Why does severe hypotension follow rapid intravenous administration of a large dose of allergen to a highly sensitized individual?

💡 Explanation

Severe hypotension occurs because widespread mast cell degranulation releases histamine and other mediators, causing vasodilation and increased vascular permeability, therefore blood pressure drops. Rather than lymphatic reabsorption or compensatory heart rate increases reversing this process, the vasodilation overwhelms compensatory mechanisms.

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