乌鸦传媒

Extracorporeal membrane oxygenation (ECMO) is usually a last resort strategy for acute respiratory distress syndrome (ARDS), but for cases from COVID-19 should it come sooner?

Starting awake ECMO prior to intubation for severe COVID-19 has been tried by a group led by Jeffrey DellaVolpe, MD, medical director of the adult ECMO program at Methodist Hospital in San Antonio.

"Early on we were very affected by looking at the numbers and seeing the really astronomical numbers of patients who were dying who were mechanically ventilated, and we said maybe the ventilator is a piece of this," he told 乌鸦传媒.

Their novel approach is venovenous ECMO for COVID-19 patients with single organ failure, minimal pressor requirement, young age, minimal comorbidities, good functional status before the infection, and a ratio of arterial partial pressure of oxygen to fraction of inspired oxygen of less than 100 despite 100% inspired oxygen (and prone positioning, if clinically feasible).

A multidisciplinary team selects COVID-19 patients for ECMO, with the idea of sparing patients from sedation, paralytics, high airway pressure, and high levels of inspired oxygen.

That's a provocative concept, commented Cara Agerstrand, MD, director of the medical ECMO program at NewYork-Presbyterian/Columbia University Irving Medical Center in New York City.

COVID-19 patients have typically received mechanical ventilation following the standard of care for severe ARDS, with lung protective settings along with prone positioning and other strategies before attempting ECMO.

"We have tried to maintain treatment for COVID-19 patients similar to other patients with severe ARDS, really following our standard of care evidence-based approach to medicine," Agerstrand noted.

There have been isolated case series and reports in the literature of early ECMO for non-COVID ARDS, DellaVolpe noted.

The rationale is to maximize ECMO's benefit by not waiting until a patient is harder to salvage, he suggested.

"The later you put ECMO on, the more time you expose them to harmful effects of the ventilator and you get people in the later phases of the disease," he said. "Those are the patients who aren't getting a whole lot of benefit out of [ECMO], and you're really just assuming a lot of harm. Those are the patients we're worried about and less likely to offer ECMO to."

Now with nearly 85 ECMO runs for COVID at his center, that's what the data is showing, he said. More pre-ECMO ventilator days was associated with a 56% increased risk of dying after adjusting for covariates, including age, sex, and comorbidities.

The next step for his group is a prospective single-arm study of early ECMO in COVID-19, which has about 20 of the targeted 40 or 50 patients enrolled. "If the result's still intriguing then it lends itself to more of a comparative study after that," DellaVolpe said.

Key questions are whether the approach staves off mechanical ventilation and improves outcomes, he said.

ECMO practice has been changing rapidly, Agerstrand said. "However, at this point in time, we don't have any evidence to pursue ECMO prior to intubation in patients with ARDS.... We don't have a lot of specific evidence for COVID-19 patients because it's such a new disease, but in general our approach from ARDS management is following our standard of care algorithm."

Her group recently published data from the global ELSO registry showing ECMO used in that way can be successful in COVID-19, with over 60% survival, similar to non-COVID ARDS.

Even if the early ECMO strategy were to prove effective, the existing highly specialized centers and highly trained multidisciplinary teams that do ECMO couldn't stretch to cover very many COVID-19 cases, she cautioned.

"The physical and practical limitations would make ECMO difficult to use for many patients," Agerstrand pointed out. "Many centers have maybe one or two ECMO machines. It's not the type of technology that, at this point, is so widely available that it could replace a much more common, less resource-intensive technology," i.e., mechanical ventilation.

And it is a high-risk, high-reward therapy with real risks, ranging from bleeding to stroke and thrombotic events, she noted. "It's not the type of technology we would want to enact if there are other ways to support a patient well."

Perhaps 80% of severe COVID-19 patients might fit these criteria, DellaVolpe said.

Figuring out which patients are most likely to benefit and least likely to be harmed will be key, he agreed.

Even for patients who do go on mechanical ventilation, consideration of ECMO should come sooner, he argued. "Early identification of patients who may benefit from further support and early discussion with centers that have capabilities for support can potentially be helpful in identifying the right patient for this," he said. "We're all still learning."

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