The aim of this study is to evaluate the effect of inhalational sedation on cerebral perfusion in patients with SAH.

It will evaluate whether the administration of isofluorane, by inducing direct vasodilation in the cerebral parenchyma, can improve the cerebral perfusion rates.

Perfusional CT will be used to study the variation of cerebral blood flow to rule out the vasodilatory effect on territories with different cerebrovascular reactivity aggravating the phenomena of distrectual hypoperfusion (theft theory).

Inclusion Criteria:

• Age > 18 years old
• Diagnosis of non-traumatic SAH
• Neurological and/or systemic presentation that requires support of vital functions and sedation. This occurs for a WFNS score (World Federation of Neurosurgical Societies) ≥ 3.
• Possibility of ICP monitoring through EVD which is necessary in case of acute hydrocephalous. In case of the neurosurgeon do not indicate the positioning of the EVD, an intraparenchymal catheter will be positioned for the ICP monitoring.
• Patients with vasospasm (area of cerebral blood flow under 30% of the best value detected in the brain of the patients at the first CT scan). This exam will be performed at 2° - 3° day post event.
• Acceptance of informed consent.

Exclusion Criteria:

• Documented outcomes of cerebrovascular disease
• Patients with acute heart failure related to ESA
• State of pregnancy
• Patients with CLCR < 30 mL/min