Abstract
The utilization of extracorporeal membrane oxygenation (ECMO) in complex thoracic surgery has become more frequent in recent years due to advances in technology, increased availability, and improved outcomes. ECMO has emerged as a vital tool to facilitate thoracic surgery for patients who would have otherwise been deemed unsuitable candidates. It has redefined the boundaries of surgical possibility where conventional methods fall short. ECMO is typically employed in specific thoracic surgery where conventional ventilation is either inadequate or it interferes with the surgical field, and in procedures demanding both ventilatory and hemodynamic support.
1
Introduction
The mechanical circulatory support (MCS) era began in 1953 with the development of cardiopulmonary bypass (CPB) to facilitate open heart surgery [ ]. Extracorporeal life support (ECLS) techniques such as CPB have been used for decades since then to assist complex thoracic surgery. However, less invasive MCS techniques, such as extracorporeal membrane oxygenation (ECMO), have been increasingly used in recent years due to advances in technology, increased availability, and improved outcomes [ ]. Similarly, in recent years ECMO has been increasingly utilized to provide respiratory and hemodynamic support to facilitate elective and emergency situations during complex thoracic surgery for patients previously deemed too high risk or not suitable for surgery [ ].
In this review, we address indications for ECMO use in complex thoracic surgery, ECMO configurations, key ECMO physiology, and practical intraoperative management considerations.
2
Extracorporeal membrane oxygenation vs cardiopulmonary bypass
ECMO has been increasingly used as an alternative to CPB for selected complex thoracic surgeries [ ]. When planning a complex thoracic surgical technique that may require extensive pulmonary or circulatory support, it is reasonable to consider the risks and benefits of using CPB versus ECMO. Major differences exist between the two ( Table 1 ).
| Cardiopulmonary Bypass (CPB) | Extracorporeal Membrane Oxygenation (ECMO) | |
|---|---|---|
| Circuit Components |
|
|
| Anticoagulation |
|
|
| Duration |
|
|
ECMO has several advantages for use in thoracic surgeries compared with CPB. Modern ECMO circuits are more biocompatible, simpler, and safer. Due to its comparatively smaller size, the ECMO circuit requires lower priming volumes, thus resulting in ess hemodilution. ECMO is a closed circuit without a venous reservoir, which eliminates the air–blood contact that occurs with CPB. Additionally, ECMO circuit tubing, unlike CPB tubing, is coated with a biocompatible, heparin-coated lining, decreasing the need for full systemic anticoagulation that is required in CPB. The aforementioned features of the ECMO circuit result in a decreased systemic inflammatory response, which clinically translates into less coagulopathy and a lower risk of bleeding, thrombosis, and need for blood transfusions [ ]. When peripheral ECMO cannulation is used, the surgeon gains an unobstructed operative field. Finally, in emergent situations where full cardiopulmonary support is required, it is possible to convert a VA ECMO circuit into conventional CPB by adding a venous reservoir.
There are some disadvantages of using ECMO compared to CPB. CPB circuits contain venous reservoirs which allow for large and rapid volume shifts that cannot be performed with ECMO. CPB allows the filtration of air, so it should be utilized when venous structures or cardiac chambers are dissected. While most on-pump cardiac surgeries also use cell savers to reprocess and return lost blood, CPB has the advantage of easy recirculation of salvaged blood through a cardiotomy suction. Cell saver is the only option for blood salvage if ECMO is utilized. However, salvaged blood might not even be used if the thoracic case is oncologic in nature. Additionally, CPB circuits contain infusion ports and stopcocks that can be used to administer medications directly through the circuit. ECMO does not have these ports, so all intravenous medications and fluids must be administered directly to the patient.
Mini-cardiopulmonary bypass (mini-CPB) systems present another option instead of a traditional CPB system, and their use is increasing in selected patients populations. Advantages include biocompatible coating of the circuit, shed blood separation, venous and arterial air filters, and a reduced priming volume, similar to an ECMO circuit. Additionally, vaporized halogenated volatile anesthetic can be added into the circuit with a fresh gas flow applied to the oxygenator. Disadvantages of mini-CPB include lack of venous reservoirs for volume management in the setting of massive bleeding and close proximity of CPB console to the OR table due to short tubing.
3
ECMO in thoracic surgery
The application of ECMO in thoracic surgery is continually increasing due to improved ECLS technology that increases safety and ease of use. Here, we review the most common thoracic surgical procedures that can benefit from the use of ECMO. The discussion of ECMO applications will be based on their intended purposes. ECMO is typically employed in specific thoracic surgery where conventional ventilation is inadequate, such as in cases where traditional ventilation may interfere with the surgical field (extensive lower airway surgery), and procedures demanding both ventilatory and hemodynamic support (large anterior mediastinal mass resections or tumors extending into the heart or large vessels) or in patients with low cardiopulmonary reserve. In general, in the case reports of ECMO utilization in thoracic surgery the outcomes have been overall positive, with the patients surviving their operations without major complications. Successful outcomes require close communication among the surgeon, anesthesiologist, and perfusionist in the operating room. However, it is worth noting that the current evidence primarily originates from well-experienced ECMO centers specializing in major thoracic surgery procedures [ ].
4
Indications for ECMO-assisted thoracic surgery
4.1
Inadequate ventilation
Thoracic surgery is often performed using one lung ventilation (OLV), which can lead to inadequate ventilation in patients with low pulmonary reserve due to previous lung resections and/or underlying pulmonary disease. Preoperative pulmonary function tests (PFTs) as well as split lung function tests can serve as predictive indicators for intraoperative hypoxemia and postoperative pulmonary capacity. Nonetheless, the feasibility of conducting these tests is not guaranteed, and unforeseen intraoperative ventilation issues may still arise despite reassuring preoperative results. While there are no defined indications or guidelines on when to initiate ECMO support due to limited preoperative pulmonary reserve, there are useful predictors to consider when making this clinical decision. The incidence of intraoperative hypoxemia (generally defined as P a O 2 less than 60 mm Hg when ventilating with an FiO 2 of 100 %) during one lung ventilation may be higher with a right sided thoracotomy, low P a O 2 during two lung ventilation, BMI greater than 30 kg/m 2 , unfavorable lung perfusion scan results, and history of prior lobectomy or pneumonectomy [ ]. The presence of any of these predictors in a patient with known intrinsic pulmonary parenchymal disease of the nonoperative lung could risk a situation of inadequate or impossible ventilation. In these scenarios, it is reasonable to consider the use of veno-venous (VV) ECMO to provide additional respiratory support. Reported successful uses of ECMO in thoracic surgery include bullectomy and lobectomy in patients with severe emphysema, bilateral lung lavage for alveolar proteinosis in patients with severe disease, lung resection following a contralateral pneumonectomy, surgery on the contralateral lung with broncho-pleural fistula, and in patients undergoing esophagectomy post left pneumonectomy [ ].
4.2
Complex lower airway surgeries
The tracheobronchial tree serves a vital role in facilitating ventilation. Any complex intervention on these structures poses a unique challenge to both surgeons and anesthesiologists. The most common technique to maintain adequate ventilation and oxygenation in these procedures is cross-field ventilation. This method provides a secure mode of ventilation, but endotracheal tubes and circuit lines in the operating field may impair surgical access and visibility. In advanced carinal and tracheal reconstructive surgeries using available conventional cross-field ventilation techniques, adequate ventilation may not always be achieved, leading to severe hypoxemia, hypercarbia or hemodynamically instability, especially in patients with low cardiopulmonary reserve [ ]. Jet ventilation is another technique that can be used to ventilate patients undergoing advanced airway reconstructive surgeries. However, jet ventilation can be inadequate in patients with severe COPD or obesity, carries a risk of barotrauma in susceptible lungs, and may potentially cause spilling of mucosal tumor cell spread [ ]. In situations where cross-field or jet ventilation techniques are unsuitable, VV ECMO can be utilized as an alternative. VV ECMO-assisted airway surgery provides an unobstructed and motionless surgical field, allowing for unlimited time to complete extended resections and reconstructions while maintaining adequate ventilation and oxygenation [ , ].
4.3
Advanced cardiovascular resections
Surgical resection of advanced cardiovascular tumors involving the pulmonary vasculature, atria, and aorta are usually accomplished using CPB support due to need for respiratory as well as circulatory support. Veno-arterial (VA) ECMO is an alternative that can provide total circulatory support with an improved risk profile for selected tumor resection cases requiring reconstruction of the superior or inferior vena cava, the pulmonary vessels, the left atrium, and the distal aorta with excellent outcomes [ , ]. Centers performing major thoracic resections can consider ECMO as an alternative to CPB for respiratory and/or circulatory support for these cases.
4.4
Anterior mediastinal masses
Large mediastinal tumors can compress the trachea, major blood vessels, and the cardiac chambers. Probably the most challenging situation is an anterior mediastinal mass compressing the bronchus on one side and the pulmonary vessels contralaterally. In awake patients, the negative pressure created during inhalation helps counteract this compression. However, general anesthesia with positive pressure ventilation in the supine position in conjunction with muscle relaxation can potentially eliminate this effect, leading to critical airway obstruction and/or a severe decrease in cardiac output. VA ECMO initiation prior to induction of anesthesia can prevent the potentially catastrophic hemodynamic collapse from a large anterior mediastinal mass [ , ].
4.5
Thoracic emergencies
ECMO can be used in thoracic emergencies as a life-saving intervention to improve ventilation and hemodynamics. The decision between the use of VV and VA ECMO in emergency situations depends on the need for immediate oxygenation with the simultaneous need for hemodynamic support. Emergencies such as severe tracheo-bronchial injuries, blunt chest trauma causing severe pulmonary parenchymal injury, inhalational injuries, pulmonary embolism, and life threatening hemoptysis are examples of critical scenarios where ECMO use has been reported [ , ].
5
The ECMO circuit and configurations
A standard ECMO circuit consists of two cannulas for vascular access, a mechanical blood pump, and a gas exchange device (an oxygenator) with an incorporated heat exchanger that are interconnected with the conduit tubing to form a closed-loop system ( Fig. 1 ). The circuit also includes a control console with monitoring ports and sensors that are strategically placed throughout the circuit to regulate blood flow, pressures, and oxygen levels. The blood is drained through the drainage cannula from the venous system, circulated through the ECMO pump for oxygenation, and reinfused either into the venous system (VV ECMO) or into the arterial system (VA ECMO).
5.1
VV ECMO
In VV ECMO, deoxygenated blood is drained from a cannula that is commonly inserted into the femoral vein targeting the right atrium. Venous blood passes through the oxygenator for oxygenation and carbon dioxide removal. Oxygenated blood is then returned into the right atrium via a return cannula, which is most commonly placed into the right internal jugular or the contralateral femoral vein. VV ECMO only provides gas exchange support, relying on the patient’s native cardiac output to pump oxygenated blood into the systemic circulation to maintain adequate perfusion. VV ECMO can be established using various configurations. In the classic configuration, VV-ECMO can be achieved with a femoral venous cannula, advanced to the junction between the inferior vena cava (IVC) and the right atrium (RA), for drainage and a right internal jugular (IJ) venous cannula, advanced through the superior vena cava (SVC) into the RA, for blood return. This configuration is known as “Fem-IJ” VV ECMO ( Fig. 2 A). When cannulation of the internal jugular is technically challenging, an alternative configuration involves bilateral femoral cannulation. The tip of the drainage venous cannula is placed in the IVC while the tip of the return cannula is positioned into the RA. This configuration is known as “Fem-Fem” VV ECMO ( Fig. 3 ). Additionally, VV-ECMO can also be established via a single site using a dual lumen cannula. This is usually inserted via the right IJ or left subclavian vein. Deoxygenated blood is drained via ports on the cannula that are located in the SVC and IVC, and oxygenated blood is returned via a port located in the RA facing towards the tricuspid valve ( Fig. 2 B). A big limitation of a dual lumen cannula is a maximum flow of 4.3 LPM with a 27 Fr cannula.
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