**1. Introduction**

Extracorporeal membrane oxygenation (ECMO) is a technique used for temporary support of patients with end-stage heart or lung failure. It can be used as a bridge to decision because it helps to gain time to stabilize the patient for further evaluation for long-term treatment such as durable mechanical circulatory pumps or transplantation. The use of ECMO as a direct bridge to cardiac transplantation may unmask the complications in these critically ill patients leading to unfavorable posttransplant outcomes in some instances; however, it is now becoming the mainstay of treatments for patients waiting on the transplant list. The history of ECMO starts with the advent of the heart-lung machine invented by Gibbon [1, 2]. Further modifications leading to devices that are sustainable for longer periods of time gave rise to the technique of ECMO used today [3–5].

The use of ECMO in humans was first initiated in the pediatric population [3, 4]. Adult ECMO gained importance and is being used increasingly since the first randomized clinical trial by Peek et al. which showed a positive outcome in adults with respiratory failure [6]. This has been followed by many reports of success in H1N1

influenza patients [7]. Anselmi et al. recently reported the use of ECMO in pregnant patients [8]. Increasing utilization of ECMO in adults has revealed some of the common complications such as bleeding and coagulopathy which impact survival in this patient population. The delicate balance between adequate anticoagulation and bleeding complications presents one of the greatest challenges of ECMO therapy today.

The ELSO (Extracorporeal Life Support Organization) was established in 1989. The ELSO was formed as an offshoot of a study group that began in 1984 discussing cases. The ELSO focuses on collection and sharing of data and has fostered a rich collaboration among the majority of centers performing ECMO. The ELSO has hence remained a good resource for surgeons, neonatologists, nurses, perfusionists, respiratory therapists, biomedical engineers, critical care physicians, and heart failure cardiologists.

A total of 73,000 ECMO procedures were recorded by the ELSO as of early 2016 of which greater than 25% were performed in adult patients [9]. From 2006 to 2011, adult ECMO volumes increased greater than four times in the United States [10]. Adult ECMO has increased in volume due to its usefulness in improving survival in ARDS (acute respiratory distress syndrome) patients [11]. Additionally, with the improvement in technology, highly specialized hospitals have evolved the capabilities to transport critically ill patients from rural areas to their critical care units making it possible for rural populations to be able to receive advanced care [12, 13].

This review will focus on the venoarterial ECMO system and its use as a bridge to other long-term durable devices and/or cardiac transplantation.
