Results and Discussion:
Prior reports of ECMO use in Covid-19 patients with severe ARDS may need
to be considered in the context of an unprecedented pandemic. Our
experience demonstrates that ECMO can be successfully employed as a
support modality for Covid-19 related ARDS in an appropriately resourced
facility with judicious candidate selection. Health systems that were
overwhelmed by Covid-19 patients were forced to abandon their normal
practices in the presence of such unanticipated clinical demands.
Standards of care change, like mass casualty events in the combat
theater, as resources and staff are critically stretched. Many of these
reports come from health systems operating at surge capacity (19). The
case series described above demonstrates that extracorporeal support has
had a beneficial role in carefully selected patients.
Of the fifteen Covid-19 ECMO patients, 11 have been successfully
liberated from ECMO (Figure 6). Of the eleven that have been
decannulated, 9 have been liberated from mechanical ventilation. At the
time this article was written, all 11 of the patients removed from ECMO
are following commands and have a chance at a good overall outcome (CPC
score of 1-2) (Table 6) (20). Of the 9 patients liberated from MV, 4
have been sent home and 5 are recovering on the wards. Two of the
patients still in the hospital are recovering from encephalopathy and
critical illness polyneuropathy (Figure 7).
The potentially promising outcomes of the Covid-19 ECMO patients exist
due to a multiplicity of reasons. The experiences of our colleagues
around the world helped systems such as ours prepare for the Covid-19
pandemic and restrict selection criteria for the application of
extracorporeal support. By selecting younger healthier patients, limited
resources were used on patients more likely to survive with a good
outcome. Instead of focusing on each individual as they presented, the
focus moved to the collective group (21). Judicious use of ECMO may
improve survival in carefully selected candidates (22).
Pre ECMO ventilator management that served to protect the lungs from
additional injury may have been another supportive factor in the
outcomes. A lung protective strategy of lower volumes and lower plateau
pressures was maintained for most of our patients’ pre ECMO ventilator
time. As soon as lung protection failed, namely plateau pressures higher
than 30cmH2O, ECMO was initiated, thereby minimizing the
period of additional lung injury (23). The patients whose lungs
experienced higher pressures and volumes prior to ECMO had longer
periods of ECMO support. Most patients also received NMB and trials of
prone positioning prior to ECMO.
The higher levels of anticoagulation used during ECMO support may have
favorably addressed the underlying thrombotic microangiopathy that
attends Covid-19 infection (24). Early recognition of an impaired
heparin response and fast transition to the alternative agent
bivalirudin may have further treated the thrombotic microangiopathy.
Early use of pre filter, high flow CRRT did appear to lower inflammatory
markers and helped to carefully adjust intravascular volume in a fashion
that did not compromise ECMO blood flow. Attempts to use post filter
replacement fluid were met with prohibitive levels of filter thrombosis
despite regional and systemic anticoagulation. The degree of cytokine
removal from the PrismaFlex CRRT machine with the HF1000 filter (Baxter
Healthcare Corporation, Deerfield, IL) remains under investigation (25).
Five of the ECMO patients have received compassionate emergency use of
convalescent plasma. All tolerated the convalescent plasma infusions
well. Three of the five have been liberated from both ECMO and MV, while
two remain on full ECMO and MV support. Further investigation is
required to assess the efficacy of the convalescent plasma.
The effectiveness of prone positioning in Covid-19 severe ARDS patients
prior to ECMO support led to an increase in prone positioning while on
ECMO support. If patients failed to show any improvement after 72 hours
of ECMO support, a trial of prone positioning was implemented. Patients
were also mobilized into a vertical position using the specialty bed.
The use of a newly FDA approved subcutaneous EEG may have enabled
earlier detection and treatment of epileptiform activity and
nonconvulsive seizures. The EEG criteria used to define seizure activity
with this new device are evolving, but treatment of the patients’
seizures improved their neurologic exams. Prolonged use of treatment
dose anticoagulation after ECMO liberation may have mitigated some of
the late thrombotic events described in prior Covid-19 populations.
The limitations of a small case series are clear. Any health systems
outcomes are clearly influenced by preparation time and whether their
beds are literally overflowing with critically ill patients. Our
experience suggests a helpful role for extracorporeal support in select
patients; however, the concerns of premature extrapolation of the data
in a small series are readily appreciated.
Greater benefits are probable in a high-volume center with an
experienced team that has time to prepare, and one that is not
completely overwhelmed by a pandemic surge of patients. The rapid
sharing of information from our colleagues in Asia, Europe, and the
United States was extremely beneficial to those downstream in the
pandemic, as care evolved dynamically as new experiences were reported.
Conclusion: In carefully selected patients at a well-resourced,
high-volume center with an experienced team, ECMO may be beneficial in
patients with Covid-19 severe respiratory failure. Efficacy of EMCO
support is greater when applied as soon as optimal evidence-based
interventions are unable to support the most critically ill Covid-19
patients.