Which of the following is least likely to cause death in anaphylaxis?

• A. Hypoxemia
• B. Vasodilation
• C. Bronchoconstriction
• D. Upper airway obstruction

Answer: (C)

In anaphylaxis, the most immediately life-threatening problems are airway compromise and widespread collapse of the circulation. Swelling of the upper airway can quickly block breathing, and the massive release of mediators causes vasodilation and plasma leakage that can lead to dangerous drops in blood pressure and poor organ perfusion. Bronchoconstriction, while it worsens breathing, is typically rapidly reversible with treatment such as epinephrine, and does not by itself progress to death as quickly as an obstructed airway or profound circulatory collapse. Because epinephrine tackles both the bronchospasm and the vascular effects, bronchoconstriction is the least likely cause of death among the listed mechanisms.