3. Delayed cerebral ischaemia
Delayed cerebral ischaemia (DCI), results from spasm of the cerebral arteries causing reduced cerebral perfusion. This may result in focal neurological deficits or a global reduction in conscious level. It is a common complication in poorer grade aSAH patients. The typical period for development of this complication is day 3 to day 14 post-bleed, but it can occur earlier. Reduced level of consciousness or new focal neurological signs are a clinical indicator of DCI.
Detection of increased velocities of blood flow in the cerebral circulation using transcranial doppler ultrasound may suggest a diagnosis of DCI. CT scans may also show areas of ischaemia. Cerebral angiography can confirm the presence of vasospasm.
Nimodipine, a calcium channel blocker that crosses the blood brain barrier, is given to patients with aSAH to prevent vasospasm, and has been shown to improve outcome. Some centres will perform balloon angioplasty and intraarterial injection of vasodilators as treatment. Ensuring euvolaemia and if necessary, augmenting blood pressure using vasopressors can be used to improve brain perfusion in a patient with DCI.