Understanding Allergies and Anaphylaxis

Sep 4, 2024

Chapter 21: Allergy and Anaphylaxis

Learning Objectives

  • Understand anatomy, physiology, and pathophysiology of hypersensitivity disorders and anaphylactic reactions.
  • Recognize and manage hypersensitivity disorders and anaphylactic reactions.

Key Concepts

  • Immunology: Study of the body's immune system.
  • Allergic reactions involve acute airway obstruction and cardiovascular collapse.

Anatomy and Physiology

  • Immune System: Protects the body from foreign substances.
    • Initiates responses to deactivate invaders.

Pathophysiology

  • Allergic Reaction: Exaggerated immune response.
    • Caused by immune system, not directly by the allergen.
    • Chemicals involved: Histamines and Leukotrienes.
  • Anaphylaxis: Severe, life-threatening reaction involving multiple organ systems.
    • Signs: Urticaria (hives), Angioedema, Wheezing, Stridor, Hypotension, Nausea, Vomiting, Abdominal cramps.

Common Allergens

  1. Food: Shellfish, peanuts may trigger anaphylaxis.
  2. Medications: Antibiotics (penicillin) and NSAIDs.
  3. Plants: Dust, pollens, ragweed, ryegrass.
  4. Chemicals: Makeup, soap, latex.
  5. Insect Bites/Stings: Bees, wasps, hornets, fire ants.
    • Stingers can inject venom for up to 20 minutes.

Patient Assessment

  • Scene Size-Up: Ensure safety, identify potential allergen sources.
  • Primary Assessment: Focus on ABCs, look for respiratory/cardiovascular distress.
  • History Taking: Identify signs/symptoms, obtain SAMPLE history.
  • Secondary Assessment: Perform rapid physical exam, check vital signs.
  • Reassessment: Monitor for changes, especially for signs of shock.

Treatment & Interventions

  • Mild Reactions: Supportive care and monitoring.
  • Anaphylaxis: Epinephrine (EpiPen) and ventilatory support.
    • Epinephrine: Sympathomimetic hormone, causes vasoconstriction, reverses anaphylactic effects.
    • Adult dose: 0.3 mg; Child dose: 0.15 mg.
    • Side Effects: High BP, increased pulse, anxiety, cardiac arrhythmias.
  • Always transport to hospital even if symptoms improve.

Emergency Care

  • Remove stingers without forceps.
  • Wash area, apply ice for short periods.
  • Position injection site below heart.
  • Provide oxygen, monitor signs.

Review Questions

  • Signs of allergic reaction caused by histamines and leukotrienes.
  • Effects of anaphylactic shock: Vasodilation, bronchoconstriction.
  • Common triggers and treatments discussed in scenarios.

Conclusion

  • Recognize, assess, and treat allergic reactions and anaphylaxis.
  • Administer EpiPen appropriately and know its effects.