There are four categories for ECMO cannulation in the adult:
VV ECMO is indicated for management of isolated respiratory failure. The success of this strategy relies on the patient's own hemodynamics and only assists with gas exchange. Blood is withdrawn from the right atrium/inferior vena cava (IVC) via a long peripheral cannula inserted via a central vein. Oxygenated blood is returned via a superior vena cava (SVC) cannula into the right atrium with flow directed at the tricuspid valve. The oxygenated blood is then pumped out the pulmonary artery, through the dysfunctional lungs, and then returned to the left heart where it is pumped to the systemic circulation. The Avalon EliteTM dual lumen cannula (DLC) (Maquet Cardiovascular, San Jose, CA), designed by Wang and Zwischenberger, is a significant advance in the arena of VV ECMO.3 Single percutaneous access of the right internal jugular vein yields several advantages: single-site cannulation, reduced risk for complications associated with femoral or central cannulation, and the ability to allow ambulation by avoiding the use of the femoral site. Placement of the Avalon cannula may be performed bedside in the intensive care unit (ICU); however, it requires either fluoroscopic or echocardiographic guidance for optimal placement of the return and infusion ports.4
VA ECMO is indicated in the setting of acute cardiogenic shock or in the setting of a primary respiratory process complicated by diminished cardiac function. Cannulation is performed with venous drainage from the right femoral vein through a long cannula placed such that optimal drainage from the right atrium is achieved. Oxygenated blood is returned via femoral arterial cannula. Cannulas may be placed percutaneously in the ICU or a direct cut-down for access to the femoral vasculature. Blood via the axillary artery by direct anastomosis of a conduit facilitates ambulation. This strategy may be an important consideration in the conversion of ambulatory VV ECMO to VA ECMO as this configuration continues to allow ambulation.5
AV ECMO/AVCO2 removal. AV ECMO utilizes the patient's native hemodynamics to drive flow through a low resistance gas exchange device, the goal being CO2 removal. This configuration is most suited to those patients awaiting lung transplantation whose primary issue is severe CO2 retention. Sometimes described as pumpless extracorporeal lung assist (pECLA), flow through the circuit is usually 15% to 20% of cardiac output, which limits its use for oxygenation. Central cannulation has also been described.6,7
Central cannulation refers to placement of ECMO cannulas via thoracotomy or sternotomy. This most commonly refers to placement of ECMO for failure to wean from cardiopulmonary bypass. The disadvantage is the need for full operating room support; however, the full array of ECMO options are available via the great vessels, and complications of peripheral cannulation are avoided.
Significant advances in commercially available oxygenator membranes have resulted in improved durability, including patients bridged to lung transplantation. Currently, most ECMO systems have replaced polypropylene with polymethylpentene (PMP) fibers. PMP membrane oxygenators are smaller, provide efficient gas exchange without plasma leak, and are associated with faster priming (saving blood and valuable time and making CO2 flushing unnecessary). In addition, the PMP oxygenators are associated with less circuit resistance, are less prone to malfunctioning due to blood trauma or blood clots, and can be functional for several weeks to months. Modern ECMO components, including PMP oxygenators, can be heparin coated, reducing excessive use of heparin, minimizing risk of over-anticoagulation, and reducing the use of blood products. Heparin-coated tubing is also associated with a reduction in the rates of leukocytes, platelets, and complement activation. New centrifugal pumps have been created offering a nonocclusive, demand-regulated pump flow that eliminates the risk of raceway tubing wear and circuit rupture, facilitating patient mobilization and ambulation.
Interventional Lung Assist (Novalung)
The interventional lung assist (iLA), or Novalung, consists of a low resistance PMP membrane designed to allow gas exchange by simple diffusion. The iLA has been successfully used to bridge patients to lung transplantation using a “pumpless” AV mode (pECLA), in which the device is attached to the systemic circulation via femoral artery, although central cannulation has also been reported in patients bridged to lung transplantation (PA–LA or PA–PV). The device is effective for CO2 removal but is less effective for O2 augmentation as it only receives approximately 15% to 20% of the cardiac output for extracorporeal gas exchange. Novalung has been compared to other CO2 removal devices in patients awaiting lung transplantation and all provided similar CO2 clearance.
Dual Lumen Cannula (Avalon Elite)
A new type of DLC (Fig. 113-1), the Avalon Elite, is placed percutaneously through the internal jugular vein; the drainage lumen is open to both the SVC and IVC, while the infusion lumen is open to the right atrium. The blood from systemic circulation flows through the SVC and IVC into the drainage lumen to the artificial lung device. The blood is oxygenated and returned via the infusion lumen into the right atrium. Compared to traditional ECMO approaches, this device offers important advantages in patients awaiting lung transplantation: it requires single-site cannulation, reduces the risk for complications associated with femoral or central cannulation, and facilitates ambulation by avoiding the use of the femoral site. The DLC has a unique design with improved flexibility (reducing kinking problems associated with rigid cannulas). The infusion lumen of the cannula is an ultra-thin membrane that collapses during insertion to allow space for an atraumatic introducer that facilitates placement. The Avalon DLC has shown recirculation fractions of 2% when fluoroscopy or transthoracic echocardiography guidance is used.
Avalon Elite™ double lumen catheter and catheter placement.
The DLC has been used to facilitate ambulation during ECMO in awake and nonintubated patients. Garcia et al.8 first reported the use of ambulatory VV ECMO using a DLC in a patient with COPD with refractory hypercapnia. The patient was able to exercise using a treadmill and a stationary bike while on ECMO and was successfully bridged to lung transplantation approximately 19 days later. Subsequent to this report, many other centers have reported similar results and have confirmed the feasibility and safety of the DLC as a bridge to lung transplantation. For VV ECMO, a single-site approach using a DLC was preferred in patients with hypercapnia and preserved oxygenation, whereas a two-site approach was chosen for patients with severe hypoxemia. Bermudez et al.9 presented their single-center experience with 17 patients that were bridged to lung transplantation. The 30-day, 1-year, and 3-year survival rates were not different when compared to nonsupported patients, and the survival was not affected by ECMO type at 2 years. Hayes et al.10 reported the use of a DLC to facilitate ambulation and transplant in four patients with cystic fibrosis and hypercapneic respiratory failure. More recently, Lang et al.11 reported their experience with ECMO as a bridge to lung transplantation in 34 patients, and reported the use of a DLC in two patients.
The cannulation strategy is frequently chosen based on: ability to facilitate ambulation (DLC via internal jugular vein is the preferred route, although central VA ECMO and iLA [PA–LA] can also allow ambulation); hemodynamic instability; and presence of severe pulmonary hypertension and/or right heart failure (central or femoral cannulation for VA ECMO is preferred). Cannulation approaches performed for bridging patients to lung transplantation include femoral vein to internal jugular vein (traditional VV), femoral vein to femoral artery (traditional VA), RA–Ao (central VA), PA–LA, and right internal jugular with DLC (ambulatory VV).
Fig. 113-2 shows our preferred cannulation strategy for ambulatory ECMO as a bridge to lung transplantation.
Preferred approach for patients bridged to lung transplantation using ECMO.