Respiratory failure. The indications for neonatal ECMO are (i) reversible respiratory failure and (ii) a predicted mortality with conventional therapy great enough to warrant the risks of ECMO. ECMO is also considered in patients with life-threatening air leaks not manageable with optimal ventilatory support and chest drainage. Oxygenation index (OI) is a measure of the severity of respiratory failure and is calculated as OI = mean airway pressure (MAP) × FiO₂/PaO₂ × 100. It is essential to document OIs from serial blood gases over time, as the OI may vary. ECMO indications vary among different centers. Commonly used criteria include two OIs of >40 within 1 hour, one OI of 60 on high frequency ventilation, or one OI of 40 combined with cardiovascular instability. An OI of 20 should prompt an early outreach to an ECMO center for potential transfer.

Cardiac failure. ECMO provides biventricular support for neonates with cardiac failure. ECMO for congenital heart defects (hypoplastic left heart syndrome, coarctation of the aorta, pulmonary atresia, total anomalous pulmonary venous return [TAPVR]) is offered as a bridge to definitive treatment until the neonate’s condition has stabilized. Other cardiac indications are failure to wean from cardiopulmonary bypass, cardiomyopathy, and pulmonary hypertension. In any neonate with respiratory failure, hypoxia, and bilateral opacities on chest radiograph, TAPVR should be excluded prior to initiating ECMO support. Once venoarterial (VA) ECMO support is initiated, pulmonary blood flow is reduced and the diagnosis of TAPVR may be difficult to make using echocardiography alone; those patients may require cardiac catheterization on ECMO to demonstrate presence or absence of pulmonary veins entering the left atrium.

Rapid-response ECMO (ECMO-cardiopulmonary resuscitation [E-CPR]). In the setting of a witnessed cardiorespiratory arrest, ECMO can be offered in centers with a rapid response team. Response times from the arrest to cannulation are ideally 15 to 30 minutes. A readily “clear-primed circuit” (an ECMO circuit
primed with normal saline rather than with blood products) and an ECMO team must be available 24 hours per day in order to offer E-CPR. Effective CPR before cannulation is essential for a favorable outcome during rapid-response ECMO.

Ex utero intrapartum treatment (EXIT) to ECMO procedure. The vessels are cannulated during a cesarean section while the neonate remains on placental
support. Indications include severe congenital diaphragmatic hernia, lung tumors, and airway-obstructing lesions, such as large neck masses and mediastinal tumors.

Contraindications. ECMO should only be offered for reversible conditions. Absolute contraindications are considered to be irreversible brain damage, significant intraventricular or intraparenchymal hemorrhage, weight <1,500 g, gestational age <34 weeks, lethal congenital abnormality, severe coagulopathy, progressive chronic lung disease, and continuous CPR for more than an hour before ECMO support.

Flow. Venous drainage is always passive from the patient to the ECMO circuit. The cessation of venous drainage (hypovolemia, cardiac tamponade, pneumothorax) causes an automatic shutdown of the circuit, as any negative pressure could introduce air into the circuit. Flow is determined by venous return and by the ECMO pump.

VA ECMO supports the cardiac and the respiratory system, and is indicated for primary cardiac failure or respiratory failure combined with secondary cardiac failure. In VA ECMO, the blood is drained from a vein (internal jugular vein, femoral vein) and returned into the arterial system (internal carotid artery). The patient’s total cardiac output (CO) is the sum of the native CO and the pump flow generated by the circuit: CO_total = CO_native + CO_circuit

Venovenous (VV) ECMO. VV ECMO supports only the respiratory system and is indicated for isolated respiratory failure. VV ECMO can also be considered in respiratory failure with hemodynamic instability, when hypotension and cardiovascular instability are thought to be caused by hypoxemia alone, as VV ECMO usually leads to rapid reversal of hypoxia and acidosis. VV ECMO spares accessing the carotid artery. In VV ECMO, the blood is drained as well as returned to the jugular vein through a double-lumen cannula. Some of the blood is immediately recirculated into the ECMO circuit. The rest of the oxygenated blood goes to the right side of the heart, into the pulmonary vascular bed, into the left side of the heart, and into the systemic circulation. As a requirement for VV ECMO, the internal jugular vein has to be large enough for a 14-French double-lumen cannula. Converting to VA ECMO is considered in the presence of additional hypotension, cardiac failure, or metabolic acidosis. Technical difficulties related to large recirculation in the venous cannula can also lead to the need to convert to VA ECMO. In our institution, the carotid artery is already identified at the time of VV cannulation. For conversion to VA ECMO, the venous cannula is left in place and an additional arterial cannula is inserted into the internal carotid artery.

Oxygen delivery is the product of CO and arterial oxygen content. During ECMO, many factors contribute to oxygen delivery. Arterial oxygen content is determined by the gas exchange in the membrane oxygenator and the gas exchange from the neonate’s lung. CO is only altered during VA ECMO and is determined by the ECMO flow and the infant’s native CO.

Carbon dioxide removal. Carbon dioxide (CO₂) removal is achieved by the membrane of the ECMO circuit and the patient’s lung. The amount of CO2 removed is dependent on the PaCO₂ of blood circulating through the membrane, the surface area of the membrane, and the gas flow through the membrane lung (“sweep gas
flow”). As physiologic pulmonary function and tidal volume improve, the PaCO₂ decreases further and ECMO settings have to be adjusted. CO₂ removal is extremely efficient during ECMO, to the point that additional CO2 has to be added into the circuit in order to prevent hypocarbia and respiratory alkalosis.

Cerebral perfusion.

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