Optic nerve sheath diameter (ONSD) had been proved to be associated with increased intracranial pressure and can be used as one of the prognostic factors in cardiac arrest patients. It is simple, quick and can be measured repeatedly. Carotid duplex and transcranial duplex(TCD) provide rapid, noninvasive, real-time measures of cerebrovascular function. It can be used to assess the vascular territory by measuring blood flow, and to evaluate factors include brain perfusion, plaque morphology, and patency of intracranial collaterals. Hence, it could act as a crucial role in neuroprognosis in post-arrest patients. In this study, the investigator aimed to analyze the ONSD diameters, ONSD/external transverse diameter (ETD) ratio, carotid duplex and transcaranial duplex parameters in different stages of post-cardiac arrest care, demographic characteristics and resuscitation information with the neurological outcome of post-cardiac arrest patients. The ONSD diameter, and ONSD/ETD ratio were compared with age-, and sex-matched normal volunteers.