In a case of severe allergic reaction, what should be done immediately if epinephrine is not available?

In a severe allergic reaction, also known as anaphylaxis, the immediate priority is to ensure airway patency, support breathing, and maintain circulation. If epinephrine is not available, providing supplemental oxygen is a critical step. Supplemental oxygen can help improve the patient's oxygen levels during respiratory distress, which is commonly associated with severe allergic reactions.

Transporting the patient promptly is essential, especially since anaphylaxis can rapidly worsen. While calling for advanced life support is also necessary, the immediate actions to support the patient's breathing and circulation are prioritized. Antihistamines, although helpful in managing milder allergic reactions, do not act quickly enough in a life-threatening anaphylactic reaction and are not a substitute for epinephrine.

Thus, delivering supplemental oxygen and transporting the patient establishes a foundational response to support their condition until further help can be obtained or until more definitive treatment with epinephrine can be administered.