A pneumothorax, or collapsed lung, occurs when air leaks into the space between the lung and the chest wall, causing the lung to partially or completely deflate. An open pneumothorax is a life-threatening medical emergency typically resulting from penetrating trauma. It is defined by an unsealed opening in the chest wall that allows air to move freely between the outside atmosphere and the pleural space surrounding the lung. This condition creates a direct pathway for outside air to compromise the mechanics of breathing.
The thoracic cavity relies on a negative pressure gradient for normal breathing, meaning the pressure inside the chest is normally less than the atmospheric pressure outside. When a penetrating injury, such as a gunshot or stab wound, breaches the chest wall, it creates a direct communication with the pleural space. If this external wound is large enough, atmospheric air rushes directly into the chest cavity through the wound during inhalation. This mechanism causes the pressure in the pleural space to quickly equalize with the outside air, preventing the lung from expanding and leading to its collapse. Because air is audibly pulled into the chest with each breath, this condition is often called a “sucking chest wound.”
Recognizing the Signs and Physiological Danger
The most immediate sign of an open pneumothorax is the presence of the open wound itself, often accompanied by a distinct, audible “sucking” or gurgling sound as the person breathes. Severe shortness of breath (dyspnea) develops rapidly because the affected lung cannot exchange oxygen. You may also observe visible bubbling or frothing at the wound site, caused by air and blood mixing as they move in and out of the defect.
The physiological consequences extend beyond simple lung collapse. With each breath, the changing air pressure inside the chest cavity causes a dangerous back-and-forth shift of the heart, major blood vessels, and trachea, known as mediastinal flutter. This movement interferes with the heart’s ability to fill with blood, significantly reducing the amount of blood pumped out to the body.
If the external wound becomes occluded—for example, if the person lies on it or if a clot forms—the air may enter the pleural space but cannot escape. This leads to a rapid build-up of pressure, converting the open pneumothorax into a tension pneumothorax.
Tension pneumothorax is the most lethal complication, as the rising pressure pushes the mediastinum completely to the opposite side of the chest. This extreme shift kinks the major veins that return blood to the heart, causing a rapid drop in blood pressure and leading to obstructive shock. Signs of this severe pressure buildup include a rapid heart rate, low blood pressure, and potentially a blue or grayish discoloration of the skin and lips, indicating severe hypoxia.
Essential First Aid Management
Immediately call for emergency medical services when managing an open pneumothorax. Bystander intervention can be life-saving by preventing the progression to a tension pneumothorax. The primary goal of first aid is to seal the external wound while still allowing air trapped inside the chest cavity to escape.
This is achieved by applying a three-sided occlusive dressing, which creates a one-way valve over the wound. The dressing, which must be airtight, should be placed directly over the wound and taped down securely on three sides, leaving the fourth side untaped.
The rationale for this three-sided seal is precise: when the patient inhales, the negative pressure pulls the untaped edge inward, sealing the wound and preventing new air from entering. When the patient exhales, the positive pressure inside the chest pushes the untaped edge outward, allowing accumulated air to escape the pleural space. This mechanism limits further lung collapse and prevents the pressure buildup that leads to a tension pneumothorax. If the person is conscious, positioning them to sit up or lie on the injured side can help ease their breathing.