ECMO v. Ventilator
for COVID-19 Patients

It has been well documented that mechanical ventilation can injure the lungs, causing ventilator-induced lung injury (VILI). Known as “respirator lung,” VILI can include air leaks and surfactant dysfunction. Mechanical ventilation can trigger a complex array of pro- and anti-inflammatory mediators, according to Martin C. J. Kneyber, et al.

In a seminal study led by HH Webb and DF Tierney, it was discovered that:

1. The ventilation of normal lungs with low pressures (PIP 14 cmH2O) does not cause significant injury
2. Ventilation with high pressures (30 or 45 cmH2O) produces perivascular edema, and that ventilation at high airway pressures (45 cmH2O) without PEEP leads to severe lung injury (gross pulmonary edema, severe hypoxia) and
3. PEEP confers protection from alveolar edema due to high inspiratory pressure ventilation.

Webb and Tierney put forth a number of thoughts based on the above results:

1. That lungs from patients with ARDS have some “normal alveoli scattered among collapsed or fluid-filled alveoli, and that although the flooded alveoli “may be protected from overinflation... we are concerned that the normal alveoli may be overinflated and damaged.”
2. That “tissue disruption secondary to a high inspiratory pressure is probably not the mechanism of the changes we observed.”
3. That surfactant dysfunction with certain ventilatory strategies likely contributed to the development of lung injury.

What Causes Lung Injury?

Dreyfuss et al, found that high pressure (PIP 45 cmH2O) ventilation of rat lungs increases extravascular water and lung albumin uptake rapidly, and longer ventilation of up to 20 minutes causes a progressive increase in lung injury.

There are also a number of factors that predispose someone to VILI, including:

• underlying lung disease
• systemic inflammation
• surfactant dysfunction
• aspiration
• pulmonary edema
• extremes of age

Zhongheng Zhang, et al, write: “Extracorporeal membrane oxygenation (ECMO) provides an alternative to rescue patients with severe respiratory failure that MV fails to maintain adequate gas exchange. The timing of ECMO initiation based on the risks and benefits of ECMO has been widely investigated. In the running of ECMO, the protective ventilation strategy can be employed without worrying about catastrophic hypoxemia and carbon dioxide retention.”

While ventilators have gotten the majority of attention during the COVID-19 pandemic, ECMO has emerged as a way to help the sickest of patients. More than a third of critically ill COVID-19 patients who have completed ECMO treatment left the hospital alive. Without ECMO, these patients would have likely died.

A study in England found that of 1,678 COVID-19 patients who required mechanical ventilation, 17% were discharged alive.

Some COVID-19 patients with ARDS who have been treated with mechanical ventilation do not respond favorably to treatment, and unlike mechanical ventilation, ECMO does not cause lung injury.

Furthermore, any long-term sequelae from ECMO occur from primary disease and not from ECMO itself.

Dr. Robert Bartlett, known as the father of ECMO, notes that the indication for the use of ECMO in COVID-19 is when a patient is in respiratory failure and not responding to mechanical ventilation.

“ECMO, like conventional mechanical ventilation, doesn't treat COVID-19, but it keeps the patient alive while the disease runs its course. The primary goal is to keep patients on ECMO long enough so that their lungs can recover. Therefore, when we start ECMO, we turn the ventilator off so the lungs are no longer exposed to the barotrauma from positive-pressure ventilation,” explained Dr. Bartlett.

ECMO was deployed early in the COVID-19 outbreak in China for those patients who did not respond to conventional treatment.

At Michigan Medicine, the facility has been treating gravely ill COVID-19 patients with ECMO and in May discharged its first survivor who underwent ECMO treatment.

"It was a typical ECMO course. The patient was gravely ill and at imminent risk of death when the ECMO decision was made. He was supported well on ECMO and eventually liberated from ECMO, then he was liberated from a ventilator and was eventually well enough to go home independently to his family. The belief is that his long-term life expectancy will be close to normal," said Jonathan Haft, MD, ECMO medical director at Michigan Medicine, and an associate professor in cardiac surgery at the University of Michigan Medical School.

Dr. Haft reported that as of May, 15 COVID-19 patients have undergone ECMO treatment, and he predicts that 50% to 60% of them will survive.

Michigan Medicine evaluates the following before placing a COVID-19 patient on ECMO:

• Whether a patient is of advanced age
• If a patient has co-morbidities
• Overall functional status
• How long a patient has been on mechanical ventilation: Dr. Haft reports that after seven days of mechanical ventilation, survival rates drop
• A patient’s lung injury score

ECMO Use at Mercy Hospital of Buffalo

Dr. Harsh Jain, a cardiac surgeon at Mercy, uses ECMO to treat COVID-19 patients, which he says helps protect their lungs if they’ve been on a ventilator.

“All that pressure that we have to use on the ventilator to get the oxygen in and the carbon dioxide out, it has negative effects on the lungs,” Dr. Jain said. “To help combat that, we can use this and help rest the lungs.”

Dr. Jain continued: “Without it, they likely would have succumbed to the infection and become a statistic like we have been talking about for the last six months. Thankfully, four of the six of them, we were able to not have them be a statistic.”

From the patient perspective, Darrell Wright was initially treated using a ventilator. But his healthcare team soon found that that wasn’t enough. He was transferred to Mercy for ECMO treatment.

“Thank God for that machine, because if it wasn’t for that, I would not be here today,” Wright said. “And thank God for all the doctors and nurses.”