Anaphylaxis: Emergency Diagnosis and Immediate Management (High-Yield Guide)

A) Clinical diagnosis

Think anaphylaxis if acute onset (minutes to hours) after a likely trigger with:

• Skin/mucosal signs: urticaria, flushing, lip/tongue swelling, angioedemaplus

• Respiratory compromise: wheeze, dyspnea, stridor, hoarsenessor

• Circulatory compromise: hypotension, syncope, shock

Also call it anaphylaxis if there is hypotension / bronchospasm / laryngeal edema after allergen exposure even without rash.

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B) Physical examination

Focus on ABCDE

Airway

• lip/tongue swelling → angioedema

• uvular edema → angioedema

• hoarseness

• stridor

Breathing

• tachypnea

• wheeze

• hypoxia

• respiratory distress

Circulation

• tachycardia

• hypotension

• weak pulse

• poor perfusion

Disability

• dizziness

• confusion

• syncope

Exposure

• urticaria

• flushing

• angioedema

  
  

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C) Labs / workup to send

Do not delay treatment for labs.

Support diagnosis

• Serum tryptase: immediate sample, repeat later if admitted

Assess severity

• CBC

• electrolytes

• BUN/Cr

• glucose

• ABG if severe

• ECG / cardiac monitor if unstable or IV adrenaline infusion needed

Later

• allergy workup / follow-up clinic in 1 week

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D) Management cheat sheet

First-line

• Adrenaline (1:1000) 0.5 mg IM stat in adult

• Repeat every 5 min if not improved

Supportive

• remove trigger

• lay flat, elevate legs

• oxygen if SpO2 <94%

• IV access

• NSS bolus

• monitor vital signs frequently

If bronchospasm

• Salbutamol nebulization

Adjuncts

• antihistamine

• steroidThese are not first-line.

If poor response after 2 IM doses

• consider IV adrenaline infusion with ECG monitoring
  

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E) Observation / disposition

• observe for biphasic reaction at least 4 hours after improvement

• admit if severe, repeated adrenaline needed, airway involvement, shock, asthma, arrhythmia, beta-blocker use, or poor home observation

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F) Ultra-high-yield memory

Anaphylaxis = acute allergy + airway / breathing / circulation problem First drug = IM adrenaline Treat first, labs later Observe for at least 4 hours

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1. Introduction

Anaphylaxis is a severe, life-threatening systemic hypersensitivity reaction characterized by rapid onset and potential progression to airway obstruction, respiratory failure, or circulatory collapse. Immediate recognition and treatment are critical, as delayed management significantly increases morbidity and mortality.

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2. Definition of Anaphylaxis

Anaphylaxis is diagnosed clinically, not by laboratory tests.

Diagnostic Criteria (Simplified for Exams)

Anaphylaxis is highly likely when there is:

A. Acute onset (minutes–hours) with:

• Skin/mucosal involvement(urticaria, flushing, angioedema)

PLUS at least one of:

• Respiratory compromise(dyspnea, wheeze, stridor, hypoxia)

• Reduced blood pressure or end-organ dysfunction(syncope, hypotension)
  

B. OR hypotension/airway compromise after allergen exposure

(even without skin findings)

⚠️ Exam Pearl

• ❗ No rash ≠ not anaphylaxis

• ❗ Airway symptoms + hypotension = anaphylaxis until proven otherwise

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3. Pathophysiology (High-yield)

• Trigger → IgE-mediated mast cell activation

• Release of mediators:

  • Histamine

  • Leukotrienes

  • Prostaglandins

Effects:

• Vasodilation → hypotension

• Increased permeability → edema (angioedema)

• Bronchoconstriction → wheezing

• Mucosal edema → airway obstruction

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4. Clinical Features

Skin

• Urticaria, pruritus

• Angioedema (lips, tongue, eyelids)

Respiratory

• Dyspnea, wheezing

• Stridor, hoarseness (⚠️ airway obstruction)

Cardiovascular

• Hypotension

• Tachycardia, shock

Gastrointestinal

• Abdominal pain, vomiting, diarrhea

🚨 Red Flags (Severe)

• Tongue swelling

• Voice change

• Stridor

• Hypotension

• Altered consciousness

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5. Management of Anaphylaxis

Management Setting

➡️ Emergency / IPD (Inpatient)Because risk of:

• Airway obstruction

• Shock

• Biphasic reaction
  

Primary Survey (ABCDE Approach)

A – Airway

• Look for:

  • Tongue swelling

  • Hoarseness

  • Stridor

• Prepare for early intubation
  

B – Breathing

• Assess RR, SpO₂

• Give high-flow oxygen
  

C – Circulation

• Monitor BP, pulse

• Establish IV access
  

D – Disability

• GCS, mental status
  

E – Exposure

• Look for rash, urticaria
  

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6. Definitive Treatment (MOST IMPORTANT)

✅ Epinephrine (Adrenaline) — FIRST LINE

Dose:

• Adult: Adrenaline (0.5 mg), 1×1 IM, repeat every 5 min if needed

• Child: 0.01 mg/kg IM

📌 From CMU guideline:

• Max adult dose = 0.5 mg

💡 Why Epinephrine?

• Vasoconstriction → ↑ BP

• Bronchodilation → ↓ wheeze

• ↓ mucosal edema → protects airway

❗ Exam Rule

✅ Give immediately ❌ DO NOT wait for labs ❌ DO NOT start with an antihistamine or a steroid

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7. Supportive Management

Fluids

• Normal saline bolus

  • Adult: 500–1000 mL IV

  • Child: 10 mL/kg

Oxygen

• If SpO₂ < 94% → give oxygen

Monitoring

• Vital signs every:

  • 10–15 min if unstable

  • 30–60 min if stable

Bronchodilator

• For bronchospasm:

  • Salbutamol nebulization

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8. Adjunct Medications (NOT FIRST LINE) ❗ Antihistamines

• Chlorpheniramine 10 mg IV q6 hr

• Only improves skin symptoms

❗ Corticosteroids

• Hydrocortisone / methylprednisolone

• Role:

  • Reduce prolonged inflammation

  • NOT life-saving in the acute phase

❌ Key Exam Trap

• Steroid ≠ emergency treatment

• Antihistamine ≠ airway protection

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9. Special Situations

Beta-blocker patient

• May have refractory shock

Treatment:

• Glucagon IV

• Atropine if bradycardia

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10. Laboratory Workup

⚠️ Important Rule

👉 Diagnosis is clinical → DO NOT delay treatment

1. Confirm Diagnosis

Serum tryptase

• Take:

  • Immediately

  • Repeat at 24 hours if admitted
    

2. Severity Monitoring

• CBC

• Electrolytes

• Renal function

• ABG (if severe)

• ECG (if unstable)
  

3. Identify Cause (Later)

• Allergy testing

• Specific IgE

• Detailed history
  

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11. Observation & Disposition

Observe for a biphasic reaction

• At least 4 hours after symptom improvement

Admit if:

• Severe anaphylaxis

• 1 dose epinephrine

• Airway involvement

• Comorbid disease (asthma, arrhythmia)

• Lives far / cannot observe symptoms

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12. Discharge Plan

Epinephrine auto-injector

• ≥30 kg → 0.3 mg ×2 doses

• <30 kg → 0.15 mg ×2 doses

Follow-up

• Allergy clinic in 1 week

Patient education

• Avoid trigger

• Recognize early symptoms

• Use epinephrine immediately

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13. Key Exam Summary

🔑 “EPI FIRST, EVERYTHING ELSE LATER”

Step	Action
1	IM Epinephrine
2	Oxygen + IV fluid
3	Monitor vital signs
4	Bronchodilator if wheeze
5	Antihistamine/steroid (adjunct only)

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14. High-Yield MCQ Pearls

• First-line drug: Epinephrine IM

• Most dangerous sign: Airway edema (stridor, tongue swelling)

• Diagnosis: Clinical, not lab

• Observation: ≥4 hours

• Biphasic reaction: can recurrent later

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Conclusion

Anaphylaxis is a time-critical emergency requiring immediate IM epinephrine, aggressive supportive care, and close monitoring. Laboratory tests support diagnosis but must never delay treatment. Early recognition and correct management are essential to prevent mortality.