Allergy

Pathophysiology

Both angioedema and urticaria involve vasoactive mediators such as histamine, serotonin and kinins.  The resultant postcapillary venule inflammation causes fluid leakage à edema.  Mechanisms include IgE mediated angioedema/urticaria (Ag ingestion or parenteral exposure), complement mediated angioedema/urticaria (i.e. serum sickness), hereditary angioedema (i.e. C-1 esterase inhibitor deficiency), and idiopathic angioedema (mast cell releasing agents in certain compounds like radioactive contract or ACEi).

  • Angioedema: involves vessels in the layers of skin below the dermis
  • Urticaria: involves vessels in layers of the skin above the dermis

Angioedema

  • Less itching as fewer mast cells and nerves in the deeper layers of the skin
  • Not as red because deeper layers involves
  • Well demarcated, localized, non-pitting edema

Urticaria

  • In 20% of cases the cause is never determined
  • Intense itching (many mast cells and nerves in epidermis)
  • Well circumscribed wheals, raised erythematous borders, central blanching

ER Assessment

  • ABC’s



 

Medications

  • 1) Diphenhydramine 50mg IV/IM/PO; in pediatrics 1-2mg/kg IV/IM/PO
  • 2) Epinephrine 0.3-0.5mg of a 1:1000 solution IM; in pediatrics 0.01mg/kg SC
  • 3) Cimetidine 300mg IV/IM; Ranitidine (Zantac) 50mg IV/IM q6-8h or 150mg PO bid
  • 4) Methylprednisone 75-125mg IV/IM; in pediatrics 1-2mg/kg IV/IM
  • 5) Hydrocortisone (Solucortef) 500mg IV; in pediatrics 4-8mg/kg IV
  • 6) If on beta blockers give Glucagon 1mg IV

Admission

Necessary when systemic symptoms do not resolve in ER for ongoing monitoring.  Patients may be discharged if their symptoms were minor and they show no recurrence after 4hr of observation.  Patients should be on a short course of steroids and antihistamines (2-4 days).  Obviously stop causative agents and document it!  In anaphylaxis a follow up with an allergist is recommended (document), as well as they should be given a prescription for an Epipen (document).  Patients should be followed-up with a GP within 48hr of discharge to evaluate outpatient therapy.

Anaphylaxis

  • Description
    • Severe allergic reaction
    • Dermal and systemic signs and symptoms manifest
    • Urticaria and/or angioedema with hypotension and bronchospasm
    • In a sensitized individual
  • Causes
    • Drugs (penicillin, ASA, sulpha)
    • Foods (tree nuts, shellfish, eggs, strawberry)
    • Insect stings/bites
  • Signs and Symptoms
    • Skin urticaria/angioedema
    • Mucous membrane edema
    • Upper respiratory tract edema and hypersecretion (rhinorrhea, cough)
    • Lower respiratory tract (bronchospams)
    • CVS (vasodilatation, shock)
    • GI (pain, N/V)
  • Most common cause of death in anaphylaxis is complete airway obstruction
  • Treatment
    • ABCs and ongoing monitoring
    • Ventilation and oxygenation (Beta2-agonist bronchodilators – ventolin)
    • Epinephrine
    • Volume resuscitation
    • Antihistamines
    • Corticosteroids
    • Glucagon

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