{'fraction_non_alphanumeric': 0.027697395618023975, 'fraction_numerical': 0.007992283312663636, 'mean_word_length': 5.1042893187552565, 'pattern_counts': {'":': 0, '<': 1, '<?xml version=': 0, '>': 1, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
VV-ECMO for surgical cure of a critical central airway obstruction

Extracorporeal membrane oxygenation (ECMO) is a form of prolonged cardiopulmonary bypass that has extensively been used in critically ill patients in an intensive care setting. Both veno-venous (VV-) and veno-arterial (VA-) ECMO have been described as a perioperative rescue or replacement of endotracheal intubation in the setting of extrinsic airway compression due to a mediastinal mass. In this paper, we will outline the utility of ECMO in the context of extrinsic airway compression and will use an illustrative case to examine how ECMO can be useful during severe airway obstruction. Our patient successfully underwent surgical resection of the mass while on VV-ECMO. His symptoms resolved quickly and is now back to his baseline quality of life.


Introduction
Extracorporeal membrane oxygenation (ECMO), also known as extracorporeal life support (ECLS) is a form of prolonged cardiopulmonary bypass that has extensively been used in critically ill patients in an intensive care setting. Its use has increased dramatically, with nearly 10,000 cases in 2017, compared to < 5000 before 2012 [1]. Its applications are diverse and largely for supportive measures only, typically in the context of severe acute respiratory distress syndrome (ARDS) [2]. However, ECMO by veno-venous route (VV-ECMO) and veno-arterial route (VA-ECMO) have also been extensively described as a perioperative rescue or replacement of endotracheal intubation in the setting of extrinsic airway compression due to a mediastinal mass [3][4][5]. In this paper, we will outline the utility of ECMO in the context of extrinsic airway compression. We present an illustrative case to examine how ECMO can be useful during severe airway obstruction when endotracheal intubation poses a significant risk of intraoperative airway compromise in this setting.

Case report
A 72-year-old man with a history of hypothyroidism on replacement was transferred to our hospital due to concern for impending airway compromise in the setting of a large mediastinal mass. He began to develop 2 days of evolving shortness of breath on exertion with worsening hoarseness of his voice. His physical exam was only notable for a hoarse voice. A computed tomography (CT) scan of the chest with contrast revealed a large, complex, diffusely hypodense, partially calcified mass of size 9.3 × 9.5 × 7.7 cm in the mediastinum that appeared to originate from the left thyroid lobe. It significantly narrowed the trachea to a maximum diameter of roughly 2 mm and displaced it toward the right (Figs. 1 and 2). Despite the luminal airway compromise, he was normoxemic and hemodynamically stable. In the weeks that followed, multiple multidisciplinary discussions took place between pulmonary, critical care, and cardiothoracic surgery consultants regarding the safest operative approach to this case.
Nasal bronchoscopy demonstrated difficulty in reaching the distal trachea due to extrinsic obstruction. It was deemed too narrow to pursue standard sedation regimens with endotracheal intubation. Rigid bronchoscopy with ECMO on standby was considered but was also deemed too risky with the dramatically narrow caliber of his airway. Further multidisciplinary discussion yielded a decision to use VV-ECMO to maintain gas exchange during surgery.
Under general anesthesia, the patient was subsequently cannulated for VV-ECMO using (19 and 21 Fr) femoral venous cannulas with the Cardiohelp ECMO system. The mass was then removed surgically via median sternotomy. After surgery, an endotracheal tube was safely placed, the patient was weaned off VV-ECMO, and was extubated the following day. He tolerated the surgery well. Pathology revealed that this presumed goiter was a follicular adenoma. One week after surgery, the patient was discharged from the hospital and has been doing well from a symptomatic standpoint. He is now back to his baseline quality of life, though his hoarseness persists due to recurrent laryngeal nerve dysfunction.

Discussion
As demonstrated by this case, ECMO can be used as a support for gas-exchange intraoperatively when it is deemed too risky to pursue endotracheal intubation. The successful use of ECMO in this setting is widely apparent in the pediatric population, but less so in the adult population, so we feel our case can help to bring attention to a plausible alternative to intubation in such a clinical scenario. In our patient, we successfully used VV-ECMO as replacement with no post-operative complications, and stable findings from a symptomatic standpoint thereafter.
Shao et al., proposed that ECMO brings several advantages over traditional cardiopulmonary bypass which include: allowing a longer duration of use, less heparin use and subsequent bleeding, and less red cell damage [7]. Bechard et al. described the high risk of perioperative life-threatening respiratory complications in patients with significant cardiac and respiratory symptoms at presentation and tracheal compression > 50% [6]. With this in mind, we pursued VV-ECMO as an alternative to endotracheal intubation with sedation.
VA-ECMO, as used by Shao et al., provides both cardiac and pulmonary support and is largely indicated in severe cardiogenic shock, defined by decreased cardiac output and myocardial contractility resulting in tissue hypoperfusion [7,10]. Although use of ECMO in our patient's setting is not part of the list of ECMO indications, it has still been repeatedly demonstrated as a viable option to minimize perioperative respiratory complications due to obstruction of the airway. As our patient showed no evidence of impending cardiac failure, and required largely only pulmonary support, VV-ECMO was chosen over VA-ECMO.
A review of the literature regarding the use of ECMO in other patients used as a replacement for endotracheal intubation when there are concerns of significant extrinsic airway compression from mediastinal masses is warranted [3][4][5][6][7][8]. The mediastinal masses in these cases were of varying etiologies, including: goiter, plasmacytoma, seminoma, lymphoma, and in our patient, follicular adenoma (Table 1) [3][4][5][6]. Shao et al., described severe rheumatoid arthritis as a major influencing factor into their decision to pursue ECMO over endotracheal intubation [7]. This is in addition to the risk of airway compromise from airway compression that was already present from the patient's goiter. It is also interesting to note that Nokes et al., had used ECMO for bronchial stenting rather than for surgery [3]. This was a palliative intervention in a patient with metastatic multiple myeloma. This diverse use of ECMO as a bypass in such settings is truly remarkable, and perhaps there are more scenarios in which ECMO can be used in a similar fashion which have yet to be demonstrated. We strongly believe more clinicians should be aware of this alternative treatment option in the setting of extrinsic airway compression. Given the clinical rarity of this kind of condition, we hope that this case will contribute greatly to the current literature.

Conflicts of interest
None of the authors have any conflicts of interest to disclose.

Financial disclosures
None.