Subcutaneous emphysema, also known as tissue emphysema and McLean’s syndrome, is an emphysema caused by the accumulation of air or gas in the subcutaneous tissue. If the patient with subcutaneous emphysema is fat, it is easy to compress the drainage tube resulting in poor drainage. For patients with higher tension pneumothorax, the incision during drainage is larger and the epidermal suture is tighter, which can easily produce subcutaneous emphysema due to gas leakage into the subcutis. 1.Chest fluoroscopy; 2.Chest ultrasound; 3.Chest CT examination. Generally, patients with subcutaneous emphysema have no conscious symptoms, and the only effect on the patient is difficulty in opening the eyes. Patients with mediastinal emphysema often complain of chest tightness or pain behind the sternum, and may also have hoarseness of voice. The subcutaneous tissue is swollen and has a spongy sensation to touch and a twisting and snowing sensation. If a rough crunching sound is heard along with the heartbeat, this is seen in mediastinal emphysema. Severe mediastinal emphysema may affect venous return, resulting in jugular venous dilatation, tachycardia, dysphonia, and even heart failure. The skin of the chest wall is swollen after chest injury, and light pressure with the fingers indicates subcutaneous emphysema if spongy sensation and twisting sounds are palpated, which is generally not easily missed or misdiagnosed. Careful clinical observation is helpful to clarify the source of emphysema. If the emphysema first manifests in the neck, its source should be considered as a possible mediastinal emphysema. X-ray examination can help to further identify the source of the emphysema.