Extracorporeal life support in thoracic surgery

INTRODUCTION

The use of extracorporeal life support (ECLS) techniques is increasing in the setting of general thoracic surgery, lung transplantation (LTx) and cardiorespiratory failure. Depending on the technique used, ECLS can provide a short- to mid-term extracorporeal mechanical support, help in carbon dioxide (CO₂) clearance, aid in oxygen (O₂) enrichment and provide cardiocirculatory support. The objective of the ECLS techniques is to supply the failing respiratory and/or cardiocirculatory system(s) to facilitate recovery (bridge to recovery), transplantation (bridge to transplantation), change to another ECLS device or configuration (bridge to bridge) or change of care strategy (bridge to decision).

‘ECLS’ is a generic term that includes all extracorporeal mechanical cardiorespiratory support techniques. In thoracic surgery, the commonly used ECLS techniques are (i) extracorporeal membrane oxygenation (ECMO), (ii) pumpless interventional lung assist device ‘Novalung’ (Xenios AG, Heilbron, Germany) and (iii) extracorporeal CO₂ removal (ECCO₂R). From a clinical standpoint, ‘ECLS’ and ‘ECMO’ are two separate terms; ‘ECLS’ provides cardiorespiratory support, whereas ‘ECMO’ is limited only to respiratory support. In this article, we will use the term ‘ECLS’ as the generic term for all extracorporeal mechanical techniques available.

The physiology of the ECLS is based on 4 cardinal points: (i) oxygenation depends on the ECLS blood flow; (ii) CO₂ clearance depends on the gas flow through the membrane (sweep gas flow); (iii) providing haemodynamic support by an injection at a systemic arterial site and (iv) maintaining optimal oxygenation to the vital organs (brain, heart and lungs) by an ECLS inflow directed to the right atrium.

This editorial aims at summarizing the rationale behind the main ECLS techniques used in thoracic surgery, clinical indications and results of ECLS.

EXTRACORPOREAL LIFE SUPPORT TECHNIQUES USED IN THORACIC SURGERY

The ECLS techniques used in thoracic surgery are listed in Table 1.

Extracorporeal membrane oxygenation

Venovenous extracorporeal membrane oxygenation

Venovenous (VV) ECMO is the most frequently used ECLS technique in thoracic surgery. In fact, VV ECMO is the gold standard for severe and refractory adult respiratory failure. VV ECMO allows optimal oxygenation of the vital organs by an inflow directed to the right atrium and the capacity to reach very high blood flows. VV ECMO is indicated in case of isolated or primary respiratory failure; its circuit includes 2 cannulae or a single double-lumen cannula (Avalon Elite double-lumen catheter; Maquet Cardiopulmonary GMbH, Rastatt, Germany) inserted percutaneously through the peripheral veins. Double-site VV ECMO is able to provide the highest blood flow and consequently enables the highest oxygen demands to be met. Single-site VV ECMO has the main advantage of keeping the groins free and therefore may be used in an ambulatory patient. The inflow lumen of this cannula is smaller than the lumen of a ‘conventional’ injection cannula. Hence, because of higher circuit resistances, blood flow and oxygenation capacity will be reduced and haemolysis will be increased. Moreover, the double-lumen cannula insertion needs guidance (transthoracic or transoesophageal echocardiography and fluoroscopy) for adequate positioning, prevention of right ventricular injury and optimal functioning.

Venoarterial extracorporeal membrane oxygenation

Venoarterial (VA) ECMO is an ECLS technique that is used to support cardiorespiratory failure. An arterial injection site is aimed at providing haemodynamic support, but the quality of oxygenation to the vital organs depends on the insertion site of the inflow cannula: (i) low in case of peripheral VA ECMO and (ii) optimal in case of central VA ECMO. The suboptimal oxygenation to the vital organs in peripheral VA ECMO is explained by the conflict between the retrograde ECMO flow and the antegrade cardiac flow (ECMO-related Harlequin syndrome: combination of a cyanotic/hypoxaemic upper part of the body and a normal lower hemibody). On VA ECMO for circulatory failure, oxygenation may also be critically compromised. It is explained by the increase in the left ventricular afterload and constitution of an iatrogenic acute lung oedema. This scenario is generally successfully managed by performing a left ventricular discharge (septostomy or insertion of an extra left-discharge cannula). In peripheral VA ECMO, it is strongly recommended to utilize a reperfusion cannula to preserve the cannulated limb from ischaemia.

The ‘sport model ECMO’ is another configuration of VA ECMO using the right subclavian/axillary artery (or the innominate artery for small patients) and the right internal jugular vein as injection and drainage sites, respectively. It allows physical therapy and ambulation in awake patients [1, 2].

Other extracorporeal membrane oxygenation configurations

In peripheral VA ECMO, additional venous drainage cannula can be added to the circuit with the aim of compensating for an insufficient backflow. This configuration represents the venovenous–arterial ECMO (VV-A ECMO). In addition, venous–arteriovenous ECMO (V-AV ECMO) is made by the addition of a second injection cannula. V-AV ECMO combines the characteristics of both VV and peripheral VA ECMO. V-AV ECMO is generally switched from a VV ECMO or a peripheral VA ECMO to add circulatory support or improve oxygenation of the vital organs, respectively.

The pumpless interventional lung assist ‘Novalung’

The Novalung device was initially used for CO₂ clearance as a pumpless femorofemoral arteriovenous (AV) ECMO and is currently used in his central configuration.

Central Novalung

By instituting a pulmonary artery to the left atrial system oxygenation shunt, the PA-LA Novalung represents an ECLS technique that mainly allows for a significant gas exchange with appropriate oxygenation to the heart and the brain as well as remodelling of the right ventricle. The flow through the PA-LA Novalung is obtained through the gradient of pressures between the pulmonary vascular resistances and the gas exchange membrane. This technique successfully allows bridging to LTx in patients with respiratory failure and/or cardiogenic shock due to end-stage pulmonary artery hypertension (PH) and obviates combined heart/lung transplantation by facilitating right ventricular recovery [3, 4].

Extracorporeal carbon dioxide removal

ECCO₂R uses small (14–24 Fr) catheters enabling a sort of ‘respiratory dialysis’. Implanted percutaneously, ECCO₂R devices produce a partial but significant decarboxylation. Therefore, this ECLS technique is indicated to correct isolated hypercapnic failure. ECCO₂R was initially performed for chronic obstructive pulmonary disease exacerbations and is now routinely used in fibrosis and cystic fibrosis patients [5].

INDICATIONS FOR EXTRACORPOREAL LIFE SUPPORT IN THORACIC SURGERY

The indications for ECLS are listed in Table 2.

Acute respiratory distress syndrome

ECLS is used in the management of severe and refractory acute respiratory distress syndrome (ARDS). ARDS is characterized by significant O₂ requirement, systemic inflammatory response syndrome, and an initially preserved cardiocirculatory function. In this setting, ECLS must be associated with a protective ventilatory strategy. In ARDS, double-site VV ECMO appears to be the most suitable ECLS strategy. In haemodynamic failure secondary to ARDS, VV ECMO remains the first therapeutic option, reserving VA ECMO for conversion for refractory hypotension [6]. Several ongoing prospective randomized trials are assessing the results and exact role of ECMO in ARDS [7]. However, it is currently validated that ARDS should be treated in renowned ARDS centres that are able to perform ECMO [8]. ECLS, and particularly VV ECMO, improves the survival of patients in case of severe and refractory ARDS following pulmonary resections [9].

Lung transplantation

Bridge to lung transplantation

The selection of the ECLS technique depends on the level of O₂ requirement and the presence of concomitant PH. In this setting, the aim of the ECLS is 2-fold: restore haematosis and patient’s fitness to transplantation to achieve better LTx outcomes. The clinicians should be focused on performing a VV ECMO in awake/ambulatory/active strategy using a single-site VV ECMO. Nevertheless, a significant systemic inflammatory response syndrome may inhibit the initial awake strategy. Rarely, the level of O₂ requirement demands the use of a double-site VV ECMO. According to reports, the results of ECMO used as a bridge to LTx in terms of percentages of transplanted patients and 1-year survival rates range from 25% to 100% and from 75% to 93%, respectively. Two factors significantly improve post-LTx outcomes: the initial diagnosis of cystic fibrosis and the use of an awake/ambulatory ECLS strategy [10–14].

Bridge to lung transplantation in patients with pulmonary arterial hypertension

In patients with end-stage PH, the use of VV ECMO could be detrimental because it would increase the right ventricular preload. In this clinical scenario, the aim of the mechanical support is to (i) decrease the right ventricular afterload allowing the right ventricular remodelling (ii) ensure the haematosis (oxygenation of the heart and the brain and decarboxylation).

Therefore, the frequently used ECLS techniques are the PA-LA Novalung (which is usually preceded by the use of peripheral VA ECMO), the ‘sport model’ ECMO and (iii) the central VA ECMO.

This strategy allows clinicians to significantly reduce the mortality of PH patients on the waiting list and to widen the indications for bilateral LTx [3, 4]. Another possible successful ECLS option is a single-site VV ECMO with an inflow directed through a patent foramen ovale or an atrial septostomy [15].

Extracorporeal life support as an intraoperative support

VA ECMO is an ECLS technique that is electively used during LTx. Compared with conventional cardiopulmonary bypass, the following advantages of ECLS have been demonstrated in the experience of authoritative lung transplant programmes: a reduced requirement for dialysis post-LTx, a lower risk of bleeding, a reduced rate of blood products transfusion, a lower rate of primary graft dysfunction (PGD) and a shorter ICU and hospital length of stay [16, 17]. Either central or peripheral VA ECMO can be used as an intra-LTx support. Central VA ECMO has several advantages:

• It ensures a high blood flow using a large inflow cannula in association with a large double-stage outflow cannula.

• It avoids peripheral ECMO-related issues such as blood flow insufficiency, limb ischaemia, vessel injury and groin infection.

On the contrary, peripheral VA ECMO has the following characteristics:

• It frees chest from cannulae and preserves the sternum from a Clamshell incision.

• It can be inserted prior to anaesthesia induction under local anaesthesia.

• It can be more easily maintained after LTx, in case of refractory hypotension or pre-existing PH.

Nevertheless, VA ECMO does not include suction and cardiotomy reservoir. With this indication, it is recommended to use VA ECMO in association with an autotransfusion device. Conventional cardiopulmonary bypass may be preferred in case of high risk of bleeding and/or if the cardiac cavities are significantly dilated.

Extracorporeal life support as bridge to recovery in severe primary lung graft dysfunction

ECLS is used in refractory Grade 3 PGD. In this setting, VV ECMO represents the most suitable ECLS strategy. The choice between the double-site and the single-site VV ECMO configuration depends on the levels of O₂ requirement. High levels of O₂ requirement would lead to a double-site strategy. In Grade 3 PGD, VA ECMO should be used as a second-line strategy for persistent haemodynamic failure. Survival rates post-LTx are increased (50–80%) if early (<48 h post-LTx) ECLS support is provided, while mid-term survival and pulmonary function tests are not affected by the initial ECLS requirement [18, 19].

Extracorporeal life support after lung transplantation in patients with pulmonary arterial hypertension

Post-LTx, patients with preoperative PH are at high risks of carrying left ventricular diastolic dysfunction and Grade 3 PGD. The Vienna and Hanover groups performed prophylactic awake VA ECMO strategies and reported good results with regard to survival, hospital length of stay and Grade 2/3 PGD [20, 21]. Although the use of VA ECMO is validated postoperatively in PH patients, its prophylactic use in these patients remains debatable.

Chest trauma

The need for ECLS may arise in case of polytrauma or isolated chest injury. The selection of the ECLS technique depends on the type of support required; in particular, VA ECMO is indicated in case of myocardial contusion with refractory hypotension, whereas double-site VV ECMO is used in case of severe and refractory ARDS. In the event of haemorrhage or high risk of bleeding, ECLS may be used without heparin within 24–72 h of the trauma without affecting survival [22]. In trauma-related ARDS, VV ECMO did not increase the number of ICU-related complications and actually improved the 60-day survival rate (64.7 vs 23.5%; P = 0.01) [23].

Extracorporeal life support in general thoracic surgery

Pulmonary resection following pneumonectomy

A large number of case reports demonstrate that VV ECMO is a suitable ECLS technique to improve haematosis during pulmonary resection following pneumonectomy or in patients with severe respiratory insufficiency with difficult one-lung ventilation [24, 25].

Tracheobronchial surgery

Several case reports and small cohort studies have reported the successful use of ECLS for tracheal procedures or endoscopic interventions [26, 27].

Lung volume reduction surgery

Few case reports describe the use of ECLS as perioperative support for lung volume reduction surgery. ECLS facilitates a safer and more feasible surgery, particularly in severe hypercapnic patients. This indication remains a matter of controversy, given the results of the National Emphysema Treatment Trial (NETT) [24, 28].

Pulmonary embolectomy and pulmonary endarterectomy

VA ECMO is frequently used in pulmonary embolism with cardiogenic shock using mobile ECMO units, if necessary. ECMO requirement after pulmonary embolectomy seems to be a predictive factor for hospital death [29, 30].

VV or VA ECMO can also be used after pulmonary endarterectomy in case of persistent pulmonary hypertension or major pulmonary oedema [31].

Pulmonary alveolar proteinosis

VV or even VA ECMO with alveolar lavage is used as an effective association to support patients with pulmonary alveolar proteinosis [32, 33].

CONCLUSIONS

ECLS is an important technological addition to the thoracic surgeon’s therapeutic armamentarium. ECLS indications are currently being extended because of improved scientific knowledge, standard-of-care strategies and biomedical engineering solutions.

With regard to ARDS, it is demonstrated that patients should be referred to ARDS centres that are able to provide a wide spectrum of care, including VV ECMO [34, 35]. The results of VV ECMO itself are debatable and currently evaluated in prospective, multicentre trials. In the field of LTx, the efficacy of the ECLS techniques is confirmed and validated by leading programmes in LTx. In fact, it has been demonstrated that ECLS supplies the failed vital function(s), bridges patients to transplant in optimal conditions and improves post-LTx outcomes. The other indications are less described, but, as an example, the literature highlights the feasibility and efficacy of ECLS during the perioperative period of various thoracic surgical procedures. Nevertheless, according to the Extracorporeal Life Support Organization (ELSO) guidelines, it is highly recommended to perform ECLS in a tertiary medical centre that is centrally located with tertiary-level medical/surgical neonatal/paediatric/adult intensive care units. It is essential to keep in mind that the complexity in caring for these critically ill patients does not lie in the insertion of the device—which is an easy procedure—but the overall management during the entire pre-, per- and post-ECLS courses. For this reason, the development of an ECLS programme requires institutional commitment, advanced technology and equipment and multidisciplinary cooperation of trained specialty personnel [36, 37].

One of the main difficulties is the selection of patients and the time to start ECLS. Currently, there are no clinical scores and reliable biophysical or biological markers to decide whether or not an ECLS technique should be used. The experience of a multidisciplinary ARDS/LTx centre remains the best assurance to improve the survival of these critically ill patients so far.

ECLS experts should optimize their fundamental and clinical knowledge with regard to techniques. Nevertheless, the practice of the ECLS in thoracic surgery is now based on strong evidence.

ACKNOWLEDGMENTS

The authors thank Ilana Adleson for expert editorial review of the manuscript.

Conflict of interest: none declared.

REFERENCES