In the UK, allergies are an increasingly common issue among the adult population. With over 20% of the population affected by one or more allergies, the UK has some of the highest rates of allergic conditions in the world. As allergy rates continue to rise, alongside increasing hospital admissions, it has never been more important for healthcare professionals to recognise the signs and symptoms of anaphylaxis and understand how to manage it effectively.
While most healthcare professionals are familiar with the immediate signs and symptoms of anaphylaxis and how to respond quickly, there is less awareness of biphasic anaphylaxis—what it is, how to recognise it, and how to manage it. For healthcare professionals, understanding biphasic anaphylaxis is vital, especially given the pivotal role we play in patient education, early intervention, and post-reaction monitoring.
What Is Anaphylaxis?
Anaphylaxis is a severe and potentially life-threatening allergic reaction that occurs rapidly, requiring immediate intervention with intramuscular adrenaline. It happens when the immune system overreacts to an allergen, releasing large amounts of histamine and other inflammatory mediators. This leads to widespread symptoms such as breathing problems, swelling, diarrhoea, vomiting, and more.
The immediate treatment for anaphylaxis is intramuscular adrenaline, commonly delivered using an auto-injector like the Epipen or Jext or via an ampoule depending on the clinical setting. Early recognition and prompt administration of adrenaline are essential because anaphylaxis can be deadly if not treated quickly. According to the Resuscitation Council UK (RCUK), 90% of people experiencing anaphylaxis will only require one dose. While the condition is serious, it’s reassuring to note that, according to UK-based research published in the British Medical Journal (BMJ), the case fatality rate for anaphylaxis remains under 1%, thanks to increased awareness and effective emergency treatment.
As a healthcare professional, you are often one of the first points of contact for patients with allergies, so recognising the signs early and understanding the correct response can be life-saving.
On average, most people who experience an anaphylactic reaction respond well to adrenaline and recover fully. However, for some, symptoms may return after initial treatment—this is known as biphasic anaphylaxis. This possibility highlights the need for continued observation and vigilance after an initial reaction, even when the patient appears to have recovered.
What Is Biphasic Anaphylaxis?
Biphasic anaphylaxis refers to a second wave of symptoms that typically occurs hours after the initial anaphylactic reaction, but can appear up to 72 hours later. After the initial symptoms subside following adrenaline treatment, the reaction can return without further exposure to the allergen. According to National Institute for Health and Care Excellence (NICE) guidelines, this occurs in approximately 5% of cases, although some studies suggest that up to 20% of people who experience an anaphylactic reaction can go on to develop a biphasic anaphylactic reaction.
On average, the second wave of symptoms range from mild to moderate but can include the same symptoms as the original anaphylactic reaction, such as wheezing, swelling, dizziness, and difficulty breathing. Although biphasic reactions are often mild to moderate, there is still a potential they can be life-threatening and often, a biphasic reaction can be difficult to distinguish from sustained anaphylaxis.
Clinical Recognition and Management of Biphasic Anaphylaxis
As a healthcare professional, you play a key role in recognising and managing both initial anaphylaxis and potentially a biphasic reaction. The first step is to recognise the initial anaphylactic reaction. A person experiencing anaphylaxis will often have an immediate onset of symptoms, including problems with airway, breathing, or circulation. These may include:
- Airway: Swelling of the throat, tongue, or upper airways.
- Breathing: Wheezing, stridor, or difficulty breathing.
- Circulation: Dizziness, confusion, pale skin, fainting, or loss of consciousness.
Immediate intervention by administering adrenaline (IM), either with an auto-injector or ampoule, is required. You should also call 999 for emergency services and monitor the patient closely. If there is no improvement within 5 minutes, a second dose of adrenaline should be administered as per RCUK Guidelines.
Recognising Biphasic Reactions in Primary Care
There are a number of different ways in which a primary care clinician may encounter a person having a biphasic reaction, as these reactions don’t only occur in hospital settings. It may be unknown that a patient required adrenaline earlier that day or that they were recently discharged from hospital after a prolonged period (usually 6 hours) of observation. However, it’s important to remember that a biphasic reaction can still occur after 6 hours. According to the RCUK, observing adults for 6–12 hours before discharge could still miss over 50% of biphasic reactions. This means a patient could present to your practice experiencing a secondary reaction, while you might be completely unaware of their initial episode—especially if it’s assumed that a hospital discharge means they are no longer at risk.
If biphasic anaphylaxis is suspected, follow the same ABC (Airway, Breathing, Circulation) approach used for the initial reaction. If the second wave occurs, adrenaline should be administered again using an auto-injector or ampoule (depending on local policy), and further medical intervention such as IV fluids, typically administered in hospital or by emergency services, may be required in severe cases.
Patient Education of Biphasic Anaphylaxis
As a healthcare professional, educating patients about allergies and the risks of biphasic anaphylaxis is essential. It’s important to inform patients not only about how to recognise the signs of anaphylaxis but also about the need for immediate medical help after a reaction, even if they’ve used their auto-injector and feel a lot better.
It’s essential to educate and emphasise the risk of a biphasic reaction. It should also be reiterated to patients that even if they’ve been discharged following an anaphylactic reaction—particularly within the past 72 hours—there’s still a chance of a secondary reaction. Although this is likely to be discussed with the patient by their discharging clinician, it’s still helpful to reiterate the information during follow-up. It’s important they know how to recognise the signs and when/how to seek urgent help.
Patients should always be encouraged to carry their auto-injectors and to fully understand when and how to use them. In addition, providing patients with an allergy action plan that includes avoidance strategies, symptoms management, and steps to take during a reaction can empower them to feel more confident in handling potential emergencies.
By equipping patients with the knowledge they need, you help them manage their allergies effectively and reduce the risks associated with both initial anaphylaxis and potential biphasic reactions.
Conclusion
Biphasic anaphylaxis is a critical condition that many do not know of. While the initial anaphylactic reaction is generally well-recognised, the potential for a second wave of symptoms, often occurring hours after the first event, requires vigilance. By staying informed, recognising the signs of biphasic anaphylaxis, and ensuring patients receive appropriate treatment and monitoring, you can help prevent serious complications and improve recovery outcomes. Additionally, providing detailed patient education around allergies, anaphylaxis, and biphasic reactions is essential for long-term management and ensuring patients know when to seek emergency care.
- https://www.allergyuk.org/about-allergy/statistics-and-figures
- http://www.anaphylaxis.org.uk
- https://www.resus.org.uk/sites/default/files/2021-05/Emergency%20Treatment%20of%20Anaphylaxis%20May%202021_0.pdf
- https://dontforgetthebubbles.com/wp-content/uploads/2020/07/Anaphylaxis-Facilitator-Guide.pdf
- https://www.bmj.com/content/372/bmj.n251
- https://www.nice.org.uk/guidance/cg134
Immediate Management of Anaphylaxis in Community Settings – Elearning
Anaphylaxis is a potentially life-threatening, serious allergic reaction to an allergen. Allergens are wide and varied, the most common of these are food substances, insect stings or medications. If it is not treated appropriately, it may cause death.
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