VA ECMO

VA ECMO removes blood from the patient’s venous system and returns oxygenated blood to the patient’s arterial system, analogous to CPB ( Fig. 2 A : Femoral VA ECMO and Fig. 2 B: “Sport Model” VA ECMO). VA ECMO provides respiratory and hemodynamic support directly to the arterial system. Cannulation sites vary depending on patient acuity, vascular anatomy, disease process, timing of anticipated recovery, or bridge decision. Peripheral cannulation sites include venous drainage from femoral or IJ veins returning oxygenated blood to femoral arteries. Central cannulation sites include venous drainage from inferior vena cava (IVC), superior vena cava (SVC), or right atrium, with oxygenated blood returned to the aorta or axillary arteries. Anesthesiologists should understand the circuit of blood leaving and entering the patient’s body and ensure that appropriate oxygenated flow reaches all parts of the body. Caution should also be observed for the possible entrainment of air in the ECMO system, which can lead to centrifugal pump failure and air embolism.

(A) (left): femoral VA ECMO: Blue blood represents deoxygenated blood drained from the femoral vein and returned as oxygenated, red blood to the femoral artery. (B) (right): “sport model” VA ECMO: Deoxygenated blood is drained from the internal jugular vein and reinfused to the subclavian or axillary artery. Figure used with permission from collectedmed.com/coachsurgery , Columbia University, New York, NY, USA.

VA ECMO can be placed in the operating room for patients who cannot be weaned from CPB for post-cardiotomy support or for partial unloading of the right ventricle of lung transplant patients with pulmonary hypertension. VA ECMO may also be used in heart transplant recipients with delayed graft function as a bridge to recovery of the transplanted organ. Support with VA ECMO for severe primary graft dysfunction following heart transplant is associated with fewer device-related complications, lower mortality, and a higher rate of graft recovery than the use of external short-term left ventricular assist devices in these patients . A recent meta-analysis evaluating the use of VA ECMO during lung transplantation, as compared to the use of CPB, resulted in statistically shorter intensive care unit (ICU) length of stay and trended toward a reduction in blood product transfusion, ventilator support, and 3-month and 1-year mortality .

In patients who are Interagency Registry for Mechanical Circulatory Support (INTERMACS) level 1 requiring emergency cardiopulmonary support, peripheral VA ECMO can be placed emergently. In a recent meta-analysis, VA ECMO extracorporeal life support (ECLS) was associated with a 13% increase in 30-day survival and a higher rate of favorable neurologic outcome at 30 days as compared to CPR without ECLS. In cardiogenic shock, ECLS is associated with a 33% higher 30-day survival as compared to intra-aortic balloon pump but no difference when compared with TandemHeart or Impella .

It is important to assess myocardial function frequently in patients on peripheral VA ECMO with persistent hypoxic respiratory failure as a transition point will exist where oxygenated blood from the ECMO outflow through the patient’s femoral artery mixes with blood ejected from the heart. It is important to note that the location of this “mixing” point is dynamic and highly dependent upon heart function, afterload, and ECMO flow. As myocardial function improves, it will move more distal from the aortic valve. Even with high/low ejection, ECMO flow and the delivery of oxygenated blood may not reach the patient’s coronary arteries or cerebral vessels. Blood flow to these vessels may therefore be supplied by the lungs and left ventricle, which will be relatively hypoxic if the intrinsic lung function is compromised. It is recommended to perform the assessment of oxygenation in the right arm (arterial blood gas sampling or pulse oximetry) as surrogate for oxygen delivery to the coronary and cerebral circulations. If deemed inadequate, strategies include conversion to VAV ECMO or revision to central VA ECMO.

It is important to monitor the left ventricle for distention during VA ECMO as the flow from the ECMO circuit may increase the afterload to a failing heart and exacerbate the workload and distension of the left ventricle . Vent placement in the left ventricle may be required to decompress the ventricle and relieve distention, optimizing chances of ventricular recovery. This can be performed by direct cannulation of the left ventricular apex during central cannulation or, in peripheral cannulation, surgical vent placement through small left anterior thoracotomy incision or femoral venous access with transseptal placement . Alternatively, an Impella or intra-aortic balloon pump could be inserted to reduce distension of and afterload on the heart .

With femoral artery cannulation, the cannula may obstruct flow to the distal leg and result in ischemia. A distal perfusion cannula to bypass the obstruction directs flow to the distal leg. Flow in the leg distal to a femoral ECMO cannula, even in the presence of a distal perfusion cannula, must be assessed routinely. Traditional vascular Doppler techniques and demonstration of flow by ultrasound color flow Doppler are useful .

VV ECMO

VV ECMO removes blood from the central venous system and returns it oxygenated to the venous system ( Fig. 3 A : Dual site VV ECMO configuration). This can be achieved by a dual-site peripheral cannulation, e.g., draining from the lower body and returning to the upper body, or single-site dual lumen cannula. With single-site access, a dual lumen catheter is positioned through the IJ vein. One lumen with two ports positioned at SVC and IVC draws blood into the ECMO circuit, and a second lumen returns blood to the RA, preferentially shunting blood across the tricuspid valve. Positioning can be performed under fluoroscopic guidance or with echocardiography; the anesthesiologist can aid in cannula positioning using transthoracic or transesophageal echocardiography ( Fig. 3 B: Single-site VV ECMO configuration). Single-site cannulation has theoretical benefits: improved patient mobilization for physical therapy, potentially lower incidence of catheter site infections and decreased circuit recirculation due to the fixed position of drainage and reinfusion ports. Single-site VV ECMO avoids femoral cannulation, facilities mobilization of patients, and offers improved in-hospital survival and lower 6-month mortality as compared to conventional ECMO for severe hypoxemic respiratory failure .

(A) (above): dual site VV ECMO: Blue blood represents deoxygenated blood being drained from the famoral vein and returned as oxygenated, red blood to the internal jugular vein. (B) (right): single-site VV ECMO: Deoxygenated blood is drained and reinfused through a single cannula in the internal jugular vein. Figure used with permission from collectedmed.com/coachsurgery, Columbia University, New York, NY, USA.