Cardiac Considerations
As described in our previous article2, we aim to
divert the majority of calculated flow target cardiac output away from
the pulmonary system into the VA-ECMO output, consistent with previously
published reports.5 The ECC circuit reduces native
cardiopulmonary blood flow to facilitate surgical exposure and
dissection, and attenuates ischemic-reperfusion
injury.5 Maintaining a balance between the ECMO flows
and native cardiac output is a necessity to achieve appropriate systemic
perfusion, avoidance of intra-cardiac clot formation, and provide
controlled reperfusion of implanted donor grafts. Communication between
the surgical and anesthesia teams is paramount. TEE,
ETCO2, and the presence of pulsatility within the
arterial and pulmonary arterial waveforms are used to determine the
ideal circuit and native blood flow.
Surgical manipulations of the heart may cause abrupt changes in cardiac
preload and contractility. Ongoing assessment of preload within the
system is vital to avoid ECMO suction events (“chattering in the
lines”).2 Due to the significant diversion of cardiac
output to the hybrid ECMO circuit, the TEE is unable to accurately
assess cardiac preload while on ECMO, yet remains useful as a direct
monitor of cardiac contractility. We utilize ETCO2 as a
semi-quantitative/qualitative monitor of system preload based on the
principle of ETCO2 correlating with cardiac
output.6, 7 During implantation of the donor lung,
mechanical ventilation is applied to the contralateral side via a
double-lumen endotracheal tube. A value of >20 mm Hg as a
goal value for our ETCO2 during hybrid ECMO was chosen
based on trauma literature which notes that value as a threshold of
adequate cardiac output during successful cardiopulmonary
resuscitation.6 Pulsatility in both the pulmonary
arterial and systemic arterial waveforms confirms biventricular output
and provides a constant assessment of systemic afterload. The loss of
pulsatility waveforms is associated with derangements of balance between
the native and mechanical cardiac outputs, including decreased
biventricular contractility, inadequate preload or inappropriately high
ECMO target flows.