Anaphylaxis

Anaphylaxis is an acute, rapidly progressive, life-threatening systemic hypersensitivity reaction caused by sudden massive release of mediators from mast cells and basophils.

It commonly begins with:

• Scalp itching

• Diffuse erythema

• Urticaria

• Angioedema

This may rapidly progress to:

• Bronchospasm

• Laryngeal edema

• Hypotension (shock)

• Gastrointestinal hyperperistalsis

• Cardiac arrhythmias

Common causes

• Antibiotics (especially penicillins)

• Other medications (NSAIDs, anesthetics)

• Radiographic contrast media

• Hymenoptera stings (bees, wasps)

• Foods — especially crustaceans, nuts, eggs, milk

Pathophysiology

Usually IgE-mediated (Type I hypersensitivity):

Allergen exposure → IgE cross-linking → mast cell degranulation → release of:

• Histamine

• Leukotrienes

• Prostaglandins

• Cytokines

Effects:

• Vasodilation → hypotension

• Increased capillary permeability → edema

• Bronchoconstriction → respiratory distress

• Mucus secretion

Signs & Symptoms

Skin (most common)

• Urticaria (hives)

• Angioedema (lips, eyelids, tongue)

• Flushing

• Generalized itching

Respiratory

• Shortness of breath

• Wheezing

• Stridor

• Hoarseness

• Laryngeal edema

Cardiovascular

• Hypotension

• Tachycardia

• Dizziness

• Syncope

• Shock

Gastrointestinal

• Abdominal cramps

• Vomiting

• Diarrhea

Neurologic

• Anxiety

• Confusion

• Collapse

Diagnostic Criteria

Clinical diagnosis — do not delay treatment for tests

Anaphylaxis is highly likely if any ONE of the following occurs rapidly after exposure to allergen:

1. Skin involvement PLUS respiratory compromise or hypotension

OR

2. Two or more of:

• Skin/mucosal symptoms

• Respiratory compromise

• Reduced blood pressure

• Persistent gastrointestinal symptoms

OR

3. Hypotension after exposure to known allergen

Investigations

(After stabilization only)

• Serum tryptase (within 1–3 hrs)

• Full blood count

• Renal and electrolytes

• Arterial oxygen saturation

• ECG if severe reaction

• Allergy testing later (skin prick/IgE)

Treatment — MEDICAL EMERGENCY

Immediate First Aid (Non-Pharmacological)

• Stop exposure to trigger

• Call emergency help

• Lay patient supine and elevate legs

• Give high-flow oxygen

• Secure airway

• Establish IV access

Pharmacological Treatment

First-line (Life-saving)

Adrenaline (Epinephrine) IM — immediately

• Adults: 0.5 mg (0.5 mL of 1:1000) IM lateral thigh

• Children: 0.01 mg/kg IM (max 0.5 mg)

• Repeat every 5–15 minutes if needed

Fluids

• Rapid IV normal saline bolus (shock)

Adjunct Medications (AFTER adrenaline)**

Antihistamines:

• Chlorpheniramine 4–16 mg POOR

• Promethazine 25–50 mg POOR

• Cetirizine 10 mg PO dailyOR

• Loratadine 10 mg PO daily

⚠ Warn patient about drowsiness

Corticosteroids

• Hydrocortisone IV (prevents biphasic reaction)

Bronchospasm

• Salbutamol nebulization

Refractory Shock

• IV adrenaline infusion (ICU care)

Observation

• Monitor at least 6–24 hours (risk of biphasic reaction)

Prevention

• Identify and avoid triggers (penicillin, foods, stings)

• Medical alert bracelet

• Prescribe adrenaline auto-injector if recurrent risk

• Educate patient and family

• Refer for allergy testing

• Exclude drug reactions or infections in recurrent acute episodes

Complications

• Airway obstruction

• Cardiac arrest

• Hypoxic brain injury

• Death

Prognosis

• Excellent with rapid adrenaline administration

• Delayed treatment increases mortality