12.1 ECMO Candidacy & Modality

12.1 ECMO Candidacy & Modality

Extracorporeal Membrane Oxygenation (ECMO) is a specialized form of cardiopulmonary bypass engineered to provide temporary, life-sustaining extracorporeal gas exchange and hemodynamic perfusion for neonates and children suffering from refractory, life-threatening cardiopulmonary failure. ECMO does not cure the underlying disease; it buys time for recovery or definitive intervention and permits reduction of injurious ventilator and oxygen exposure.

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Indications & Clinical Entry Criteria

ECMO carries substantial procedural, neurologic, infectious, and hematologic risk. Consider it when potentially reversible or bridgeable cardiopulmonary failure continues despite optimized conventional and rescue therapy. Consultation should occur before irreversible organ injury; the final decision integrates trajectory, diagnosis, anatomy, comorbidities, bleeding risk, goals of care, and the receiving center’s criteria.

Primary Clinical Indications in Neonates and Children

1. Severe Neonatal Acute Hypoxemic Respiratory Failure:
   • Persistent Pulmonary Hypertension of the Newborn (PPHN)
   • Meconium Aspiration Syndrome (MAS)
   • Congenital Diaphragmatic Hernia (CDH) (pre-operative stabilization or post-operative rescue)
   • Severe Neonatal Respiratory Distress Syndrome (RDS)
   • Neonatal Sepsis / Sepsis-Induced Cardiomyopathy
2. Pediatric Acute Respiratory Failure:
   • Severe Pediatric Acute Respiratory Distress Syndrome (PARDS) refractory to prone positioning, neuromuscular blockade, and high-frequency ventilation
   • Severe viral pneumonia (e.g., respiratory syncytial virus, influenza, adenovirus)
   • Status asthmaticus with intractable hypercapnic respiratory acidosis and dynamic hyperinflation
   • Massive pulmonary hemorrhage or severe aspiration syndromes
3. Refractory Cardiogenic Shock / Extracorporeal Cardiopulmonary Resuscitation (E-CPR):
   • Acute fulminant viral myocarditis
   • Post-cardiotomy low cardiac output syndrome (failure to wean from cardiopulmonary bypass after congenital heart surgery)
   • Intractable ventricular arrhythmias or cardiomyopathy
   • In-hospital cardiac arrest refractory to standard PALS resuscitation (E-CPR)

Oxygenation Index (OI): A Severity and Trajectory Metric

In neonates with hypoxemic respiratory failure, OI combines the mean airway pressure required for support with arterial oxygenation. Serial values can prompt early ECMO-center consultation, but OI is not an automatic cannulation order:

$OI = \frac{\text{mPAW} \times FiO_2 \times 100}{PaO_2}$

Where:

• $\text{mPAW}$ is Mean Airway Pressure in $\text{cmH}_2\text{O}$
• $FiO_2$ is the Fraction of Inspired Oxygen (expressed as a decimal from $0.21\text{ to }1.0$)
• $PaO_2$ is Arterial Partial Pressure of Oxygen in $\text{mmHg}$ obtained from a pre-ductal or post-ductal arterial line

+-----------------------------------------------------------------------------+
|                  WHEN TO CONTACT AN ECMO CENTER EARLY                       |
+-----------------------+-----------------------------------------------------+
| Signal                | Interpretation                                      |
+-----------------------+-----------------------------------------------------+
| Rising OI / high      | Persistent values near or above 40 are traditional  |
| support intensity     | high-risk signals, not automatic cannulation rules. |
+-----------------------+-----------------------------------------------------+
| Refractory gas        | Recheck airway, circuit, recruitment, hemodynamics, |
| exchange or acidosis  | disease treatment, and reversibility while calling. |
+-----------------------+-----------------------------------------------------+
| Worsening perfusion   | Rising lactate, oliguria, ventricular dysfunction,  |
| or organ function     | or shock increases urgency and affects modality.    |
+-----------------------+-----------------------------------------------------+
| Patient context       | Anatomy, neurologic and bleeding risk, duration of   |
|                       | injury, goals, transport, and center criteria decide.|
+-----------------------+-----------------------------------------------------+

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Contraindications to Extracorporeal Life Support

ECMO candidacy requires explicit risk-benefit review. The factors below have traditionally limited neonatal or pediatric ECMO, but many are relative rather than universal exclusions and thresholds vary by center, equipment, diagnosis, and evolving practice:

+-----------------------------------------------------------------------------+
|             FACTORS THAT MAY LIMIT NEONATAL/PEDIATRIC ECMO                  |
+-----------------------+-----------------------------------------------------+
| Risk factor           | Why it may limit candidacy                           |
+-----------------------+-----------------------------------------------------+
| Gestational Age       | Extreme fragility of the germinal matrix vessels;   |
| < 34 Weeks            | Germinal-matrix fragility raises intracranial       |
|                       | bleeding risk; current center criteria apply.      |
+-----------------------+-----------------------------------------------------+
| Birth Weight          | Peripheral and central vessels are too small to     |
| < 1.8 to 2.0 kg       | Cannula size and achievable flow may limit support; |
|                       | thresholds depend on equipment and center outcomes. |
+-----------------------+-----------------------------------------------------+
| Severe Intracranial   | Severe or expanding hemorrhage can make             |
| Bleeding              | anticoagulation and cannulation risk unacceptable;  |
|                       | review imaging, trajectory, and center criteria.     |
+-----------------------+-----------------------------------------------------+
| Genetic or structural| Prognosis, reversibility, goals of care, and        |
| conditions            | potential benefit require individualized review.   |
+-----------------------+-----------------------------------------------------+
| Prolonged Mechanical  | Longer exposure to injurious ventilation may reduce |
| Ventilation           | reversibility; duration is not a stand-alone cutoff. |
+-----------------------+-----------------------------------------------------+
| Uncontrolled Systemic | Massive active intracranial or visceral bleeding    |
| Hemorrhage            | that cannot be surgically controlled.               |
+-----------------------+-----------------------------------------------------+

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ECMO Modalities: Venoarterial (VA) vs. Venovenous (VV)

Selecting the appropriate ECMO modality depends entirely on whether the patient requires pulmonary gas exchange support alone or combined cardiopulmonary and hemodynamic support.

+-----------------------------------------------------------------------------+
|                        VA ECMO VS. VV ECMO ARCHITECTURE                     |
+-----------------------------------------------------------------------------+
|                                                                             |
|   [ VENOARTERIAL (VA) ECMO ]                 [ VENOVENOUS (VV) ECMO ]       |
|   Total Cardiopulmonary Support              Isolated Pulmonary Gas Exchange|
|                                                                             |
|   Drainage: Right Internal Jugular           Drainage: Right Internal       |
|             Vein (Right Atrium)                        Jugular (Caval ports)|
|                       |                                      |              |
|                       v                                      v              |
|   +-----------------------+                  +-----------------------+      |
|   | Pump + Membrane Lung  |                  | Pump + Membrane Lung  |      |
|   +-----------------------+                  +-----------------------+      |
|                       |                                      |              |
|                       v                                      v              |
|   Reinfusion: Right Common Carotid           Reinfusion: Right Atrium via   |
|               Artery (Aorta)                             Dual-Lumen Avalon  |
|                       |                                      |              |
|                       v                                      v              |
|   Systemic Arterial Circulation              Right Heart -> Native Lungs    |
|   (Non-pulsatile, bypasses heart & lungs)    (Pulsatile, heart does work)   |
|                                                                             |
+-----------------------------------------------------------------------------+

1. Venoarterial (VA) ECMO

• Cannulation sites: Neonatal peripheral VA ECMO often drains the right internal jugular vein and returns to the right carotid artery. Central or other peripheral configurations are possible according to size, anatomy, prior surgery, urgency, and center expertise. Carotid management may involve ligation or reconstruction.
• Physiological action: VA ECMO returns oxygenated blood to the arterial circulation and provides direct circulatory plus gas-exchange support. Native heart and lung flow may continue, so the degree of bypass and pulsatility depends on ECMO flow and native function.
• Cardiovascular consequences: Arterial reinfusion can increase left-ventricular afterload and distension; monitor pulsatility, ventricular ejection, pulmonary edema, and the need for unloading.
• Risks and complications: Bleeding, vascular injury, limb or cerebral ischemia, thromboembolism, infection, hemolysis, differential oxygenation in some configurations, and neurologic injury require continuous surveillance.

2. Venovenous (VV) ECMO

• Cannulation Sites: Modern neonatal and pediatric VV ECMO is predominantly accomplished using a single bicaval dual-lumen catheter (e.g., Avalon Elite or OriGen catheter) placed surgically or percutaneously into the right internal jugular vein. The drainage ports open in the superior vena cava and inferior vena cava, while the reinfusion port directs oxygenated blood across the tricuspid valve into the right atrium. In older children, two separate cannulas may be placed (drainage from femoral vein, reinfusion into internal jugular vein).
• Physiological Action: VV ECMO drains systemic venous blood, oxygenates and decarbondioxylates it, and returns it directly back into the venous circulation. Blood then flows through the patient's native right ventricle, pulmonary vascular bed, and left heart. VV ECMO provides pulmonary gas exchange only; it provides NO direct cardiac output support. The patient's native myocardium must be capable of generating adequate cardiac output and maintaining blood pressure.
• Physiological features: VV support avoids an arterial return cannula and preserves native cardiac ejection and pulsatility. It generally has less direct systemic-embolization risk than VA, but embolic, thrombotic, cannulation, recirculation, hemolysis, and neurologic complications remain possible, especially with intracardiac shunts or circuit failure.
• Unique Limitation: Recirculation: A fraction of newly oxygenated blood exiting the reinfusion port is immediately drawn back into the drainage port without passing through the systemic circulation, reducing oxygenation efficiency.

Clinical Comparison: VA vs. VV ECMO

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