Anaphylaxis

Anaphylaxis is the most severe form of allergic reaction. It develops within minutes and involves not just the skin but the whole body: the airways swell and blood pressure drops sharply. Without help it can end in death; with adrenaline given in time it passes almost without trace. Everything is decided in the first few minutes, so it is worth knowing what to do — not only if you have an allergy yourself, but if you are the person standing nearby.

How to recognise it

The reaction usually starts within minutes of contact with whatever the person is allergic to; after food it may unfold more slowly, over half an hour or an hour. Think anaphylaxis when at least one of the following appears quickly:

• breathing: swelling of the lips, tongue or throat, a lump and tightness in the throat, a hoarse voice, a barking cough, wheezy or noisy breathing, air hunger;
• circulation: sudden weakness, dizziness, greying vision, fainting, cold clammy skin, grey or blue lips and face;
• awareness: confusion, fear, a sense of impending doom; in a child, floppiness, unusual drowsiness, being impossible to rouse;
• abdomen: cramping pain, vomiting, diarrhoea — particularly if the reaction is to food or to a sting.

Often, though not always, there are hives, itching, flushing and swollen eyelids as well.

There may be no rash at all. In roughly one person in ten anaphylaxis runs its course with no skin signs whatsoever — only breathlessness or collapsing blood pressure. Waiting for a rash as confirmation is one of the main reasons help arrives too late.

The first minutes decide everything

• Give the adrenaline auto-injector straight away — into the outer surface of the thigh, roughly halfway down, through clothing if necessary. Not into the buttock and not into the arm. If you are unsure whether it is anaphylaxis, give it: being wrong costs almost nothing, waiting costs a great deal.
• Call 112 and say it plainly: suspected anaphylaxis.
• Lay the person down and raise their legs. If breathing is difficult, let them sit up, but not stand. Lay a pregnant woman on her left side. If they are vomiting or unconscious, put them on their side.
• Do not let them get up or walk. Standing suddenly when blood pressure has collapsed is dangerous in itself: the heart is left with nothing to pump. There are recorded deaths at exactly the moment someone rose to their feet after starting to feel better.
• Remove the cause if you can: take out the sting, stop the drug that is being given.
• No improvement after 5 minutes — a second injection of adrenaline, into the other thigh.

Call an ambulance in every case, even if the person is fine after the injection. In some people the reaction returns hours later, usually within the first day, as a second wave — with no fresh contact with the allergen at all.

Why an antihistamine tablet is not the answer

This is the commonest and most dangerous misconception. Antihistamines relieve itching, hives and a runny nose, take around half an hour to start working, and do nothing for a swelling larynx or a falling blood pressure. Steroids act later still. An asthma inhaler opens the airways but does not raise blood pressure or reduce swelling in the throat.

Adrenaline is the only treatment that acts on every front at once: it tightens the blood vessels and raises blood pressure, reduces swelling of the linings and opens the bronchi. It goes into the thigh muscle because absorption from there is fastest. Reviews of fatal cases show the same thing year after year: adrenaline was given late or not at all, while a tablet was taken and the person waited.

What sets the reaction off

• Food. In children more often milk, egg, tree nuts and peanut, wheat; in adults nuts, peanut, fish, shellfish, sesame and soya.
• Medicines. Antibiotics, above all the penicillins, painkillers from the non-steroidal anti-inflammatory group, anaesthetic drugs and contrast agents used in scans.
• Insect venom — wasps, bees, hornets, bumblebees.
• Latex — gloves, catheters, condoms and some rubber goods.
• Sometimes no cause is ever found. That form is followed up by an allergy specialist, and investigation matters especially here.

Some circumstances do not cause a reaction on their own but lower the threshold: physical exertion, alcohol, taking anti-inflammatory painkillers, an acute infection, lack of sleep, menstruation. A food someone has eaten calmly for years can produce a severe reaction if they go for a run straight after the meal.

Two unusual causes deserve a separate mention, because not everyone keeps them in mind. The first is a reaction to red meat that comes on three to six hours later, often at night; it develops in people who have been bitten by a tick, and that delay makes it look nothing like an ordinary food allergy. The second is an excess of mast cells: in these people reactions to insect stings turn out unexpectedly severe. Both are picked up by blood tests and both change the plan.

One more thing matters: certain heart and blood pressure medicines — beta blockers and ACE inhibitors — make the reaction more severe and weaken the effect of adrenaline. If you have had anaphylaxis, tell the doctor who prescribes them; an equivalent alternative sometimes exists.

What happens in hospital

Observation is needed even when improvement is rapid. In hospital adrenaline is repeated if necessary, oxygen is given, fluids run into a vein, and blood pressure, breathing and oxygen levels are monitored. Antihistamines and steroids may be added, but their role is a supporting one.

How long the observation lasts depends on how severe the reaction was and how quickly it was stopped: from a few hours in mild cases to a day or longer in severe ones or where adrenaline had to be repeated.

In the first few hours it is worth taking blood for tryptase — this test later helps confirm that what happened really was anaphylaxis. Later on it tells you very little.

Discharge should not end with the words "avoid the allergen". On leaving it is sensible to have two adrenaline auto-injectors, a clear written action plan and a referral to an allergy specialist: investigation will show exactly what triggered the reaction.

Living with it afterwards

• carry two auto-injectors at all times, not only "when they might be needed": the second one is there in case the first fails or the dose has to be repeated;
• teach family, colleagues, childminders and teachers how to use them — in the middle of a reaction the person themselves may no longer be able;
• practise with a trainer device that has no needle and no drug, so your hands know the sequence;
• watch the expiry date and replace the injector early; store it at room temperature — not in the fridge and not in a car in the sun;
• wear a bracelet or carry a card naming the allergy: it will speak for you when you cannot;
• read the ingredients on the packet every time, even for a familiar product, because recipes change;
• state the allergy in cafés and restaurants directly, naming the allergen, rather than hinting at it;
• declare a drug allergy before any procedure, operation, dental appointment or scan with contrast.

For severe reactions to wasp and bee stings there is a treatment that cuts the risk of another anaphylaxis several times over: a course of venom immunotherapy. The decision rests with an allergy specialist. It is one of the few situations in which the cause can be removed rather than merely avoided.

Online consultation

An online consultation is no substitute for help during a reaction that is unfolding: if it is happening now, what is needed is adrenaline and 112. What a doctor can do by video is go through an episode that has already happened — help you work out what most probably triggered it, explain which allergy tests are worth doing, check that you have everything you need to hand, and put together a written plan in case it happens again.

This material is for information only and does not replace medical advice.