During scene size-up, first ensure that the scene is safe. The Pt's environment or recent activity may indicate the source of the reaction, such as a sting or a bite from an insect, a food allergy at a restaurant, or a new medication.
A respiratory problem reported by dispatch may be an allergic reaction, but until a field impression of allergic reaction is firmly established, be mindful of other potential causes of respiratory distress as well. Do not neglect the possibility that traumatic injury may be present, secondary to the medical emergency.
When a Pt presents with an allergic reaction, quickly identify and treat any immediate or potential life threats. It is essential that you pay careful attention to the Pt's ABCs, as deterioration can occur at almost any time and with little warning.
Allergic reactions may present as respiratory or cardiovascular distress in the form of shock. Pts experiencing a severe allergic reaction will often appear very anxious. If your general impression finds the person anxious and in distress, immediately call for ALS backup.
Sometimes Pts who are known to have severe allergies wear a medical identification tag (ex: necklace/bracelet). Such clues could provide crucial info. in situations where the Pt is found unresponsive or is otherwise unable to answer questions about their medical history.