Anaphylaxis

Definition

• Anaphylaxis: A severe, systemic hypersensitivity reaction characterized by multi-system involvement, which can lead to shock, airway compromise, and even death if not treated promptly.

Causes

• Common triggers include foods (e.g., nuts, shellfish), medications (e.g., antibiotics, non-steroidal anti-inflammatory drugs), insect stings (e.g., wasps, bees), and latex.
• Some cases are idiopathic, with no identifiable cause.

Pathophysiology

• Anaphylaxis involves an IgE-mediated immune response, leading to the release of histamine and other mediators from mast cells and basophils. This causes vasodilation, increased vascular permeability, and smooth muscle contraction.

Clinical Features

• Skin: Urticaria (hives), angioedema, flushing, or pruritus.
• Respiratory: Dyspnoea, wheezing, cough, and throat tightness, potentially leading to airway obstruction.
• Cardiovascular: Hypotension, tachycardia, and in severe cases, shock.
• Gastrointestinal: Abdominal pain, vomiting, and diarrhoea.
• Neurological: Dizziness or loss of consciousness.

Diagnosis

• Primarily clinical, based on the rapid onset of symptoms affecting the skin/mucosa AND at least one of the following: respiratory compromise, reduced blood pressure or associated symptoms, persistent gastrointestinal symptoms.
• Serum tryptase levels may be elevated post-event and can support the diagnosis.

Management (UK Guidelines)

1. Immediate Actions:
   • Remove the Trigger: If possible, immediately remove the source of the allergen (e.g., stop drug administration).
   • Call for Help: Activate emergency medical services or alert the emergency response team in a hospital setting.
2. Medication:
   • Adrenaline: The first-line treatment for anaphylaxis.
     • Administer an intramuscular injection into the mid-outer thigh.
     • Adult and child >12 years: 500 micrograms IM (0.5 mL)
     • Child 6–12 years: 300 micrograms IM (0.3 mL)
     • Child 6 months to 6 years: 150 micrograms IM (0.15 mL)
     • Child <6 months: 100–150 micrograms IM (0.1–0.15 mL)
     • Repeat every 5 minutes as necessary.
     • Antihistamines and Corticosteroids: Although not primary treatments, they can be used adjunctively to help control symptoms. Antihistamines can help with itching and hives, while corticosteroids can prevent delayed reactions.
3. Airway Management:
   • Give high flow oxygen
   • Ensure the airway is open and clear. In severe cases, intubation may be required.
4. Fluid Resuscitation:
   • Administer intravenous fluids to counteract hypotension, especially in the case of shock.
     • Adults: 500–1000 mL
     • Children: 10 mL/kg
5. Observation and Monitoring:
   • Monitor vital signs and clinical state continuously. Patients should be observed for at least 6-12 hours as biphasic reactions can occur.
6. Long-Term Management:
   • Allergen Identification and Avoidance: Refer to an allergy specialist for identification of specific allergens and advice on avoidance strategies.
   • Adrenaline Auto-Injector: Prescribe for patients at risk of future anaphylaxis and ensure they and their families are trained in its use.
   • Patient Education: Provide information on anaphylaxis recognition and the importance of wearing medical alert identification.