Immunology - Anaphylaxis Flashcards
What is anaphylaxis?
How may they present?
An acute medical emergency
May present with anaphylactic shock, (severe hypotension, tachy, dyspnoetic (difficult breathing), comatose (unresponsive), pale, cold extremities, puffed up face + tongue, itching = pruritus, central cyanosis (blue tongue))
What is the definition of anaphylaxis?
An acute allergic reaction to an antigen (eg.bee sting) to which the body has become hypersensitive
Caused by release of chemical mediators by mast cells & basophils
What happens in first exposure?
Venom picked up by dendritic cell and engulfed
Presents it to T cell - activated
T cell produces cytokines, which stimulate B cells
B cells produce Ig E antibodies- released into blood
Bind to mast cells & basophils (by signal transduction cascade)
What happens in the subsequent exposure (worse response)?
Mast cells & basophils already have Ig E antibodies on their surface, bind to antigen & release pro inflammatory molecules
Histamine binds to H1 receptors = vasodilation
What does histamine cause to happen?
Causes smooth muscle in bronchi & GI tract to contract
- tougher for food & air to get through
= BV dilation & increased permeability (vasodilation) - swelling or edema & hives
What other molecule is released and by what cell?
Tryptase by mast cells
What does tryptase do?
A type of protease that breaks down proteins causing tissue injury
Causes of anaphylaxis?
Drugs - antibiotics, insulin, beta lactam, chemo drugs
Food - nuts, eggs, seafood, cows milk
Proteins - blood transfusions, tetanus
Latex
Can be idiopathic too
Symptoms of anaphylaxis
ABCDE
Airway - hoarse voice, stridor
Breathing - wheeze, fatigue, cyanosis, O2 <92%
Circulation- low BP, shock, confusion, cold , pale
Disability- dizziness, confused
Exposure - flushed, itchy, hives, angioedema
What is it called when symptoms reoccur hours later?
Biphasic
What is it called when symptoms last for days?
Protracted
What tests would be done for anaphylaxis?
Main - mast cell tryptase - 3 timed sample - elevated for 4-6 hours
12 lead ECG
Chest x ray
U&Es
Blood gases
What treatment is given for anaphylaxis?
IM adrenaline (500micrograms)
Medical emergency = ABCDE
Airway management, O2, IV fluids, apply monitoring = pulse oximetry, ECG, BP
If necessary consider, anti histamines - chlorphenamine) or cortisol (hydrocortisone)
Why is adrenaline given?
- Blood vessel constriction - decreases swelling and increases BP - alpha
- Increase heart Contractility & heart rate - stimulate B1 adenoreceptors
- Relaxes smooth muscle (that line bronchi) - helps open airway = bronchodilation- B2 receptors
What are anti histamines used for?
Reverse actions of histamine
Used for skin symptoms
Get rid of inflammation
