Penetrating Chest Trauma

“Prehospital Pathophysiology” provides an opportunity for EMS providers to either refresh their knowledge related to the etiology of a certain disease or expand their knowledge base regarding common and not-so-common disease processes. This column is for both basic- and advanced-level prehospital care providers. The authors hope that through this column, EMS providers will gain a more thorough understanding of disease processes. If you would like to see a specific topic addressed in this column, send your request via e-mail to emseditor@aol.com.

Penetrating chest trauma most frequently involves mechanisms such as stabbing and gunshot wounds (GSW), although there are a variety of ways the chest can be penetrated—some of them very dramatic (industrial incidents, fence poles).

This article focuses specifically on hemothorax, pneumothorax, tension pneumothorax and pericardial tamponade. Also discussed will be assessment and treatment problems relating to the pathophysiology of these injuries.

Physiology/Pathophysiology

Penetrating chest trauma frequently creates serious or fatal injury because of the vital structures and processes that are housed within the chest cavity. Maintaining adequate intrapleural and intrapulmonic pressures within the chest cavity is essential for adequate breathing.

The lungs are surrounded by thin, durable membranes called pleura. The parietal pleura lines the chest wall. The visceral pleura is attached to the surface of the lung. Between the two pleural layers is a small amount of fluid, which serves both as a lubricant and a means to provide surface tension to keep the lungs inflated. A fluid bond between the visceral and parietal pleura creates a steady pull between the two pleural layers, which leads to a constant intrapleural negative pressure. The fluid bond is analogous to a water glass being placed upside down on a wet countertop. When the glass is pulled straight upward, the fluid bond creates a suction (negative pressure) and the glass can’t be pulled upward off the countertop unless the fluid bond seal is broken. The lung is comprised of elastin fibers that have a natural recoil tendency. This recoil property wants to pull the lung inward away from the thoracic wall; however, the fluid bond in the pleural space overcomes the elastin recoil and keeps the lungs from completely collapsing. If the fluid bond were eliminated, the lungs would collapse to approximately 5% of their normal resting size. The integrity of the pleural layers and appropriate pressure within the chest are essential for adequate breathing. A break in the continuity and integrity of the pleural layer would reduce the fluid bond and allow the elastin recoil to collapse the lung.

It is believed that the pleural space can hold between 3–4 liters of blood or air. Air will cause a dramatic reduction in surface tension when the pleura lose contact with each other, resulting in the inability to expand the affected lung. The volume of blood that can collect in the pleural space is enough to cause exsanguination. Blood or other fluids in the pleural space can also cause alveolar collapse in the areas where these substances are present.

It should be noted that during deep exhalation, the diaphragm rises as high as T4/T5. This means that an injury in the area of diaphragmatic movement may involve the chest, abdomen or both. A final issue with anatomy is that many providers fail to consider the patient’s “upper back” part of the chest cavity. The upper back is actually the posterior of the chest cavity and must be considered during assessment and care of the patient, especially in the event of penetrating trauma leading to pneumothorax or tension pneumothorax.

Hemothorax

Hemothorax is a collection of blood in the pleural space. As noted above, this space will hold between 3–4 liters of blood. Although blood in this capacity will prevent gas exchange due to alveolar collapse, it also can cause death from blood loss without one drop of blood ever leaving the body. This means that hemothorax can affect the body in two ways: hemodynamically and by impeding alveolar gas exchange.