**3. Definition of in-hospital and out-hospital cardiac arrest**

Cardiac arrest is a major cause of unexpected death in developed countries with a low probability of patient survival. Survival is influenced by several variables common to both inhospital and out-of-hospital arrest, such as time to recognition of the cardiac arrest, time to initiation of CPR, rhythm presentation, first defibrillation [2, 11, 12]. In current resuscitation guidelines for in-hospital cardiac arrest (IHCA) patients [13], CPR using ECMO (E-CPR) has been assigned a low-grade recommendation. It is reported that ECMO for out-of-hospital cardiac arrest (OHCA) has worse outcomes compared with ECMO for IHCA patients [7, 14]. In the United States, more than 166,000 patients experience an OHCA annually [15] and approximately 60% are treated by emergency medical services. OHCA survival to hospital discharge range from 0.3% in Detroit [16] to 20.4% in Slovenia [17].Five clinical criteria to predict survival from OHCA [18] have recently been reported. They are: cardiac arrest witnessed by a bystander, arrest witnessed by emergency medical personnel, provision of bystander CPR, shockable cardiac rhythm, and return of spontaneous circulation (ROSC) in the field. These criteria are applicable on IHCA too.
