What action should be taken to prevent chilling of a casualty in shock?

To prevent chilling of a casualty in shock, it is essential to keep them warm with a blanket. When someone is in shock, their body is unable to maintain normal physiological responses, which can lead to a drop in body temperature. This is especially critical because maintaining a stable body temperature is vital for the functioning of bodily systems and for recovery.

Using a blanket provides an immediate and effective way to add warmth, improving circulation and comforting the casualty, which can help stabilize their condition. This action also reduces the risk of hypothermia, which is particularly important in shock situations as the body is already under significant stress.

Other methods, like using ice packs or encouraging movement, can worsen the situation. Ice packs would further lower body temperature, which is counterproductive. Encouraging movement can strain the body and lead to increased energy expenditure, which is not advisable during shock when the body needs to conserve energy. Exposure to fresh air may also cool the body further, which is undesirable in this context. Thus, providing warmth through a blanket is the most appropriate and effective action.