A client's ankle is edematous after an ankle sprain. Which physiological mechanism is responsible for the swelling?

A) Histamine-mediated vascular permeability leading to fluid transudation: Correct. Ankle edema following an ankle sprain is often due to inflammation and increased vascular permeability. Histamine, released from mast cells and basophils during the inflammatory response, causes vasodilation and increases vascular permeability. This leads to the leakage of fluid from the blood vessels into the surrounding tissues, resulting in edema. B) Bradykinin cascade resulting in the accumulation of substance P: While bradykinin is involved in the inflammatory response and can contribute to pain and vasodilation, it does not directly cause fluid transudation leading to edema in the context of an ankle sprain. C) Thromboxane A activation of chemical mediators: Thromboxane A is involved in platelet aggregation and vasoconstriction rather than increasing vascular permeability and edema formation. D) Neutrophil migration secondary to chemotaxis: Neutrophil migration is part of the inflammatory response and can contribute to tissue damage and inflammation, but it is not the primary mechanism responsible for the development of edema following an ankle sprain.