History of cough or dyspnea with supine positioning must be investigated.
Tumors (thymoma, teratoma, thyroid CA, lymphoma, hygroma, cyst) of the anterior mediastinum cause obstruction of three structures: the tracheobronchial tree, the main PA (and atria) and the SVC. If the patient can tolerate the supine position, a CT scan should be obtained to define the involvement of each structure.
Note that most mediastinal mass deaths occur in children, because their airways are more compliant and they less commonly manifest symptoms
Obstruction of the tracheobronchial tree usually occurs at the level of the carina (in most cases, distal to the end of the ET tube). Flow volume loops may show a pattern characteristic of variable intrathoracic obstruction – forced expiration will increase pleural pressure, causing narrowing of the airway lumen and obstruction to flow. A plateau flow will occur as the airway is maximally narrowed. During inspiration, pleural pressure is negative, the airways distend, and the flow volume loop may appear normal. That said, flow volume loops are unreliable and should not be relied upon. The most important diagnostic modality is CT scan.
Loss of spontaneous ventilation is thought to predispose patients to airway collapse due to loss of the tone of the chest wall and distending forces of active inspiration. Muscle relaxation may also alter the extrinsic support of the airway and lead to airway obstruction.
Compression of the main PA and atria is much less common because the PA and atria are usually somewhat shielded by the aorta. Position change is thought to precipitate deterioration. Maintenance of preload, PA pressure, and cardiac output may attenuate compression of the main PA.
Compression of the SVC may cause SVC syndrome, resulting in venous distention of the upper body, edema of the head and neck, and cyanosis. In addition, respiratory symptoms may result from venous engorgement of the airways and mucosal edema. A change in mentation secondary to cerebral venous engorgement may occur in severe cases.
Key Points Re: Mediastinal Masses
- Consult with surgeon and have surgeon PRESENT on induction
- Have rigid bronchoscope available on induction
- Never rely on cardiopulmonary bypass “standby”
- ALWAYS maintain spontaneous ventilation when possible
- Only use general anesthesia as a last resort (local/regional techniques are preferable)