Nathalie Roy and Joshua N. Baker
Introduction
In recent years there has been a trend toward the increasing use of ECMO prior to lung transplantation, with increased survival in the recent era. However, survival post transplantation remains lower than the non-ECMO patient cohort. The prevalence of utilization of this technology and results vary across centers in the United States. In the patient with acute respiratory failure, it can be used as bridge to transplantation, bridge to decision, and bridge to recovery. Its best indication in the setting of lung transplantation reside in patient optimization for transplantation rather than patient salvage.
Many modes and cannulation strategies for ECMO have been described in recent years. Venovenous cannulation is the more prevalent in the transplantation population and can be performed with a double-lumen cannula, multiple venous cannulas, or right atrial to pulmonary artery cannulation. Venoarterial cannulation has also been described pre-lung transplantation although it is rarely our approach. In the context of ECMO for lung transplantation, ambulatory ECMO, if achievable, is preferable.
INDICATIONS AND CONTRAINDICATIONS
Indications
Acute or rapidly progressing respiratory failure in a patient listed for lung transplantation
Chronic respiratory failure leading to deconditioning and malnutrition in a patient listed for lung transplantation
Impending intubation or short time intubated
Contraindications
Systemic sepsis
Advanced age
Serious comorbidities precluding lung transplantation
Time spent on the ventilator >7 days
Figure 5.1 ECMO circuit for patient ambulation. The various components are mounted on an IV infusion pole. C, centrifugal pump; O, oxygenator; M, monitoring console; T, oxygen tank with gas blender.
PREOPERATIVE PLANNING
ECMO circuit components and ambulatory setup (Fig. 5.1)
Principle
Deoxygenated blood is removed from a central vein (femoral or internal jugular vein), pumped through a membrane leading to CO2 removal and oxygenation and returned pre-lung (central vein, right atrium, pulmonary artery) in the case of venovenous (VV) ECMO. In the case of venoarterial (VA) ECMO, blood can be returned to the femoral or axillary artery, left atrium, and the aorta. The carotid artery is usually used for VA ECMO in neonates and infants.
Components
1. Cannulas: Double-lumen flow directed (Avalon Elite; Maquet, San Jose, CA), drainage and perfusion cannulae inserted percutaneously or centrally.
Cannula size, mainly of the drainage cannula or component, is the major determining factor in total pump flow. Factors taken in consideration for selection are patient size and length.
2. Heparin-bonded (Carmeda; Medtronic, Minneapolis, MN) 3/8″ tubing.
3. Centrifugal pump (CentriMag; Thoratec, Pleasanton, CA or RotaFlow; Maquet, San Jose, CA).
Connected to monitoring console.
4. Oxygenator (Quadrox: Maquet, San Jose, CA).
Comprising two chambers (gas and blood) divided by a semipermeable hollow fiber membrane, allowing for carbon dioxide (CO2) and oxygen (O2) diffusion. CO2 is more soluble than O2 and diffuses easily through the membrane. CO2 clearance is, therefore, a result of gas flow (sweep gas) across the membrane. Oxygenation will be determined by pump flow and gas blender (O2/air); pump flow relative to the patient’s cardiac output will be the major determinant of the patient’s PO2.
Connected to heater/cooler for temperature management.
SURGERY
Venovenous (VV) ECMO
Venovenous (VV) dual cannulation strategy (Fig. 5.2)
Indication
Primarily for the patient with respiratory failure as a bridge to recovery or bridge to decision.
Advantages and Disadvantages
The advantages are: The technique is performed rapidly, often at the bedside, and does not require fluoroscopy or Transesophageal echo (TEE).
However, there is a higher incidence of recirculation, and as a result, it is difficult to extubate, or mobilize and exercise these patients. For patients in whom the decision is made to list for lung transplantation after the initiation of ECMO, this strategy can be used as a bridge to a different cannulation arrangement.
Figure 5.2 Venovenous dual site cannulation. The drainage and perfusor cannulas have to be distanced to prevent recirculation.
Concept: Blood Recirculation Fraction
With this cannulation arrangement, the inflow and outflow cannulas have to be separated by as much distance as possible to reduce the blood recirculation fraction.
Technique
The right neck and femoral areas are prepped in the sterile field, and the ECMO lines are divided and brought up. Right internal jugular access and femoral venous access (just above the inguinal ligament) are obtained using a 4-Fr micropuncture needle (Cook, Bloomington, IN), Seldinger technique, and 4-Fr introducer.
100 IU/kg of heparin is administered to the patient
The femoral vein is usually the site of the drainage cannula. We often choose a long (no. 23 to 25) multistage cannula.
The right internal jugular vein is usually the preferred site for the insertion of the perfusor cannula. We opt for an arterial no. 19 perfusor cannula.
Alternate sites for cannulation are the left internal jugular vein and and the subclavian vein, but we recommend that fluoroscopy be used during cannula insertion to prevent vascular injury if these alternate sites are considered.
After femoral access is obtained, a super-stiff Amplatz (Cook, Bloomington, IN) 0.038″ guidewire advanced to the level of the inferior vena cava (IVC) and right atrial (RA) junction. Successful venous dilatations are performed, followed by the insertion of the venous multistage cannula to the level of the diaphragm to prevent. The cannula is de-aired and connected to the inflow limb of the circuit.
Using the same technique, the perfusor is inserted and positioned to the level of the SVC-RA junction. Once de-aired and connected to the outflow limb of the ECMO circuit, time-out is performed to verify (1) the flow direction, (2) the absence of air entrapped in the circuit, and (3) adequate anticoagulation with an activated clotting time (ACT). Only then ECMO is initiated.
Caveats
Recirculation can be significant with this strategy. It can be suspected when a low arteriovenous O2 difference between the inflow and outflow limbs of the circuit. It worsens when pump flows are increased on ECMO. If the patient remains desaturated, it often requires a change in cannulation strategy.
Single cannula (Fig. 5.3): Dual-lumen flow directed cannula (Avalon Elite: Maquet, San Jose, CA)
Concept
A single cannula provides inflow and outflow. The inflow has an IVC and SVC port, and the outflow is flow directed and aimed at the tricuspid valve.
Indication
The best use of this technology is patient optimization prior to lung transplantation.
Advantages and Disadvantages
Single cannula in the upper body favors early extubation, mobilization, and ambulation.
Disadvantage is limitation of flow.
Figure 5.3 Dual-lumen flow directed cannula. The cannula is positioned with the drainage ports in the IVC and SVC. The reinfusion port and cannula flow is directed toward the tricuspid valve orifice under TEE guidance.
Prerequisite
Patent right superior vena cava (SVC).
Near-normal right ventricular (RV) function and no significant pulmonary hypertension (PH). However, the presence of a PFO (naturally occurring or catheter-created) may allow the support of a patient with pH with this cannulation strategy.
Cannula Selection
Based on ideal bodyweight for height. If possible, we aim to insert a no. 27-Fr or no. 31-Fr cannula in all patients to obtain adequate flows.
The patient’s vessels are assessed with a bedside ultrasound in the ICU.
OR Setup and Patient Positioning
Central lines are moved away from the right neck vessels.
We use both fluoroscopy and transesophageal echo during cannula insertion.
The patient is positioned supine on the OR table (reversed), with the head slightly turned to the right. The neck, chest, and abdomen to the level of the umbilicus are prepped into the operative field.
A scrubbed assistant is useful for wire control, and limiting the blood loss in between sequential dilatations and cannula insertion.
Technique
Using ultrasound guidance, the right internal jugular vein is accessed in the inferior third of the neck using a 4-Fr micropuncture needle (Cook, Bloomington, IN). Using a Seldinger technique, a 4-Fr introducer catheter is placed in the SVC.
One hundred International Units per kilogram (100 IU/kg) of unfractionated heparin is administered to the patient and the ECMO circuit lines are divided, brought up to the operative field, and secured in place.
Under fluoroscopic guidance, a super-stiff Amplatz 0.038″ guidewire (Cook, Bloomington, IN) is carefully positioned into the IVC.
A small incision is made in the neck, and the tract is sequentially dilated.
The Avalon cannula is then positioned on the wire and inserted with the outflow port directed toward the tricuspid valve orifice (critical step).
The cannula is positioned under fluoroscopic guidance with the tip of the catheter in the IVC, and the superior inflow port in the SVC. Once inserted, the cannula is difficult to rotate on its axis; therefore, orientation of the outflow port is critical as the cannula is being inserted.
The wire and dilator are removed, and the cannula is clamped in its inflow (inferior) and outflow (superior). De-airing is performed, followed by connection to the corresponding limbs of the ECMO circuit. An ECMO time-out is performed as previously described.
The cannula is then secured at the skin in multiple areas and is maintained to the patient’s head using a bandana. Certain groups have described a tunneled approach to provide additional stability to the cannula. The exiting site can be infra- or supraclavicular though the caveat is potential kinking of the cannula.
Central right atrial to pulmonary artery (RA-PA) ECMO (Fig. 5.4A–C)
Indications
Patient with PH and/or mild RV dysfunction.
Bridge to transplantation, to decision, or to recovery.
Prolonged anticipated need for ECMO support.
Patient Position
The operative table is reversed should a need for fluoroscopy guidance arise.
The patient is supine with the arms tucked in on the operative table.
Skin is prepped from the chin to the knees.
Very careful hemostasis is critical to the success of this procedure.
Technique
An upper midline incision is performed, and an upper hemisternotomy off the right edge is performed. Very careful hemostasis of the bone edges is performed and the marrow is controlled using Gelfoam. This approach is conducive to a subsequent lung transplantation via a midline sternotomy or a clamshell incision in the fifth intercostal space.
A Finochietto or Squarehole retractor is used and is expanded carefully.
The thymus is split and retracted, and the pericardium is opened and retracted with deep sutures to bring the heart into view, with extra care not to injure the phrenic nerve.
One hundred IU/kg unfractionated IV heparin is administered to the patient and the ECMO lines are divided and brought up to the field.
Two purse-string sutures are placed on the right atrium with pledgetted (pericardial or felt) 3-0 prolene. With gentle traction on the tourniquets, this helps bring the pulmonary artery into view. Two diamond-shaped purse strings are placed in the proximal main pulmonary artery (MPA), with great care taken to avoid the pulmonary valve.
Incisions for the cannulas are made at the inferior right costal margin (Fig. 5.4B). The lateral cannula will be the venous inflow, and the medial cannula, the arterial outflow in the pulmonary artery. Very carefully, tracts are made to reach the level of the upper sternotomy, avoiding the right pleural space if possible. A straight chest tube is used to bring the cannulas through the skin to avoid fatty deposition inside the cannulas.
The RA cannula (venous cannula no. 28 to 32) is inserted to ∼5 to 7 cm with an attempt to position the end at the IVC-RA junction to minimize suction events and flow interruption. It is de-aired and connected to the inflow limb of the circuit, as described.
Figure 5.4 A: Venovenous RA-PA surgical approach. B: The cannulas are tunneled from the right costal margin inside a straight thoracostomy tube. Right atrial and main pulmonary cannulations are performed. C: Final result and planning approach for bilateral lung transplantation.
The arterial cannula (no. 23 arterial) is inserted ∼2 to 3 cm with care to have the tip in the MPA. It is de-aired and connected to the outflow limb of the circuit, as described, and ECMO is initiated.
Two flexible drains (no. 19 Fr) are positioned in the pericardial space and will remain in place for the duration of ECMO.
The sternal edges are reapproximated with four (4) wires: One for the horizontal segment and three for the vertical portion.
Venoarterial (VA) ECMO
In the setting of PH and hypoxemia, some centers have advocated the use of VA ECMO as a bridge to transplantation. The cannulation strategy consists of using a venous drainage cannula inserted percutaneously via the right internal jugular vein, and an arterial outflow placed via a graft in the right axillary artery. This has allowed teams using this approach to mobilize the patients. However, the caveats of this technique are the higher incidence of upper extremity edema, brachial plexus injury, and bleeding in view of the need to keep the ACT in higher ranges than for VV ECMO (180 to 220 seconds). Historically, the patients transplanted after VA ECMO have had reduced survival though this data does not reflect the current early mobilization strategy.
POSTOPERATIVE MANAGEMENT
Management of the Patient on ECMO
ECMO for BTT requires an experienced and dedicated multidisciplinary team to be successful. The team should comprise cardiothoracic surgeons, intensivists, neuropsychiatrists, ECMO bedside specialists (perfusionists, respiratory therapists, and nurses), ECMO-trained bedside nurses, physiotherapists, nutritionists, and social workers.
ECMO flow is targeted to maintain the SaO2 >90%, and the sweep is adjusted to normalize PCO2 progressively. In terms of anticoagulation maintenance, we use an ACT target for 160 to 180 seconds for VV ECMO. Our goal is early extubation, management of anxiety and delirium, early mobilization and exercise program, and optimization of nutrition. The hemoglobin target >10 and platelet transfusion threshold is <20 K unless there is active bleeding. Antibiotherapy is directed at treating the active infections.
COMPLICATIONS
Delirium: Most patients on ECMO experience delirium at some stage. Often, they are intubated and heavily sedated at the time of ECMO initiation. Severe hypoxemia as a trigger to delirium causes neuropsychiatric states that are very challenging to control.
Stroke: Hemorrhagic, or embolic in the setting of a PFO or an atrial septostomy.
RV dysfunction: Often a result of severe PH, it results in hypoxemia and hypotension in patients with single or dual percutaneous approaches.
Hypoxemia: More often related to cannula malposition in percutaneous approaches. It can also be observed when the patient’s cardiac output increases. Some centers have reported little need to change flows during exercise. This has not been our experience; we have noted some desaturation with ambulation, even in our centrally cannulated patients. This can be ameliorated by increasing pump flows during exercise and keeping the hemoglobin at higher targets (>10 to 12).
Pericardial tamponade: From guidewire perforation during insertion of percutaneous cannulae, or as a result from mediastinal bleed when central cannulation is used. To reduce the incidence of this latter complication, we leave soft pericardial drains in place.
Stress gastritis, ulceration, GI bleeding: Often as a result of anticoagulation and platelet dysfunction. Our supported patients are kept on IV esomeprazole.
Platelet dysfunction: We have noticed a high incidence of platelet dysfunction in our patients supported on ECMO long term, often resulting in bleeding from venopunctures, nasoenteric tube insertion, etc. DDAVP can be administered in this setting and ameliorates the bleeding diathesis.
Transfusions: May result in increased patient sensitization prior to transplantation.
Thrombosis: Clot formation in circuit and around cannulae, requiring replacement of individual components, ECMO circuit and occasionally surgical intervention such as pulmonary embolectomy.
HIT and HITT: Requires the use of an alternate agent for anticoagulation such a Bivalirudin, and a non-heparin bounded circuit.
Component failure
Infection: It is important to avoid the excess use of antibiotics. Consultation with a transplantation ID specialist is often warranted.
CONCLUSIONS
In the context of acute respiratory failure, ECMO can be used as bridge to recovery, bridge to decision, or bridge to transplantation. In the recent era, the survival of patients transplanted after ECMO has significantly improved, possibly reflecting the new paradigm of patient optimization rather than salvage. Although controversy remains as ECMO results in reprioritization of patients in the lung allocation score (LAS) era, and lung donors are scarce. Thus, ECMO is carefully employed pre-lung transplantation with a goal to achieve correction of hypoxemia and acidosis, permit early patient extubation, mobilization and adherence to an exercise program, as well as optimization of their nutritional status prior to lung transplantation.
Recommended References and Readings
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