Mediastinal masses present special anesthetic considerations, as they can be associated with hemodynamic compromise from pulmonary artery and cardiac compression, neurologic problems (increased ICP, headache, and altered mental status) from obstructed venous drainage in the upper thorax (i.e. superior vena cava syndrome), or respiratory compromise from airway obstruction and loss of lung volumes. The most common masses in the anterior mediastinum are the four “T”‘s: Thymoma, Teratoma, Thyroid carcinoma and Terrible lymphoma.
Preoperative pulmonary function testing in patients with known mediastinal masses can help clarify the nature of the mass and guide the anesthetic management. Mediastinal masses can be either extrathoracic or intrathoracic depending on their extent:
An extrathoracic lesion will cause flattening of the inspiratory (lower) limb as the airway collapses during negative pressure inspiration.
An intrathoracic mass, on the other hand, typically flattens the expiratory (upper) limb, as it obstructs the airway during expiration.
A fixed lesion (i.e. tracheal stenosis) will flatten both the inspiratory and expiratory limbs.
While PFT’s are helpful, they are not always reliable for predicting airway collapse with induction. The most important determining factors for whether these patients are safe for general anesthesia are a CT scan and history of related symptoms. Patients are graded by symptoms as either: Asymptomatic, Mild: Can lie supine with some cough/pressure sensation, Moderate: Can lie supine for short periods but not indefinitely, and Severe: Cannot tolerate supine position.
With a CT scan and determination of symptoms, patients are deemed safe, unsafe, or uncertain for anesthesia as follows:
- Asymptomatic adult, CT < 50% tracheobronchial obstruction
- Severely symptomatic adult or child
- Children with CT tracheobronchial obstruction > 50%, regardless of symptoms
- Mild/moderate symptomatic child with CT tracheobronchial obstruction < 50%
- Mild/moderate symptomatic adult with CT tracheobronchial obstruction > 50%
- Adult or child unable to give history
It is imperative to note that sedation and paralysis in these patients (i.e. during induction), especially with anterior and superior masses, could result in airway collapse. This is a result of reduced lung volume from general anesthesia that causes a proportional reduction in tracheobronchial diameter, bronchial smooth muscle relaxation allowing greater compressibility, and paralysis of the diaphragm that eliminates the normal transpleural pressure gradient that helps stent the airways. Typically, if airway obstruction occurs it is distal to the endotracheal tube, and it is impossible to force the tube past the obstruction to stent it open. If the obstructing mass is very proximal on CT, awake fiberoptic intubation is a possibility. In “uncertain” candidates, local and regional techniques should be employed if possible. Otherwise, inhaled induction maintaining spontaneous ventilation is a good idea.