The patient with an anterior mediastinal mass who undergoes general anesthesia is at risk of developing severe perioperative complications, including complete airway obstruction, severe hypoxemia, profound hypotension, and cardiac arrest.
Predictors of perioperative complications in these patients include significant respiratory symptomatology at baseline, greater than 50% tracheal narrowing on CT scan, pericardial effusion, and SVC syndrome.
The basic tenets of anesthesia for these patients include preservation of spontaneous breathing, securing the airway beyond the point of obstruction, the ability to rapidly change the patient's position, and preparation of options for managing emergencies, including rigid bronchoscopy, helium-oxygen gas mixture and CPB.
A 15-year-old male patient complains of several weeks onset of cough and dyspnea, especially on lying flat. A chest x-ray taken to rule out pneumonia shows an anterior mediastinal mass. He has no other medical problems and takes no medications other than vitamins. Vital signs: BP 105/70, HR 95, room air SpO2 96% (sitting up). Laboratory studies are unremarkable except for leukocytosis and mild anemia. He is referred for a surgical biopsy of the mass.
For the anesthesia practitioner, mediastinal masses have been described as a catastrophe waiting to happen. Complete airway occlusion and cardiovascular collapse are well-recognized complications of general anesthesia in these patients, related to pressure on and compression of nearby major airways, blood vessels, the lung and the heart. Mildly symptomatic or even asymptomatic patients might develop severe airway and vascular obstruction during induction of general anesthesia, endangering the patient's life.1 It is important, therefore, to understand the anatomy and pathophysiology of mediastinal masses, to perform an adequate preoperative evaluation of the patient, and to formulate a clear anesthetic plan to ensure safe delivery of anesthesia.
Anatomy of the Mediastinum
The mediastinum extends from the thoracic inlet superiorly to the diaphragm inferiorly, and is bound between the left and right pleural sacs and lungs laterally, the sternum anteriorly and the vertebral column posteriorly (Figure 12–1). It is divided into the superior and inferior mediastinum by a plane passing through the sternal angle and the fourth thoracic vertebra. The inferior mediastinum is further divided into the anterior mediastinum which lays between the sternum and the heart, the middle mediastinum which includes the heart, the major airways and blood vessels and the esophagus, and the posterior mediastinum between the posterior pericardial sac and the vertebral column.2 For clinical purposes, it is useful to consider any tumor that is anterior to a line drawn between the trachea and the posterior border of the heart as an anterior mediastinal tumor, as these are the tumors that tend to cause respiratory and vascular compression. In one series of 48 children with mediastinal masses undergoing surgery under general anesthesia, 48% (23 of 48) of patients had an anterior mediastinal mass, while of the 7 patients who developed complications during anesthesia, 6 (86%) had an anterior mediastinal mass.3