23.5 — Anaphylaxis and the Severe Asthma Attack

In fatal anaphylaxis, the median time from the trigger to cardiac arrest is 5 minutes for an injected drug, 15 minutes for a sting, and 30 minutes for food.

And the single most consistent finding in reviews of anaphylaxis deaths is that adrenaline was given late or not at all.

Not that the wrong drug was given. That the right drug was delayed — while people waited to see if it got worse, gave an antihistamine first, or hesitated over whether it really counted as anaphylaxis.

The rule that follows is the most important sentence on this page: when in doubt, give the adrenaline.

Adrenaline given to someone who turns out not to have anaphylaxis causes a racing heart, tremor and anxiety for about 20 minutes. Adrenaline withheld from someone who does have it can cost their life.

Anaphylaxis

What is happening

A severe, rapid, systemic allergic reaction (Chapter 13.6).

The immune system has previously made IgE antibodies to the trigger. On re-exposure, those antibodies sit on mast cells throughout the body, the allergen cross-links them, and the mast cells release their contents all at once — histamine and a cascade of other mediators.

And what those mediators do explains every symptom:

Blood vessels dilate and become leaky — so fluid pours out of the circulation into the tissues. Blood pressure collapses. Tissues swell.

Airway smooth muscle contracts — wheeze and breathlessness.

The tissues of the throat and tongue swell — the airway closes from the inside.

And the two ways it kills follow directly: the airway swells shut, or the circulation collapses.

Recognising it

Anaphylaxis is a sudden-onset reaction with airway, breathing or circulation problems, usually with skin changes.

Airway: swelling of the tongue, lips or throat; a hoarse voice; a feeling of the throat closing; difficulty swallowing; and stridor — a harsh noise on breathing in.

Stridor is the sound of a narrowing upper airway and it is an ominous sign.

Breathing: wheeze; breathlessness; rapid breathing; blue lips; exhaustion; and confusion from lack of oxygen.

Circulation: pale, clammy skin; fast weak pulse; dizziness or collapse; and low blood pressure.

Skin, in around 80 to 90 percent: widespread hives; flushing; itching, classically of the palms, soles and scalp; and swelling of the face and eyelids.

And the point worth emphasising: skin signs are absent in 10 to 20 percent of cases. No rash does not mean no anaphylaxis. Fatal cases are over-represented among those without skin signs, partly because they are recognised later.

Other features: abdominal pain, vomiting and diarrhoea — particularly with insect stings; a sense of impending doom; and in children, sudden floppiness or drowsiness.

And a common first symptom people report is a metallic taste, tingling in the mouth, or an odd sense that something is very wrong.

The triggers

Food — peanuts, tree nuts, milk, egg, fish, shellfish, sesame, soy and wheat account for the majority. The commonest cause in children and young people.

Insect stings — wasps, bees, hornets, and fire ants.

Drugs — antibiotics, particularly penicillins; NSAIDs; anaesthetic agents; and contrast media. The commonest cause of fatal anaphylaxis in older adults.

Latex.

And two situations worth knowing because they confuse people:

Food-dependent exercise-induced anaphylaxis — where the food alone is fine and the food followed by exercise causes a reaction. Wheat is the classic.

Alpha-gal syndrome — an allergy to red meat that develops after certain tick bites, with a delayed reaction 3 to 6 hours after eating. The delay makes the connection very hard to spot.

Idiopathic — no trigger identified, in a proportion of cases.

Treatment — exactly

1. Adrenaline. Immediately. Intramuscular. Into the outer mid-thigh.

Not subcutaneous, not intravenous by a bystander, and not into the buttock.

The outer thigh muscle has a rich blood supply and absorbs it fastest. It can be given through clothing.

Doses, using an auto-injector:

Adults and children over 30 kg: 300 micrograms (some devices 500 micrograms).Children 15 to 30 kg: 150 micrograms.Under 15 kg: 150 micrograms is generally used where that is what is available.

How to use an auto-injector — and the details differ by brand, so read the device:

Grip it in a fist with the needle end pointing down.Remove the safety cap.Push it firmly against the outer mid-thigh until it clicks.Hold it in place — 3 seconds for most current devices, 10 for some older ones. Follow the label.Remove and massage the site for 10 seconds.Note the time.

And a specific safety point: hold the leg still, particularly a child's. Injecting into a moving leg has caused the needle to bend or lacerate. In a young child, hold the leg firmly or have someone else do it.

2. Call an ambulance. Say the word "anaphylaxis".

Do this immediately after the adrenaline, or have someone else do it at the same time.

Everyone who has had anaphylaxis goes to hospital, even if they recover completely. The reason is in the next section.

3. Position them correctly, and this genuinely matters.

Lie them flat, with the legs raised.

If they are having difficulty breathing, let them sit up — but be ready to lie them down again.

If they are pregnant, lie them on their left side.

If unresponsive but breathing, use the recovery position.

And the critical instruction: do not stand them up, and do not let them walk.

Deaths have occurred within seconds of a person in anaphylaxis standing up. The circulation is depleted and depends on blood returning from the legs; standing removes that return and the heart empties. This has a name in the literature — the empty ventricle syndrome — and it is a well-documented cause of sudden death during anaphylaxis, including in people who appeared to be improving.

Keep them down.

4. Second dose of adrenaline after 5 minutes if there is no improvement.

Which is why two auto-injectors are carried, not one. Around 1 in 5 people needs a second dose.

5. Remove the trigger if you can do so quickly.

Stop a drug infusion. Remove a bee sting by scraping it out sideways with a fingernail or card rather than squeezing it, which injects more venom.

Do not make them vomit food, and do not waste time looking for the cause.

6. If they stop breathing normally, start CPR (Chapter 23.2).

7. Antihistamines and steroids are not treatment for anaphylaxis.

They may be given later for the skin symptoms. They do not work fast enough and they do not act on the mechanisms that kill.

Giving an antihistamine instead of adrenaline is one of the identified patterns in anaphylaxis deaths.

Why hospital is required afterwards

Biphasic reactions.

In up to around 5 to 20 percent of cases depending on the series, symptoms return hours after the initial reaction has settled — typically 4 to 12 hours later, occasionally longer — without any further exposure.

Which is why observation is standard, usually for several hours and longer for severe reactions, for those needing more than one dose of adrenaline, and for people with asthma.

And on discharge: an adrenaline auto-injector prescription and training, a written emergency plan, and referral to an allergy specialist.

Living with a severe allergy

Carry two auto-injectors at all times. Not one, and not in the car.

Check expiry dates. Adrenaline degrades, and a discoloured or cloudy solution should be replaced.

Everyone around the person should know how to use it — family, school, colleagues, friends. Practise with the trainer device.

Wear a medical alert bracelet.

A written allergy action plan, and for a child, a copy at school with staff trained.

Read every label, and ask in restaurants every time.

And two facts worth knowing: asthma that is poorly controlled substantially increases the risk of fatal anaphylaxis, which makes asthma control part of allergy safety. And beta blockers can make anaphylaxis harder to treat, because they blunt adrenaline's effect — which is worth flagging to any doctor prescribing them.

Immunotherapy — gradual desensitisation — is highly effective for insect venom allergy, reducing the risk of a systemic reaction substantially, and is available for some food allergies in specialist centres.

The severe asthma attack

Around 450,000 people die of asthma each year, and most of those deaths are considered preventable (Chapter 21.1).

Recognising severity

Moderate: worsening symptoms, peak flow 50 to 75 percent of best, still able to talk in sentences.

Severe: unable to complete a sentence in one breath; breathing rate over 25 a minute; heart rate over 110; peak flow 33 to 50 percent of best.

Life-threatening, and these are the signs that must be recognised:

A silent chest. No wheeze at all.

And this is the most dangerous misreading in respiratory medicine. A wheeze is the sound of air being forced through narrowed tubes. When too little air is moving to make any sound, the chest goes quiet. A person who was wheezing loudly and is now quiet has usually got worse, not better.

Exhaustion, and reduced respiratory effort.

Confusion or drowsiness — a sign of carbon dioxide accumulating.

Blue lips or fingers.

A slowing heart rate or low blood pressure — a very late and ominous sign.

Peak flow under 33 percent of best.

Inability to speak at all.

Treatment — exactly

1. Sit them upright.

Do not lie them down. Do not make them walk anywhere.

Leaning slightly forward with arms supported on a table lets the accessory breathing muscles work.

2. Reliever inhaler, through a spacer if at all possible.

One puff at a time, taking 5 breaths from the spacer after each.

Repeat every 30 to 60 seconds, up to 10 puffs.

And the spacer is not optional politeness — a severely breathless person cannot coordinate a metered-dose inhaler, and without a spacer very little of the drug reaches the lungs (Chapter 22.10).

If there is no spacer, one can be improvised from a plastic bottle with a hole cut for the inhaler mouthpiece.

3. Call an ambulance if:

The inhaler is not helping after 10 puffs.They are too breathless to speak in full sentences.Symptoms are getting worse.Or you are worried at all.

Say the word "asthma attack".

4. Keep giving the reliever while waiting — repeat the 10 puffs every 10 minutes if needed. You cannot meaningfully overdose someone in a genuine attack; the side effects are tremor and a fast heart.

5. Stay calm and stay with them. Panic worsens breathing, and a frightened person breathing faster and shallower makes the mechanics worse.

Coach slow breathing out — pursed lips, longer exhalation than inhalation.

6. Steroids are given early by professionals — prednisolone, or hydrocortisone if they cannot swallow. They take hours to work, which is precisely the argument for starting them at the beginning rather than waiting (Chapter 22.12).

Why people die from asthma

Reviews of asthma deaths find the same pattern repeatedly:

Over-reliance on the reliever inhaler and under-use of the preventer.

Not recognising how severe the attack was — by the patient, the family, and sometimes by clinicians.

Delay in seeking help.

No written action plan.

Previous severe attacks not treated as a warning.

And psychosocial factors — the people who die are disproportionately those who missed appointments and were not engaged with care.

Which means the prevention is not exotic: take the preventer, have a written plan, and go early.

After an attack

Everyone who has had a severe attack should be reviewed within 48 hours.

And an attack means the treatment plan was insufficient, so it is a prompt to review inhaler technique, adherence, triggers and step-up treatment — not simply to be relieved it is over.

The two rules

For anaphylaxis: adrenaline first, into the thigh, and keep them lying down.

For asthma: sit them up, ten puffs through a spacer, and treat a silent chest as the emergency it is.

And for both: the mistake that kills is waiting.

What the next page fixes

Chapter 23.6 covers poisoning and overdose — what to do, what never to do, and the specific antidotes worth knowing about.