooth muscle, and an influx through the damaged vascular membrane into the smooth vascular muscle is likely to cause vasospasm . Endothelin and nitric oxide are produced by the blood vessel endothelium. They both have a vital role in maintaining vessel tone, and changes in their concentrations may contribute to vasospasm . It is thought that oxyhaemoglobin scavenges nitric oxide and causes the release of endothelin. Endothelin is a potent vasoconstrictor, and increased levels are likely to increase smooth muscle contraction and vasospasm . Nitric oxide causes vasodilation and diffuses from the endothelium into the adjacent smooth muscle, where it triggers a process whereby intracellular calcium is removed, resulting in smooth muscle relaxation . If nitric oxide is scavenged this process will not occur and vasoconstriction will persist. Prevention, reversal and treatment of cerebral vasospasm are areas of ongoing research. There is no evidence to support the efficacy of one treatment over another, and because the pathogenesis of delayed cerebral vasospasm seems to be multifactoral, several different interventions may be required .