99. What is Hamman’s sign?

Hamman’s sign (a.k.a. Hamman’s crunch) is a “mediastinal crunch” heard upon auscultation in the setting of mediastinal emphysema (air in the mediastinum). With each heartbeat, the air is displaced creating this auscultatory finding. This sound is similar to “crackles” that can be heard in the lungs in patients with pulmonary fibrosis. Mediastinal emphysema can occur after esophageal rupture or after cardiac surgery.