The main purpose of this study is to analyse the on-going coagulation process after aSAH. For investigation the investigators use the rotational thromboelastometry (ROTEM) which is a point-of-care test using a variety of activators to provide a targeted and a dynamic analysis of coagulation cascade. This is a prospective, observational clinical study done in 16 aSAH patients treated in Tampere University Hospital intensive care unit and 16 control patients (elective craniotomy due to non-ruptured intracranial aneurysm.

Inclusion Criteria:

• Age ≥ 18 years
• Acute subarachnoid haemorrhage (confirmed by computed tomography, CT, or cerebrospinal fluid erythrocyte count over 1000 x 106/l) AND confirmed origin either with computed angiography (CTA) or digital subtraction angiography (DSA)
• Onset of symptoms ≤ 12 hours
• Expected to stay 72 hours in the ICU

Exclusion Criteria:

• Pregnancy
• Any long-term anticoagulant medication, except for low-dose aspirin (<150 mg/day)
• Known active cancer

Acute aneurysmal subarachnoid haemorrhage patients