As he watched her vital signs deteriorate, he
thought, “If only we could remove the blood from
her body by bypassing the lungs, and oxygenate
it, then return it to her heart, we could almost
certainly save her life.” 1
The modern successor to Gibbon’s original idea
for a heart lung machine is extracorporeal membrane oxygenation (ECMO). ECMO is best seen as
a bridge for a reversible or recoverable insult that’s
otherwise refractory to conventional management.
ECMO has been used in neonates and adults
across a wide range of illness from meconium
aspiration to cardiac arrest. Traditionally, the
decision-making process and placement of the
patient on ECMO has occurred in hospital ICUs
or surgical theaters. But as ECMO devices become
cheaper, smaller and more portable, this previously scarce resource is becoming more widely
available in nontraditional settings, such as the
ED and physician-led EMS services in Europe.
There are two types of EMCO: VV (veno-venous)
and VA (veno-arterial), which refer to the source
and target of blood flow between the two large-bore catheters and the pump. (See Table 1.) Most
often, the cannulas, which resemble very long
and large bore IVs, are inserted into the femoral vessels.
In VA, or “heart-lung,” ECMO, deoxygenated
venous blood from the right atrium is drained via
one cannula and passed through a membrane oxygenator, which serves to oxygenate the blood and
remove carbon dioxide, after which the now normally arterialized blood is pumped back into the
proximal aorta under pressure via a return cannula to complete the circuit. (See Figure 1, p. 25.)
VA ECMO is required for severe cardiac failure and hemodynamic collapse with or without
concomitant respiratory failure. By bypassing
the entire cardiopulmonary system, the heart is
allowed time to recover from an insult while systemic perfusion and oxygenation to the whole
body are maintained. This type of ECMO has
been used to support patients with refractory
cardiac arrest, as in Case 1 or 2.
VV ECMO, a type of “lung bypass,” is used to
treat severe respiratory failure such as the drowning in Case 3. With VV ECMO, no cardiac support
is provided as oxygenated blood from the ECMO
circuit is directed back into the right side of the
heart at the level of the right atrium where it then
passes through the normal pulmonary flow cycle
without the need to undergo gas exchange in
the lungs and on into the systemic circulation.
This essentially allows the membrane oxygenator to perform the role of the lungs, while the
rest of the patient’s normal circulatory function
ECMO in OHCA
A potential role for ECMO in the treatment of
out-of-hospital cardiac arrest (OHCA) is especially appealing. Closed chest compressions
produce inadequate blood flow to sustain vital
organs for an extended period of time, in most
cases providing as little as 5.5% of mean aortic
blood flow. 2
As a method of circulating blood during cardiac arrest, ECMO has now been dubbed “
extracorporeal life support (ECLS)” or “extracorporeal
cardiopulmonary resuscitation (ECPR)” and can
achieve physiologic levels of blood flow while the
heart is stopped.
Although progress has been made in the survival of OHCA patients in recent years through
attention to high-performance CPR and early
defibrillation, many victims with hearts “too
young to die” still fail to respond to excellent
ALS care. ECPR may extend OHCA survival in
the future to these victims.
Through early identification of ECMO candi-
dates and the delivery of excellent prehospital care
en route, EMS providers are on the front line of
this potential lifesaving intervention.
Although evidence for ECPR is limited to case
series, published studies suggest a neurologically
intact survival benefit for select patients with
OHCA when compared to historical controls.
A systematic review provided a pooled survival
Table 1: Indications for the two types of ECMO
Note: Lists are not complete.