Which of these is an example of passive rewarming?

Passive rewarming refers to methods that allow the body's own heat production to increase the patient's core temperature without direct application of external heat sources. Wrapping a patient in a blanket is an example of passive rewarming. This method helps to trap body heat and insulate the patient, enabling them to warm themselves naturally.

In contrast, the other options involve direct heat application or active measures to increase body temperature. Having a patient drink warm fluids, placing heat packs, and immersing the patient in warm water all introduce external heat sources that actively assist in the warming process rather than allowing the body to rely on its own mechanisms. Such methods would be categorized as active rewarming rather than passive.