A nurse cares for a patient who has a sprained ankle. The patient notices that the ankle is swollen, red, and hot to touch. Which of these explains why the patient's ankle is hot to touch?

Choice A rationale Exudate accumulation, which is fluid and cells leaking from blood vessels, certainly contributes to the swelling (tumor) associated with a sprained ankle and inflammation. However, the feeling of heat (calor) is primarily a direct result of vasodilation and the subsequent increase in the volume of warm blood flowing into the injured area, raising the local tissue temperature. Choice B rationale The cardinal sign of inflammation described as heat (calor) is a direct physiological consequence of arteriolar vasodilation at the site of injury. This increased vascular permeability and localized hyperemia results in a greater volume of warm, oxygenated blood entering the capillary beds of the sprained ankle, which raises the local skin and tissue temperature. Choice C rationale An infection is a potential cause of inflammation but is not the mechanism that explains the localized heat. The process of an infection would still trigger the inflammatory response, including vasodilation and increased blood flow, which is the direct cause of the elevated local temperature observed on palpation. Choice D rationale A thermal injury, such as a burn, is a type of injury that causes inflammation and heat, but a sprained ankle is a mechanical injury (ligament tear/stretch). In a sprain, the heat is a result of the body's inflammatory response to the tissue damage, not a direct application of external heat or thermal damage itself.