Final answer:
An open pneumothorax should be treated with an occlusive dressing that is adhered on three sides to create a one-way valve, using either a commercial vented chest seal or an improvised sterile material if necessary.
Step-by-step explanation:
Applying a dressing to an open pneumothorax, also known as an open chest wound or a sucking chest wound, requires specific care to prevent air from being drawn into the chest cavity and causing a tension pneumothorax. The recommended approach is to use an occlusive dressing that adheres on three sides. This type of dressing allows air to escape from the chest cavity on exhalation but prevents air from entering on inhalation, acting as a one-way valve.
Emergency medical services often use a commercial vented chest seal for this purpose. If a commercial dressing is not available, an improvised occlusive dressing made from a sterile material can be taped on three sides over the wound. It's crucial to monitor the patient closely for signs of a developing tension pneumothorax and to be prepared to provide additional care as necessary.