Anaphylaxis and anaphylactic shock

Anaphylaxis and anaphylactic shock 

Updated: 06/20/22

© Jun Wang, MD, PhD

Definition
  • Anaphylaxis: Severe, generalized or systemic, rapid onset, life threatening allergic reaction
    • Uniphasic anaphylaxis: most common type, usually peaks within an hour after symptoms appears and resolved either spontaneously or after treatment within an hour
    • Biphasic anaphylaxis: a uniphasic anaphylaxis, followed by an asymptomatic period and a second reappearance of presentations of anaphylaxis without additional exposure to allergen
    • Protracted anaphylaxis: anaphylactic reaction lasting hours or days without complete resolving of presentations
  • Anaphylactic shock: Anaphylaxis with life-threatening hypotension, a type of distributive shock
Common triggers
  • Medication: beta-lactam antibiotics, radiocontrast, etc
  • Blood products: esp for patients with Isolated IgA deficiency
  • Food: nuts, milk, certain sea food
  • Insect sting: wasp, honeybees, fire ants, etc
Pathophysiology
  • Key words: basophils, mast cells
  • Activation of basophils and/or mast cells
    • Immunologic: Mediated by IgE, IgG, Immune complex/complement
    • Non immunologic: activation of basophils/mast cells without involvement of immune factors
      •  Activation of complement directly by medications
      • Activation of mast cells by vancomycin
      • Histamine release by opioid
      • Cold urticaria, etc
  • Release of granule contents
    • Histamine: Activate H1 and H2, causing tachycardia, hypotension, vasodilation, increased permeability, bronchospasm, pruritis
    • Cytokines: inflammatory reaction
    • Protease: collagen and proteoglycan degradation
  • Other mediators: platelet activating factor, Nitric oxide, arachidonic acid metabolites, etc
  • Biphasic anaphylaxis: detailed pathophysiology unclear, likely associated with activation of secondary inflammatory reactivities by inflammatory cells recruited during the initial event
Clinical presentations
  • Sudden onset, rapid progress
  • Multiorgan manifestations
  • Symptoms
    • Skin and mucosa: pruritis
    • Respiratory: nasal congestion, rhinorrhea, sneezing, throat tightness, etc
    • Cardiovascular: weakness, syncope, chest pain, palpitations
    • Gastrointestinal: dysphagia, nausea, vomiting, diarrhea, etc
    • Neurologic: Headache, dizziness, blurred vision, etc
  • Physical examination
    • Skin and mucosa: flushing, urticaria, angioedema, cutaneous/conjunctival infection, swelling, etc
    • Respiratory: angioedema,, laryngeal edema, mucus hypersecretion, bronchospasm, etc
    • Cardiovascular: tachycardia, rarely bradycardia (due to conduction defects, etc)
    • Gastrointestinal: abdominal distension, etc
    • Neuroloical: altered mentation, depressed consciousness, agitation, combative
Key Laboratory findings
  • Elevated serum/plasma tryptase: more common if associated with inset venom or medication
  • Plasma histamine: typically peak within 5-15 minutes and decline to baseline in an hour
  • Urine histamine and histamine metabolites
  • Skin testing: allergen, IgE-independent reactions
Diagnostic criteria
  • Acute onset of skin and/or mucosal manifestations including generalized urticaria and one of the following
  • Rapid development of two or more of the presentations listed below after exposure to a likely allergen
    • Skin/mucosa manifestations such as urticaria, angioedema,, etc 
    • Respiratory compromise: Dyspnea, wheeze/bronchospasm, stridor, reduced peak expiratory flow, hypoxemia
    • Hypotension or end organ dysfunction: hypotonia, syncope, incontinence, etc
    • Persistent gastrointestinal presentations: crampy abdominal pain, vomiting
  • Allergen induced 30% or more reduction of blood pressure
Management
  • Medical emergency that need immediate recognition and intervention
  • Removal of triggering factors: Blood products, medication, etc
  • High-flow oxygen, airway management, cardiac monitoring, IV access, even for asymptomatic pt if history positive for severe allergic reaction and re-exposed to allergen
  • Pharmacological management: epinephrine, antihistamines, corticosteroids, bronchodilators, etc


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