Fig. 1.

Flow diagram of the study design. Patients will be randomly allocated 1:1 to the hydrogen group or the control group using content-blinded cylinders. Trial gas inhalation will be initiated after intensive care unit admission and continued for 18 h. Multidisciplinary treatments, including targeted temperature management, will be performed in all patients according to the latest International Liaison Committee on Resuscitation (ILCOR) guidelines. CPC Cerebral Performance Categories scale, GCS Glasgow Coma Scale, PCAS Post-cardiac arrest syndrome, PEEP Positive end-expiratory pressure, ROSC Return of spontaneous circulation, SpO ₂ Peripheral oxygen saturation