What you need to know about anaphylaxis

EpiPens, the most commonly used auto-injector of adrenaline for treating anaphylactic shock. Getty Images

A new study by Alqurashi and colleagues published yesterday in the Annals of Allergy, Asthma and Immunology provides valuable new insight into what is called a “biphasic” anaphylactic reaction in kids.

Anaphylaxis is a severe allergic reaction that usually occurs very quickly after exposure to a trigger that one is allergic to, such as a food or a bee sting.

It is often life threatening.

Worldwide, the rates of anaphylaxis have gradually been increasing, at the same time as recognition of allergies in general is also increasing.

An anaphylactic reaction is usually isolated, but can sometimes have a second, delayed phase of reaction (in which case it is called a “biphasic” reaction).

READ MORE: Anaphylactic reactions can have rebound effect

Although guidelines recommend observing kids for a long period of time to watch for this delayed reaction, the dilemma is that it hasn’t been clear from prior studies what proportion of kids are likely to have this, what risk factors might predict who will get this, and how long a child actually needs to be observed for.

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Obviously, in the context of our overcrowded emergency rooms, that last point is an important practical consideration.

These authors reviewed records from the two largest pediatric emergency departments in the country – CHEO in Ottawa and Sickkids in Toronto – and identified all kids that presented with anaphylaxis in 2010.

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They then looked for proof of a biphasic reaction, defined by the presence of a second reaction which occurred at least one hour after resolution of the initial episode, with new signs and/or symptoms despite no new exposures, and severe enough to require therapy.

READ MORE: Health Canada issues recall for children’s allergy medication

They identified 484 anaphylaxis episodes, and found evidence of a biphasic reaction in about 15% of cases.

Half of those delayed reactions required treatment with epinephrine.

Also, about three quarters of delayed reactions occurred within 6 hours, and while the child was still in the ER, while the remaining quarter occurred after discharge.

This was a larger and more clearly characterized cohort of patients than any previously reported.

Accordingly, they were able to identify certain factors which increased the risk of a biphasic reaction.

These included age between six and nine, cases where there was a delay in getting to the ER (more than 90 minutes after initial symptoms), and kids who had a generally more severe initial anaphylaxis reaction – including those needing more than one dose of epinephrine, those needing puffers for respiratory symptoms, and those with a specific vital sign test called a wide pulse pressure upon arrival in the ER.

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This association with severity of the anaphylaxis episode had also been suggested in previous studies, and supports the theory that a biphasic reaction is the product of a long-lasting inflammatory response.

READ MORE: What doctors are warning parents about allergies and asthma in kids

But what does this study tell us about how we should manage kids with anaphylaxis in the ER?

Although authors don’t provide a prediction score, they do note that these risk factors have a sensitivity of about 96% and a specificity of about 20% for a delayed (biphasic) reaction.

In other words, 96% of kids who can be expected to have a delayed reaction will have one of these five risk factors.

Accordingly, kids without any of these risk factors may be discharged quite confidently after a standard observation period of about six hours.

The other message that one might take from this study is that earlier ER presentation and earlier epinephrine (“Epi-pen”) administration might reduce the risk of biphasic reactions.

This is a good reminder for parents to have their Epi-pen handy and not to hesitate to use it on the way to the hospital.

Because anaphylaxis is generally under recognized, and delays increase the risk for complications, today’s top five list focuses on the symptoms of anaphylaxis.

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Top Five Symptoms of Anaphylaxis

  1. Rapid onset of symptoms after exposure Symptoms usually start within minutes to a few hours, and usually after an obvious exposure such as a bee sting or food consumption.
  2. Skin symptoms: About 90 percent of people will have some type of skin change, such as hives, itching, flushing, and/or swollen lips or tongue.
  3. Respiratory symptoms About 70 percent of people will have respiratory system changes ranging from nasal congestion to a change in voice, to shortness of breath and/or wheezing.
  4. Gastrointestinal symptoms About 45 percent of people will get nausea, vomiting, diarrhea, and/or abdominal pain.
  5. Cardiovascular symptoms: About 45 percent of people will have symptoms such as dizziness, fainting, and/or low blood pressure.

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