Final answer:
The three-sided taped bandage over a sucking chest wound allows air to escape from the chest cavity while preventing more from entering, to maintain negative pressure necessary for lung inflation and prevent lung collapse.
Step-by-step explanation:
The purpose of a three-sided taped bandage over a sucking chest wound is to create a seal that prevents air from entering the chest cavity through the wound while still allowing air to escape from the chest cavity. This treatment is crucial because the normal negative pressure within the chest cavity is necessary for the lungs to expand during inhalation. If air enters the chest cavity, it can lead to a collapsed lung, known as a pneumothorax. The three-sided bandage allows air that has already entered the chest cavity to escape, especially during exhalation, and prevents further air from entering the cavity during inhalation, helping to maintain the necessary negative pressure for lung inflation.