The clinical progress of each patient will be monitored daily. The development of a focal neurological deficit and/or a drop in the Glasgow Coma Scale by 2 points or more following vasospasm will be the criteria adopted to define an episode of DID [Pickard 1989]. Other factors which can affect consciousness, including systemic infection and infection of central nervous system, will be recorded for final analysis. Clinical outcomes will be assessed at the end of the trial and at the time of discharge. Durations of hospitalisation and NCCU stay will be observed.