Extracorporeal Life Support for Cardiopulmonary Failure

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53 Extracorporeal Life Support for Cardiopulmonary Failure

Extracorporeal life support (ECLS) or extracorporeal membrane oxygenation (ECMO) involve the use of mechanical devices during life-threatening cardiac or pulmonary failure. ECMO can provide partial or total support, is temporary, and requires systemic anticoagulation. ECMO is not a treatment; it is a life-support system that allows time for evaluation, diagnosis, and treatment of the condition which caused heart or lung failure. The indication for ECMO is high risk of mortality despite and after optimal treatment.

ECMO controls gas exchange and perfusion, stabilizes the patient physiologically, decreases the risk of ongoing ventilator- or vasopressor-induced iatrogenic injury, and allows ample time for diagnosis, treatment, and recovery from the primary injury or disease. Right atrial venous blood is drained through a large cannula, pumped through an artificial lung and back into the patient, either into the aorta (venoarterial [VA]) or into the right atrium (venovenous [VV] mode). VA access puts the artificial lung in parallel with the native lungs and substitutes for both heart and lung function. VV access puts the artificial lung in series with the native lung. These modes of access are shown in Figures 53-1 and 53-2. For respiratory failure, VV access is preferred because normal hemodynamics are maintained, and there is little risk of systemic embolism. For total support in either mode, the blood flow required is 60 to 100 mL/kg/min (the entire cardiac output); large-bore, low-resistance cannulas are required to achieve this amount of flow. The flow is limited by resistance in the venous access catheter. For vascular access, the cannulas are placed via the large vessels in the neck or groin. Cannulas can be placed by direct cutdown access to these vessels or, more commonly, via percutaneous placement over a guidewire. After cannulas are placed, the circuit primed with crystalloid solution is attached, heparin is given for anticoagulation, and extracorporeal flow is established at 50 to 100 mL/kg/min. The membrane lung is ventilated with 100% oxygen.

Figure 53-1 Venovenous (VV) access via a double-lumen cannula in the right atrium. Extracorporeal blood flow mixes with native venous return in the right atrium and ventricle. If there is no native lung function, systemic arterial saturation is 75% to 85%. Parameters in the boxes are measured and used to control the system.

Figure 53-2 Venoarterial (VA) access via the femoral vessels. Extracorporeal blood flow in the aorta is retrograde and mixes with native blood flow in the proximal aorta. Parameters in the boxes are measured and used to control the system.

When adequate extracorporeal flow and gas exchange are achieved, the ventilator is turned down to resting settings (typically FIO₂ 0.3, pressure 20/10, rate 4). In many cases, the patient can be extubated, and the extracorporeal circuit takes over all respiratory and cardiac function. As the native heart and lungs improve, the extracorporeal flow is decreased proportionately, and when heart and lung function are fully restored, the patient is weaned from extracorporeal support, and cannulas are removed.

The major complication associated with ECMO is bleeding, which occurs in 10% to 30% of patients. Bleeding is managed by reducing or discontinuing the heparin infusion, optimizing the native coagulation status, and direct surgical control. Failure of the membrane lung or pump occurs in less than 5% of patients and is managed by replacing the device. Other uncommon complications are related to cannulation, systemic air embolism, thromboembolism, and infection.

ECMO is used in a variety of clinical circumstances, and results depend on the primary indication. ECMO provides life support, but it is not treatment. The clinical outcome depends on the response to treatment for the primary condition. Because ECMO is a life-support technique, the primary outcome variable is survival. Survival outcome for nine categories of patients is shown in Figure 53-3. Survival ranges from 30% in extracorporeal cardiopulmonary resuscitation (ECPR) to 95% for neonatal meconium aspiration syndrome.

Figure 53-3 Summary of cases in the ELSO registry in 2010 (elso.med.umich.edu).

The devices for extracorporeal support used in the past carried a significant risk of blowout, air embolism or thromboembolism, and device failure. The current generation of devices are much simpler and inherently safer. The major change is in the membrane lung. The Kolobow spiral coil membrane lung ¹ has been reliably used for ECMO for over 30 years. This membrane lung works well for weeks at a time but has an affinity for platelets, causing thrombocytopenia, and has high blood flow resistance, requiring high pressure generated by the pump for high blood flow. When centrifugal pumps are used to generate high pressure, hemolysis and thrombosis can occur, so most of the experience with ECMO has been with modified roller pumps.

The new membrane lungs from Maquet, Novalung, Medos, and Dideco are nonporous hollow fiber devices with low blood flow resistance, allowing safe use of the centrifugal pumps designed for prolonged use (e.g., Maquet Rotaflow, Levitronix Centrimag). The polymethylpentene fibers in these lungs, combined with nonthrombogenic coatings, decrease the need for platelet transfusion and for continuous heparin infusion in some cases. New vascular access devices have wire-reinforced walls, allowing very thin cannula walls to minimize blood flow resistance.

The major use of ECLS has gone from neonatal respiratory failure to many causes of cardiorespiratory failure in all age groups. The Extracorporeal Life Support Organization (ELSO; elso@med.umich.edu) is an international consortium of medical centers with major ECMO programs. ELSO maintains a registry of ECMO cases. The types of cases represented in the ELSO Registry are shown in Figure 53-3. The indications, practice management, and outcome are quite different in each of these patient groups.

Neonatal Respiratory Failure

The major application of ECMO began with neonatal respiratory failure. The first successful case was reported in 1975, and ECMO became standard treatment in major neonatal centers.² In retrospect, the reason for this success was that regardless of primary diagnosis, the major pathophysiology in neonatal respiratory failure is persistent fetal circulation (PFC), a condition that is almost always reversible in a few days. In the early 1980s, PFC was treated by hyperventilation to induce alkalosis, which is damaging to the neonatal lung. ECMO eliminated this iatrogenic injury and allowed time for PFC to resolve. Neonatal ECMO was proven effective and beneficial in four prospective randomized trials, an effect that was confirmed in a Cochrane meta-analysis.³^–⁷ A major lesson learned from the neonatal experience was the advantage of resting the native lungs by extracorporeal support.

Inhaled nitric oxide administered with high-frequency oscillation was shown to be effective treatment for PFC in the 1990s.^8,⁹ The need for extracorporeal support thereafter decreased significantly. The exception is PFC combined with lung hypoplasia in congenital diaphragmatic hernia patients. This condition is now the primary indication for ECMO in newborn infants. Vascular access in neonates is always gained via the neck vessels, usually by placement of a double-lumen catheter into the right atrium via the jugular vein.

Pediatric Respiratory Failure

Severe respiratory failure in children arises from a wide range of conditions including viral infections in infants and trauma in 18-year-olds. The indication for ECMO is failure to respond to optimal ventilator and supportive care. Vascular access is venovenous, usually with a double-lumen catheter placed via the jugular vein. Green demonstrated the efficacy of ECMO in pediatric respiratory failure in a matched-pairs analysis using a large multicenter database.¹⁰ In that analysis, survival with ECMO was 75% compared to 50% with conventional management.¹⁰

Adult Respiratory Failure

Hill reported the first successful ECMO case in an adult with respiratory failure in 1972.¹¹ This led to a prospective randomized trial of ECMO in acute respiratory distress syndrome (ARDS) in 1975-1978. After 90 patients, the trial was stopped for futility.¹² In retrospect, this study was undertaken prematurely in inexperienced centers using conventional and ECMO management methodologies that would not be used today. Nonetheless, the report of this trial essentially stopped research on ECMO for ARDS for many years. Over the ensuing decades, a few centers reported 50% survival in severe ARDS.¹³ A second prospective randomized trail was conducted in the United Kingdom from 2004-2007, within which the best conventional care in many intensive care units (ICUs) was compared to protocolized care including ECMO in a single center.¹⁴ Twenty-eight day survival was 76% in protocolized care compared to 50% with conventional care. Six-month survival free of disability was 63% versus 47%.

The H1N1 worldwide flu epidemic in 2009 renewed interest in ECMO for ARDS. Investigators in Australia and New Zealand reported 78% survival in 68 H1N1 patients managed with ECMO.¹⁵ In the recent studies suggesting benefit with ECMO, new ECMO devices were used, emphasizing the safety and simplicity of the second generation of ECMO. At present, vascular access is gained by a large double-lumen catheter placed via the right internal jugular vein, or by drainage from the inferior vena cava via the femoral vein and reinfusion into the right atrium via the jugular vein. On ECMO, the ventilator is set at rest settings to avoid ongoing iatrogenic injury. Native lung function usually becomes even worse before it gets better and, ECLS support is usually required for 10 to 20 days.

Another approach to extracorporeal gas exchange is selective CO₂ removal (ECCOR).¹⁶ In ECCOR, a membrane lung is used with low blood flow to remove CO₂, so mechanical ventilation is not necessary, and oxygen is supplied by insufflation of the native lungs. Gattinoni reported 56% survival with ECCOR in ARDS in 1986.¹⁷ Morris later reported a small randomized trial that showed no survival difference between patients treated with ECCOR and conventional therapy.¹⁸

ECCOR has been studied and refined by Zwischenberger and others.¹⁹ ECCOR using a low-resistance membrane lung perfused by a femoral arterial venous shunt or pumped VV access is being studied in the management of ARDS in Europe. ECCOR is ideal for CO₂ retention syndromes like status asthmaticus but does not provide sufficient oxygenation for full respiratory support.

Lung transplantation has been very successful in the management of end-stage lung disease but is rarely considered in intubated ventilated patients because nosocomial pneumonia and multiple organ failure usually occur before a donor is found. ECMO is rarely used as a bridge to transplant for the same reason.²⁰ In addition, many patients with respiratory failure awaiting lung transplant have right ventricular failure requiring venoarterial access.²¹ Recently, some centers have reported success with ECMO as a bridge to lung transplantation, using an implantable (paracorporeal) membrane lung allowing extubation, ambulation, and rehabilitation while bridging to lung transplantation.²²

Cardiac Failure in Children

The major application of ECMO today is to support children with profound cardiac failure.²³ Most of these patients are infants who show cardiovascular deterioration immediately after operations for congenital heart disease. Support with VA ECLS is used as a bridge to recovery from myocardial stunning, and if recovery does not occur, as a bridge to a cardiac-assist device and perhaps transplantation.²⁴ Other applications for ECMO include myocarditis and myocardiopathy. Venoarterial access is required via the neck vessels or using direct cardiac cannulas if the chest is already open.

Cardiac Failure in Adults

Unlike the pediatric population, the major application of ECLS in adult cardiac failure is cardiogenic shock following myocardial infarction, myocardiopathy, myocarditis, or inability to come off cardiopulmonary bypass following cardiac operation.²⁵^–²⁷ Venoarterial access is required in these settings. The femoral vessels are used in almost all cases because of a 10% to 15% incidence of stroke when the carotid artery is used in patients with profound shock or cardiac arrest. Vascular access is usually percutaneous, although direct cutdown access is the most reliable in patients with profound cardiogenic shock. Centers in Paris²⁸ and Taiwan²⁹ have reported a large experience in cardiogenic shock using ECMO to stabilize hemodynamics while proceeding to cardiac catheterization and revascularization of the myocardium if needed, followed by cardiac recovery or bridging to a ventricular assist device and perhaps transplantation.

Extracorporeal Support During Cardiopulmonary Resuscitation

Extracorporeal support during cardiopulmonary resuscitation (ECPR) is the extension of VA support in cardiogenic shock to patients in overt cardiac arrest.^30,³¹ Venoarterial access is used, usually by direct vessel exposure. The neck vessels are used for children up to the age of 5 or 6, and the femoral vessels for older children and adults. The use of ECPR requires having a primed circuit and a cannulation team immediately available. With the new simplified devices, and with appropriate training of emergency room physicians, the use of ECPR is increasing in major academic hospitals.

Other Applications of ECMO

ECMO is being investigated for applications to other conditions where perfusion and gas-exchange support is needed. Controlled warming after accidental hypothermia has been reported with ECMO.³² A major advantage for ECMO compared to conventional techniques is to avoid or treat the cardiac arrhythmias that often occur during rewarming. Maclaren and others from Australia have reported the use of ECMO in profound septic shock in children.³³ They found that very high blood flow achieved with direct cardiac vascular access led to 75% survival in profound septic shock. When the team and circuit can be quickly assembled in the setting of massive pulmonary embolism, the results are very good.³⁴ The management of prematurity using ECMO as an artificial placenta to avoid intubation and mechanical ventilation is being studied in the laboratory.

The major limitation to organ transplantation is availability of donors. The largest potential source of donors is donation after cardiac death (DCD). However, this technique is rarely used because of poor organ function and long periods of lung ischemia. Several centers are using VA ECMO after cardiac death to resuscitate abdominal organs ³⁵ and lungs to transplantable status.³⁶ Organs resuscitated in this fashion function as well or better than those obtained from conventional brain-dead donors.