What should be done for a casualty with a sucking chest wound?

For a casualty with a sucking chest wound, sealing the wound with an occlusive dressing is critical. A sucking chest wound indicates that there is an open injury to the thoracic cavity, which can allow air to enter the pleural space, potentially leading to a collapsed lung (pneumothorax). An occlusive dressing helps to prevent air from entering the wound during inhalation, thus stabilizing the chest wall and allowing the lung to re-inflate if enough negative pressure is restored. This immediate action helps to manage the respiratory distress and can be lifesaving until further medical intervention can be provided.

The other options do not address the immediate need to protect the chest cavity from air entry. Applying a tourniquet would not be appropriate as it is intended for limb bleeding control and could worsen the situation if applied improperly to a thoracic injury. Administering oral fluids is not advisable for a casualty with a chest wound, as they may have compromised airway or respiratory function and could choke. Immediate chest compressions are indicated for cardiac arrest situations, not for managing a chest wound. Therefore, sealing the wound with an appropriate occlusive dressing is the most important and effective step to take in this situation.