Definition
Extracorporeal membrane oxygenation (ECMO) is a prolonged form of extracorporeal life support used to treat neonates with life-threatening respiratory or cardiac disorders who fail to respond to maximal medical management. Extracorporeal life support (ECLS) is a term used synonymously with ECMO though it often implies a broader array of functions that may include oxygen delivery, carbon dioxide elimination, cardiac support, or combinations of these functions.
Incidence/prevalence
Disorders treated with ECMO
Respiratory diseases (Table 33-1)
The neonatal respiratory disorders most commonly treated with ECMO cause hypoxemic respiratory failure that is often complicated by persistent pulmonary hypertension of the newborn; such disorders include meconium aspiration syndrome, congenital diaphragmatic hernia, sepsis/pneumonia, primary persistent pulmonary hypertension, and air leaks.
Respiratory distress syndrome accounted for a significant number of ECMO cases in the 1980s but this number has declined with the introduction of exogenous surfactant treatment in 1990. Furthermore, the introduction of inhaled nitric oxide and high-frequency mechanical ventilator devices and strategies in the mid-1990s has been associated with a significant decline in number of neonatal respiratory failure cases receiving ECMO.
The peak number of neonatal respiratory ECMO cases reported to an international registry maintained by the Extracorporeal Life Support Organization was 1516 in 1992; there were 801 neonatal respiratory cases reported in 2011.
As a consequence, neonatal cases treated with ECMO are more often than not sicker than in the 1980s and 1990s, not responsive to advances in care (such as surfactant, inhaled nitric oxide, high-frequency ventilation, and gentle ventilation strategies), and have less frequently encountered disorders associated with hypoxemic respiratory failure such as surfactant protein deficiencies, alveolar capillary dysplasia, and pulmonary interstitial glycogenosis.
Cardiac diseases (Table 33-2)
The neonatal cardiac disorders most commonly treated with ECMO are predominantly hypoplastic left heart syndrome and other complex congenital disorders; anomalous pulmonary venous return, disorders with decreased pulmonary blood flow, and left-sided obstructive lesions account for a substantial number of ECMO cases.
Most neonatal ECMO cases involving cardiac disorders receive ECMO following surgery because of poor cardiac function after cardiopulmonary bypass and/or a pulmonary hypertensive crisis, usually presenting within 24 hours of surgery. Advances in cardiac surgery that involve complex surgical procedures with ECMO as an adjunct treatment have contributed to an increase in the numbers of neonatal ECMO cases having congenital cardiac disorders rather than respiratory illnesses.
The number of neonatal cardiac ECMO cases grew from 104 in 1992 to 374 in 2011.
Pathophysiology: how ECMO works
Historical highlights of ECMO
Initial experiences in treating neonates in the 1970s and early 1980s led to widespread dissemination by the beginning of the 1990s. Investigators in the United Kingdom performed a randomized trial comparing ECMO to conventional treatment in the mid-1990s and proved that ECMO significantly increases survival in high-risk neonates without increasing morbidity. Death or severe disability in the ECMO treated cases was 33% versus 62% in the conventionally treated control group.
ECMO circuit (Figure 33-1)
Components: The essential components of a cardiopulmonary life support circuit include an artificial lung for exchange of oxygen and carbon dioxide (eg, oxygenator), a mechanical pump to move blood through the extracorporeal circuit, a blood warming device, servoregulation equipment to adjust flow from the mechanical pump according to pressures generated within the circuit by blood flow returning to the heart of the patient, extracorporeal tubing, and an anticoagulant such as heparin to reduce clot formation within the circuit and newborn infant. Some institutions use a compliance bladder to reduce swings in negative pressure generated by drainage of blood returning to the heart.
Vascular access: venovenous and venoarterial ECMO Extracorporeal circuits are connected to the neonatal vascular system through large cannulas that are usually placed into the right internal jugular vein, right common carotid artery, right atrium or aorta.
Venovenous (VV) ECMO: Neonates with respiratory failure and adequate cardiac function may have a single, double-lumen catheter placed into the right internal jugular vein with the tip in the right atrium. Venous blood exits into the extracorporeal circuit from the right atrium and oxygenated blood returns to the right atrium; this is venovenous ECMO. On occasion, venovenous ECMO is accessed by two venous catheters that are placed into large veins for drainage and return functions.
Venoarterial (VA) ECMO: Neonates with respiratory or cardiac failure complicated by severely compromised cardiac function are treated with venoarterial ECMO. Venoarterial ECMO access in cases of respiratory failure is generally accomplished with a venous drainage catheter placed into the right atrium by way of the right internal jugular vein and a return catheter placed into the aortic arch by way of the right internal carotid artery. Venoarterial ECMO in cases of cardiac failure following cardiac surgery is often accomplished through catheters placed through the open sternum directly into the right atrium (drainage) and aorta (return).
Risk factors
Respiratory and/or cardiac disease processes unresponsive to conventional management.
Clinical presentation and diagnosis
See chapters on neonatal respiratory disease (Chapter 7), congenital diaphragmatic hernia (Chapter 31), and congenital heart disease (Chapter 32).
Management
Indications
The primary indication for treatment of neonates with ECMO is severe cardiac or respiratory compromise that is unresponsive to maximal medical treatments.
Candidates are also greater than or equal to 34 weeks’ gestation and greater than 2 kg birthweight because of high risk for hemorrhage complications and technical limitations with vascular access in less mature and smaller infants.
Contraindications
Contraindications for treatment with ECMO include lethal malformations/congenital anomalies, severe irreversible central nervous system damage (most frequently associated with hypoxia-ischemia), and a large degree of intracranial hemorrhage.
Contraindications include gestational age less than 34 weeks, birthweight less than 2 kg, irreversible organ failure (unless organ transplant is a consideration), diseases with a grave prognosis, and high levels of mechanical ventilation and oxygen treatment for a prolonged duration of time (generally greater than 14 days).
Evaluations and preparations
Neonates presenting with critical illness who may be candidates for ECMO are often evaluated to determine candidacy and preparations are instituted to initiate ECMO if it is the best option of care. Urgent diagnostic tests may be needed, especially echocardiography to establish presence of congenital heart disease versus pulmonary hypertension, head ultrasonography to detect intracranial hemorrhage or anomalies, neurologic examination to exclude severe dysfunction of the central nervous system, and tests of coagulation that indicate necessary treatments before systemic heparin administration.
Urgent preparations for ECMO may also be needed. Consent from parents is required. Obtaining consent from parents who are at the delivery or referral hospital is potentially complex because of the effects of maternal anesthesia, grief, and physical separation from the treating clinicians. Thorough explanations and consent may take 30 minutes or longer.
Preparation and cross-matching of red blood cells for circuit priming is required for neonatal ECMO and may take several hours; timely submission of patient blood samples to the blood bank is important to reduce the time needed for red blood cell preparation. Other blood products such as platelets, fresh frozen plasma, and cryoprecipitate are also used during ECMO initiation and must be prepared.
Mobilization of the many clinicians who participate in the evaluation and implementation of neonatal ECMO occurs simultaneously with blood preparations. ECMO specialists who prime and manage the ECMO circuit, pediatric cardiologists to interpret echocardiograms, pediatric general and cardiovascular surgeons to place cannula, and pediatric radiologists to interpret head ultrasonograms assist the neonatologists and neonatal intensive care staff to implement and manage ECMO.
Prompt referral and transfer to the nearest ECMO center ensures timely activation of the ECMO team and avoids potentially life-threatening delays in care.
Duration of ECMO
The duration of ECMO is typically measured in days to weeks.
Prognosis
Life-saving but high-risk procedure
ECMO is a life-saving treatment.
ECMO, however, is an invasive high-risk treatment that is technically challenging and requires intensive personnel support and high-volume blood exposure, especially in neonates and young infants. The need for intravascular catheters, anticoagulation, and mechanical devices in critically ill infants may be associated with a number of complications involving hemorrhage, thrombosis, and device failure. Such complications are managed by extensively trained support specialists and may be associated with short- and long-term morbidities and mortality.
Patient outcomes, however, most often reflect the complications of underlying illnesses and associated organ failures, not because of technical complications of ECMO.
As the technology and management of ECMO advances, devices and treatment strategies are anticipated to improve outcomes and reduce ECMO-related complications.
Survival (Tables 33-1 and 33-2)
Overall survival to hospital discharge for cases of neonatal respiratory and cardiac ECMO through 2012 is 75% and 40%, respectively.
Many cases recover cardiac and pulmonary function sufficiently to come off ECMO but die from the inciting primary disorder or complications of their illness. Survival is generally a function of the underlying disorders and severity of illness before treatment with ECMO.
Neonates with respiratory failure such as meconium aspiration syndrome and persistent pulmonary hypertension of the newborn without comorbidities (eg, congenital anomalies or hypoxic-ischemic encephalopathy) have the highest rates of survival.
Neonates with congenital anomalies such as congenital diaphragmatic hernia and critical congenital heart disease with comorbidities have the lowest rates of survival.
Overall survival to discharge for neonatal respiratory cases receiving. ECMO has drifted from a peak of 85% in 1988 to 69% in 2012. This trend reflects an increased severity of illness in ECMO candidates because less severely ill cases are now rescued because of advances in care, such as inhaled nitric oxide, surfactant treatment of respiratory distress syndrome and meconium aspiration syndrome, high-frequency ventilation, and gentle ventilation strategies. In contrast, overall survival to discharge in cases of neonatal cardiac disease receiving ECMO was 40% in 1992, dipped to 31% in 2000, and has climbed to 45% in 2012.
Complications (Tables 33-3 and 33-4)
Risk for multiple complications: Complications pertaining to ECMO treatment in neonatal respiratory and cardiac disorders may involve mechanical systems and patient issues with hemorrhage, nervous system injury, kidney function, cardiovascular function, respiratory system performance, infections, and metabolic imbalances.
Mechanical complications: Mechanical complications frequently involve clots within the circuit components, especially the oxygenator and bladder used for servoregulation; such thrombotic complications reflect the limitations of heparin as an anticoagulant and the presence of sites within circuit components associated with low blood flow. Oxygenator failure, pump raceway tubing ruptures, and clots within hemofilters used for renal replacement treatment are mechanical complications that often occur with prolonged durations of ECMO support and component wear, and reflect the severity of illness of the patient. Such complications are also associated with higher risk of mortality, as expected.
Medical complications: Bleeding complications during ECMO frequently involve surgical sites and cannulation sites. Mortality is increased with less frequently encountered bleeding complications, particularly hemorrhage within the gastrointestinal tract and disseminated intravascular coagulation. Mortality is also more common with neurologic complications such as central nervous system hemorrhage, seizures identified by electroencephalography, and brain death. Renal dysfunction, by almost all metrics, is associated with high rates of mortality. The need for chest compressions and presence of cardiac tamponade, pulmonary hemorrhage, pneumothorax-requiring treatment, culture-proven infection, and severe metabolic acidosis are other complications occurring during ECMO with the highest associated rates of death.
Long-term medical, neurodevelopmental, behavioral, cognitive, and psychosocial outcomes.
Neonatal respiratory cases: There is limited information about the outcomes of neonates with respiratory disorders treated with ECMO during early school age and beyond.
The United Kingdom Collaborative Trial of Neonatal ECMO evaluated those discharged alive at 7 years of age, either treated with ECMO or treated conventionally, and found cognitive function was found to be normal in 76% of cases of severe respiratory failure and the General Conceptual Ability Scores were similar. Both study groups were found to have similar degrees of learning problems, especially in visual spatial skills, creative writing, concentration, memory, and reading comprehension. Cognitive scores trended higher than actual ability scores. About 20% in both groups received special education.
Neuromotor function was normal in 40% of patients.
Respiratory morbidity (wheezing requiring treatment) was more frequent in controls (56%) than in the ECMO group (22%).
Behavior problems, most commonly hyperactivity, were more frequently described in the control group by parents than in the ECMO group by both parents (38% vs 18%) and teachers (24% vs 13%).
Progressive hearing loss was found in two of 90 ECMO cases and five of 90 wore hearing aids.
Overall, 55% of ECMO patients and 50% of control patients survived with no disability.
Neurodevelopmental, intellectual, medical, and behavioral outcomes were more favorable in neonates with meconium aspiration syndrome and least favorable in infants with congenital diaphragmatic hernia.
Neonatal cardiac cases: School, teenage, and adult outcomes following ECMO in neonates with congenital heart disease are infrequently reported because of the complexity of factors affecting outcomes in such infants and focus of most reports on neonates and young infants at the time of treatment. Neonates and infants with increasingly complex congenital heart disease regardless of need for ECMO are at high risk for neurodevelopmental and behavioral impairment. Many of these infants have impairments in cognition, socialization, communication, attention, impulse control executive function, behavior, mood, and anxiety. Consequently, special education and habilitation with speech, physical therapy, occupational and psychosocial therapy may be needed. The need for ECMO in patients with complex congenital heart lesions indicates a group of patients at particularly high risk for mortality and long-term morbidity.
50% or more of pediatric, predominately neonates and young infants, cardiac ECMO survivors have significant abnormalities in neurologic and developmental outcomes.
95% of 5-year-olds treated with ECMO following cardiovascular surgery as neonates or during infancy for congenital heart lesions have good heart function.
Growth is impeded in these same infants as median height and weight are at the 28th and 36th percentiles, respectively.
Moderate to severe impairment in cognitive function, gross motor skills, and/or sensory function characterizes 70% of long-term survivors treated with ECMO; 19% have severe disability.
Risk factors for poor outcomes in neonates with congenital heart diseases in addition to treatment with ECMO include complex heart disease, open heart surgery, prematurity, circulatory arrest prior to ECMO, mechanical support with a ventricular assist device, heart transplantation, prolonged hospitalization, perioperative seizures, genetic or syndromic disorders, microcephaly, and abnormalities on neuroimaging.
Quality of life was assessed in 5- to 18-year-old children following cardiac surgery and ECMO as neonates and infants; the quality-of-life indicators included physical and psychosocial perceptions of functionality. The physical quality of life of these children following surgery plus ECMO is lower than in the general population but similar to that of other cardiac disease patients not subjected to ECMO; this suggests that the ECMO procedure alone may not have a large impact on long-term outcomes.
The underlying cardiac disease, severity of illness, associated noncardiac disorders, number of surgical procedures and anesthetic exposures, and need for long durations of intensive care and hospital stays have greater impact on outcomes than the ECMO treatment itself.
The psychosocial quality-of-life metric for the children receiving heart surgery and ECMO is similar to that of the general population; this suggests that such procedures have benefit despite the high risk for mortality (about 60%) and long-term morbidities (50% or more).
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