According to Britannica, surgical emphysema, also known as subcutaneous emphysema, is a health condition caused by air bubbles getting trapped under the skin. This condition is usually caused by ruptured lung tissue due to a traumatic accident, a bacterial infection called gas gangrene, or as a complication of surgery.
During a traumatic accident, the air that is released from ruptured air sacs in the lungs tries to find its way out and may pass through the lung tissue to the mediastinum. According to About.com, the mediastinum is the region between the lungs which is composed of the aorta, heart, and part of the trachea and esophagus. After passing through this area, the air will then rise to the neck region and get trapped under the skin where the pressure can cause partial collapse of the carotid arteries and reduce the flow of blood to the brain.
The most common symptoms of surgical emphysema are pain in the chest, difficulty in breathing and swallowing, inflammation around the neck, changes in the voice, skin pain, blue discoloration of the skin, and problems with blood circulation. Britannica notes that severe cases may require a sufferer to undergo treatment in a hyperbaric chamber to relieve pressure.