Anaphylaxis is a severe, life-threatening allergic reaction that develops quickly. In hospitals, the most common triggers are medicines, especially antibiotics, anaesthetic drugs and contrast media. In the community, they include foods, insect stings and latex. Nurses giving IV antibiotics, starting a blood transfusion or administering a vaccine must be ready to act in seconds.
How to recognise anaphylaxis
The Resuscitation Council UK describes anaphylaxis as a sudden onset with life-threatening airway, breathing and/or circulation problems, usually with skin or mucosal changes:
- Airway: swelling of the throat or tongue, hoarse voice, difficulty swallowing, stridor (a high-pitched noise on breathing in).
- Breathing: shortness of breath, wheeze, rising respiratory rate, falling SpOâ‚‚, exhaustion.
- Circulation: pale and clammy skin, fast heart rate, low blood pressure, dizziness, collapse, cardiac arrest.
- Skin and mucosa: hives (urticaria), flushing, swelling of the lips and eyelids. But skin changes are absent in up to 1 in 5 cases, so do not wait for a rash.
- Gastrointestinal symptoms such as vomiting and abdominal cramps can also occur.
Hives or swelling alone, without airway, breathing or circulation problems, is usually not anaphylaxis, but watch closely because it can progress.
Immediate actions
- Call for help (resuscitation team, or emergency services in the community).
- Remove the trigger if possible: stop the infusion or transfusion. Do not delay treatment trying to find the cause.
- Position the patient: lie them flat, with legs raised if they are hypotensive. Let them sit up if breathing is difficult. Do not let them stand or walk, even if they feel better, as this can cause sudden cardiac arrest. Pregnant women should lie on their left side.
- Give intramuscular (IM) adrenaline into the anterolateral (outer) thigh.
- Give high-flow oxygen, establish IV access and give IV fluids if hypotensive, as prescribed or per protocol.
- Repeat IM adrenaline after 5 minutes if there is no improvement.
- Monitor continuously: SpOâ‚‚, pulse, BP, ECG if available. Be ready to start CPR.
IM adrenaline doses (1 mg/mL, also written 1:1,000)
| Age | Dose | Volume of 1 mg/mL |
|---|---|---|
| Adults and children over 12 years | 500 micrograms | 0.5 mL |
| Children 6–12 years | 300 micrograms | 0.3 mL |
| Children 6 months to 6 years | 150 micrograms | 0.15 mL |
| Infants under 6 months | 100–150 micrograms | 0.1–0.15 mL |
Never give 1 mg/mL (1:1,000) adrenaline intravenously. IV adrenaline is only for experienced specialists, using a dilute solution with full monitoring. An auto-injector (such as an EpiPen) can be used if it is the quickest option available.
Refractory anaphylaxis
If breathing or circulation problems continue despite two doses of IM adrenaline, the patient has refractory anaphylaxis. Specialist teams may start an adrenaline infusion and give large fluid volumes. Get expert help early.
What about antihistamines and steroids?
Current UK guidance says antihistamines and steroids are not first-line treatments for anaphylaxis. They do not treat the airway, breathing or circulation problems, and giving them must never delay adrenaline. Oral non-sedating antihistamines may be used afterwards for skin symptoms.
After the reaction
- Observe for a period set by guidance (often at least 6–12 hours depending on severity), because symptoms can return (biphasic reactions).
- Blood test for mast cell tryptase where available: as soon as possible after starting treatment, then 1–2 hours later.
- Document the suspected trigger clearly in the notes, and update the allergy record and wristband.
- Report suspected drug reactions to your national pharmacovigilance system (such as NAFDAC in Nigeria, the MHRA Yellow Card in the UK or FDA MedWatch in the US).
- Before discharge: teach the patient to avoid the trigger, how and when to use an adrenaline auto-injector if prescribed, and arrange referral to an allergy specialist.
Be prepared
- Ask about allergies before every first dose and every new drug, and check the wristband.
- Know where the anaphylaxis kit is and check it every shift.
- Stay with the patient for the first minutes of any first-dose IV antibiotic or transfusion.
- Vaccination sessions must always have adrenaline and trained staff on site.
Related: Blood transfusion reactions · Drug calculation formulas · SBAR escalation
Based on Resuscitation Council UK, Emergency treatment of anaphylaxis (2021), and World Allergy Organization guidance. Educational content: follow your local anaphylaxis protocol.