Background:
Extracorporeal support has improved survival in select neonatal and pediatric patients for over forty years. Over the last two decades, extracorporeal membrane oxygenation (ECMO) has emerged as an acceptable and potentially beneficial rescue modality in select adult populations. In severe respiratory failure, ECMO provides time for the lungs to rest and recover by augmenting gas exchange with the extracorporeal circuit.
A review of the outcomes in patients with Middle East Respiratory Syndrome Coronavirus (MERS-CoV) treated with ECMO demonstrated a decrease in hospital mortality rate and length of intensive care unit (ICU) stay compared to those managed with conventional therapy alone (1). Early reports regarding the use of ECMO in patients with Severe Acute Respiratory Distress Syndrome Coronavirus 2 (SARS-COV-2 or Covid-19) pneumonia have been mixed. Despite the similarities of MERS-CoV and the current novel coronavirus disease, recent reports have raised concerns regarding the high mortality rates observed in an early series of ECMO supported Covid-19 patients (2, 3). Similarly, a pooled analysis of five recent studies (4, 5, 6, 7, 8) suggested ECMO produced neither harm nor benefit in Covid-19 patients with ARDS. The authors of these analysis compared mortality in patients supported with ECMO for both MERS and Covid-19 and concluded Covid-19 patients had a significantly higher mortality than MERS (94.1% vs. 65.0%) when treated with ECMO. The authors further state that this data raises “questions about the real utility of ECMO in this outbreak” (8). Initial reports from United States hospital systems that had been both surprised and overrun with critically ill Covid-19 patients, demonstrated unfavorable results with supporting patients with ECMO, leading centers to abandon this support modality for these patients (9).
We present a single-center analysis and preliminary outcomes regarding the use of ECMO in 15 patients with severe respiratory failure due to Covid-19 all of which had failed maximal conventional ventilatory management and interventions as presented. These initial promising results prompted communication of our experience, despite its preliminary nature.
Methods :
All patients placed on ECMO due to COVID-19 pneumonia from March 10th, 2020 to April 30th, 2020 were identified. Data was manually extracted from the medical records of all fifteen patients into the ECMO registry. All patients were admitted to either the medical surgical intensive care unit (MSICU) or cardiovascular intensive care unit (CVICU) between March 15th, 2020, and April 27th, 2020. This study was approved by the Institutional review board.
Patients were managed by the ECMO team, which consisted of an experienced ECMO physician, cardiac surgeon, ECMO nurse, ECMO specialist and respiratory therapist. Prior to the Covid-19 pandemic, ECMO patients had only been cared for in the CVICU. Do to overwhelming number and severity of the respiratory failure, extension into the MSICU was necessary. Placement and care of ECMO patients within the MSICU was a new practice and required sharing of resources from the CVICU and included CVICU ECMO nurses, physicians and ECMO specialists to care for the ECMO patients. The CVICU nurse were additionally tasked with training the MSICU nurses.
Patient Selection for Extracorporeal Support -
Extensive discussions with a multidisciplinary team composed of ECMO physicians, cardiac surgeons, medical intensivists, and senior ECMO providers led to more restrictive criteria than is usually utilized for respiratory ECMO patient selection. The experiences in Asia, Europe and early United States were considered while preparing for this global pandemic.
Specific criteria for patients to be considered and accepted for VV ECMO include (Figure 1):
A) Ventilated less than 10 days with no additional serious comorbidities
B) Patients less than 60 years of age
C) PaO2/FiO2 ratio < 100 and/or patients that were not adequately supported despite:
1. Lung protective ventilation:
(Tidal Volume (Vt) < 6ml/kg Ideal body weight (IBW), Plateau Pressure (PPlat) < 30mmHg*)
2. Neuromuscular blockade (NMB)
3. Prone positioning
D) Hypercapnic acidosis compromising perfusion with failed above interventions
The term “serious comorbidities” refers to the fact that patients with chronic organ dysfunction due to co-morbidities outside of diabetes mellitus (DM), hypertension (HTN), and hyperlipidemia (HLD) were excluded. As indicated, an age less than 60 years was initially utilized as the upper limit for ECMO candidacy. This age limit was further reduced to patients <55 years as ECMO resources became limited. If the P/F ratio was >100 and lung protective ventilation was not providing adequate gas exchange (compatible with perfusing vital organs), the patient was considered for ECMO. For the purposes of defining the above criteria: Failure of adequate gas exchange was defined as an oxygen saturation less than 85%, PaO2 < 50mmHg, or an acidosis compromising perfusion (pH < 7.2 with hypercarbia) for more than 3 hours. Perfusion compromise was defined as a mean arterial pressure less than 65mmHg. Failure of lung protective ventilation is defined as the requirement of a PPlat > 30mmHg and/or a Vt > 6ml/kg IBW for more than 3 hours to achieve adequate gas exchange. Pulmonary vasodilator therapy with inhaled epoprostenol or inhaled nitric oxide were used as adjunctive measures in addition to lung protective ventilation.
Covid-19 patients with concomitant hemodynamic instability due to a reversible cause were evaluated for Veno-Arterial (VA)-ECMO on a case by case basis. An example of a potentially reversible cause would be acute right heart failure. When VA-ECMO is initiated, the family is informed that 5-7 days of support will be provided. If there is no improvement after this allotted time, goals of care and discontinuation of ECMO will be discussed. The ECMO team decided that extracorporeal CPR (eCPR) will not be offered for this patient population.
The decision to place patients on ECMO was made by a multidisciplinary team approach that included an experienced ECMO physician, cardiac surgeon, and intensivist. For patients that were borderline or at higher risk, additional ECMO intensivists and cardiac surgeons were consulted. In anticipation of limited resources, ECMO was deployed for patients with the perceived highest chance of survival based on their age and prior level of health.