Consequently, with anaphylaxis, this would be an immediate reaction to the trigger which is then followed by a recurrence of symptoms after an interval of time. Being exposed again to the allergen is not necessary for a biphasic reaction to occur.
This reaction can happen between 2 and 72 hours after the first incident, so perhaps long after discharge from the hospital. This can occur in as many as 20 percent of cases. The biphasic reaction can be less, equally or more severe than the initial reaction, ranging from mild symptoms to a potentially fatal reaction. Biphasic reactions do not always show the same symptoms as the initial reaction.
Predicting if a second reaction will occur is not easy but the more severe the reaction or when two auto-injectors are initially needed, the higher the chance of a recurrence.
Being aware of possible biphasic response is important if you are caring for someone, so you can monitor them closely just in case. If you are administering first aid then it may be worth telling them, or their parents or guardians, to watch for additional symptoms after hospital discharge.
Knowing this is important, but remember that every patient is sent to the hospital after experiencing anaphylaxis and will be advised on the actual care they think is needed after discharge.
Finally, always make sure you have a spare auto-injector once discharged from hospital, just in case, and that you monitor the patient closely for up to 72 hours after the first attack in the case of a Biphasic anaphylactic response.
For more details, we have an Anaphylaxis video online course at www.proanaphyliais.co.uk