◆ Extra-corporeal life support (ECLS) is an essential tool for the modern intensivist and surgeon.
◆ The addition of extracorporeal therapy should be considered when pathology is reversible and conventional therapy is failing.
◆ There are different types of extracorporeal therapies, each with their own nuances, which need to be understood in order to be used effectively and appropriately.
◆ Techniques required for providing successful ECLS in adult respiratory and cardiac failure are described in this chapter.
◆ Increasing use of mobile extracorporeal membrane oxygenation (ECMO) and extracorporeal cardiopulmonary resuscitation (ECPR) demonstrate how extracorporeal support has progressed and advanced in recent years.
Extracorporeal life support (ECLS) is a general term to describe prolonged, but temporary support of heart and lung function using mechanical devices. Device applications require a combination of vascular access catheters, connecting tubing, a blood pump, a gas exchange device (oxygenator), a heat exchanger, measuring and monitoring devices, and systemic anticoagulation.
There are various sub-types of ECLS (with varying degrees of overlap) including:
◆ Extracorporeal lung assist ECLA (low flow extracorporeal membrane oxygenation (ECMO) to prevent intubation or minimize ventilation).
◆ ECMO (high flow ECLS to replace lung and/or heart function, used synonomously with ECLS).
◆ Extracorporeal carbon dioxide removal (ECCO2R, same as lung assist).
◆ Extracorporeal cardiopulmonary resuscitation (ECPR, emergency cardiac support in cardiac arrest).
When blood pumps alone are used for cardiac support then ECLS is termed as left ventricular assist device (LVAD), right ventricular assist device (RVAD), or biventricular assist device (BiVAD).
The Extracorporeal Life Support Organization’s (ELSO) recent international summary (July 2012)  shows that to date over 50,000 patients have been treated with ECLS (Fig. 104.1). Adult respiratory activity has increased year-on-year (Fig. 104.2) following the publication of the CESAR trial  and successful use of ECMO in the H1N1 outbreaks of 2009 and 2010, which have raised awareness of ECMO use in adults globally .
With improved knowledge and experience in adult respiratory extracorporeal techniques, use in adult cardiac support has also increased (Fig. 104.3) .
No ECMO programme can be run without a dedicated team with extensive knowledge of and ability to manage all of the following—patient selection, patient transport (including mobile ECMO), ECMO circuit, ECMO circuit–patient interaction, ECMO complications, specific patient and disease management pre, during and post-ECMO, and advanced ventilator techniques for pre- and post-ECMO patients. This requires engagement and teamwork across several disciplines.
The ECMO/ECLS circuit has undergone significant changes in the last few years, which has resulted in a shorter more biocompatible circuit.
The essential components (venous drainage line, blood pump, or oxygenator with gas supply, heat exchanger, arterial return) of an ECMO circuit are shown in Fig. 104.4.
Newer tubing materials and heparin coating have resulted in ELCS circuits causing less patient systemic inflammatory response, having decreased heparin requirement for systemic anticoagulation and reduced thrombotic complications.
The traditional silicone oxygenator has been replaced by the hollow fibre polymethlypentene (PMP) oxygenators, which have lower resistance, better gas exchange, lower priming volumes, increased efficiency, cause less consumption of platelets and clotting factors, and survive longer.
Mendler type centrifugal blood pumps are superseding the occlusive roller pump and the first generation centrifugal pump. These are smaller and non-occlusive, and so are inherently safer. The central hole in the rotor of the Mendler type pump prevents clot build-up and has improved heat dissipation, making it mechanically more reliable. ECLS circuits overall are shorter as centrifugal pumps generate active suction and do not depend on gravity for venous drainage. They generate a new problem of negative pressure on the drainage side of the circuit. The main disadvantage of this negative pressure is that it increases the risk of air entrainment if access ports are placed in the drainage side of the circuit. As air in the circuit is the nemesis of the ECMO specialist removing circuit access ports from the drainage side of the circuit and placing them post-centrifugal pump/pre-oxygenator (i.e. in the positive pressure side of the circuit) almost completely eliminates the risk of air entrainment.
Fig. 104.5 illustrates how the ECMO circuit has changed over the years with the first photo showing the simplified modern circuit.
Definite proof that new systems (centrifugal pump, PMP oxygenator) are better than traditional systems (silicone oxygenator and roller head occlusive pump) is lacking, but various single centre reports are encouraging. Sivarjan et al.  compared two groups of paediatric ECMO patients in different time periods, 1998 (Biomedicus centrifugal pump and silicone oxygenator) and 2001 (Jostra centrifugal pump and quadrox oxygenator). Patient survival improved from 24 to 49% in the latter group and mechanical complications per 10,000 hours fell from 70 to 50; pump heads used from 160 to 110 and oxygenators from 130 to 110.
Despite advances in technology, a significant number of adult patients fail maximal medical therapy and ultimately require ECMO. A proportion of these patients can be moved to an ECMO centre in a timely manner by conventional means, but increasingly they rapidly become too unstable, requiring emergency cannulation/ECPR in their own centre, and transport on ECMO to an ECMO centre.
Advances in technology and experience mean that ECMO centres should now consider mobile ECMO retrieval as a standard part of their service provision.
This requires medical, nursing, and perfusion professionals to be available round the clock, and trained in ECMO and transport medicine. It also requires a dedicated transport system (trolley and vehicle), which can be adapted to the transport mode (air/rotary/fixed wing).
Veno-venous ECLS support
In veno-venous (VV) ECLS support blood is drained from the venous circulation and re-infused back into the venous circulation after passing through the extracorporeal circuit. It requires the patient to have adequate cardiac output to pump the oxygenated blood around the body. Oxygenation is proportional to ECMO flow. High flow VV ECLS is for oxygenation (ECMO) and low flow for CO2 removal (ECCO2R).
Cannulation for VV support is traditionally through the right internal jugular vein into the right atrium and via the femoral vessels, and the degree of ECMO support provided depends on cannula size and site. Percutaneous access over a wire via the Seldinger technique has been a major advantage in ECMO cannulation. Traditionally, a two cannula approach is used in adults. A 23–28F (external diameter) single lumen catheter inserted into the inferior vena cava (IVC) via either femoral vein and a second 23–28F cannula inserted into the right atrium (RA) via the right internal jugular vein will give adequate support for most adult patients (up to 5 L/min flow). Direction of flow is optional, drainage from the neck (with a shorter cannula) allows higher flow, but has more recirculation while drainage from the groin gives less drainage and recirculation, but may provide better oxygen delivery. Additional drainage cannulae can be placed in the other femoral vein with drainage from IVC and RA, and reinfusion into IVC, if flow is inadequate.
Recently, the bicaval double lumen venous cannula has allowed a single point of venous access with inherently low levels of recirculation making ECMO much more efficient. The Bicaval double lumen cannula, Avalon Elite® (Maquet) is designed to be inserted percutaneously via the right internal jugular vein with its tip placed in the IVC. Drainage holes placed proximally and distally to sit in SVC and IVC minimize recirculation as oxygenated blood is returned via a separate return hole placed in the middle of these two drainage ports and directed toward the tricuspid valve (Fig. 104.6).
Cannulae are available in sizes 16–31F and provide adequate flows in most patients up to 100 kg. Insertion requires X-ray screening to confirm wire then cannula position in IVC and to minimize complications, particularly misplacement/pneumothorax and cardiac perforation. If additional flow is required, a second femoral drainage cannula (23f biomedicus) can be inserted percutaneously into the lower IVC via either femoral vein.
Advantages of the bicaval double lumen cannula include single site access (reducing the risk of vascular injury, cannula site bleeding, and infection) and reduced circuit length (less contact activation, mobile ECMO, improved patient mobility). A perceived disadvantage of the bicaval cannula is a reduced ECMO flow compared with two single cannulae. However, as there is reduced recirculation this does not impact on oxygen delivery. It is recommended that flows should be maintained above 2.5 L/min in adults in order to avoid clot formation.
VV ECMO can provide total CO2 removal, but provides less O2 delivery than veno-arterial (VA) support. It relies on adequate pumping of the native heart to distribute the extracorporeal oxygenated blood to the body. Many centres default to VA ECMO support in patients who have high inotropic requirements secondary to severe respiratory failure. However, one potential benefit of VV support is that the highly oxygenated blood returned back to the right atrium flows through the heart and into the coronary arteries, resulting in improved oxygen delivery to the myocardium and cardiac function.
The goal of ECMO for respiratory failure is to support gas exchange so that the iatrogenic side effects of intensive care treatment (such as ventilator-associated lung injury and sedation complications) can be minimized. Patients are therefore transitioned immediately to ‘rest settings’ on the ventilator, this is either a low frequency, high PEEP, low positive inspiratory pressure (PIP) strategy (i.e. 25/15 rate 10, FiO2 0.3) or a low pressure high-frequency oscillatory ventilation approach, i.e. MAP 10–15 cmH2O for patients with severe barotrauma and air leak. Once the acute phase of the illness has passed patients are either extubated or (more commonly) tracheostomized, while still on ECMO, woken up, and allowed to breathe for themselves. Many teams are now able to mobilize patients on ECMO.
VA support in adult patients is reserved for those cases with profound cardiac failure or in the situation of cardiac arrest when it is termed as ECPR.
Blood is drained from the venous system (from RA via RIJ or IVC via the femoral vein and returned into the arterial system via the aorta (via common carotid, axilliary, or the femoral artery).
The right internal jugular is preferred for venous drainage as it is the shortest route, but femoral venous access is sometimes more easily achievable. Direct right atrial access after cardiac surgery is also possible if the sternum is left open, although the risk of infection is high and the decision whether to change the cannula insertion site to percutaneous in the neck or groin should be made early.
Historically, the common carotid artery was the preferred route for the arterial return cannula, largely as a result of early ECMO experience with VA support in neonates. Because the carotid artery could be ligated distally, distal perfusion was not required, and it delivered fully oxygenated blood direct to the aortic root. Unfortunately, 15% of adults develop an intracranial ischaemic injury following carotid ligation. The right femoral artery is now the preferred site for arterial return (it is usually slightly bigger than the left). In centres who perform purely VA ECMO for all adult cardiac and respiratory indications, the femoral artery is directly accessed using a cut-down technique, a distal perfusion cannula is placed electively into the superior femoral artery and then the arterial cannula (17, 19, or 21F) is inserted into the femoral artery under direct vision. This minimizes compromise to the distal collateral circulation of the leg. Other centres electively insert a distal perfusion catheter into the posterior tibial artery once the patient has stabilized on ECMO. Whichever technique is used for femoral artery cannulation, the associated leg should be monitored hourly for signs of compromised distal perfusion. Compartment syndrome of the leg requiring fasciotomies is not an infrequent complication of VA ECMO.
Total bypass of the cardiopulmonary system during VA ECMO is not recommended. Some blood is required to flow through the patient’s heart to supply the coronary arteries. As the blood going through the heart in VA ECMO is deoxygenated, oxygenation of coronary artery blood is dependent on oxygenation via ventilatory support of the lungs. It is routine, therefore, for the amount of ventilatory support to be higher in VA ECMO (FiO2 routinely 40% or above), although care should still be taken to minimize ventilator-induced lung injury.
An adverse effect of VA ECMO is that it increases left ventricular afterload, which may result in complete left ventricular failure. Chemical afterload reduction may not be adequate to manage the situation. Patients can require a left atrial vent (line into left atrium connected to the venous drainage line of ECMO circuit) if the chest is open or an atrial septosomy. If a patient has these interventions it should be noted that mixed venous saturations taken from the venous line below the vent will be falsely elevated, as oxygenated blood from the left heart will be vented into the right atrium or the venous side of the ECMO circuit, and so a true mixed venous gas should be taken proximal to the site of mixing. Near-infrared spectroscopy (NIRS) can be a useful adjunct in tailoring oxygen delivery in this situation.
The goal of VA ECMO is to provide adequate haemodynamics, oxygenation, and perfusion, while optimizing the conditions for cardiac and respiratory rest and recovery.
Other extracorporeal respiratory therapies
Mini ECMO/novalungtm/ILA activetm
In recent years miniature extracorporeal lung assist (ECLA) devices have become available, e.g. NovalungTM (Germany). These devices require percutaneous cannulation of the femoral artery and vein, utilizing the patient’s own blood pressure to drive blood across the low resistance oxygenator. More recently, Novalung has released the ILA activeTM device, which allows venous cannulation only using a double lumen cannula (24F NOVAPORT twinTM) and relying on a centrifugal pump to drive blood through the oxygenator. Nova lung is limited to lower flows 1–2 L/min and are only able to provide CO2 removal to support patients with moderate respiratory failure. The technique can avoid the need for intubation and mechanical ventilation in high-risk patients, shorten the duration of mechanical ventilation and allow suitable patients to be awake and mobile prior to lung transplantation. The ILA activeTM device will allow flow up to 8l/min, but would require a larger cannula than 24F to achieve this flow, so it is usually used in low flow ECCO2R mode. Other ECCO2R devices include A-Lung and DECAP.
Use of ECPR is relatively new. It can be viewed as an extreme form of cardiac support using VA ECMO cannulation for cardiac arrest. Cannulation is usually of the femoral vessels (artery and vein) using percutaneous techniques.
Adult in-hospital cardiac arrest results in an 80% mortality (survival range 10–40% depending on underlying rhythm at onset of the arrest) . ELSO registry data shows survival to hospital discharge of 29% in 591 adults who required ECPR . Shin et al.  demonstrated that when ECMO was used early as part of an overall plan for the resuscitation of adults with cardiac arrest, there was improved survival and quality of life when compared with conventional CPR. This was only demonstrated when ECMO was considered (within 10 minutes of onset of arrest) and implemented (within 60 minutes of arrest) early. In the event of an unexpected arrest, even with an unsuccessful outcome ECPR and VA ECMO support may give relatives and clinical teams time to reflect and come to terms with the loss of the patient.
ECLS is an essential tool for the modern intensivist, cardiologist and surgeon. The addition of extracorporeal therapy should be considered in all cases when pathology is potentially reversible and conventional therapy is clearly failing.
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