A 21-year-old female with type 1 diabetes mellitus presenting with a one-day history of headache, nausea, and vomiting was admitted to the emergency room. After multiple episodes of vomiting, she complained of sore throat and chest tightness. At the time of admission, her blood pressure was 100/60 mmHg, and her heart rate was 102 beats/minute. Her breathing was deep, rapid, and labored with a respiratory rate of 20 breathes/minute. The patient's body temperature was 37.4℃. On auscultation of her chest, a systolic crunching and popping sound was heard at the cardiac apex and at both sternal borders (Hamman's sign). Laboratory findings showed high anion gap metabolic acidosis with an arterial blood pH of 7.23, serum glucose level of 588 mg/dL, bicarbonate level of 4.6 mmol/L, and serum ketone level of 12,757 µmol/L. A chest radiography showed mediastinal air along both cardiac borders and extending along the anterior mediastinum up both sides of the neck (Fig. 1, 2).