Aneurysmal subarachnoid hemorrhage (SAH) can lead to devastating outcomes for patients, like cognitive decline. This is caused by early brain injury (EBI) followed by delayed cerebral ischemia (DCI). Neuroinflammation, triggered by the complement system, has been investigated to be a key mediator in the pathophysiology of EBI and DCI. Inhibition of the complement system is therefore considered to be a potentially important new treatment for SAH. This trial aims to study the safety and efficacy of C1-inhibitor Cinryze, an approved inhibitor of the complement system, compared to placebo in patients with SAH. By temporarily blocking the complement system we hypothesize limitation of delayed cerebral ischemia and a more favourable clinical outcome for SAH patients due to a decrease in the inflammatory response.