Why can a patient who is having an anaphylactic reaction have angioedema?

• A. Capillary beds become more permeable and fluid leaks into the interstitial space.
• B. Bronchoconstriction causes blood vessels to decrease in diameter.
• C. Histamine release causes inflammation of veins.
• D. Colloid osmotic pressure increases and fluid is forced into interstitial space.

Answer: (A)

During anaphylaxis, mast cells and basophils release histamine and other mediators that make capillary walls leakier. This increased capillary permeability allows plasma to escape into the surrounding interstitial tissue, leading to swelling known as angioedema. The edema often involves deeper layers of skin and mucosa, such as the lips, tongue, and airway, which is why angioedema can be a prominent and dangerous feature of an anaphylactic reaction.

Other ideas don’t fit as well because bronchoconstriction affects the airways rather than the capillary leakage that causes deeper tissue swelling; histamine’s role is in increasing vascular permeability rather than inflaming veins; and increasing colloid osmotic pressure would pull fluid back into vessels rather than drive it outward into interstitial space.