**2. The ECMO circuit**

The ECMO circuit (**Figure 1**) in its most basic form consists of a pump that is capable of pumping blood it receives from the drainage cannula to the membrane oxygenator which then leads to a heat exchanger. The oxygenated temperatureoptimized blood is then returned to the patient by the return cannula. ECMO cannulation can be done centrally through the right atrium and ascending aorta or peripherally via the femoral artery and vein. The type of cannulation used whether central or peripheral influences the outcomes as the complications differ. When central cannulation is used, bleeding requiring transfusions is higher. In central cannulation higher rates of reoperation are also noted. Increased complications will decrease survival and increase resource utilization. On the other hand, peripheral cannulation has been noted to produce fewer bleeding complications. It can be

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*Extracorporeal Membrane Oxygenation as a Bridge to Cardiac Transplantation*

placed in a shorter time and at the bedside. However, the complication of limb

When both heart and lungs have to be bypassed, the venoarterial ECMO

The Seldinger technique is used typically to achieve the cannulations.

**3. Indications and contraindications for VA-ECMO**

decompensation of chronic heart failure, and postcardiotomy shock.

ECMO circuits are set up depending on the organs that need to be bypassed.

(VA-ECMO) is used as shown in (**Figure 1**). The VA-ECMO circuit provides both gas exchange and hemodynamic support as blood is pumped from the venous to the arterial systems. On the other hand, if only the lungs need to be bypassed, the veno-venous circuit (VV-ECMO) facilitates only gas exchange with no hemodynamic support. In VV-ECMO blood is removed taken out of the venous system and

VA-ECMO is designed to provide cardiac and pulmonary support. Deoxygenated blood is drained from the venous system, and oxygenated blood is returned into the arterial circulation, in a similar fashion to standard cardiopulmonary bypass. In the VA-ECMO system, central cannulation is achieved by draining blood directly from the right atrium and returning oxygenated blood to the proximal ascending aorta. Peripheral cannulation uses blood drained from the proximal femoral vein/jugular vein which is oxygenated and then returned to the carotid/axillary/femoral artery.

Two types of pumps are currently available for use in ECMO circuits. They are centrifugal pumps and roller pumps. Centrifugal pumps are smaller and pump blood by providing a pressure differential across a pump head that contains a magnetically driven impeller revolving at speeds up to 3000 revolutions per min. On the other hand, roller pumps push blood across the circuit by progressively compressing segments of tubing along a curved pathway. Centrifugal pumps have been associated with a lesser degree of hemolysis compared with roller pumps and decreased requirement of anticoagulation. Therefore, centrifugal pumps are being

The major indication for VA-ECMO is cardiogenic shock as defined in the ELSO guidelines [14]. This includes inadequate tissue perfusion due to hypotension and low cardiac output despite volume repletion, inotropes, vasopressors, and intraaortic balloon counterpulsation use. Common causes for cardiogenic shock are acute myocardial infarction (AMI), myocarditis, peripartum cardiomyopathy, acute

Septic shock is an indication in some centers. The guidelines on prognostication of survival without ECMO are based on the IABP score in postcardiotomy patients [15] and the Samuels score also in postcardiotomy patients [16]. In a retrospective analysis, Samuels et al. [16] showed that early insertion of mechanical support reduces multi-organ failure in these patients. In hospital mortality, correlates with increasing inotropic support needed to get patients off cardiopulmonary bypass following cardiac surgery. The combination of pharmacological criteria together with hemodynamic presentation should be used for mechanical support initiation in cardiogenic shock. Earlier institution of mechanical support devices tends to lower incidence of postoperative multi-organ failure and improve discharge rates [16]. The advantage of VA-ECMO is that it provides quick biventricular support and can be achieved at the bedside for poor oxygenation, biventricular failure, refractory malignant arrhythmias, and heart failure with severe pulmonary failure. VA-ECMO can be used as a bridge to recovery, AMI after revascularization, myocarditis, postcardiotomy shock, chronic heart failure, and non-revascularizable AMI.

*DOI: http://dx.doi.org/10.5772/intechopen.84935*

oxygenated and pumped back into it.

increasingly used in in adult patients.

ischemia occurs equally in both types of cannulations.

**Figure 1.** *VA-ECMO circuit.*

#### *Extracorporeal Membrane Oxygenation as a Bridge to Cardiac Transplantation DOI: http://dx.doi.org/10.5772/intechopen.84935*

placed in a shorter time and at the bedside. However, the complication of limb ischemia occurs equally in both types of cannulations.

ECMO circuits are set up depending on the organs that need to be bypassed. When both heart and lungs have to be bypassed, the venoarterial ECMO (VA-ECMO) is used as shown in (**Figure 1**). The VA-ECMO circuit provides both gas exchange and hemodynamic support as blood is pumped from the venous to the arterial systems. On the other hand, if only the lungs need to be bypassed, the veno-venous circuit (VV-ECMO) facilitates only gas exchange with no hemodynamic support. In VV-ECMO blood is removed taken out of the venous system and oxygenated and pumped back into it.

VA-ECMO is designed to provide cardiac and pulmonary support. Deoxygenated blood is drained from the venous system, and oxygenated blood is returned into the arterial circulation, in a similar fashion to standard cardiopulmonary bypass. In the VA-ECMO system, central cannulation is achieved by draining blood directly from the right atrium and returning oxygenated blood to the proximal ascending aorta. Peripheral cannulation uses blood drained from the proximal femoral vein/jugular vein which is oxygenated and then returned to the carotid/axillary/femoral artery. The Seldinger technique is used typically to achieve the cannulations.

Two types of pumps are currently available for use in ECMO circuits. They are centrifugal pumps and roller pumps. Centrifugal pumps are smaller and pump blood by providing a pressure differential across a pump head that contains a magnetically driven impeller revolving at speeds up to 3000 revolutions per min. On the other hand, roller pumps push blood across the circuit by progressively compressing segments of tubing along a curved pathway. Centrifugal pumps have been associated with a lesser degree of hemolysis compared with roller pumps and decreased requirement of anticoagulation. Therefore, centrifugal pumps are being increasingly used in in adult patients.
