Extracorporeal Life Support for Cardiopulmonary Failure

Published on 22/03/2015 by admin

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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.

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.

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 lung1 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.

image 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.37 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.

image 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

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