Final answer:
Subcutaneous emphysema is a condition where gas or air is present under the skin, often indicating serious underlying lung issues such as emphysema or a collapsed lung, leading to reduced gas exchange and trapped air in the tissues.
Step-by-step explanation:
Subcutaneous emphysema indicates the presence of air or gas in the subcutaneous layer of the skin. This condition is often associated with underlying lung diseases such as emphysema or conditions that cause a collapsed lung, like spontaneous pneumothorax. In emphysema, which is frequently caused by smoking, the walls of the alveoli are damaged, leading to reduced gas exchange in the lungs and trapped air that can escape into surrounding tissues, including the subcutaneous layer. This complication requires immediate medical attention as it can signify serious underlying pathology and may result in further complications like difficulty breathing and chest pain, similar to symptoms experienced in other respiratory conditions such as pneumonia and pulmonary edema.