In this chapter, we tackle one of the most sobering and important topics related to extracorporeal membrane oxygenation (ECMO) – selection of patients for ECMO. In doing so, we are trying to reconcile two very important and weighty decisions:
- 1.
Can I choose someone for ECMO who would be likely to do well with ECMO?
- 2.
Can I spare someone the risks of ECMO if they are unlikely to benefit?
These can be challenging to parse out and can weigh heavily on clinicians. To better understand this dynamic, let’s return to our graph comparing ECMO to conventional care ( Fig. 7.1 ).
The green line (ECMO) starts out the graph significantly higher than the blue line (conventional care), which represents that ECMO has a cost in terms of risk. Simply cannulating means inserting large cannulas into major blood vessels leading to all of the associated risks – pseudoaneurisms, damage to underlying structures, extremity ischemia, dissection, etc. Even if your team is excellent at cannulating with very few complications, you are exposing blood to foreign surfaces and altering the coagulation cascade, which could alter bleeding and hemodynamics down the road. Even from a resource standpoint, putting someone on ECMO can be expensive and resource intensive.
Given all this, you may be asking yourself some hard questions.
“Aren’t people either not sick enough to even consider ECMO or so sick that ECMO would not be of benefit?”
Or even more so, “Why even put someone on ECMO?”
These questions get to the heart of the challenge of selection for ECMO. While challenging, there is a sweet spot that exists – teams that are truly adept at selection are able to identify that select group of patients that is likely to do poorly without ECMO and will improve with ECMO ( Fig. 7.2 ). This is the art of selection, which we will spend this entire chapter trying to refine.
So how can we get better at finding this select group of patients?
To tease out this select patient population, let’s consider the following rules, to help us hit that sweet spot with regards to selection for ECMO.
Rule 1: Reversible etiology of cardiac or respiratory failure
Rule 2: Conventional therapy is harming the patient more than helping
Rule 3: Cardiac/respiratory failure has to be severe enough to justify the risks of ECMO
Rule 4: Patient is not too far gone so that ECMO will not be of benefit
Let’s explore a little more of what is behind each rule.
Rule 1: Reversible Etiology of Cardiac or Respiratory Failure
This is an essential rule and an acknowledgement that ECMO does little to fix the underlying disorder. Rather, a path must exist towards eventual recovery or destination (such as a transplant, long-term device, etc.).
Often, while recovery can exist, there is some barrier that is preventing this, whether it is the high ventilator requirements or escalating pressors. What the patient needs is time to allow for eventual recovery. This time is what ECMO can offer ( Fig. 7.3 ).
The reversibility of the underlying cause of severe respiratory/cardiac failure will be a strong factor in a patient’s candidacy for ECMO. Ideally, the more readily reversible the condition, the better, especially if the risk of decompensation without ECMO is significant. A patient with severe, refractory status asthmaticus, with an anticipated recovery of 24–48 hours on ECMO, has very different risk profile from a patient with ARDS from bacterial pneumonia, who may have an anticipated recovery of weeks to months. Likewise, a patient with a normal heart and cardiogenic shock from a pulmonary embolism may carry a very different risk profile from a patient with chronic cardiomyopathy and decompensated heart failure.
Rule 2: Conventional Therapy Is Harming the Patient More Than Helping
We spent a great deal of time in Part 1 defining and outlining the dose-related toxicity of conventional care. All the things that can be done in the intensive care unit (ICU) to optimize oxygen delivery (pressors, inotropes, oxygen, positive pressure ventilation, fluid, blood) come with a cost that compounds with increasing dose.
These interventions combine diminishing returns with increased toxicity at higher levels. This means that the higher the dose of conventional supportive care is not only needed for sicker patients, but actually that conventional supportive care itself can be harmful at higher doses.
ECMO has to spare some degree of this toxicity. The more toxicity that can be potentially spared, the stronger the rationale for ECMO.
Rule 3: Cardiac/Respiratory Failure Has to Be Severe Enough to Justify the Risks of Ecmo
It is one thing to say that conventional therapy is harming the patient more than helping. It is quite another to say that the degree that it is harming the patient is severe enough that sparing this harm is worth the risks of placing a patient on ECMO.
Let’s suppose for example that you have a patient on a ventilator for pneumonia. The ventilator is set at 100% FiO 2 , and he has been on this oxygen level for days.
Is there toxicity associated with this level of support? Certainly.
Does this toxicity justify the risks of ECMO? Maybe not.
To answer this question, we would need to really understand how dependent the patient was on this high level of support and what trajectory the patient was on. Otherwise, our graph may look something like Fig. 7.4 , with the conventional support line increasing from left to right but not increasing to the degree that it would intersect with the ECMO line.
