ANAPHYLAXIS

✓ Medically ReviewedDISEASEID: MDBT0052🚨 TRIAGE: EMERGENCYICD-10: T78.2

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Definition

CLINICAL DEFINITION

Anaphylaxis is a severe systemic hypersensitivity reaction (whole-body immune overreaction). It starts rapidly within minutes to hours of trigger exposure. It involves airway, breathing, and circulation compromise (oxygen and blood flow failure). Skin or mucosal changes (hives or swelling) may occur but can be absent. Diagnosis is clinical and treatment must not be delayed for tests.

IN PLAIN ENGLISH

Anaphylaxis is a sudden severe allergy affecting the whole body. It can close the airway (breathing tube) quickly. Blood pressure can drop dangerously low. Skin may show hives (itchy welts) or swelling. It needs emergency adrenaline (life-saving injection) at once.

COMMON MISCONCEPTION / WHAT IT DOES NOT MEAN

Anaphylaxis is not simple hay fever (mild nose allergy). It is not isolated hives (skin welts only) without systemic features. It is not vasovagal syncope (reflex faint) without airway or immune signs. It is not asthma alone (lower airway narrowing only) without systemic involvement. Overlap can occur but systemic features define anaphylaxis.

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Word Breakdown

ana-

=up, back or against

phylax-

=guard or protection

-is

=process or condition

Literal Meaning: condition of against protection

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Abbreviations

IM=Intramuscular - injection into muscle, the route for emergency adrenaline

IgE=Immunoglobulin E - allergy antibody driving most anaphylaxis

IV=Intravenous - into vein, route for fluids and backup drugs

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Synonyms & Variants

Anaphylactic reaction›Anaphylactic shock›

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Category-Specific Context

Anaphylaxis is a Disease process rather than a single symptom (subjective complaint). It represents a systemic hypersensitivity state (body-wide immune emergency). It overlaps with allergy, immunology, and emergency care. It can be triggered by foods, drugs, venoms (insect stings), and latex (rubber protein). Management focuses on rapid reversal rather than long-term control alone.

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Clinical Context & Usage

CLINICAL SETTINGS

Emergency departmentPrimary care and urgent careAnaesthesia and operating theatreAllergy clinicIntensive care unitCommunity, schools and food settings

USAGE & DOCUMENTATION NOTES

Use anaphylaxis for rapid systemic reactions with airway, breathing, or circulation involvement (vital function compromise). Do not wait for skin signs (hives or swelling) to diagnose. Document trigger, timing, severity, and adrenaline (emergency injection) response. Refer all cases to allergy (immune specialty) for trigger workup. Provide action plan and auto-injector (pre-filled pen) training before discharge.

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Primary Causes & Pathophysiology

PATHOPHYSIOLOGY

Most anaphylaxis is IgE-mediated (allergy antibody driven). Trigger cross-links IgE on mast cells (tissue immune cells) and basophils (blood immune cells). Mediators (chemical signals) like histamine (vessel-leak chemical) release rapidly. Vasodilation (vessel widening) and increased permeability (leakiness) cause shock (circulation failure). Bronchospasm (airway tightening) and mucosal edema (swelling) cause breathing failure.

PRIMARY CAUSES

Peanut

IgE-mediated mast cell activation causing vasodilation and airway edema after sensitisation

Tree nuts

IgE-mediated systemic mediator release with cardiovascular and respiratory collapse

Shellfish and fish

IgE-mediated histamine and leukotriene release causing shock and bronchospasm

Cow milk and hen egg

IgE-mediated reaction especially in children causing rapid systemic symptoms

Hymenoptera venom from bee, wasp or ant sting

IgE-mediated venom hypersensitivity with massive mediator release

Natural rubber latex

IgE-mediated latex protein reaction with mucosal and airway involvement

Exercise, cold or idiopathic triggers

Non-IgE or mixed mast cell activation with cofactor augmented mediator release

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Drug-Induced Causes

💊 Beta-lactams including penicillins and amoxicillin ↗

Mechanism: IgE-mediated hypersensitivity with mast cell degranulation

→ Stop drug immediately, give intramuscular adrenaline, seek emergency care and refer to allergy

💊 Non-steroidal anti-inflammatory drugs (NSAIDs) ↗

Mechanism: IgE-mediated or COX-related leukotriene shift with airway and vascular effects

→ Stop drug, give adrenaline for systemic features, avoid culprit and test alternatives

💊 Neuromuscular blockers including rocuronium and suxamethonium ↗

Mechanism: IgE-mediated or direct mast cell activation during anaesthesia

→ Stop infusion, give adrenaline, support airway and circulation, refer for anaesthetic allergy testing

💊 Iodinated contrast media ↗

Mechanism: Direct mast cell and complement activation with anaphylactoid physiology

→ Stop injection, give adrenaline, monitor for biphasic course and plan premedication workup

💊 Vancomycin infusion ↗

Mechanism: Rate-related direct histamine release causing flushing and hypotension

→ Stop or slow infusion, give adrenaline if systemic anaphylaxis features, re-challenge only with slow protocol

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Epidemiology

Prevalence:Anaphylaxis is uncommon but increasingly recognised worldwide. It affects all ages and both community and hospital settings. Food triggers dominate in children (paediatric age group). Drug and venom triggers dominate in adults.

Age Group:All ages from infancy to old age. Food-induced events (food-triggered episodes) dominate in children and adolescents. Drug and venom events (medication and sting episodes) dominate in adults. Risk persists lifelong in sensitised (allergy-primed) individuals.

Geographic Distribution:Anaphylaxis occurs worldwide in all regions and climates. Food patterns vary by diet and exposure (local eating habits). Venom risk rises with outdoor exposure. Reporting varies but true risk is global.

Red Flags & Triage ★

TRIAGE LEVEL

🚨 EMERGENCY

DO NOT MISS — LIFE-THREATENING PRESENTATIONS

Airway obstruction needing early airway help
Hypotension and shock needing fluids and adrenaline
Biphasic recurrence within hours
Cofactors such as exercise, alcohol, infection or NSAIDs
Need for allergy referral and auto-injector provision

URGENT EVALUATION TRIGGERS

Stridor, wheeze or hypoxia after exposure
Systolic hypotension, collapse or confusion
Tongue, lip or laryngeal swelling
Rapidly spreading hives with systemic symptoms
Prior anaphylaxis with re-exposure

Contraindications & Precautions

CONTRAINDICATIONS

There are no absolute contraindications to intramuscular adrenaline for anaphylaxis

SPECIAL PRECAUTIONS

Carry adrenaline auto-injector at all times if at risk
Avoid known triggers and check food and drug labels
Inform schools, workplaces and anaesthetists about allergy history
Observe for biphasic recurrence after emergency treatment

Complications

DOWNSTREAM CLINICAL COMPLICATIONS

Upper airway obstruction from laryngeal edema
Cardiovascular collapse and shock
Respiratory failure from bronchospasm
Biphasic anaphylaxis with late recurrence
Hypoxic brain injury and death

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Confused With (LASA & DDx) ★

LEXICAL (LASA) — SIMILAR NAMES

Prophylaxis

Similar spelling to anaphylaxis leading to prescribing or documentation mix-up

Anaphylactoid

Older term now grouped under anaphylaxis causing classification confusion

CLINICAL DIFFERENTIAL DIAGNOSES (DDx)

Asthma exacerbation

Key Distinguishing Feature: Wheeze without hypotension, urticaria or trigger-linked systemic collapse

Hereditary angioedema

Key Distinguishing Feature: Non-pruritic swelling without hives and poor adrenaline response, C1-esterase defect

Vasovagal syncope

Key Distinguishing Feature: Bradycardia and pallor with rapid recovery, no airway edema or hives

Septic shock

Key Distinguishing Feature: Fever and infective source with slower onset, not trigger-linked minutes

Mastocytosis with mediator release

Key Distinguishing Feature: Recurrent flushing with baseline tryptase elevation and clonal mast cells

Panic attack with hyperventilation

Key Distinguishing Feature: Tingling and rapid breathing without hypotension, wheeze or swelling

Urticaria without anaphylaxis

Key Distinguishing Feature: Hives only without airway, breathing or circulation compromise

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Clinical Pearls

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Give intramuscular adrenaline into mid-outer thigh without delay when anaphylaxis is suspected.

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Skin signs may be absent in up to one in five cases, so normal skin does not rule out anaphylaxis.

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Position patient supine with legs raised unless breathing is easier sitting, and avoid sudden standing.

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Take timed tryptase samples to support later allergy review and trigger confirmation.

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Always refer to allergy, provide action plan, and check auto-injector technique before discharge.

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Example Usage & SOAP

CLINICAL SENTENCE

""22-year-old with peanut exposure developed wheeze and low pressure from anaphylaxis needing adrenaline.""

IN A SOAP NOTE

S: Sudden breathlessness, throat tightness and dizziness 10 min after peanut biscuit. O: BP 78/42, HR 128, RR 28, SpO2 89 percent on air, Temp 37.1C, widespread wheeze and lip swelling. A: Anaphylaxis with shock and airway involvement. P: IM adrenaline thigh, high-flow oxygen, IV fluids, monitor, tryptase timing, allergy referral and auto-injector training.

DIFFERENTIAL DIAGNOSIS CONTEXT

Young adult with wheeze and collapse after penicillin was assessed for asthma versus anaphylaxis. Presence of hypotension, angioedema (swelling) and rapid trigger link favoured anaphylaxis. Asthma alone rarely causes shock (circulation failure). Adrenaline was given as emergency treatment.

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Classifications & Scoring

GRADING SYSTEM

Ring and Messmer scale

Four-grade severity scale from skin signs to cardiac arrest for perioperative hypersensitivity reactions

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Prognosis

SHORT-TERM OUTCOME

Most treated promptly recover fully within hours. Delay in adrenaline (emergency injection) worsens outcomes. Biphasic recurrence (return hours later) can occur within 4 to 12 hours. Observation is needed even after initial improvement.

LONG-TERM PROGNOSIS

Long-term outlook is good with trigger avoidance (staying away) and action planning. Recurrence risk remains if trigger re-exposure occurs. Allergy follow-up improves identification (finding cause) and safety. Fatality is rare but possible without rapid treatment.

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References & Coding

ICD-10 DIAGNOSTIC CODE

T78.2

LITERATURE CITATIONS & GUIDELINES

[1]World Allergy Organization Anaphylaxis Guidelines 2020

[2]NICE CG134 Anaphylaxis 2011

[3]Resuscitation Council UK Emergency treatment of anaphylaxis 2021

MEDICAL DISCLAIMER — This content is intended for educational purposes and qualified healthcare professionals only. Always refer to current clinical diagnostic criteria, institutional protocols, and official guidelines. Medobo is not responsible for clinical decisions made based on this content.