24 - Hypersensitivity and Anaphylactic Shock Flashcards
What is shock
Failure to maintain adequate cardiac output
What are the different types of shock
Hypovolemic
Obstructive
Cardiogenic
Distributive
Hypovolemic shock causes
Haemorrhage
Severe fluid loss
Obstructive shock causes
Pulmonary embolus or tamponade so fluid accumulates
Causes of cardiogenic shock
Myocardial Infarction
Valvular disease
Myocarditis
Cardimyopathy
Causes of distributive shock
Septic
Anaphylactic
Neurogenic
IgG
can block pathogen binding, activate complement, & opsonise antigen for phagocytes. It is specially transported across the placenta
IgM
block pathogen binding, activate complement
IgA
block pathogen binding. present in secretions: tears, digestive juices, breast milk
IgE
Activates mast cells
IgD
not secreted, & function is unknown
How are mast cells and basophils activated
1 - Cross linking of surface Ige by antigen
2 - Complement - C3a and C35
3 - Via nerves
4 - Direct contact with pathogen
What is type 1 sensitivity
Mast cell activation and release of mediators
What are some examples of mediators
Histamine
Leukotrienes
Prostaglandins
What is the action of histamine
Increase in permeability of post capillary venules, vasodilation of arterioles, contraction of smooth muscles, itch
What is the action of leukotrienes
Increase permeability of post capillary venules, chemotaxis
What is the action of prostaglandins
Arteriolar dilation
Pain
Fever
What is Atopy
the inherited predisposition to make IgE to common environmental antigens
Clinical manifestations of type 1 hypersensitivity
- Local. Allergic rhinitis, asthma, atopic eczema, some urticaria, some angioedema
- Systemic: anaphylactic shock. patient does NOT have to be atopic to get anaphylactic shock.
Clinical manifestations of anaphylactic shock
Drop in BP - redistribution (often warm peripheries) Urticaria (hives) Sore, red itchy eyes Angiodema (swelling in SC tissue) Bronchoconstriction - wheeze, respiratory obstruction Nausea and vomiting Diarrhoea Headache Feeling of impending doom Cardiac arrest and death
Antigens that trigger anaphylaxia
Drugs - B lactams have cross reactivity, NSAIDs, Insulin, local and general anaesthetics
Food - Peanuts, milk, eggs
Arthropod venoms - bee stings
Acute treatment of anaphylaxia
Intramuscular adrenaline - 500micrograms in 0.5mls
Epipen can be self administered - 300micrograms in 0.3mls
Oxygen
IV Fluids
Antihistamines
Glucocorticosteroids
Antihistamine example
Chlorpheniramine (10mg IM or IV)
Glucocorticosteroid example
200mg hydrocortisone
Differential diagnosis
Anaphylactoid shock - pseudo, non allergic
Idiopathic angiodema, hereditory angiodema (do not respond to adrenaline)
What is anaphylactoid shock
Same as anyphylaxis but no IgE involved
Mast cells and basophils are activated by a different mechanism
IV contrast media
What can you use to treat hereditary angiodema
C1 esterase inhibitor
How to prevent anaphylaxis
Take careful history
Desensitisation
Omalizumab - IgE monoclonal antibody (too expensive and requires injections forever)
