Objective: To explore neuroprotective properties of xenon in patients after aneurysmal subarachnoid hemorrhage (SAH). Primary endpoint: Global fractional anisotropy of white matter of diffusion tensor imaging (DTI). Hypothesis: White matter damage is less severe in xenon treated patients, i.e. global fractional anisotropy is significantly higher in the xenon group than in the control group as assessed with the 1st magnetic resonance imaging (MRI). After confirmation of aSAH and obtaining a signed assent subjects will be randomized to the following groups: Control group: Standard of Care (SOC) group: Air/oxygen and Normothermia 36.5-37.5°C; Xenon group: Normothermia 36.5-37.5°C +Xenon inhalation in air/oxygen for 24 hours. Brain magnetic resonance imaging techniques will be undertaken to evaluate the effects of the intervention on white and grey matter damage and neuronal loss. Neurological outcome will be evaluated at 3, 12 and 24 months after onset of aSAH symptoms Investigational drug/treatment, dose and mode of administration: 50±2 % end tidal concentration of inhaled xenon in oxygen/air. Comparative drug(s)/placebo/treatment, dose and mode of administration: Standard of care treatment according to local and international consensus reports. Duration of treatment: 24 hours Assessments: Baseline data Information that characterizes the participant's condition prior to initiation of experimental treatment is obtained as soon as is clinically reasonable. These include participant demographics, medical history, vital signs, oxygen saturation, and concentration of oxygen administered. Acute data The collected information will contain quantitative and qualitative data of aSAH patients, as recommended by recent recommendations of the working group on subject characteristics, and including all relevant Common Data Elements (CDE) can be applied. Specific definitions, measurements tools, and references regarding each SAH CDE can be found on the weblink here: https://www.commondataelements.ninds.nih.gov/SAH.aspx#tab=Data\_Standards.