Anaphylaxis Flashcards
Define anaphylaxis
Anaphylactic shock is a rapid onset, severe Type 1 IgE-mediated hypersensitivity reaction that occurs when an individual is exposed to certain precipitants. E.g nuts, eggs, stings
HYPOTENSION AND LIFE THREATENING
What is Type I hypersensitivity?
Classical allergy, mediated by the inappropriate production of specific IgE antibodies to harmless antigens
E.g allergies
What is Type II hypersensitivity?
Caused by IgG and IgM antibodies that bind to antigens cells or tissues leading to cell or tissue damage
E.g Goodpastures, blood transfusion reactions & haemolytic disease of newborn
What is Type III hypersensitivity?
Caused by antibody-antigen complexes being deposited in tissues, where they activate the complement system and cause inflammation
E.g Rheumatoid arthritis, farmers lung
What is Type IV hypersensitivity?
A delayed type hypersensitivity reaction caused by T helper cells traveling to the site of antigens, recruiting macrophages and causing inflammation
E.g poison ivy, gold and nickel, mantoux test
What is the name of the classification system for hypersensitivity reactions?
Gell and Coombs
What are the symptoms of anaphylaxis?
Skin reactions: widespread urticaria, itching, flushed skin
Respiratory symptoms: swollen tongue/lips, sneezing, wheezing
Gastrointestinal symptoms: abdominal pain, nausea, vomiting, diarrhoea
Tachycardia
Hypotension
What is the blood test specific for anaphylactic reactions?
Anaphylaxis can be confirmed by measuring serum levels of mast cell tryptase.
This is usually taken after the patient is stabilised.
What is the mechanism of anaphylaxis
Exposure of susceptible individuals to allergen results in the production of IgE antibodies and the release of inflammatory mediators from mast cells.
Local histamine release causes bronchoconstriction, vasodilation and increased vessel permeability.
Does anaphylaxis require prior exposure?
YES - there is a sensitisation reaction that occurs on first exposure (which does not result in anaphylaxis), and it is only on subsequent exposure to an allergen, that anaphylaxis occurs.
What is the inital management of anaphylaxis?
Initial assessment of acutely unwell child is with an ABCDE approach, assessing and treating:
A – Airway: Secure the airway
B – Breathing: Provide oxygen if required. Salbutamol can help with wheezing.
C – Circulation: Provide an IV bolus of fluids
D – Disability: Lie the patient flat to improve cerebral perfusion
E – Exposure: Look for flushing, urticaria and angio-oedema
What medications are used in the management of anaphylaxis?
Once a diagnosis of anaphylaxis is established, there are three medications given to treat the reaction:
Intramuscular adrenalin, repeated after 5 minutes if required
Antihistamines, such as oral chlorphenamine or cetirizine
Steroids, usually intravenous hydrocortisone
What are the risk factors for anaphylaxis?
There is an increased risk of anaphylaxis in those with a family history of atopy, bronchial asthma and those on corticosteroid/ACEi/beta-blocker therapy.
Define prevalence?
The NUMBER OF CASES of a disease in a specific population at a particular time point or over a specific point in time
Define incidence?
The rate of NEW CASES of a disease occurring in a specific population over a particular period of time
