Materials and Methods
Patients were identified within an IRB-approved, prospectively maintained ECMO database (IRB approval # 11D.185) at our institution from August 1, 2010 to September 15, 2020. Patients who were confirmed to have influenza or COVID-19 who underwent ECMO were included in this study. Data from these patients was retrospectively extracted and details were further studied by reviewing medical records. Inclusion criteria included a positive COVID-19 test and a diagnosis of ARDS. ECMO placement was determined by a multidisciplinary team that included a cardiac surgeon, a pulmonary-critical care physician, and a cardiovascular intensivist.
The indications for ECMO placement were the same as those listed in our previous paper,26 and Table 1 includes the list of contraindications for ECMO placement in COVID-19 patients. The exclusion criteria for COVID-19 patients may be more restrictive than in non-COVID-19 patients, due to the limited resources available during the first wave of the pandemic and challenges due to increased isolation needs.
During the first wave, our institution did not utilize veno-arterial ECMO (VA-ECMO) in patients with COVID-19, due to limited resources and an unclear understanding of the reversibility of the disease. In influenza patients, 7 patients were placed for VA-ECMO for cardiac dysfunction. However, these VA-ECMO patients were excluded from this study to ensure the appropriate comparisons.
Due to resource allocation and isolation concerns, COVID-19 and influenza patients were treated differently. We traditionally used single double-lumen cannula (Avalon© cannula, Avalon Laboratories, Rancho Dominguez, CA) for VV- ECMO patients, but this had to be modified for COVID-19. In COVID-19 patients, VV-ECMO was placed using the femoral and internal jugular veins (Figure 1). This change in insertion practice did not result in procedural complications, but it did affect body mass index (BMI) restrictions. All cannulation was performed in the ICU without transport to either the operating room or catheterization lab unless an issue occurred during the bedside cannulation. Since single dual lumen ECMO cannula placement always requires fluoroscopy and echocardiography, which requires additional personnel including radiology technicians and an echocardiography technician, the utilization of the Avalon© cannula was discouraged.26
Due to the COVID-19 pandemic, our institution did not offer a mobile ECMO program outside of our hospital network to avoid possible exposure of required personnel including the ECMO surgeon, perfusionist, and transfer nurses at the local site. Instead of activating mobile ECMO cannulation teams, we encouraged local cardiac surgeons to place ECMO at their institutions and then transport the patient to our facility.
The general management of ECMO has been described in one of our prior papers.28,29 Briefly, after placement of ECMO, the ventilator was set to the ARDSnet protocol.18 The typical setting was pressure controlled ventilation, rate 15 per minute, PEEP 15 cm H2O, delta P 15 cm H2O, and inspiratory time 1.5 seconds until recovery of the respiratory function.30 Paralytics were discontinued within 24 hours of ECMO initiation, unless ventilatory desynchrony resulted in hemodynamic instability. Sedatives were used to achieve a RAS score of negative 1-2. Blood pressure was maintained at a mean arterial pressure of at least 60 mm Hg with vasopressors and/or fluid as appropriate. A heparin drip was started once PTT fell below 50 seconds after cannulation and maintained at an anti-Xa level of 0.3-0.5 IU/ml. If bleeding complications were observed, the anticoagulation was held and then restarted at a lower anti-Xa goal of 0.1-0.3 IU/ml.
Timing of the decannulation was determined by chest x-ray findings, lung mechanics, and gas exchange. Before decannulation, the sweep gas was discontinued for at least 24 hours to ensure the lungs were able to exchange oxygen and carbon dioxide appropriately. For COVID-19 cases, we encouraged bed-side decannulation and discouraged transporting to operating room to limit exposure to COVID-19.
For our primary comparison, all adult patients who met our inclusion criteria were divided by their cause of ARDS, either influenza or COVID-19. The baseline characteristics, clinical characteristics, and outcomes were calculated and compared between the two groups. The primary endpoints of this study were ECMO survival and 30-day survival. ECMO survival was defined as surviving at least 24 hours post decannulation.
Data was expressed as the number with percentage, mean +/- standard deviation, or median (quantile) as appropriate. The two groups were compared using chi-squared tests for categorical variables and standard t-tests for continuous variables as appropriate, with significance accepted at a P-value less than 0.05.