Extracorporeal Membrane Oxygenation
What:
Prolonged cardiopulmonary support is called extracorporeal membrane oxygenation (ECMO), extracorporeal life support, or extracorporeal lung assist.
Criteria for the initiation of ECMO include acute severe cardiac or pulmonary failure that is potentially reversible and unresponsive to conventional management. Examples of clinical situations that may prompt the initiation of ECMO include the following:
Who:
· Hypoxemic respiratory failure with a ratio of arterial oxygen tension to fraction of inspired oxygen (PaO2/FiO2) of <100 mmHg despite optimization of the ventilator settings, including the tidal volume, positive end-expiratory pressure (PEEP), and inspiratory to expiratory (I:E) ratio. The Berlin consensus document on acute respiratory distress syndrome (ARDS) suggests ECMO in severe respiratory failure (PaO2/FiO2 <70)
· Hypercapnic respiratory failure with an arterial pH less than 7.20
· Ventilatory support as a bridge to lung transplantation.
· Cardiac/circulatory failure/Refractory cardiogenic shock
· Massive pulmonary embolism.
· Cardiac arrest
How:
During ECMO, blood is drained from the native vascular system, circulated outside the body by a mechanical pump, and reinfused into the circulation. While outside the body, the blood passes through an oxygenator and heat exchanger. In the oxygenator, hemoglobin becomes fully saturated with oxygen, while carbon dioxide (CO2) is removed. Oxygenation is determined by flow rate, where elimination of CO2 can be controlled by adjusting the rate of countercurrent gas flow through the oxygenator
There are two types of ECMO – venoarterial (VA) and venovenous (VV).
Both provide respiratory support, but only VA ECMO provides hemodynamic support
VV or Veno-Venous - blood is extracted from the vena cava or right atrium and returned to the right atrium. VV ECMO provides respiratory support, but the patient is dependent upon his or her own hemodynamics.
· Venous drainage from large central veins -> oxygenator -> venous system near RA
· Support for severe respiratory failure (no cardiac dysfunction)
· Pathology: pneumonia, ARDS, acute GVHD, pulmonary contusion, smoke inhalation, status asthmaticus, airway obstruction, aspiration, drowning
· Specific contraindications: unsupportable cardiac failure, severe pulmonary hypertension, cardiac arrest, immunosuppression (severe)
· For VV ECMO, venous cannulae are usually placed in the right or left common femoral vein (for drainage) and right internal jugular vein (for infusion). Alternatively, a double lumen cannula is available
VA or Veno-Arterial: peripheral or central- During VA ECMO, blood is extracted from the right atrium and returned to the arterial system, bypassing the heart and lungs. VA ECMO provides both respiratory and hemodynamic support
· For VA ECMO, a venous cannula is placed in the inferior vena cava or right atrium (for drainage) and an arterial cannula is placed into the right femoral artery (for infusion). Femoral access is preferred for VA ECMO because insertion is relatively easy. The main drawback of femoral access is ischemia of the ipsilateral lower extremity
support for cardiac failure (+/- respiratory failure)
pathology: graft failure post heart or heart lung transplant, non-ischemic cardiogenic shock, drug OD, sepsis, PE, cardiac or major vessel trauma, massive pulmonary hemorrhage, pulmonary trauma, acute anaphylaxis
specific contraindications: aortic dissection and severe AR
GENERAL CONTRAINDICATIONS
Absolute
progressive non-recoverable cardiac disease (not transplant candidate)
progressive and non-recoverable respiratory disease (irrespective of transplant status)
chronic severe pulmonary hypertension
advanced malignancy
>120kg
unwitnessed cardiac arrest
Relative
age > 75
multi-trauma with multiple bleeding sites
CPR > 60 minutes
multiple organ failure
CNS injury
Procedure: Once it has been decided that ECMO will be initiated, the patient is anticoagulated (usually with intravenous heparin) and then the cannula are inserted. ECMO support is initiated once the cannula are connected to the appropriate limbs of the ECMO circuit. Cannulas are usually placed percutaneously by Seldinger technique. The largest cannulas that can be placed in the vessels are used.
Things to consider for the Emergency Physician
Emergency Physicians have an important role in identifying patients that might benefit from ECMO
Be cognizant of central line placement choice
Transfer out to center with ECMO capabilities earlier
Make sure patient is not bleeding (recent surgeries, recent hemorrhagic CVA)
When calling for ECMO, try to figure out what type of ECMO would benefit the patient
Perform Bedside POCUS to determine cardiac function
Consider certain therapies with caution if you anticipate ECMO initiation- Lipid Emulsion therapy likely a contraindication as it affects the ECMO circuit
Be familiar with the common contraindications to ECMO- Age, BMI etc
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