Paeds - allergies Flashcards
What is the definition of an allergy, an allergen and an atopy?
Allergy = hypersensitivity of the immune system to allergens
Allergens = proteins that the immune system recognises as foreign and potentially harmful, leading to an allergic immune response.
These proteins are types of antigens. (the antigens that trigger the hypersensitivity reactions are called allergens)
Atopy = a predisposition to having hypersensitivity reactions to allergens, or the tendency to develop conditions atopic conditions (eczema, asthma, hayfever, allergic rhinitis, food allergies)
What is the Coombs and Gell classification?
Used to describe the underlying pathology of different hypersensitivity reactions:
Type 1 = IgE antibodies to a specific allergen trigger mast cells and basophils to release histamines and other cytokines. Results in an immediate reaction.
(Eg. food allergy reactions where exposure to allergen results in an acute reaction like itching, facial swelling, urticaria, anaphylaxis)
Type 2 = IgG and IgM antibodies reac to an allergen and activate the complement system resulting in direct damage to local cells.
(Eg. haemolytic disease of the newborn and transfusion reactions)
Type 3 = Immune complexes accumulate and cause damage to local tissues
(autoimmune conditions Eg. SLE, RA, Henloch-Schonlein purpura)
Type 4 = cell mediated hypersensitivity reactions caused by T lymphocytes. T cells are inappropriately activated, causing localised inflammation and damage.
(Eg. organ transplant rejection, contact dermatitis)
How would you investigate for an allergy?
- a detailed hx
- timing after exposure to allergen, prev and subsequent exposure and reaction to allergen, symptoms (rash, swelling, breathing difficulty, wheeze, cough), fhx of atopy or personal hx of atopy
-
Skin prick testing and RAST testing assess sensitisation not allergy
- ie patient can be sensitised but it may still be safe to eat that food
- Food challenge testing is gold standard
- Patch test is helpful for diagnosing allergic contact dermititis
How would you manage an allergy patient following an exposure?
How would you prevent future reactions?
- antihistamines eg. cetirizine
- steroids (eg. oral prednisolone, topical hydrocoritsone, IV hydrocortisone)
- IM adrenaline in anaphylaxis
Prevention
- prophylactic antihistamines if exposure is inevitable eg. hayfever
- give patient an adrenaline auto-injector if they are at risk of anaphylaxis
- avoid allergen
- certain specialist centres offer immunotherapy (gradual exposure to the allergen over months, to reduce their reaction to them)
What is allergic rhinitis?
IgE mediated Type 1 hypersensitivity reaction.
- environmental allergens cause an allergic inflammatory response in the nasal mucosa
- Presents with…
- runny blocked itchy nose
- sneezing
- itchy red and swollen eyes
- fhx or personal hx of atopy
- Can be seasonal (eg. hayfever), perennial (eg. dust mite allergy), occupational (ie associated with school or work environment)
What are some common triggers for allergic rhinitis?
- Tree pollen or grass allergy = seasonal symptoms eg. hayfever
- House dust mites and pets = persistent symptpmos worse in dusty rooms at night (pillows can be full of house dust mites)
- Pets = persistent symptoms when the pet is present
- Other allergens eg. mould = symptoms after exposure
How would you manage allergic rhinitis?
- avoid the triggers
- house dust mites = hoover and change pillows regularly, allow good ventilation in the home
- hayfever = stay indoors during high pollen counts
- pets =. minimise contact with pets
-
Oral antihistamines prior to inevitable exposure
- non-sedating antihistamines = cetirizine, loratadine, fexofenadine
- sedating antihistamines = chlorphenamine, promethazine
- Nasal corticosteroid sprays (eg. fluticasone, mometasone) can be taken regularly to suppress local allergic symptoms
- Nasal antihistamines can be used for rapid onset symptomsin response to a trigger
- Referral to immunologist if symptoms are unmanageable
What is good nasal spraying technique?
- hold spray in left hand when spraying right nostril and vice versa
- spray slightly outward away from nasal septum
- do not sniff at the same time as spraying as this sends mist straight to back of the throat
- if they can taste the spray at the back of the throat, it has gone too far
What is anaphylaxis?
a life threatening medical emergency!!!
- caused by severe type 1 hypersensitivity reaction
- Immunoglobulin E (IgE) stimulates mast cells to rapidly release histamine and other pro-inflammatory chemicals
- this is mast cell degranulation
- This results in rapid onset of symptoms that compromise Airway, Breathing and/or Circulation,
How would anaphylaxis present?
- hx of exposure to allergen
Rapid onset of allergic symptoms…
- urticaria
- itching
- antio-oedema, with swelling around lips and eyes
- abdominal pain
Additional symptoms…
- SOB
- Wheeze
- swelling of larynx = stridor
- tachycardia
- lightheadedness
- collapse
How would you manage anaphylaxis?
- call for help and refer to resus guidelines
- A-E approach
- Medications:
- IM Adrenaline, repeated after 5 mins if required
- Antihistamines eg. oral chlorphenamine or cetirizine
- Steroids eg. IV hydrocortisone
How would you monitor and follow up a child after an anaphylactic reaction?
- Admit and observe the child as they can have biphasic reactions (a second anaphylactic reaction after successful treatment of the first)
- Confirm anaphylaxis by measuring serum mast cell tryptase within 6 hours of the event
- Tryptase is released during mast cell degranulation and stays in blood for 6 hours before gradually disapearing
- Educate child and family on avoiding allergens and spotting anaphylaxis
- Parents should be educated on BLS
- Educate child on how to use an adrenaline auto-injector
How would you correctly use an adrenaline auto-injector?
- confirm diagnosis of anaphylaxis
- prepare device (remove safety cap on non needle end)
- Grip device in a fist with the needle end pointing downwards (do not put thumb over the end as if it is upside down you risk injecting it into your thumb)
- Administer the injection by firmly jabbing the device into the outer portion of the mid thigh until device clicks
- hold EpiPen for 3 seconds
- hold Jext for 10 seconds
- Remove device and gently massage the area for 10 seconds
- can give second dose with a new pen after 5 mins if required
- Phone an emergency ambulance
What is this?
Urticaria (also known as hives)
- caused by the release of histamine and other pro-inflammatory chemicals by mast cells in the skin
- may be associated with a patchy, erythematous rash
- can be associated with angioedema and flushing of the skin
- Urticaria can be acute or chronic
What is acute urticaria?
typically triggered by something that stimulates mast cell degranulation.
Eg.
- allergies to food or medications or animals
- contact with chemicals, latex or stinging nettles
- medications
- viral infections
- insect bites
- dermatographism (rubbing of skin)
