Eligibility Criteria

Inclusion Criteria

Clinico-radiological assessment consistent with acute hemispheric ischaemic stroke; presentation within 6 hours of the onset of symptoms or within 6 hours of when last seen unaffected; Perfusion cerebral CT scan demonstrating evidence of hypoperfused but still viable hemispheric brain tissue comprising at least 100% of the hypoperfused “region at risk”; National Institutes of Health Stroke Scale (NIHSS) >= 8; Written informed consent from patient, or if appropriate and approval granted, from Person Responsible.

Exclusion Criteria

Rapidly improving neurological deficit or deficit that has resolved to NIHSS <8 at time of randomisation; Very severe acute stroke syndrome with Middle Cerebral Artery (MCA) plus Anterior Communicating Artery/Posterior Communicating Artery (ACA/PCA) or any acute MCA syndrome where, at the time of assessment, the site chief investigator considers hemicraniectomy may be required within 36 hours from onset; Any intracranial haemorrhage on baseline imaging; Any known serious co-morbid condition likely to complicate therapy such as a history of cardiac failure requiring pharmacotherapy, chronic liver disease, abdominal or pelvic mass causing femoral or inferior vena caval obstruction, Inferior Vena Cava (IVC) filters; Acute pulmonary oedema, respiratory, renal or hepatic failure as judged by the treating physician; Life expectancy < 3 months due to co-morbid conditions; Pre-morbid modified Rankin scale of >2; Pregnancy (women of child bearing potential will have a urine pregnancy test); Known allergy to pethidine.