Discussion
The dramatic increase in ECMO
utilization over the last decade has provided a wealth of data and
experience that has enhanced physician comfort with treating these
complicated patients. However, it has also brought unique challenges
associated with increasingly complex physiology. Some patients supported
with VA ECMO may develop differential hypoxemia resulting in poor
cerebral, myocardial, and upper body oxygenation and many whose initial
presentation is combined cardiopulmonary failure cannot be adequately
supported with standard percutaneous configurations. While central
cannulation is another possible strategy, it is usually not a preferred
approach unless the patient is already undergoing cardiac surgery or has
severely diseased peripheral arteries precluding placement of adequately
sized cannulae for optimal support. Another strategy used in such
circumstances is axillary artery cannulation, which can be a good
alternative to femoral artery reinfusion. Its advantages include less
differential hypoxemia, less secondary left ventricular distension and
greater mobility on ECMO. However, it is usually performed utilizing a
side graft technique, is not suitable for urgent or emergent situations,
and can potentially lead to upper extremity hyperperfusion and
compartment syndrome. In a patient supported with percutaneous VA ECMO
utilizing a femoral arterial reinfusion cannula, an additional venous
reinfusion cannula ensures oxygenated cardiac preload and hemodynamic
support that satisfies these physiologic requirements.
As with previous studies, our cohort is small and heterogeneous although
largely older and obese with frequent cardiac and pulmonary
comorbidities. The median SOFA-0 score of 15 and SAVE score of -12
(95.2% predicted ICU mortality and 18% in-hospital survival
respectively) highlight the extreme severity of illness prior to ECMO
cannulation.(15) Half of our patients were placed directly on VA-V due
to comorbid cardiopulmonary failure at presentation, and the remaining
patients were initiated on VA with differential hypoxemia as the most
common indication for VA to VA-V conversion. Although it was initially
hypothesized that VA-V conversion may reduce neurologic complications,
the 14% incidence of anoxic brain injury is consistent with other
reports across both standard and VA-V
configurations.11 However, the survival rate of 64%
compares favorably with 2016 ELSO Report adult statistics (43-65% in
respiratory failure and 42-51% in shock and cardiomyopathy) as well as
previous VA-V case series (39-42.9%). Notably, during the same period,
three patients received an axillary graft for reinfusion as a substitute
for traditional femoral arterial cannulation, but their data is not
included in our analysis.
ECMO provides respiratory and circulatory support to facilitate native
organ recovery (or less commonly bridge to transplant). As it is
utilized in increasingly complex patients, it is not unexpected that the
incidence of comorbid cardiopulmonary failure and sequelae such as
differential hypoxemia will continue to grow. This is supported by the
use of VA-V in 7.7% (14 out of 181) of our ECMO patients from 2016 to
2019, compared to less than 1.5% in the largest previous case
series.11 It is important to note that the cannulation
strategy may not be fixed for the duration of ECMO support. Patient
physiology, or clinical conditions and requirements, may change over
time (e.g. the heart may recover faster than the lungs) and
modifications in ECMO configurations may occasionally be necessary. The
conversion from the initial ECMO strategy to a different modality should
always be strongly considered if the patient’s perfusion is inadequate,
gas exchange is suboptimal, or complications result from the initial
cannulation strategy. However, one should always be cautious with
additional cannula placement due to the ongoing anticoagulation for
ECMO, higher risk of bleeding (particularly in arterial vasculature),
and risk of another port for infection or thrombosis.(9) Since the small
number of patients with presentations prompting consideration of VA-V
cannulation precludes larger randomized trials, clinical decision making
is heavily influenced by smaller case series and expert opinion. Despite
lack of reduction in neurologic complications, we believe that combined
cardiopulmonary failure and differential hypoxemia necessitate
additional venous reinfusion to supply oxygenated cardiac preload and
subsequent upper body delivery. At minimum, our data indicates
maintained survival with VA-V cannulation, which is notable as these are
the ECMO patients with the highest severity and complexity of illness.
As such, we advocate for early consideration and proactive VA-V
cannulation in these situations.