Chapter 25

• During one-lung ventilation, the mixing of unoxygenated blood from the collapsed upper lung with oxygenated blood from the still-ventilated dependent lung widens the alveolar-to-arterial (A-a) O2 gradient and often results in hypoxemia.
• There are certain clinical situations in which the use of a right-sided double-lumen tube is recommended: (1) distorted anatomy of the left main bronchus by an intrabronchial or extrabronchial mass; (2) compression of the left main bronchus due to a descending thoracic aortic aneurysm; (3) left-sided pneumonectomy; (4) left-sided single lung transplantation; and (5) left-sided sleeve resection.
• If epidural opioids are to be used postoperatively, their intravenous use should be limited during surgery to prevent excessive postoperative respiratory depression.
• Postoperative hemorrhage complicates about 3% of thoracotomies and may be associated with up to 20% mortality. Signs of hemorrhage include increased chest tube drainage (>200 mL/h), hypotension, tachycardia, and a falling hematocrit.
• Bronchopleural fistula presents as a sudden large air leak from the chest tube that may be associated with an increasing pneumothorax and partial lung collapse.
• Acute herniation of the heart into the operative hemithorax can occur through the pericardial defect that is left following a radical pneumonectomy.
• Nitrous oxide is contraindicated in patients with cysts or bullae because it can expand the air space and cause rupture. The latter may be signaled by sudden hypotension, bronchospasm, or an abrupt rise in peak inflation pressure and requires immediate placement of a chest tube.
• Following transplantation, peak inspiratory pressures should be maintained at the minimum pressure compatible with good lung expansion, and the inspired oxygen concentration should be maintained as close to room air as allowed by a Pao2 >60 mm Hg.
• Regardless of the procedure, a common anesthetic concern for patients with esophageal disease is the risk of pulmonary aspiration.

Indications and techniques for thoracic surgery continually evolve. Common indications now include thoracic malignancies (mainly of the lungs and esophagus), chest trauma, esophageal disease, and mediastinal tumors. Diagnostic procedures such as bronchoscopy, mediastinoscopy, and open-lung biopsies are also common. Anesthetic techniques for providing lung separation have allowed the refinement of surgical techniques to the point that many procedures are increasingly performed thoracoscopically.

Thoracic surgery presents a unique set of physiological problems for the anesthesiologist. These include physiological derangements caused by placing the patient in the lateral decubitus position, opening the chest (open pneumothorax), and the need for one-lung ventilation.

### The Lateral Decubitus Position

The lateral decubitus position provides optimal access for most operations on the lungs, pleura, esophagus, the great vessels, other mediastinal structures, and vertebrae. Unfortunately, this position may significantly alter the normal pulmonary ventilation/perfusion relationships. These derangements are further accentuated by induction of anesthesia, initiation of mechanical ventilation, neuromuscular blockade, opening the chest, and surgical retraction. Although perfusion continues to favor the dependent (lower) lung, ventilation progressively favors the less perfused upper lung. The resulting mismatch increases the risk of hypoxemia.

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