Anaphylaxis is a severe, life-threatening allergic reaction. It involves the immune system releasing chemicals, leading to a sudden drop in blood pressure and airway narrowing. Biphasic anaphylaxis is a distinct type where symptoms return after initial improvement, without further allergen exposure. This delayed second wave complicates treatment and requires careful monitoring.
Understanding Biphasic Anaphylaxis
Biphasic anaphylaxis unfolds in two phases. After an initial allergic reaction and treatment, a symptom-free interval occurs. This period ranges from minutes to hours, often peaking within 8 to 11 hours, but symptoms can recur up to 72 hours later. The exact mechanism is not fully understood, but it involves a second, delayed release of inflammatory mediators.
This condition differs from monophasic anaphylaxis, where symptoms resolve and do not return. The symptom-free period can be deceptive, as individuals may believe they have fully recovered. Recurrent symptoms can be as severe as the initial reaction.
Biphasic reactions occur in up to 20% of anaphylaxis cases. Factors increasing this likelihood include the severity of the initial episode, requiring multiple doses of epinephrine for stabilization, or delayed epinephrine administration.
Recognizing the Symptoms
Symptoms can manifest during both the initial and subsequent phases, involving multiple body systems. Skin reactions are common, including hives, itching, flushing, and angioedema (swelling).
Respiratory symptoms include difficulty breathing, wheezing, and throat tightness. Shortness of breath, a persistent cough, or a hoarse voice may occur. Swelling of the throat or tongue can obstruct airways, leading to noisy breathing or a choking sensation.
Cardiovascular signs include dizziness, lightheadedness, or fainting, due to a rapid or weak pulse and low blood pressure. Gastrointestinal symptoms include nausea, vomiting, abdominal pain, or diarrhea. Some individuals also report a feeling of impending doom, confusion, or anxiety. Vigilance for any of these symptoms during the symptom-free interval is important, as their reappearance indicates a biphasic reaction.
Emergency Response and Ongoing Care
Immediate action is important at the first sign of anaphylaxis. Administering epinephrine without delay is the primary treatment. Following epinephrine administration, emergency services should be called immediately.
Medical observation in a healthcare setting is important after an anaphylactic reaction. This period allows monitoring for symptom recurrence. Observation times of 4 to 8 hours are recommended, sometimes longer for severe initial symptoms or delayed epinephrine use. An observation time of at least 6 hours can exclude recurrence in over 95% of patients.
Consulting an allergist or immunologist after an anaphylactic episode is important for ongoing care. This specialist can identify triggers, develop a personalized emergency action plan, and provide guidance on avoiding future exposures. Individuals at risk should carry two epinephrine auto-injectors, as a second dose may be required if symptoms persist or return.