Percutaneous dilatational tracheostomy (PDT) is a popular airway management technique in the intensive care unit (ICU).Occasionally the first dilation may be challenging when using Ciaglia and colleagues' method, and a second dilation may be needed to insert the tracheostomy tube. In these circumstances, potentially life-threatening complications, such as hemorrhage and hypoxia, may arise. The investigators found the reasons for difficulty in achieving smooth dilation of the stoma.The investigators compared the traditional method with the improved method.