Prior to a scheduled operation for a 45-year-old male patient with tongue cancer, a tracheotomy performed under intravenous sedation to prevent asphyxia due to extensive bleeding resulted in pneumomediastinum and subcutaneous emphysema. The planned operations were postponed until reduction of the pneumomediastinum was confirmed. During operation, airway pressure was kept low to prevent tension pneumomediastinum along with a sufficient depth of anesthesia, controlled analgesia, and continuous administration of muscle relaxants. Postoperatively, sedation was used to avoid stress and complications with the vascular anastomosis site. In this case, air leakage into the soft tissues was one of the possible causes of the event associated with increased airway pressure. Although the incidence of such complications is relatively low, caution should be exercised after tracheostomy.