Worakij Chalermskulrat, MD and Namita Sood, MD
The University of North Carolina at Chapel Hill, Chapel Hill, NC
Case Presentation
BC is a previously healthy 20-year-old college student who had a prior two-week history of upper respiratory illness and failed to improve with a course of oral antibiotics. He subsequently developed productive cough, progressive shortness of breath and presented to the urgent care with respiratory distress. He had no fever, night sweats, chest pain, weight loss, dysphagia or hoarseness of voice. On physical exam, he was alert, afebrile, tachypneic and using accessory respiratory muscles. The lung exam revealed poor air movement with inspiratory and expiratory stridor and wheezing. The rest of the exam was unremarkable. CXR revealed a 15-cm anterior mediastinal mass without tracheal narrowing or deviation. Laboratory studies were within normal limits. His respiratory distress progressed very rapidly upon admission. The arterial blood gas had a pH of 7.40, PaCO2 37 mm Hg, PaO2 66 mm Hg and O2sat 95% on 100% FiO2. A trial use of heliox failed to result in any clinical improvement. A direct fiberoptic laryngoscopy was unrevealing. He was emergently endotracheally intubated under general anesthesia in order to secure his airway and for a possibility of tracheostomy. CT scan of the neck and chest showed a large homogeneous mediastinal mass encasing all superior mediastinal structures and causing subtotal external compression of the trachea, carina, and especially the left main stem bronchus. There were atelectasis of the left lower lobe, a small left pleural effusion, hyperinflation of the right lung, and a pericardial effusion. He received intravenous corticosteroids and one fraction of radiation therapy. His hypoxemia eventually resolved with low-tidal volume mechanical ventilation. Subsequently a mediastinoscopy and Chamberlain procedure were performed and the mass was biopsied. He was continued on radiation therapy, intravenous steroids and antibiotics with rapid clinical and radiographic improvement. He was successfully extubated on hospital day six. The pathology was most consistent with lymphoblastic lymphoma or T-cell acute lymphoblastic leukemia (ALL). Staging procedures revealed a nonmalignant, uncomplicated pleural effusion and was negative for extrathoracic involvement. He was treated with an intensive ALL-type chemotherapy protocol.
Discussion
The airway management for extrinsic airway compression caused by rapidly growing medistinal masses represents a therapeutic challenge. It is crucial to assess the severity of obstruction at both the tracheal and bronchial levels after excluding extrathoracic obstruction. Signs and symptoms are not reliable tools. CT scan of the chest permits thorough evaluation of tumor extension and accurate measurement of the airway diameters.
Tracheostomy would prove futile if the obstruction is distal to the trachea. Moreover the use of general anesthesia for tracheostomy may adversely enhance the effect of the extrinsic compression as a result of the reduction in lung volume, relaxation of bronchial smooth muscles, and a reduced transpleural pressure gradient. This may lead to a total airway obstruction and cardiopulmonary arrest. In a study of 50 children, those with greater than 50% reduction of the cross-sectional area of the airway as measured on the CT scan developed near total or total airway obstruction during induction or emergence from general anesthesia(1) and it is recommended to have their femoral vessels cannulated in readiness for cardiopulmonary bypass(2). Therefore awake intubation is the procedure of choice, with or without endoscopic guidance. Also any cystic component discovered by CT scan should always receive percutaneous needle decompression under local anesthesia.
The combination of radiation therapy and corticosteroids is standard therapy in an emergency situation awaiting definitive diagnosis. Despite the risk of causing tissue edema, radiation therapy is recommended prior to an elective mediastinoscopy regardless of symptoms. However radiation induced necrosis often makes histologic diagnosis and the decision for a long-term definitive treatment difficult.
We believe that our patient developed acute hypoxemic respiratory failure from fixed and dynamic airflow limitation aggravated by an uneven degree of bronchial obstruction. This caused simultaneous atelectasis in one lung and hyperinflation in another, especially during positive pressure ventilation. This scenario gave rise to enhanced blood flow to the atelectatic lung causing refractory shunt. Low tidal volume ventilation management with avoidance of muscle relaxant improves the degree of V/Q mismatch and/or shunt. The role of therapeutic airway stenting is not entirely clear. In more refractory cases, bronchial ventilation or femoral veno-arterial ECMO support have been performed successfully.
Conclusion
The airway obstruction in patients with anterior mediastinal mass are often underestimated. A CT scan is mandatory as a first step of the evaluation. The comprehensive team approach for the management of acute respiratory failure is crucial and timely. The team should consist of an ENT surgeon, a cardiothoracic surgeon, an anesthesiologist, and cardiopulmonary bypass personnel with fully assembled equipment. The goals are to achieve the most accurate diagnosis, to maintain airway patency and gas exchange, and to prevent underappreciated potentially fatal complications.
Reference
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