Pneumothorax and Other Chest Pathology

Ultrasound imaging can prevent and diagnose pneumothorax. Chest sonography is therefore an essential skill for those performing regional blocks. Regional anesthesia is the leading cause of pneumothorax during anesthesia, and twice as likely as the next leading cause.¹ This is particularly surprising given that line placement is another potential cause of perioperative pneumothorax.

The incidence of pneumothorax after traditional supraclavicular block has been reported to be as high as 0.5% to 6%.² This high incidence has led to concern that supraclavicular blocks should not be performed on outpatients. Pneumothorax after ultrasound-guided regional block has been reported.³

Several risk factors for pneumothorax and chest tube placement have been identified in patients undergoing interventional procedures.⁴ These include the needle traversing aerated lung or a lung fissure, lung hyperinflation from chronic obstructive lung disease, and positive-pressure ventilation.

Surprisingly, even when the needle traverses aerated lung, the pneumothorax risk is only about 50%, probably because in many cases the lung heals on its own. In some studies, chronic obstructive lung disease doubled the risk for pneumothorax, with an even greater risk for chest tube placement. This risk is thought to be related to lung hyperinflation and the fragile composition of the lung.

Because of the marked acoustic impedance mismatch with soft tissue, the pleura generates a brighter echo than the surface of the first rib. Comet-tail artifact can be observed deep to strongly reflecting structures, such as the lung.^5,6 The comet-tail artifact usually manifests as dense, continuous echoes.

Lung sliding is the to-and-fro movement of the lung caused by respiration. Because most of the translational motion of ventilated lung is generated from descent of the diaphragm, lung sliding is smallest at the apex and maximal at the base. Therefore, lung sliding can be difficult to appreciate during supraclavicular views of the brachial plexus. In this location, the first rib and pleura are best distinguished by the absorption of ultrasound by the bone and comet-tail artifact that arises from the pleural line. The presence of lung sliding or comet-tail artifact rules out pneumothorax.^7,8

FIGURE 65-1 Loss of the comet-tail artifact from the pleural line (A). Sonogram of the control lung is shown for comparison (B). In this example the loss of the comet-tail artifact was from massive hydrothorax.

FIGURE 65-2 Sonography can be used to reveal the lung point, which is the border between fully aerated and collapsed lung (A). In this example the cause of formation of the lung point was pleural effusion (B).