Introduction:
Venoarterial extracorporeal membrane oxygenation is a temporary mechanical cardiopulmonary support during a cardiogenic shock or combined cardiopulmonary failure. It provides complete and immediate reinforcement and support to cardiac and pulmonary function during the precipitation of a cardiogenic shock or cardiac arrest unmanageable by standard treatment approaches.
What Are the Components of the VA-ECMO Circuit?
A VA-ECMO comprises a venous cannula for inflow and drainage, an arterial cannula for outflow and return, a pump, and an oxygenator. The VA-ECMO can be set up as peripheral access or central access. A central VA-ECMO primarily supports a patient in the operating room and is used for a short duration. It is especially used in patients after cardiotomy surgery who are unable to manage after cardiopulmonary bypass. A peripheral VA-ECMO is used outside the operation theater during a cardiogenic shock or arrest via access made through skin or vein or artery exposure of the femoral artery and femoral vein or internal jugular vein.
What Are the Indications of Venoarterial Extracorporeal Membrane Oxygenation?
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Cardiogenic Shock: It is the most common indication of VA-ECMO. Cardiogenic shock is characterized by decreased pumping of the heart and reduced contractility of heart muscles leading to less tissue perfusion. It can occur due to some sudden cause like myocardial infarction (MI) or due to longstanding cardiopulmonary problems. Using VA-ECMO improves the patient survival rate in-hospital and is even better when used along with revascularization. The cardiogenic shock due to fulminant myocarditis and sepsis-associated cardiac muscle pathology is also managed by VA-ECMO. These causes are non-ischaemic.
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Postcardiotomy: It is used successfully in patients with heart incisions who are unable to recover immediately from cardiopulmonary bypass.
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Septic Shock: Originally, VA-ECMO was considered a contraindication for septic shock. But nowadays, several studies support the fact that this is a lifesaving treatment approach in pediatric patients. In newborns and children, this is used as a treatment to salvage them. But their use for septic shock in adult patients is very limited, especially in refractory septic shock.
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Pulmonary Embolism: In recent years, VA-ECMO has been used broadly for pulmonary embolism with failure of the right heart. It is used as a temporary measure during decompensation until a definitive treatment like thrombectomy is established.
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Cardiopulmonary Resuscitation: Along with cardiopulmonary resuscitation (CPR), VA-ECMO is used as E-CPR, which is extracorporeal CPR which is used to establish circulation during a heart attack when used in combination with other basic life support modalities. It showed increased chances of survival and decreased major neurological decline in high-risk patients.
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Cardiac Transplantation: VA-ECMO is also utilized for stage 4 heart failure. It is used with great success in patients post-heart transplantation with graft failure or myocardial rejection along with the instability of body hemodynamics. It is important to detect the rejection early. With early detection and commencement of VA-ECMO, the positive outcomes have increased. VA-ECMO has recently found use in helping out in left ventricular assist device (LVAD) implantation or heart transplantation in heart failure patients. It is used even in patients with very poor prognosis with failing heart function.
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Cardiac Arrest: VA-ECMO will help stabilize the patient after a cardiac arrest by increasing the oxygen perfusion to the heart and the lungs. But it has a serious side effect of an increase in left ventricular afterload.
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Pulmonary Hypertension: Pulmonary hypertension can occur in patients with compromised cardiac function leading to right heart failure. So, VA-ECMO will help the pulmonary function to rest while heart surgery is performed.
What Complications Does VA-ECMO Have?
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Thrombosis: It is the most common adverse complication. Anticoagulation is the management of thrombosis. An activated partial thromboplastin time (aPTT) of 60-80 seconds should be maintained for the management of thrombosis.
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Limb Ischemia: It is also a common complication of VA-ECMO. The determination of cannula size and positioning relating to the patient’s blood vessels. A medical emergency called compartment syndrome can occur, which is a painful build of pressure in the muscles due to internal bleeding. It can lead to necrosis of muscles and acidosis and can become even worse, like the removal of the lower limb. The limb can be saved by providing a catheter distal to the entry site of ECMO for tissue reperfusion.
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Infection: Patients are prone to nosocomial infections (infections acquired during the process of receiving healthcare).
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Bleeding: As a consequence of bleeding and thrombosis, hemolysis (destruction of red blood cells), acquired deficiency of Von Willebrand factor (a factor involved in the clotting of blood), and thrombocytopenia(low levels of platelet count in the blood) can occur.
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Neurologic Complications: The longer the time on VA-ECMO, the more the chance of developing left ventricular distension. The presence of VA-ECMO makes it difficult for the left ventricle to work against, and also it increases the afterload for the heart. Following this, pulmonary edema can occur. The management for this is left ventricular decompression by a direct approach or an atrial septostomy, using balloon pumps in the aorta or catheter pumps.
How Is VA-ECMO Used for Septic Shock?
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Septic shock is a dangerous state of low blood pressure due to an infection in the bloodstream.
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The type of ECMO used for septic shock is central because the vasogenic shock (hypotension due to reduction in systemic vascular resistance) requires a large amount of blood flow through ECMO, which is possible only with central access.
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It uses a cannula of the largest size and is inserted directly into the ascending aorta and right atrium.
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The efficiency of central ECMO, achieving an outflow rate of 10 liters per minute, has given better results.
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But there is always a risk of bleeding, so to avoid the risk, bilateral cannulation through the femoral artery can be done.
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Despite good outcomes, the use of VA-ECMO for high flow does not consistently do good for septic shock.
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Only when there is a combination of septic shock and cardiogenic shock with high central venous pressure or pressure from occlusion of the pulmonary artery, VA-ECMO is used.
Conclusion:
The success of VA-ECMO in managing refractory septic shock is very poor due to the questionable survival of patients during hospital stays and weaning. The higher lactate levels in arteries before and after ECMO can be the reason for the risk of mortality. VA-ECMO is beneficial in treating neonates and children during septic shock, but its use in adult septic shock is limited and needs to be researched further.
