01OverviewDefinition, clinical context and the essential points that orientate the chapter.
Use an ABCDE pattern. Airway features include tongue or throat swelling, hoarse voice and stridor; breathing features include tachypnoea, wheeze, fatigue and hypoxia; circulation features include hypotension, collapse, confusion and cardiac arrest. Skin or mucosal changes support the diagnosis but may be absent in a substantial minority.
Adrenaline errors are preventable: use the intramuscular route, correct 1 mg/mL concentration, adult 500-microgram dose and outer mid-thigh. Start treatment from clinical diagnosis; do not wait for tryptase or intravenous access. Refractory disease needs senior critical-care support and an adrenaline infusion by experienced staff rather than repeated intravenous boluses.
Clinical decisions in Anaphylaxis recognition and treatment depend on trajectory and consequence. Re-examine evolving skin, repeat focused systemic assessment when the patient changes, and reconcile every result with morphology and timing; a normal early test cannot neutralise worsening pain, mucosal injury or organ dysfunction.
Key points
- Do not require skin signs: anaphylaxis can be diagnosed from sudden life-threatening airway, breathing or circulation compromise after a plausible exposure.
- Give adrenaline intramuscularly into the anterolateral thigh; the adult healthcare dose is 500 micrograms using 0.5 mL of 1 mg/mL solution.
- Repeat intramuscular adrenaline after five minutes if ABC problems persist and call expert help after two doses for refractory anaphylaxis management.
- Lie the patient flat with legs raised; if breathing is difficult allow a supported sitting position with legs extended, and never let them stand or walk.
- Give high-concentration oxygen, monitor ECG, oxygen saturation and blood pressure, obtain intravenous access and use rapid crystalloid for hypotension.
- Antihistamines do not treat airway or circulatory compromise and corticosteroids are not routinely advised for the initial emergency treatment.
- Anaphylaxis recognition and treatment must be assessed by lesion duration, onset, distribution, symptoms, mucosal findings, systemic physiology and the full medicine timeline rather than by colour alone.
- For Anaphylaxis recognition and treatment, document the working diagnosis, excluded emergencies, uncertain culprit or trigger, treatment response and the exact safety-net given.
02AetiologyUnderlying causes, associations and risk factors, with why each one matters.
Foods, medicines and stings
Foods predominate in younger patients, while antibiotics, perioperative agents and insect venom are important adult causes; any exposure history requires timing and route.
Cofactor amplification
Exercise, acute infection, alcohol, NSAIDs and menstrual factors can lower the reaction threshold and explain inconsistent responses to the same exposure.
Unidentified trigger
A proportion of episodes remain idiopathic after specialist assessment, but hidden medicines, chlorhexidine, cofactors and mast-cell disease should be considered.
03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.
- 1Systemic mast-cell activation
IgE-dependent or non-IgE pathways release mediators that increase vascular permeability, constrict airways and reduce vascular tone across several organ systems.
- 2Airway and breathing failure
Mucosal oedema narrows the upper airway while bronchospasm and ventilation-perfusion mismatch cause wheeze, hypoxaemia and rising respiratory effort.
- 3Distributive shock
Vasodilation and plasma leakage reduce venous return and blood pressure, so rapid crystalloid is often required alongside repeated adrenaline.
- 4Adrenaline reversal
Alpha effects restore vascular tone and reduce oedema, while beta effects support cardiac output, bronchodilation and suppression of further mediator release.
04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.
Tongue swelling, difficulty swallowing, hoarse voice, stridor or rapidly progressive throat tightness indicates upper-airway threat.
Wheeze, hypoxia, increased work, exhaustion or silent chest after a sudden exposure indicates life-threatening lower-airway involvement.
Hypotension, collapse, confusion, clammy skin or cardiac arrest represents anaphylactic shock when onset and context fit.
Wheals, flushing and angioedema are common but lack of visible rash does not exclude anaphylaxis when ABC features are present.
Severe cramping or repeated vomiting supports anaphylaxis after non-food exposure and can accompany systemic food reactions, but does not replace ABC assessment.
05InvestigationsWhat to request, why it matters and how to interpret it.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Continuous physiological monitoringFirst step - Why
- Track response and detect deterioration during emergency treatment.
- Interpretation and limitations
- Attach pulse oximetry, ECG and frequent blood pressure monitoring, but never wait for equipment before giving clinically indicated adrenaline.
- 02
Serial mast-cell tryptase - Why
- Support later confirmation when the diagnosis is uncertain or reaction followed medicine, venom or anaesthesia.
- Interpretation and limitations
- NICE advises samples as soon as possible after treatment starts and ideally one to two hours, no later than four hours, after onset; obtain a baseline later.
- 03
Focused trigger and cofactor history - Why
- Define plausible exposures for specialist investigation and immediate avoidance.
- Interpretation and limitations
- Record all foods, medicines, stings, latex, chlorhexidine, exercise and cofactors in the hours before onset without assigning causation prematurely.
- 04
Blood gas, electrolytes and organ tests - Why
- Assess severe shock, respiratory failure or treatment complications.
- Interpretation and limitations
- These results guide critical care but do not confirm or exclude anaphylaxis; lactate may rise from shock and adrenaline.
- 05
Specialist allergy testing after recovery - Why
- Identify trigger and cross-reactivity safely outside the acute event.
- Interpretation and limitations
- Skin or specific-IgE testing is selected from the exposure history and timed by the allergy service; indiscriminate panels generate irrelevant sensitisation.
06Differential diagnosisRealistic alternatives and the features that help distinguish them.
Vasovagal episode
Pallor, bradycardia and rapid improvement when supine suggest a faint, unlike persistent hypotension, wheeze, urticaria or angioedema.
Acute severe asthma
Isolated bronchospasm can resemble anaphylaxis, but allergen timing, hypotension and skin or mucosal signs support systemic reaction; adrenaline is safe when doubt remains.
Bradykinin angioedema
Non-itchy swelling without wheals, hypotension or bronchospasm may reflect ACE inhibition or C1-inhibitor disease and needs parallel airway planning.
Panic and dysfunctional breathing
Tingling and tachypnoea can accompany fear, but objective upper-airway noise, wheeze, hypoxia or hypotension cannot be attributed to anxiety.
07ManagementImmediate care, first-line treatment, alternatives and escalation.
01Immediate ABC responseGive intramuscular adrenaline nowFirst stepSudden illness produces airway, breathing or circulation compromise with or without skin findings.+
- 1Call emergency support, remove the trigger when feasible, position safely and give adult intramuscular adrenaline 500 micrograms into the anterolateral thigh.
- 2Provide high-concentration oxygen, continuous monitoring and rapid intravenous crystalloid for hypotension while repeating intramuscular adrenaline after five minutes if needed.
- 3EscalationAfter two appropriate doses with persistent ABC problems, escalate to experienced critical-care staff for refractory anaphylaxis and an intravenous adrenaline infusion.
02After initial recoveryObserve according to recurrence riskAirway, breathing and circulation have stabilised after emergency treatment.+
- 1Choose at least two, six or twelve hours of observation from symptom resolution according to severity, timing, adrenaline doses, comorbidity and access to emergency care.
- 2Take indicated tryptase samples without delaying treatment, watch for biphasic symptoms and reassess immediately if any ABC feature returns.
- 3Before discharge, provide written information, trigger avoidance advice, specialist referral and auto-injectors with demonstration when indicated.
03Long-term preventionMake the next response fasterA patient survives suspected anaphylaxis and needs diagnostic clarification and practical protection.+
- 1Record the suspected trigger, reaction features, timing and treatments in the allergy record without prematurely naming an unproven substance.
- 2Ensure two in-date auto-injectors are available when prescribed, practise device-specific technique and explain calling emergency services after use.
- 3Investigate through allergy services, address school or workplace plans and review cofactors rather than relying on a generic avoidance list.
Key medicines and prescribing safety2 treatments · regimens, roles and cautions+
Adrenaline 1 mg/mL for intramuscular injection
Adults receive 500 micrograms intramuscularly, equivalent to 0.5 mL of 1 mg/mL solution, in the anterolateral thigh; repeat after five minutes if ABC problems persist.Do not delay for venous access or antihistamine; avoid subcutaneous injection and inadvertent intravenous bolus, monitor closely, and escalate after two doses for infusion expertise.
Adrenaline auto-injector 300 micrograms
Adults prescribed this device inject one 300 microgram dose into the outer thigh at anaphylaxis onset, call emergency services and use the second device after five minutes if not improving.Prescribe the strength appropriate to weight and device guidance, teach the exact brand, carry two devices, check expiry and storage, and do not use it as permission to delay emergency contact.
08ComplicationsImportant consequences, why they occur and why they matter clinically.
Refractory anaphylaxis
Persistent ABC compromise despite two appropriate intramuscular doses requires expert management, intravenous adrenaline infusion and aggressive fluid resuscitation.
Biphasic reaction
Symptoms may recur after apparent resolution, with risk increased by severe presentation, delayed adrenaline, repeated doses or ongoing allergen absorption.
Hypoxic neurological injury
Delayed airway and circulation treatment can cause cardiac arrest, cerebral hypoxia and permanent disability even when the original trigger is later removed.
Future accidental exposure
Poor trigger documentation, absent auto-injector training or failure to refer leaves the patient vulnerable to a preventable recurrent emergency.
09Monitoring and follow-upTreatment response, safety checks and longer-term review.
- During treatment, reassess ABC continuously and document the time, route and dose of every adrenaline administration and fluid bolus.
- Select observation duration from severity, biphasic risk, comorbidity, time of day and access to emergency treatment rather than applying one interval to everyone.
- Confirm allergy referral, written emergency instructions, auto-injector supply and device technique before discharge after anaphylaxis.
- At every review of Anaphylaxis recognition and treatment, record lesion evolution, new mucosal or systemic features, medicine changes, treatment adherence and adverse effects.
- Give a named route for urgent reassessment if breathing, circulation, fever, skin pain, blistering, facial swelling, reduced urine output or other organ symptoms develop during Anaphylaxis recognition and treatment.
10Special situationsVariants, exceptions and circumstances that change the usual approach.
Position is treatment
Standing after apparent improvement can precipitate catastrophic loss of venous return, so posture must be actively supervised.
Rash is supportive not required
A sudden hypotensive or bronchospastic reaction after a likely trigger remains anaphylaxis when the skin looks normal.
Tryptase is retrospective
Sampling can support later investigation but a normal result does not reverse the clinical diagnosis or justify withholding adrenaline.
Refractory care changes route
Persistent shock after two intramuscular doses calls for expert infusion management, not an improvised intravenous bolus.
Observation follows risk
Severe reaction, delayed adrenaline, repeated doses and poor access to care increase the appropriate monitoring period.
11Common pitfallsFrequent interpretation and management errors.
- 01
Giving nebulised bronchodilator while postponing adrenaline in a wheezing hypotensive patient.
- 02
Using a 1:10,000 formulation or intravenous bolus by mistake during initial treatment.
- 03
Allowing a recovering patient to walk to the ambulance or bathroom after anaphylaxis.
- 04
Using antihistamine response as proof that airway and circulation are safe.
- 05
Discharging with an auto-injector prescription but no demonstration, second device or specialist referral.