Inclusion Criteria:  age of 18 years or older out of hospital cardiac arrest of non-traumatic cause with CPR and subsequent ROSC Glasgow coma scale (GCS) ≤ 7 or sedation 30 minutes after ROSC achievment  Exclusion Criteria:  unavailable first measurment of the optic nerve sheath diameter (ONSD) measured by transorbital ultrasonography 24±6 hours after ROSC achievement refractory cardiac arrest craniocerebral injury intracranial tumor active intracranial bleeding haemorrhagic stroke and/or subarachnoid haemorrhage in the last 3 months facial trauma affecting the eye area active neuroendocrine tumor, small cell lung cancer, non-small cell lung CPC 3-5 before cardiac arrest sclerosis multiplex and/or optic neuritis of other etiology