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.