Nearly half of the survivors of subarachnoid haemorrhage (SAH) retain irreversible neurological damage resulting from the early lesions associated with the initial bleeding, and the occurrence of possible delayed cerebral ischaemia (DCI). The early diagnosis of the occurrence of an DCI is therefore a major challenge in order to optimise management before irreversible lesions are formed. However, the means of diagnosis are often not available, and up to a third of DCI are discovered on follow-up images when the lesions are already present. Among the markers of brain injury, S100 calcium-binding protein B (S100B) is an astrocyte protein released into the bloodstream at the time of the appearance of a brain lesion. Its short half-life makes it a prime candidate for patient follow-up to diagnose a new ischemic lesion and assess the effectiveness of its management.

Among the elements at the origin of DCI, the occurrence of proximal vasospasm is the main element on which we can have a therapeutic action. The strategy implemented in the department consists of performing a mechanical angioplasty when proximal vasospasm is detected with a decrease in downstream cerebral perfusion. Nevertheless the benefit of this therapeutic action is discussed and there is currently no early marker of the effectiveness of this procedure.

Inclusion Criteria:

• Adults
• Patient hospitalised in the neurological intensive care unit for a subarachnoid haemorrhage.
• Delayed cerebral ischaemia suspected during routine care.
• Presence of a catheter (arterial or venous) for repeated sampling.
• Patient having been informed and having formulated his non-opposition or close to the patient having been informed and having formulated his non-opposition. In this case, the patient's non-opposition will be collected as soon as his condition allows it.

Exclusion Criteria:

• Pregnant or breastfeeding women in class.
• Patients under legal protection, guardianship, curatorship, under judicial safeguard.
• Patients participating in a study that may interfere with this study.
• Persons under psychiatric care under duress

Adult patients hospitalized in neurological intensive care unit for subarachnoid hemorrhage, in whom the onset of delayed cerebral ischemia is suspected will be included.