The aim of this clinical trial is to study the impact of ultra-early transnasal evaporative cooling after cardiac arrest and subsequent hypothermia at hospital, on survival with complete neurologic recovery, compared to currently recommended normothermia. The study population will consist of patients 18-79 years old, with out-of-hospital cardiac arrest with initial shockable rhythm. The main research question it aims to answer is whether there is a difference in survival with complete neurologic recovery at 90 days after cardiac arrest between the group of patients that received ultra-early cooling, compared to the group that was treated with normothermia. Participants will be randomized to two groups. One group (the intervention group) will receive ultra-early trans-nasal evaporative cooling initiated by EMS personnel at the scene of the cardiac arrest, and subsequent systemic hypothermia for 24 hours at hospital arrival. The other group (the control group), will receive standard of care (advanced cardiac life support and normal body temperature (normothermia)).