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.