The investigators hypothesize that

1. if decrease in SctO2 level is caused by the degree of hypothermia, SctO2 level in the 33-TH may be lower than that in the 36-TH group.
2. if decrease in SctO2 level is not caused by the degree of hypothermia but caused by brain injury, SctO2 level may be associated with only the prognosis of cardiac arrest victims regardless of core temperatures.

The primary objective of this study is to compare the 72-hour changes in SctO2 level between the 36-TH and 33-TH groups in cardiac arrest victims.

1. Subject Identification and Screening For each cohort, patients will be identified after acquisition of sustained return of spontaneous circulation (ROSC) (> 30 minutes). If the patients meet inclusion/exclusion criteria, patients will be enrolled in the study. The investigators will obtain written informed consent from all of the patients or their representatives.

2. Assignment of Subject Number A unique identification number will be given to study subjects in an attempt to de-identify their information. Subject numbers will be assigned in sequential order. The subject number will consist of four digits. The first two digits will designate the study site. The last two digits will designate the subject by number in sequential order (i.e., subject number 01 01 will be the first subject at site 1; 01 02 will be the second subject at site 1, etc.).

3. Study Methods

   • Randomization to 36-TH (core body temperature (BT) 36℃) or 33-TH (core BT 33℃) group will be performed by a web based randomization site (http://mrcc.snuh.org).
   • Start target temperature management using external cooling device (Arctic Sun) within 1 hour post-ROSC.
   • SctO2 monitoring starts within 1 hour post-ROSC and maintain for 72 hours.
   • 36-TH (core BT 36℃) or 33-TH (core BT 33℃) for 24 hours
   • Rewarming 0.25℃/h in 33-TH group
   • Core temperature < 37.5℃ for 72 hours

   All patients will be treated per the postresuscitation care protocol. Target treatment will include

   • Target: central venous pressure (CVP) (8 - 12 mmHg), mean arterial pressure (MAP) (> 65 mmHg), central venous oxygen saturation (ScvO2) (> 70%)
   • Seizure control, shivering control as appropriate
   • Coronary intervention as soon as possible if needed
   • Infection control if indicated
   • Other supportive care

   Monitoring data including

   • CVP, MAP, ScvO2, lactate, neuron specific enolase (NSE), end-tidal carbon dioxide (EtCO2), input-output (I/O) balance
   • Intermittent electroencephalography (EEG) monitoring (2 times/72 hours)
   • Laboratory data including arterial blood gas analysis (ABGA), complete blood count (CBC), liver function test (LFT), electrolyte, blood urea nitrogen/creatinine (BUN/Cr), et al.
   • SctO2
   • Core (esophageal or bladder) temperature

4. Data Collection

Study data will be collected in the following manner:

• All data will be collected on appropriate Case Report Forms.

Inclusion Criteria:

• Comatose patients successfully resuscitated from cardiac arrest

Exclusion Criteria:

• < 18 years old
• Definite non-cardiac cause arrest
• Contraindication to TH Active bleeding, coagulopathy, fatal arrhythmia, severe infectious condition
• Presence of advanced directives to withhold or withdraw life-sustaining treatment
• Expected survival < 72 hours
• Underlying low CPC (≤ 3)
• No informed consent
• Follow-up loss

Primary and secondary outcomes were assessed by an investigator blinded to this study.