Anaphylaxis Flashcards
Define anaphylaxis
- Acute life-threatening multisystem syndrome caused by sudden release of mast cell and basophil-derived mediators into the circulation
- Sudden onset of respiratory or cardiovascular compromise, usually with a history of allergen exposure in sensitised individuals
What are the two types?
- Immunogenic - IgE-mediated or immune complex/complement-mediated
- Non-Immunogenic - mast cell or basophil degranulation WITHOUT the involvement of antibodies (e.g. reactions caused by vancomycin, codeine, ACE inhibitors)
Explain aetiology
o On first exposure, a susceptible person forms IgE antibodies specific to the antigen presented. IgE antibodies attach to high-affinity Fc receptors on basophils and mast cells.
o On subsequent exposure, binding of antigen to the IgE antibodies triggers the degranulation of mast cells. Histamine, prostaglandin D2, leukotrienes, platelet-activating factor, tryptase, nitric oxide, and eosinophil and neutrophil chemotactic factors have diverse effects on target organs and lead to the clinical manifestations of anaphylaxis.
o These manifestations include increased vascular permeability, vasodilation, and myocardial dysfunction, leading to hypotension and cardiovascular collapse, as up to 50% of intravascular volume can shift to the extravascular compartment in minutes.
o Altered smooth muscle tone results in bronchospasm and asthma in the respiratory tract, and may also lead to uterine cramps. Activation of the autonomic nervous system causes tachycardia, anxiety, and mucus hypersecretion. Increased platelet aggregation and subsequent recruitment of more immune cells complete the picture of the systemic inflammatory response
What are the common causes?
o Drugs (e.g. penicillin)
o Latex
o Peanuts
o Shellfish
o NOTE: anaphylaxis can be caused by the repeat administration of blood products in a patient with selective IgA deficiency (due to the formation of anti-IgA antibodies)
o Specific recommendations have been made for the special case of influenza vaccine in egg-allergic children
Epidemiology
- COMMON
- The incidence of food allergic reactions that are coded as anaphylaxis is highest in young children. [9] In children, food allergy is most prevalent in the industrialised world and the emerging economies of southeast Asia, possibly due to an increased exposure to processed food. Food allergy affects both sexes equally.
What are the presenting symptoms?
- Wheeze
- Shortness of breath and a sense of choking
- Swelling of lips and face
- Pruritus
- Rash
- Diaphoresis (sweating)
- Angor Animi (sense of impending doom)
- Dizziness, tremor, disorientation
- Abdominal pain, vomiting, diarrhoea
- NOTE: patients may have a history of other hypersensitivity reactions (e.g. asthma, allergic rhinitis)
What are the signs?
- Tachypnoea
- Wheeze, over-inflated chest, use of accessory muscles
- Inspiratory stridor
- Cyanosis
- Swollen upper airways and eyes
- Bronchospasm
- Rhinitis and bilateral conjunctivitis
- Urticarial rash
- Hypotension
- Tachycardia
- NOTE: variety of signs so clinical evaluation should include all organ systems
What are the investigations?
Clinical diagnosis
• LATER: Serum tryptase (normal-high), histamine levels or urinary metabolites of histamine may help support the clinical diagnosis, rarely used
• Following an attack to prevent recurrence
o Allergen skin testing - identifies allergen and can avoid
o IgE immunoassays - identifies food-specific IgE in the serum
What’s the management plan?
- ABCDE
- High flow oxygen
- IM Adrenaline
- Chlorpheniramine (antihistamine)
- Hydrocortisone (corticosteroids)
- If continued respiratory deterioration, may require bronchodilator therapy
- Monitor pulse oximetry, ECG and BP
If patient is cardiopulmonary arrest, CPR with intubation and ventilation, IV fluids, IV adrenaline
What are the possible complications?
- SHOCK, MI
- Recurrence
- Organ damage can result from shock
What’s the prognosis?
good with prompt treatment
