Anaphylaxis kills through two mechanisms and people prepare for the wrong one. The airway closing is the version everyone pictures. Circulatory collapse is the version that more often kills quickly, and it is the one where a well-meant action — standing someone up to walk them to help — can be fatal within minutes.
1. What counts as anaphylaxis
The working definition is deliberately simple, because a precise one is no use at speed: sudden onset, rapid progression, and an Airway, Breathing or Circulation problem. Skin changes are common but neither necessary nor sufficient — a substantial minority of fatal reactions have no rash at all.
| System | What you are looking for |
|---|---|
| Airway | Swelling of throat or tongue, difficulty swallowing, a hoarse voice or a change in voice, stridor. A change in voice is early and is missed constantly |
| Breathing | Wheeze, breathlessness, increasing respiratory rate, fatigue, confusion from low oxygen, cyanosis late |
| Circulation | Pale and clammy, fast weak pulse, dizziness on sitting or standing, collapse, drowsiness |
| Not sufficient on their own | Hives, itching, flushing, swelling of lips or eyes. Gastrointestinal symptoms alone usually are not anaphylaxis either — with the exception of an insect sting, where vomiting and abdominal pain can be part of it |
A sense of impending doom is a clinical sign, not anxiety. People in anaphylaxis frequently say something is badly wrong before anything measurable has changed. Take it as data.
2. Adrenaline, and how much
Intramuscular adrenaline into the anterolateral middle third of the thigh, as soon as anaphylaxis is recognised. Through clothing if necessary. Not subcutaneous, not the upper arm, not delayed for anything.
Auto-injectors — the school and home version
| Strength | Roughly who |
|---|---|
| 150 µg | Children about 7.5–25 kg — broadly under 6 years |
| 300 µg | Over about 25 kg — broadly 6 years and above, and most adults |
| 500 µg | Available for larger adolescents and adults; prescribed on clinical judgement |
- Two devices, always. A second dose is needed in a meaningful minority of reactions, and one device is not a plan. Nobody should leave hospital after anaphylaxis with fewer than two.
- Repeat after 5 minutes if the features have not resolved. Auto-injector labelling often says 5 to 15; the resuscitation guidance says 5, on the reasoning that waiting 10 or 15 minutes is too long in someone with airway, breathing or circulation compromise.
- An expired device is weaker, not inert. If it is all you have, use it, and say so to the ambulance crew.
- Giving adrenaline to someone who turns out not to have anaphylaxis is a small thing. Withholding it from someone who does is not. The asymmetry is the whole argument, and if you are hesitating, that hesitation is the diagnosis.
From an ampoule — a clinical act, included because clinicians read this
Adrenaline 1 mg/mL (1:1000), intramuscular, repeated after 5 minutes if not improving. These are the Resuscitation Council UK doses, chosen to be easy to draw up safely rather than to be precisely weight-derived.
| Age | Dose | Volume of 1:1000 |
|---|---|---|
| Adult and child over 12 | 500 µg | 0.5 mL |
| Child 6–12 years | 300 µg | 0.3 mL |
| Child 6 months to 6 years | 150 µg | 0.15 mL |
| Under 6 months | 100–150 µg | 0.1–0.15 mL |
Two warnings about that table. Intravenous adrenaline for anaphylaxis is a critical-care act with a different concentration and a real potential to kill through dosing error — IM is first line even where IV access exists. And this table is here for people who already know how to use it; if you are reading it to work out what to do, the answer is the auto-injector and 999.
3. Position — the error that kills quietly
Lie them flat. Raise the legs. Do not let them stand or walk.
- In anaphylactic shock the circulation is failing because fluid has left the blood vessels. Lying flat with the legs raised returns what is left to the heart and brain. Standing removes it.
- Deaths have occurred within minutes of someone being stood up or walked — to a car, to a medical room, to an ambulance. This is described in the guidance as a specific, avoidable cause of death, and it is the most counterintuitive instruction on this page because helping someone usually means moving them.
- If breathing is the dominant problem and lying flat makes it worse, let them sit up — but sitting, not standing, and lie them down again the moment they feel faint.
- Pregnant: lie on the left side.
- Unresponsive and breathing: recovery position.
- If they have collapsed, do not sit them up to "help them breathe". That reverses the one thing keeping blood in the head.
4. What does not work, and why people reach for it anyway
| Intervention | Why it is not the answer |
|---|---|
| Antihistamines | They act on histamine at H1 receptors in skin and mucosa, over tens of minutes to hours. They do nothing useful for laryngeal oedema, bronchospasm or a collapsing circulation, which is what kills. They are third-line, they are for the itch and the hives, and they must never delay adrenaline. An oral antihistamine given to someone who then deteriorates has cost the only minutes that mattered. |
| Corticosteroids | No longer recommended for routine emergency treatment — a 2021 change that has not fully propagated. They work far too slowly to help the acute event, the evidence they prevent biphasic reactions did not hold up, and early steroid administration has been associated with increased intensive care admission. |
| An oropharyngeal or nasopharyngeal airway | These hold the tongue forward. In anaphylaxis the obstruction is swelling at and below the larynx — below where the device ends — so it cannot relieve it, and inserting one in a semi-conscious person may cause vomiting or laryngospasm and make things worse. Nothing short of a tube past the swelling, or a surgical airway, bypasses laryngeal oedema, and neither is a first-aid procedure. Adrenaline is what shrinks the swelling. |
| Their inhaler, alone | A bronchodilator helps the wheeze and does nothing for the airway swelling or the circulation. Useful after adrenaline in someone with wheeze, useless instead of it. |
| "Let us see if it settles" | The reasonable-sounding one, and the commonest. Anaphylaxis can progress from hives to collapse in under ten minutes, and the reactions that kill are frequently the ones that looked mild at five minutes. |
5. Judging severity, and what the monitors will and will not tell you
You are not grading it to decide whether to treat — airway, breathing or circulation involvement means adrenaline and 999, full stop. You are grading it to know how fast this is moving and what to tell the ambulance.
| Observation | What it adds | How it misleads |
|---|---|---|
| Voice and breathing sounds | The most useful single observation. Hoarseness, a "thick" voice, stridor, or difficulty swallowing saliva all signal airway involvement early | Nothing much — this is the one to trust. Listen to them speak a full sentence |
| Pulse | Rising rate with a weakening pulse is circulatory involvement | Anxiety raises it too. A falling rate late in a deteriorating person is pre-terminal, not improvement |
| Blood pressure | A genuine fall confirms shock | Falls late. Children in particular compensate hard and hold their pressure until they are close to collapse. Do not take a normal reading as reassurance, and never delay adrenaline to obtain one |
| Oxygen saturation | Useful for tracking breathing over time and for the handover | Frequently normal in early anaphylaxis, including in reactions that go on to kill. It measures oxygen carried, not an airway about to close or a circulation emptying. A normal SpO2 in someone with a hoarse voice means nothing at all |
| Skin | Hives support the diagnosis | Their absence does not exclude it. Pallor and clamminess matter far more than rash |
6. Timing, transport and afterwards
Adrenaline first, then 999
Say the word "anaphylaxis" when you call — it changes the response. Call even if they are improving.
Repeat at 5 minutes if not improving
Two doses without improvement is refractory anaphylaxis, which needs an intravenous adrenaline infusion in hospital. That is the point at which nothing else you can do on scene will substitute for arrival.
Do not drive them yourself
Tempting when the hospital is close. An ambulance carries adrenaline, oxygen and people who can manage an arrest in the vehicle. A car carries none of that, and the position they will sit in is the wrong one.
Everyone goes to hospital, even if they look well
Because of biphasic reactions — a second wave hours after full recovery from the first, without further exposure. Observation is risk-stratified; in practice children under 16 are generally observed for at least six hours, and longer after a severe reaction, a second dose, or a history of asthma.
Nobody leaves without two auto-injectors and a written plan
And a referral to allergy services. An anaphylaxis episode with no plan attached is an episode that will repeat under worse conditions.