Neonatal Extracorporeal Membrane Oxygenation (ECMO): Key Considerations
Extracorporeal Membrane Oxygenation (ECMO), also known as Extracorporeal Life Support (ECLS), is an advanced technology that provides temporary respiratory and/or cardiac support for critically ill neonates when conventional treatments are insufficient. It acts as a bridge to recovery, transplantation, or other supportive systems, but it is not a cure. ECMO is an invasive, time-limited procedure associated with significant risks, including hemorrhagic, thrombotic, infectious, and neurological complications. It utilizes a mechanical pump and an artificial membrane to temporarily perform the work of the heart and lungs. It is essential to understand that ECMO is not a cure in itself but serves as a life-sustaining bridge during periods of organ recovery or while awaiting further interventions like ventricular assist device placement, or transplantation. There are two primary modalities of this support: veno-arterial (VA) and veno-venous (VV) ECMO. While VV ECMO provides only respiratory support by performing the work of the lungs, VA ECMO is used for patients with either cardiac or respiratory failure, such as those in cardiogenic shock, because it supports both organ systems. Placing a patient on ECMO requires a highly coordinated multidisciplinary team consisting of a surgeon to place the cannulas, a perfusionist to manage the circuit, an ICU physician for overall patient management, and a bedside nurse to provide direct care and administer medications. The period surrounding cannulation is recognized as one of extreme vulnerability. Patients requiring ECMO are, by definition, unstable, and the combined stresses of anesthesia, intubation, and surgical manipulation can precipitate sudden cardiovascular collapse. Anticipation and preparation are therefore paramount. Sedatives, inotropes, vasopressors, and resuscitation medications are prepared in advance. Intubation is carefully timed, often supported by bolus and continuous infusions of agents such as epinephrine and dopamine. Cardiopulmonary resuscitation may be required, and team roles are clearly assigned. Systemic anticoagulation with heparin is administered immediately prior to cannulation to prevent clot formation upon blood contact with artificial surfaces. After initiation, continuous reassessment of circuit efficacy is essential and evaluation of perfusion is important. Inadequate flow or suboptimal cannula positioning can impair organ recovery and must be corrected promptly through surgical adjustment, volume optimization, or flow modification. Laboratory markers of end-organ perfusion and injury are closely monitored. Equally important is the development of a shared mental model among the bedside team regarding the goals of ECMO support, how success will be measured, and when escalation or reassessment is required. The early hours of an ECMO run are highlighted as particularly decisive in determining outcomes
Phases of ECMO Support: ECMO support typically follows a structured pathway:
Transition to ECMO: This initial phase involves rapid assessment, establishing vascular access, managing hemostasis, and preparing the circuit.
Stabilization: The first 24 hours focus on using ECMO to reperfuse, reoxygenate, and reventilate the patient, while also assessing for any damage incurred prior to or during cannulation.
ECMO Support ('Main run'): This is the main period of support, where continuous monitoring, complication management, and preparation for recovery or alternative pathways are key.
Transition Off ECMO: Weaning the patient from ECMO support as their native organ function recovers.
"Elevator" Evaluation for ECMO Candidacy:
When considering ECMO, a quick "elevator" evaluation assesses several critical factors:
High Risk of Mortality: ECMO is typically reserved for patients with a high risk of mortality (around 50% in most scenarios) despite maximal conventional therapy.
Reversible/Recoverable Condition or Reasonable Chance of Transplantation: The underlying condition should ideally be reversible, or there should be a viable path to recovery or organ transplantation.
Conventional Treatment Optimized: All conventional treatments should be optimized before initiating ECMO. Simple issues, like an endotracheal tube leak, can sometimes be resolved to avoid ECMO entirely.
Contraindications to ECMO:
Contraindications may include chromosomal disorders (e.g., Trisomy 13, 18, but not 21), irreversible brain damage, and uncontrolled bleeding or Grade III/IV intraventricular hemorrhage (IVH).
Relative Contraindications include prematurity (less than 34 weeks post-menstrual age or weight less than 2 kg/2.5 kg at some centres), mechanical ventilation for more than 10-14 days (especially with extremely damaging ventilation), and irreversible organ damage (unless transplant is planned).
Indications for Neonatal ECMO ECMO is indicated for severe respiratory or cardiac failure
Candidates for ECMO typically present with severe cardiac or respiratory failure and face a high risk of imminent death. The therapy is best suited for reversible conditions, although it is also utilized during extreme circumstances like cardiopulmonary resuscitation (E-CPR) to support a patient while the underlying pathology is investigated. The criteria for exclusion from ECMO are continuously evolving; for example, oncology patients were once considered an absolute contraindication, but this is no longer the case. Current considerations that may preclude a patient from being cannulated include the lack of available cannulation sites due to vessel occlusion or the presence of significant neurologic injury.
Cannulation Strategies The choice of cannulation (VA or VV) depends on the patient's condition, the surgeon's preference, and center experience.
VA ECMO (Veno-Arterial): Provides both respiratory and cardiac support by diverting venous blood, oxygenating it, and returning it to the arterial system, bypassing the heart and lungs.
The circuit functions by draining blood from the patient's venous circulation through a cannula using a pump. This blood is moved forward through an oxygenator, which acts as an artificial lung where gas exchange occurs, before being returned to the arterial circulation via an arterial cannula. The choice of pump, either a roller head or a centrifugal pump, often depends on the patient's weight. At some institutions, roller pumps are preferred for patients under 10 kilograms to avoid the shear stress and hemolysis associated with centrifugal pumps, while centrifugal pumps are used for those over 10 kilograms to avoid the risk of tubing rupture from high positive pressure.
Central Cannulation: Direct access to the heart and aorta, requiring an open chest (sternotomy). Often used for postcardiac surgery patients.
Peripheral Cannulation: Typically involves the internal jugular vein and carotid artery in the neck for neonates, or femoral vessels for older children. For VA ECMO, the arterial cannula is often connected to a graft to avoid obstruction of the aorta.
Deoxygenated Coronary Perfusion: A key consideration in VA ECMO is that the coronary arteries will receive deoxygenated blood from the native heart, which is pumping against the ECMO flow.
The strategy for cannulation is determined by the patient's clinical history and physical size. If a patient requires support immediately following cardiac surgery, cannulas are routinely placed centrally, with the venous cannula in the right atrium and the arterial cannula in the aorta, exiting through a surgically open sternum. For other patients, such as those with myocarditis, neck cannulation is a common approach where blood is drained from the right internal jugular vein and returned through the right common carotid artery. While femoral vessels can be utilized in patients weighing more than 20 kilograms, they are often too small in younger pediatric populations, and smaller cannulas can create higher pressures that make it difficult to maintain adequate blood flow.
VV ECMO (Veno-Venous): Provides only respiratory support (oxygenation and CO2 removal) by taking venous blood, oxygenating it, and returning it to the venous system (right atrium). The native heart maintains circulatory function.
Single Lumen Catheters: Commonly used in neonates, with specialized designs to pull deoxygenated blood and return oxygenated blood through the same catheter, aimed towards the tricuspid valve.
Advantages of VV ECMO: Avoids arterial (carotid) ligation, maintains pulsatile flow, and provides oxygenated blood to the pulmonary artery (oxygen is a pulmonary vasodilator) and coronary arteries.
Recirculation: A common complication where oxygenated blood from the return cannula is immediately re-aspirated by the drainage cannula, reducing efficiency. Good cannula placement and sufficient ventricular function are crucial to prevent this.
The ECMO Circuit
The ECMO circuit is a complex system that mimics the functions of the lungs and/or heart.
Components: Includes drainage cannulae, a pump, an oxygenator (artificial lung), a heat exchanger, and return cannulae. A bridge connecting the venous and arterial lines is common, allowing recirculation of blood within the circuit without stopping flow to the patient, useful during wean trials.
Pumps:
Roller Pumps: Mechanically squeeze tubing to propel blood. They offer precise flow control but have a risk of circuit rupture if distal pressure is too high.
Centrifugal Pumps: Use a spinning magnet to create flow. They avoid blowouts but are more sensitive to afterload (patient's peripheral vascular resistance) and can cause more hemolysis, especially at low flow rates.
Pressure Dynamics: The circuit operates with negative pressure before the pump (sucking blood in) and positive pressure after the pump (pushing blood out). Medications and blood products are typically administered on the positive pressure side of the circuit.
Blood Prime: All neonatal ECMO circuits require a blood prime due to the large dead space volume relative to a neonate's total blood volume.
Oxygenator (Artificial Lung): Responsible for gas exchange (oxygenation and CO2 removal) and temperature regulation.
FiO2 (Fraction of Delivered Oxygen): Controls oxygenation.
Sweep Gas Flow: Controls CO2 removal. This is the primary means of adjusting CO2 on ECMO.
Membrane Lung Performance: Oxygenators have a limited lifespan (typically 5-7 days for membrane oxygenators) due to fibrin accumulation, which can impair gas exchange. Monitoring pressure gradients across the oxygenator helps detect this.
Before connection, the ECMO circuit must be primed with fluids, typically packed red blood cells and fresh frozen plasma, to match the patient's blood products and minimize rapid shifts in electrolytes, pH, and osmolarity. These precautions are vital to reduce the risk of brain injury or arrhythmias during the initiation of support. The process of cannulation itself is a period of extreme clinical instability and high risk for cardiac arrest. Medical teams must anticipate the need for sedatives, analgesics, and resuscitation medications like epinephrine, as the physiologic stress of intubation or the surgical procedure itself can trigger circulatory collapse. Immediately prior to cannulation, systemic anticoagulation with heparin is administered to prevent the patient's blood from clotting upon contact with the artificial surfaces of the circuit.
Once the cannulas are secured and the circuit is ready, blood flow is initiated slowly to prevent arrhythmias related to electrolyte imbalances. The target flow rates are generally around 100 mL/kg/min for patients under 20 kilograms, whereas a cardiac index of 2.4 to 3 is targeted for larger patients. Following the initiation of ECMO, anticoagulation is often maintained, and the position of the cannulas must be confirmed using imaging such as an X-ray or echocardiogram. The first few hours of support are critical; the team must monitor organ-specific laboratory markers to ensure the circuit is providing sufficient support and adjust flows or surgical placement as needed. Success depends on the bedside team maintaining a shared mental model regarding the goals of support and the specific triggers for contacting the provider team.
The mechanical pathway of an extracorporeal membrane oxygenation (ECMO) circuit begins with the drainage of blood from the patient through a venous cannula, which in many pediatric cases is placed in the internal jugular vein. This blood is pulled through the circuit by a pump—either a roller head or a centrifugal design—and then pushed into a membrane oxygenator that serves as an artificial lung. Within this oxygenator, gas exchange occurs as blood passes through hollow fibers. A blender is used to adjust the fraction of inspired oxygen (FiO2) delivered to the oxygenator, allowing clinicians to increase oxygen delivery to the blood without necessarily changing the overall blood flow rate. Simultaneously, carbon dioxide is removed through the use of "sweep gas," with the rate of removal determined by the sweep gas flow rate. The oxygenator also incorporates a heat exchanger to regulate the patient's blood temperature, though clinicians must be aware that this can mask a fever during an infection
Routine Management and Monitoring on ECMO: Daily surveillance is crucial and involves both patient and circuit assessment.
Maintaining the health of the circuit requires constant monitoring of various pressure readings to ensure performance and patient safety. Venous pressure represents the negative force used to pull blood from the patient and is highly dependent on adequate intravascular volume. If a patient becomes volume-depleted, the venous pressure becomes more negative, which can lead to complications such as hemolysis, vessel injury, or air entrainment. Clinicians may observe "chattering" or "rattling," which refers to pulsating movements in the tubing caused by a mismatch between the patient's venous drainage and the circuit flow. ECMO rattling (or "chattering/chugging") indicates turbulent flow, usually caused by venous collapse (suck-down) due to excessive negative suction on the venous cannula. It is primarily caused by hypovolemia, high pump speed (RPM) relative to inflow, or cannula obstruction. Immediate action involves reducing RPM, checking for kinking, and volume resuscitation.
The transmembrane gradient, or Delta P, measures the pressure differential across the oxygenator membrane. An increasing Delta P often signals a growing clot burden within the membrane, which can eventually impair gas exchange or lead to an abrupt stop in blood flow.
Because the circuit's polyurethane surfaces and connector sites are foreign to the body, they naturally activate the patient's coagulation cascade. This necessitates the use of anticoagulation, typically with heparin or direct thrombin inhibitors like bivalirudin, to prevent thrombus formation. Managing this requires a delicate balance between preventing clots and avoiding excessive bleeding, a task made more complex in pediatric patients whose hematologic profiles vary significantly by age. Clots on the venous side are often trapped by the membrane if they dislodge, but arterial side clots are far more dangerous as they can travel to the brain and cause a stroke or completely block the arterial cannula.
Patient Assessment:
Respiratory: Ventilator settings (often "rest settings" for lung protection), lung compliance, chest X-ray, blood gases.
Hemodynamic: Conventional support (vasopressors/dilators), arterial blood pressure (ABP), central venous pressure (CVP), mixed venous saturation (SvO2), lactate, perfusion, urine output.
Left Atrial Decompression: Critical for cardiac recovery in VA ECMO if the left ventricle is unable to eject blood. Signs of left heart distention include pulmonary edema, dilated cardiac cavities, very negative venous pressures, and high left atrial pressure (goal <10 mmHg). Decompression can be achieved via a surgical left atrial vent, a septostomy (Rashkind procedure in the cath lab), or cautious use of low-dose inotropes.
In cases of severe left ventricular failure or myocardial stunning on VA ECMO, the left side of the heart can become severely distended and congested, impairing coronary perfusion and hindering cardiac recovery. Left atrial (LA) decompression aims to relieve this tension. Methods include: Surgical placement of a left atrial vent if the chest is open. Rashkind septostomy in the cath lab if the chest is closed. Careful use of low-dose inotropes to promote enough myocardial contraction to prevent stasis and distension without increasing oxygen consumption significantly. Monitoring for inadequate LA decompression includes elevated LA pressure (goal <10 mm Hg), pulmonary edema on X-ray despite negative fluid balance, very negative venous pressures, and elevated proBNP.
Hematology: Balancing bleeding and thrombosis risks, checking for clots or bleeding, daily labs (ACT, aPTT, Anti-Xa, TEG/ROTEM, CBC, ATIII, Fibrinogen, Platelets).
Infection: Temperature is regulated by the ECMO circuit, so fever is not a reliable sign. Monitor CRP and look for unexplained variations in anticoagulation.
Neurology: Daily head ultrasounds (HUS) for the first 3-5 days are common to monitor for intracranial hemorrhage (ICH), which is a serious complication.
Circuit Assessment: ECMO flow, venous and arterial pressures, membrane lung performance (pressure gradient, sweep gas output), and visual inspection for fibrin/clot buildup.
The primary goal of patient management on veno-arterial (VA) ECMO is often to provide cardiac rest and promote myocardial recovery. By utilizing higher circuit flows, clinicians can decompress the heart and reduce myocardial oxygen demand, often allowing for the reduction or elimination of inotropic support. If recovery is not evident, further investigations such as cardiac catheterization or imaging may be necessary to identify reversible lesions or determine candidacy for a ventricular assist device or transplant. Throughout this process, blood pressure and afterload must be carefully managed. Avoiding hypertension is particularly critical in infants to reduce the risk of intracranial hemorrhage.
While the lungs are bypassed for gas exchange, they are typically maintained on lung-protective "rest" settings—such as a low rate, modest PEEP, and low peak pressures (example: 10 x PIP 20/ PEEP 10)—to prevent collapse, trauma, and oxygen toxicity while awaiting recovery.
A specific challenge in VA ECMO for cardiac indications is the development of left atrial hypertension. Even while a patient is on support, blood continues to return to the left side of the heart due to venous return such as through bronchial vessels flow. Because the circuit does not directly drain the left side of the heart, blood can back up if the left ventricle lacks sufficient contractility, potentially leading to pulmonary edema or hemorrhage. This is addressed by decompressing the left atrium through an atrial septostomy or the placement of a left atrial vent, procedures that can be performed in a catheterization lab or surgically if the chest is open. In smaller patients, a septostomy alone may provide adequate decompression, while larger patients may require a vent connected back to the venous side of the circuit. Indeed, for larger patients who exceed 30 kilograms, a septostomy alone may not be adequate. In these cases, clinicians may need to advance a venous cannula through the septostomy and directly into the left atrium. This additional cannula is then connected into the main venous tubing using a Y-connector, allowing the ECMO pump to assist in decompressing the left atrium and preventing the backup of blood.
Supportive care during an ECMO run includes meticulous fluid and nutritional management. Many patients experience fluid overload, which can be managed via ultrafiltration or continuous renal replacement therapy (CRRT) integrated into the circuit. Nutrition is another priority, as adequate caloric intake is linked to better survival; clinicians may use total parenteral nutrition (TPN) or enteral feeding via a nasogastric tube if gut perfusion is stable. Sedation is also tailored to the patient’s needs, often requiring higher doses of medications like fentanyl because the circuit can sequester the drug. Sedation can be used also to diminish metabolic demand when flow rates are insufficient to support adequate perfusion despite the addition of cardiovascular agents.
When an ECMO circuit cannot provide sufficient flow to maintain adequate end-organ perfusion, as evidenced by rising serum lactate or creatinine levels, medical teams may utilize several supplementary strategies. To support the circulation, clinicians can employ vasoactive medications, such as epinephrine, to increase the patient's mean arterial blood pressure. Another critical strategy involves decreasing the patient's metabolic demand through the use of deep sedation and neuromuscular blockade. If the inadequacy is caused by the physical limitations of the circuit, such as a cannula acting as a fixed resistor, the team may also consider repositioning or upsizing the cannulas to facilitate higher flow rates. These interventions are often necessary when the patient exhibits signs of uncompensated hemodynamic deterioration despite initial circuit adjustments.
As the field evolves, there is an increasing emphasis on maintaining a calm, awake state when possible to allow for rehabilitation and even mobilization. Effective ECMO support relies on clear communication and a shared mental model among the multidisciplinary team. Daily rounds and handoffs must include specific details such as cannula sizes, target flow rates, sweep gas settings, and the trend of the transmembrane gradient. Beyond the technical aspects, providing emotional and social support for the family and the medical staff is essential, given the extreme nature of the therapy and the high stakes involved for the sickest patients. Setting realistic expectations and providing a systems-based approach to care helps maintain the health of both the patient and the caregiving team.
Anticoagulation
Maintaining appropriate anticoagulation is critical to prevent circuit thrombosis while minimizing bleeding. This is particularly challenging in neonates due to their immature hemostatic system and lack of reserve capacity.
Unfractionated Heparin (UFH): The most commonly used anticoagulant. It has a short half-life and is reversible with protamine. However, its efficacy can be limited by low antithrombin (ATIII) levels in neonates, sometimes requiring ATIII replacement (e.g., with FFP).
Direct Thrombin Inhibitors (DTIs): Such as bivalirudin, are gaining use. They do not depend on ATIII and can inhibit clot-bound thrombin. Their short half-life is an advantage, but they lack reversal agents and require careful management, especially during weaning or in areas of blood stasis. Clot may formed if there is stasis (example: left atrial stasis).
Monitoring: A combination of tests is often used, as no single test is ideal. These include Activated Clotting Time (ACT), activated Partial Thromboplastin Time (aPTT), Anti-Xa assay, and viscoelastic tests like Thromboelastography (TEG) or Rotational Thromboelastometry (ROTEM). These tests can be affected by factors like hemolysis and hyperbilirubinemia.
Ultrasfiltration and CRRT
Patients on veno-arterial (VA) ECMO often struggle with the sequelae of fluid overload, which can stem from various clinical causes. One of the primary advantages of the ECMO circuit is its ability to facilitate ultrafiltration of the blood. This process allows clinicians to effectively decrease the patient’s central venous pressure by removing excess volume, which is often a necessary step to optimize overall hemodynamics. The use of ultrafiltration is particularly beneficial when clinical priorities require the administration of large volumes of fluid for essential treatments, such as medications or total parenteral nutrition (TPN). While TPN is vital for providing the calories, proteins, and fats necessary for metabolic demands and wound healing, the volume of fluid required to deliver adequate nutrition frequently exceeds the patient's optimal fluid intake. By utilizing careful ultrafiltration through the ECMO circuit, medical teams can remove this additional volume while still ensuring the patient receives necessary nutritional support. In addition to volume management, the ECMO circuit can be used to perform continuous renal replacement therapy (CRRT) if a patient requires solute clearance due to acute kidney injury or failure. Despite the availability of this technology, some institutional approaches emphasize utilizing the patient's native renal function as much as possible before initiating ultrafiltration or CRRT. This cautious strategy is intended to safeguard the patient against unintended volume depletion, which could potentially lead to an added prerenal insult to the kidneys. The mechanical process of moving fluid typically utilizes a hemoconcentrator or hemofilter, similar to those used for conventional ultrafiltration during cardiopulmonary bypass. Beyond fluid balance, research into ultrafiltration techniques has shown that they can assist in managing the inflammatory response associated with extracorporeal support. For example, modified ultrafiltration has been shown to remove cytokines and inflammatory mediators, which may help mitigate the systemic inflammation triggered when blood comes into contact with the foreign surfaces of the circuit.
Weaning from ECMO
Weaning is a gradual process that involves reducing ECMO support as the patient's native organ function recovers. When a patient exhibits signs of recovery, the team must assess their readiness for decannulation. There are no strict criteria, but typically the underlying cause of cardiac/respiratory failure must be resolving, and the patient should demonstrate optimized hemodynamics, including resolved lactic acidosis, normal gas exchange, and adequate blood pressure on minimal vasopressor support. A weaning trial is conducted by slowly decreasing the circuit flow while observing the capacity of the heart and lungs to resume their functions. If the patient shows evidence of uncompensated respiratory or hemodynamic deterioration during this trial, ECMO flow is increased to restore stability.
Timing and Duration: Average ECMO run times vary by diagnosis (e.g., Meconium Aspiration Syndrome: 5-6 days; Congenital Diaphragmatic Hernia: median 2-3 weeks, but can be longer). Longer runs (beyond 4-6 weeks for CDH) may have limited benefit, but universally accepted limits are not established.
Signs of Recovery:
Respiratory: Improved lung compliance, clearing chest X-ray, good lung expansion on low ventilator settings (e.g., PEEP 10, Delta 10, RR 10 for "rest settings"), and reduced oxygen requirements.
Cardiac: Development of a pulsatile arterial trace (if previously flat), signs of intrinsic cardiac output, improving ventricular function on echocardiography, decreasing left atrial pressures, and minimal or no need for inotropes/vasopressors.
Weaning Strategies:
Gradual Flow Reduction: ECMO flows are progressively decreased (e.g., from 90-100 mL/kg/min down to 50 mL/kg/min or less) while conventional support is increased.
Clamp Trial: The classic method involves clamping the cannulae proximal to the patient and opening a bridge to recirculate blood within the circuit. This allows complete separation of the patient from the circuit for a trial period (15 minutes to 2 hours) to assess their tolerance without ECMO support. Adequate anticoagulation must be maintained in the circuit during the clamp trial to prevent thrombosis.
Pump-Controlled Retrograde Trial-Off: A newer technique that uses the patient's native cardiac output to maintain circuit integrity, acting as a "stress test" without clamping the circuit.
Post-Weaning Considerations: If successful, decannulation follows. If unsuccessful, the patient can return to full ECMO support, and further investigations for the cause of weaning failure (e.g., residual cardiac lesions, pulmonary issues) are pursued.
The "clamping of the bridge test" is a classic approach used to assess a patient's readiness for weaning off support. It is often referred to as a clamp trial.
Outcomes, Complications and Prognosis
Overall survival to hospital discharge for neonates on ECMO for respiratory disease is around 73%. For cardiac indications, survival is typically lower, around 40%. Survival rates vary significantly by specific diagnosis (e.g., Meconium Aspiration Syndrome: 92%; Congenital Diaphragmatic Hernia: ~50%; Cardiac Diagnoses: 35-45%). Longer ECMO runs are associated with increased risk of complications and generally lower survival. Survivors of neonatal ECMO, particularly those with CDH, are at increased risk for long-term morbidities, including chronic lung disease and neurodevelopmental delay. For more in-depth information and specific guidelines, the Extracorporeal Life Support Organization (ELSO) website (www.elso.org) is an invaluable resource, offering comprehensive practice guidelines and registry data.
While ECMO provides a vital bridge to recovery or further intervention, it is associated with significant morbidity and mortality risks that require constant mitigation. Bleeding is among the most frequent complications, often arising from anticoagulation, sepsis, or disseminated intravascular coagulation. Because neurologic or gastrointestinal bleeding may present late, clinicians must monitor for unexplained decreases in hematocrit and regularly track laboratory markers such as fibrinogen and PTT. Migrating or dislodged cannulas can also cause bleeding or hemorrhagic shock, making it essential to verify cannula positions through physical measurements and routine imaging. In some cases, severe bleeding may even necessitate the temporary discontinuation of anticoagulation.
Thrombosis remains a constant threat as the foreign surfaces of the circuit naturally activate the coagulation cascade. Clots forming on the arterial side of the circuit are particularly dangerous because they can dislodge and travel to the brain, resulting in a debilitating stroke, or to other organs like the kidneys. Routine neurological checks are necessary to assess for new-onset seizures or changes in status that might indicate an embolic event. Clots on the venous side or within the oxygenator, while less likely to reach the patient, can lead to oxygenator failure and may require a circuit change. To prevent such formations, systemic anticoagulation with agents like heparin or bivalirudin is maintained, though this requires a delicate balance to avoid exacerbating the risk of hemorrhage.
Mechanical and environmental factors also introduce risks, such as air emboli and limb ischemia. Because the venous limb of the circuit operates under negative pressure, air can be entrained through any disruption or open access point. While small amounts of air are often vented by the oxygenator, large volumes can cross into the arterial side and cause organ damage or neurologic injury. Limb ischemia is another concern, particularly with femoral cannulation, where the cannula position or compartment syndrome can compromise distal blood flow. Furthermore, the continuous compression of tubing in roller head pumps can lead to tubing rupture over time; clinicians mitigate this through the practice of walking the raceway to distribute mechanical strain.
Outcomes for pediatric cardiac ECMO vary based on the patient's age and underlying condition. The mean duration of support is approximately seven days, and patients who require longer support often accumulate more complications and have lower survival rates. Survival to hospital discharge is generally lower for neonates, patients with congenital heart disease, or those placed on ECMO during cardiac arrest (ECPR), where the predicted survival is less than 50 percent. For specific conditions like acute viral myocarditis, registry data suggests a survival chance of about 50 percent. Successful cases often involve transition to oral heart failure medications and eventual transfer to lower levels of care after decannulation and extubation.
Flow rates
The usual flow rates for Extracorporeal Membrane Oxygenation (ECMO) vary depending on the type of support (respiratory or cardiac), the patient's size, and underlying physiological factors.
General Considerations
For pediatric patients, ECMO circuits are typically modified from adult circuits, aiming for less tubing and dead space while including infusion ports for medications.
The goal is to achieve the desired flow rate without excessive venous pressure. Using the biggest and shortest cannula possible is crucial, similar to managing an airway in ECMO. To allow for the least amount of hemolysis.
In VA ECMO, systemic oxygen extraction is continuously monitored via the drainage cannula (SvO2). The goal is to maintain oxygen delivery (DO2) at least three times oxygen consumption (VO2), with an SvO2 greater than 66%.
The desired blood flow rate for an oxygenator should be over 500 mL/min.
Neonatal Respiratory ECMO
For respiratory ECMO in neonates, the typical aim is about 100 mL/kg/min.
Oxygenation is affected by blood flow, hemoglobin, and oxygen saturation. Support is usually initiated with a sweep gas of 100% FiO2.
In VV ECMO, pump flow increases might not directly result in higher patient saturation due to recirculation, which is influenced by cannula position, patient volume status, native cardiac function, and flow rates.
Neonatal Cardiac ECMO
For cardiac ECMO in neonates, the usual target flow is about 150 mL/kg/min.
If a baby with cardiac ECMO has a BT shunt, the flow rate might need to be higher, around 180 mL/kg/min.
Pump flow is gradually increased until adequate flow is achieved, then decreased to the lowest level that supports cellular metabolic demands.
Ideally, an arterial pulse pressure of at least 10 mm Hg should be maintained, indicating systemic ventricular ejection and reducing the risk of thrombosis. If the heart is not contracting at all or very little, the arterial trace might appear as a flat line because the ECMO is supplying all the cardiac output.
If systemic perfusion is inadequate (e.g., low urine output, poor perfusion), pressure can be increased by increasing pump flow, transfusing blood products, or titrating vasopressor infusions.
Larger Children (Pediatric Cardiac ECMO)
Monitoring and Adjustment
During ECMO support, daily assessment includes checking if support is adequate, monitoring for complications, evaluating the circuit, and checking thromboprophylaxis.
Oxygenation can be increased by increasing the FiO2 to the oxygenator or by increasing the blood flow. Carbon dioxide (CO2) clearance is controlled by the sweep gas flow rate, which can be adjusted to maintain the patient’s PaCO2 within target ranges (e.g., 40-45 mm Hg for neonates).
If a centrifugal pump is used (which is common), it is sensitive to afterload. High blood pressure, pain, or waking up can increase peripheral vascular resistance and impede flow.
In the case of troubleshooting, a decrease in venous pressure (ECMO preload) might indicate hypovolemia, cardiac compression, or a displaced/obstructed/kinked cannula. Actions include giving volume or temporarily decreasing flow. An increase in pre-membrane pressure could indicate an issue with the oxygenator or an obstruction.
Weaning
When planning to wean a patient off ECMO, flows are progressively decreased. For respiratory support, flows might be around 90-100 mL/kg/min when evaluating for weaning.
A minimum flow must be maintained through the centrifugal pump to prevent retrograde flow within the circuit. During weaning trials, the bridge line can be opened to allow recirculation within the circuit, maintaining flow without stopping it entirely.
In cardiac ECMO, weaning begins by gradually decreasing ECMO flow once signs of myocardial recovery are observed, such as increasing pulse pressure, rising systolic pressure, and improved ventricular function on echocardiography. The goal is to reach minimal ECMO support, typically around 50 mL/kg/min, before a trial-off.
ECMO criteria:
CDH (ELSO): The decision to initiate ECMO for CDH patients involves considering several physiological parameters that indicate a failure of conventional therapies. While there are no uniformly accepted and rigidly followed criteria for ECMO initiation in CDH, ELSO consensus indications based on expert opinion include:
ECMO Programs and Multidisciplinary Care
The structure of pediatric ECMO programs varies significantly across medical centers, often depending on the size of the staff and the specific expertise available. In most institutions, the program is primarily operated by a dedicated team of nurses and respiratory therapists, with the perfusion team serving in a supportive and consultative role. In contrast, other centers may have more overlap between perfusion and ECMO specialists, especially when managing complex devices like ventricular assist devices (VADs) that require integrated oxygenators. Regardless of the specific staffing model, the trend in modern programs is toward high levels of interdisciplinary collaboration, where perfusionists, nurses, and physicians act as a unified resource for troubleshooting and education.
One of the most critical moments for this collaboration occurs in the operating room when a patient fails to come off cardiopulmonary bypass and must be transitioned to ECMO. This transition is typically a highly coordinated "dance" that can take as little as ten seconds once the decision is made to disconnect the bypass tubing and connect the primed ECMO circuit. A major concern during this phase is the timing of heparin reversal agents; if protamine or other reversal agents are administered too early or without clear communication, the ECMO circuit can clot almost instantly, leading to catastrophic failure. Success in these high-stakes moments relies on the ECMO team and the perfusionists working in tandem to ensure the circuit is ready before the patient's native circulation is compromised.
The design and maintenance of the ECMO circuit have evolved toward a philosophy of simplification and miniaturization. Clinicians have found that reducing the number of connectors, pigtails, and stopcocks significantly lowers the risk of thrombosis and unexpected mechanical failures. The introduction of advanced technology, such as integrated pressure sensors and digital oxygenator readouts, further assists in this effort by eliminating the need for external transducers and stagnant fluid lines that can harbor clots. This "less is more" approach is driven by the recognition that every additional component in the circuit provides a surface for clot formation or a potential point of entry for air entrainment.
Anticoagulation remains a central challenge in ECMO management, with institutions increasingly weighing the benefits of bivalirudin against traditional heparin. While heparin remains the primary choice in many neonatal and general pediatric intensive care units, cardiac ICUs are trending toward the use of bivalirudin, particularly for patients with VADs or those requiring long-term support. Bivalirudin is often perceived as easier to manage in a daily clinical setting, though it requires a highly streamlined circuit to prevent clots from forming in stagnant areas near connectors. Some centers have noted that the success of bivalirudin in the cardiac ICU has begun to influence practices in other departments, leading to a more standardized approach to anticoagulation across the hospital.
Managing the delicate balance between bleeding and clotting is complicated by the systemic inflammation triggered by exposure to the artificial surfaces of the circuit. This immune hyper-response is particularly evident in patients who are septic or those transitioning directly from the operating room, as they have already undergone the inflammatory stress of bypass. When severe bleeding occurs, teams may use factor VII or prothrombin complex concentrates like FEIBA to achieve hemostasis, though these interventions carry a risk of circuit thrombosis. FEIBA (Factor Eight Inhibitor Bypassing Activity) is an anti-inhibitor coagulant complex used to treat bleeding in patients with hemophilia A or B who have developed inhibitors (antibodies) against their factor replacement therapy. Because it works by forcing the blood to clot, thrombosis (the formation of unwanted blood clots) is a significant, well-documented risk associated with its use. In some instances, the risk of bleeding is so great that clinicians may choose to run the circuit without any anticoagulation for a short period, prioritizing the patient's survival over the integrity of the circuit. Techniques like modified ultrafiltration (MUF) are also utilized to remove inflammatory cytokines and manage volume, allowing for the administration of necessary blood products without overloading the patient.
The human element of ECMO care is as important as the mechanical components, necessitating robust education and simulation programs. Annual "wet labs" and crisis management simulations allow the multidisciplinary team to practice responses to rare but high-stress events, such as cannula dislodgement or massive air entrainment. These simulations are vital for developing a shared mental model and improving communication between team members who may be "siloed" in their respective roles. By spending time in different clinical environments, such as ICU staff visiting the operating room to observe complex procedures like the Norwood, team members gain a deeper appreciation for the pressures and expertise of their colleagues. This mutual understanding fosters a culture where expertise is shared freely, ensuring that the most knowledgeable person can "fill the gaps" in patient management during a crisis.
