Capillary leakage and airway edema are most likely to occur during which condition?

• A. Asthma without edema
• B. Allergic reaction
• C. Dehydration
• D. Infection

Answer: (B)

When an allergic reaction occurs, mast cells release histamine and other inflammatory mediators. These chemicals make the capillary walls more permeable, so fluid leaks from the blood into surrounding tissues. In the airway, this fluid shift causes mucosal swelling (airway edema) and thickening of the airway walls. The combination of edema and often concurrent bronchospasm narrows the airway and can obstruct breathing, which is a hallmark of an allergic reaction or anaphylaxis.

In contrast, asthma without edema centers more on bronchoconstriction than capillary leakage; dehydration reduces fluid in tissues, not increases it; and infection can cause edema but not the characteristic widespread capillary leakage driven by allergic mediators.