VENO-ARTERIAL ECMO(VA ECMO)

INTRODUCTION OF VA ECMO

DEFINITION

Veno-Arterial Extracorporeal Membrane Oxygenation (VA ECMO) is a life-saving medical intervention used in critically ill patients with severe cardiac or respiratory failure. It involves the temporary extracorporeal support of both the heart and lungs by routing blood from a large vein (usually the femoral vein) through an oxygenator that adds oxygen and removes carbon dioxide before returning it to a large artery (usually the femoral artery) to circulate throughout the body. VA ECMO serves as a bridge to recovery by providing temporary support while allowing the heart and lungs to rest and heal.

INDICATION OF VA ECMO

• VA ECMO is used to provide both respiratory and cardiac support.

• Cardiac conditions with low cardiac output (cardiac index < 2L/min/m) and hypotension (systolic blood pressure <90 mmHg) despite inotropic and intra-aortic balloon pump support.

• Cardiogenic shock secondary to either acute coronary syndrome, refractory cardiac arrhythmia, sepsis leading to cardiac depression, myocarditis, pulmonary embolism, drug toxicity, cardiac trauma, anaphylaxis, acute decompensated heart failure, septic shock; where cardiac activity is compromised and unable to pump out the adequate blood to meet the body’s demand.

• Postoperative heart failure: Inability to wean from cardiopulmonary bypass after cardiac surgery; ECMO is very useful post-operatively to provide rest for the heart and helps in recovery after the surgery.

• Post heart transplant: after heart or lung-heart transplantation in cases of primary graft failure

• Bridge to long-term VAD support or bridge to heart/lung transplant.

• Periprocedural for high-risk cardiac interventions.

CANNULATION SITES OF VA ECMO 

PERIPHERAL CANNULATION	CENTRAL CANNULATION
1.Femoral vein-femoral artery	aorta - right atrium
2.femoral vein-axillary artery	aorta-bicaval
3.IJV-carotid artery
4.IJV-axillary artery

PATIENT MANAGEMENT IN VA ECMO

1. Initial assessment

2. Cannulation & initiation

3. Hemodynamic monitoring

4. Ventilator management

5. Anticoagulation management

6. Fluid management

7. Organ support

8. Complication management

9. Weaning & decannulation

10. rehabilitation

COMPLICATION OF VA ECMO

1. Bleeding

2. Thrombosis

3. Infection

4. Hemolysis

5. Circuit malfunction

6. Organ dysfunction

7. Vascular complication

8. Metabolic distrubances

9. Complication related to immobilization

10. Psychosocial complication 

OUTCOMES OF VA ECMO

1. Survival

2. Recovery of organ function

3. Neurological outcomes

4. Quality of life

5. Long-term survival & morbidity

WEANING PROTOCOL OF VA ECMO

• The initial cause of cardiogenic shock must have resolved or been corrected prior to weaning from VA ECMO. Depending on the initial cause of VA ECMO initiation, the weaning process will start at different times for different disease processes. Every patient will have a different weaning strategy and an individual plan.

• To begin a weaning trial, the patient should have MAP >70 with or without inotropic or device support, low vasopressor/inotropic support, oxygen saturation greater than 95%, central venous oxygen concentration greater than 70%, normal ventilation and oxygenation of the patient's lungs with improving chest Xrays, echocardiographic data with an ejection fraction greater than 25% to 30%.

• Weaning is started by reducing the overall pump flow on the ECMO circuit.

• The patient will need to have inotropic drugs at reasonable levels for support. The patient may also have an aortic balloon pump or a left ventricular device in place for added support. Weaning attempts can still be started with these mentioned drugs/devices in place. Some centers recommend weaning ECMO before removing the left ventricular support device.

• When the pump is slowly titrated down, the patient will start to develop more pre-load, and the heart can be monitored for how well the left ventricle can eject.

• Each time the ECMO flow level is decreased, the cardiac function should be continuously monitored using echocardiography. Noninvasive cardiac function monitoring can be used, or a pulmonary artery catheter can be placed to monitor second to second cardiac function changes.

• Strict attention to the ventilator settings and respiratory support must always be accounted for. Pulmonary blood flow will significantly increase, thus changing your PEEP and tidal volume settings.

• The maximum flow rate on the majority of ECMO machines is around 6 liters per minute. When weaning VA ECMO, we recommend weaning at increments of 0.5 liters per minute to 1.0 liter per minute changes when decreasing the flow rates. Flow rates should not drop below 2.0 to 2.5 l/min as this will cause clotting in the cannulas and circuit.

• Each time a decrease in flow rate is made, this rate should be maintained for at least 60 minutes to monitor the patient's decompensation. If the patient shows any signs of failure to have adequate cardiac output, signs of inadequate tissue perfusion, increasing blood lactate levels, or any echocardiographic findings of ventricular demise should prompt the physician to place the patient back on full support and monitor the patient for recovery of their cardiac function on full ECMO support.

• When weaning from VA ECMO, the patient may show signs of stability with a left ventricular ejection fraction greater than 25% with a normal cardiac index greater than 2.5 L/min. These are good signs for ECMO weaning.

• If the patient shows signs of hemodynamic instability or signs of distress at any time, the patient should be changed to full ECMO support. When monitoring with a transesophageal echo or transthoracic echo when weaning, we need to look for signs of rising left or right-sided filling pressures, progressive ventricular dilation, worsening or new signs of mitral or tricuspid regurgitation, any sign of hypoxia or hypercarbia on arterial blood gas, any sign of ventilator changes with elevated peak pressures or plateau pressures. Also, look for signs of increasing vasopressors support when the patient has signs of hypotension with a map less than 60.

• Once the patient has completed weaning from the ECMO circuit, the heparin infusion can be stopped, and the pump flow on the ECMO machine will be raised. This is performed to avoid any clot accumulation. Some institutions will administer a positive inotrope at this time to help facilitate cardiac output after the cannulas have been clamped. If the patient is deemed liberated/weaned from ECMO support at this time, the patient can be decannulated with the removal of the cannulas. This could be performed at the bedside if the percutaneous placement of the cannulas was performed. If central cannulation or surgical cutdown were performed, the cannulas would need to be removed in the operating room.

• Once the patient has been completely weaned from ECMO, the patient will need continuous monitoring of their cardiac output, oxygen saturation levels, lactic acid levels, pH, urine output, and vent settings to confirm the patient can maintain perfusion of their organs.

• After liberating the patient from ECMO support, patients sometimes have signs of an inflammatory response requiring an increase in their inotropic support. This is not uncommon when weaning from ECMO.