VV-ECMO 101: Going “On Pump” for Acute Pulmonary Failure

Introduction and Historical Context

The history of extracorporeal life support (ECLS) and cardiopulmonary bypass (CPB) has been an exercise in making the impossible possible. Early acute extracorporeal membrane oxygenation (ECMO) prototypes involved machines that took up half the room, barely did what they were supposed to do, and had terrible outcomes (1). However, improved CBP technology and increased experience with circuits yielded pared down ECMO circuits with improved safety profiles and better reliability, eventually leading to better prospects (2).

In 2009 a virulent flu season caused many young people to succumb to ARDS, and it was then that a prospective study provided the first major evidence of ECMO providing benefit for severe ARDS (3-5). After this, physicians and scientists alike began to wonder if ECMO technology might have just needed time to mature. The CESAR trial demonstrated convincing data for regionalization for ECMO centers of excellence (5). While the intervention arm (i.e. getting transferred to an ECMO center if they had severe ARDS) had most patients just get more evidenced based ARDS care (and avoid going “on pump”), transfer to ECMO centers was generally associated with improved outcomes with a significant number of ECMO survivors. It was this cadre of studies that reinvigorated research and utilization of ECMO, and in 2018, EOLIA (a true randomized trial for severe ARDS and VV-ECMO) was performed. Though stopped for being unlikely to cross significance thresholds (demonstrating non-inferior outcomes for patients in severe ARDS), a thorough analysis of treatment groups showed high crossover rates into ECMO within the control group (6). The implication of EOLIA, along with evolving retrospective registry data, suggests that VV-ECMO is an important salvage modality that may lower risk of death substantially for several refractory disease states.

Patient Selection and Indications

The most important thing to remember about ECLS is that it is meant to buy time for a reversible disease. The price of that time, though, is paid not only in resource utilization but also the need for anticoagulation, bleeding complications, and intense physiologic stress. While VV-ECMO pump runs can persist for many weeks (at experienced centers, and usually for awaiting transplant), they typically last for a few days or 1-2 weeks. Whatever the indication, all patients need “somewhere to go” after therapy. There needs to be a multidisciplinary team, protocols in place, and common expectations across team members within a center. These patients require massive resource utilization and round-the-clock care daily. At most hospitals, these patients qualify as the most fragile patients on campus. In short, ECLS and VV-ECMO is a team sport that requires strategy up-front; it is not something one clinician can initiate in isolation.

The requirements of VV-ECMO are considerable. While modern circuits are heparin bonded, most centers require full anticoagulation initially to prevent thrombo-embolic complications (though this can change depending on patient needs). Invasive access is a must, with adult ECMO cannulas ranging from 15-25 French, with additional venous and arterial access required for medications and blood gas measurement (7). It’s common for patients on VV-ECMO to have “pump-runs” that range from 5-15 days, and then after that they can require long courses of mechanical ventilation, ICU stays, and prolonged rehabilitation (1, 8). All this means that VV-ECMO should be reserved for people who are sick from reversible disease, are refractory to evidenced based care, AND can withstand the degree of support. As an example, severe ARDS is a leading indication for VV-ECMO but should really only be attempted after maximizing the what we know saves lives in ARDS: good ARDSnet vent settings, trial of prone position, and diuretic/steroid administration as appropriate (9-15). See Table 1 for a breakdown of indications, contraindications, and cautions.

That caveat said, VV-ECMO remains a critical intervention for patients with devastating disease but high likelihood of recovery with support. Clinicians should be on the lookout for patients failing conservative therapy early in their course and initiate transfer to capable centers if needed.