⚠️ Chapter 6: Anaphylaxis Epinephrine First · Airway · Fluids · H1/H2 Blockers · Steroids

Life-threatening systemic reaction · IM epinephrine 0.01 mg/kg · Airway compromise · Hypotension · Biphasic reaction

⚠️ Anaphylaxis: Acute Life-Threatening Systemic Reaction

🩸 Definition & Triggers
Acute systemic reaction from mast cell/basophil mediator release. Triggers: foods (peanuts, shellfish, milk), drugs (penicillin, NSAIDs), latex, insect stings, idiopathic.
🚨 Clinical Features
• Respiratory: stridor, wheezing, dyspnoea, laryngeal oedema
• Cardiovascular: hypotension, shock, arrhythmias
• Cutaneous: urticaria, angioedema, flushing
• GI: nausea, vomiting, diarrhoea
• Feeling of impending doom
💉 FIRST-LINE: EPINEPHRINE
• IM dose: 0.01 mg/kg (0.01 ml/kg) of 1:1000, max 0.3-0.5 mg
• Repeat every 5-20 min as needed
• IV epinephrine (0.05-0.1 ml/kg of 1:10,000) for refractory shock
💧 Supportive Measures
• 100% oxygen, secure airway (early intubation if stridor/altered sensorium)
• Rapid fluid bolus: 20 mL/kg crystalloid, repeat as needed
• H1 antihistamine: diphenhydramine 1-2 mg/kg IV
• H2 blocker: ranitidine 1 mg/kg IV
• Corticosteroids: hydrocortisone 1 mg/kg or methylprednisolone 0.5-1 mg/kg
🔄 Refractory Anaphylaxis
• IV epinephrine infusion: 0.05-0.2 mcg/kg/min
• Vasopressors (dopamine 5-10 mcg/kg/min)
• Glucagon: 0.04 mg/kg IV (if on beta-blockers)
• Prolonged resuscitation encouraged
⚠️ Biphasic Reaction
Recurrence of symptoms hours after apparent remission (up to 72 hours). All patients require observation (8-24 hours after resolution).
📌 Critical Pearl: Epinephrine is the ONLY first-line drug. Do NOT delay for antihistamines or steroids. IM into thigh (vastus lateralis) for fastest absorption. If airway compromise from angioedema, intubate early — can become impossible later.

🩺 Step-by-Step: Anaphylaxis Management Algorithm

1
Recognise anaphylaxis
Sudden onset of respiratory symptoms (stridor, wheeze, dyspnoea) OR hypotension (or end-organ dysfunction) AND/OR skin/mucosal changes (urticaria, angioedema) after exposure to known trigger. Feeling of impending doom.
2
Immediate actions
• Remove trigger (stop medication, remove insect stinger)
• Call for help (MET/code)
• Place patient recumbent, elevate lower extremities (if no respiratory distress)
3
FIRST-LINE: Epinephrine IM
• Dose: 0.01 mg/kg (0.01 ml/kg) of 1:1000 epinephrine
• Maximum: 0.3 mg (child) / 0.5 mg (adolescent)
• Site: mid-anterolateral thigh (vastus lateralis)
• Repeat every 5-20 minutes if no response
4
Airway & Breathing support
• 100% oxygen via non-rebreather mask
• If stridor, desaturation, altered sensorium → bag-mask ventilation
• Intubate EARLY by most experienced clinician (angioedema worsens quickly)
• Consider cricothyroidotomy if cannot intubate/ventilate
5
Circulation support
• Establish IV/IO access (two large-bore if possible)
• Rapid fluid bolus: 20 mL/kg isotonic crystalloid, repeat as needed (may require 40-60 mL/kg)
• If hypotensive despite epinephrine and fluids → IV epinephrine infusion (0.05-0.2 mcg/kg/min) or vasopressors
6
Adjunctive medications (second-line)
• H1 antihistamine: diphenhydramine 1-2 mg/kg IV
• H2 blocker: ranitidine 1 mg/kg IV
• Inhaled beta-agonist (albuterol) for bronchospasm
• Corticosteroids: hydrocortisone 1 mg/kg or methylprednisolone 1 mg/kg IV (prevent biphasic reaction)
7
Refractory anaphylaxis & special situations
• IV epinephrine infusion if no response to 3 IM doses
• Glucagon 0.04 mg/kg IV (if on beta-blockers)
• Prolonged resuscitation encouraged — better outcomes than other causes of arrest
• Observe for biphasic reaction (up to 72 hours)