**2. ECMO in cardiac arrest**

Cardiac arrest is defined as the sudden cessation of cardiac activity as the victim is unresponsive, has no circulation, and is unable to breathe. The sudden cessation of cardiac activity may result in the death of the victim if not identified and treated quickly. It is a major public health hazard that impacts an estimated 356,500 people out of hospital and 209,000 people in the hospitals each year. An acute coronary

syndrome is the most common cause of CA. Other common causes include pulmonary embolism, dyskalemia, acute respiratory failure, hypovolemia, sepsis, and poisoning [27]. Cardiac arrest can occur in hospital (IHCA) or outside hospital (OHCA). In a person with OHCA, cardiopulmonary resuscitation (CPR) should be initiated immediately. Mass public awareness, basic life support (BLS) training for general population, widespread availability of defibrillators, rapid response paramedic teams, and in-hospital CPR response teams, development of protocols for effective CPR have led to early and effective institution of CPR in patients with both OHCA and IHCA, especially in the developed countries; however, outcome remains dismal with <10% survival. The most important reason for high mortality after CA is the prolonged absence of blood flow to the brain and other vital organs leading to anoxic brain injury and irreversible damage to the other organs.

Till two decades back, conventional CPR (CCPR) including both basic life support and advanced cardiac life support (ACLS) was the best treatment plan for patient with CA as it would give them the best chance of survival. The purpose of doing CCPR in a patient with CA is to maintain the cerebral and coronary perfusion till the heart recovers its rhythm and contractility as the absence of cerebral blood flow for more than 3–5 minutes results in severe irreversible anoxic brain injury [28]. Studies have shown that despite effective CCPR, cerebral blood flow is only 30–40% of the resting blood flows [29]. Also, cardiac recovery with CCPR remains poor as it is unable to unload the distended LV. The distension of the heart after CA results in stretching of myofibrils beyond the physiological Frank-Starling limits. The myocardial stretching not only results in myocardial stunning but also myofibrils are unable to return to their normal resting tone unless the ventricle is empty. Therefore, despite effective BLS and ACLS, 30-day survival for a patient with OHCA is only 8–10.7%, while for IHCA the survival rate is 17–28% [30–32]. This high mortality rate led to develop new ways to treat people with CA. One of the techniques that have been developed is combining CPR with ECMO, which is known as extracorporeal cardiopulmonary resuscitation (ECPR) [33].

After the publication of few case reports about the successful use of ECMO in patients with in-hospital CA in 2008, there was renewed interest in use of ECMO in patients with out-of-hospital cardiac arrest (OHCA). Still, the use of ECMO on patients with OHCA in the United States is scarce (0.69% patients in 2014) with variable but encouraging survival (6–56%) [34–37]. A systematic review of 25 studies including patients with OHCA and IHCA showed quite variable and inconsistent outcomes with the use of ECPR. However, results of ECPR were consistently better in IHCA. This is due to difficulty in initiation of ECMO in the field. Therefore, patients with OHCA should be rapidly transported to the hospital and during transport, an automated external defibrillator (AED) should be used for automated cardioversion. Once patients arrive at the hospital, AED should be removed and ECMO is placed and initiated. Further study is needed to determine the effectiveness of the process and the survival rate [38].
