Introduction
One of the main concerns of coronavirus disease 2019 (COVID-19) infection is development of acute respiratory distress syndrome (ARDS). Although the definition of ARDS has changed over the decades, its clinical context remains the same: a rapidly progressive inflammatory syndrome that impairs oxygen transport in the lungs.1–3 Historically, the most common viral cause of adult ARDS prior to COVID-19 infection was influenza pneumonia, and the complication of ARDS from influenza is known to be associated with an increased mortality.4,5 The pulmonary injury in ARDS due to COVID-19 has been shown to resemble other viral causes of ARDS, and as expected, the severity of ARDS is associated with significantly worsened mortality among COVID-19 patients.1,6,7
Due to the high mortality rate of ARDS due to COVID-19, there has been a high demand for refractory treatment options in patients who do not improve upon standard ventilation and treatment. Thus, extracorporeal membrane oxygenation (ECMO) was used in select cases of COVID-19 with refractory ARDS and severe hypoxemia.7–10 ECMO is a temporary form of mechanical cardiopulmonary support, used in patients with severe cardiac and/or respiratory shock. ECMO was first clinically used in 1972 and has been increasingly incorporated into standard practice in the past two decades.11–13 Despite controversial and conflicting evidence on its overall efficacy, ECMO has become a common treatment for patients with refractory ARDS.13–16
In cases of influenza, ECMO can be used adjunctive support in cases complicated by severe ARDS.17 With knowledge learned from years of critical care and development of protocols, there is a good understanding of how to properly care for patients with influenza.18,19 It is known that in the setting of influenza, immunosuppression with steroids increases the duration of viral shedding and worsens mortality,20 so high dose immunosuppression is usually avoided. If traditional therapies fail to stabilize the patient, early initiation of ECMO in critically ill patients with influenza can improve their chance of survival by promoting lung protective ventilator strategies without compromising required gas exchange. The amount of benefit provided by ECMO in complement to anti-influenza agents is unclear, though outcomes have been acceptable.17 In contrast, we have not identified a specific, proven treatment protocol for COVID-19 infection despite the widespread use of supportive measures such as remdesivir, lung-protective ventilator strategies, anti-inflammatory agents, and steroids.21 Despite initial support for some of these agents, some subsequent research has been less optimistic.21,22
While ARDS due to COVID-19 has been compared to ARDS caused by influenza, severe cases of COVID-19 continue to demonstrate high mortality rates, and the similarities and differences between the two diseases are not well understood. Similarly, despite recent studies on the use of ECMO in COVID-19 patients,23–25 there remains a lack of evidence documenting the overall efficacy of ECMO in treating ARDS due to COVID-19. This paper will compare the outcomes and efficacy of ECMO in treating patients with ARDS due to COVID-19 or influenza to better understand the prognosis of ARDS due to COVID-19 and the use of ECMO in treating it.