anaphylaxis Flashcards
this includes the anaphylaxis lecture notes
define anaphylaxis
= a severe, potentially life-threatening allergic reaction that can develop rapidly.
It is a generalised or systemic hypersensitivity reaction.
Both of the following criteria should be met:
- Sudden onset and rapid progression of symptoms.
- Life-threatening airway and/or breathing and/or circulation problems usually associated with skin and mucosal changes
list some signs/symptoms of anaphylaxis
feeling lightheaded or faint
breathing difficulties due to bronchoconstriction– such as fast, shallow breathing, or wheezing
high heart rate (trying to overcompensate)
confusion and anxiety
Hives/urticaria (raised itchy red rash)
Swelling (angioedema) of eyes,lips,face,hands,feet
Central cyanosis - blue discolouration
Stomach pain
what type of hypersensitivity reaction is anaphylaxis? and why?
type 1 because its IgE mediated
explain how sensitisation to an antigen happens?
Initial exposure to antigen (sensitisation)
Antigen presenting cells present the antigen to T helper cells
T helper cells stimulate B cells to differentiate into plasma cells and produce IgE antibodies against this antigen
IgE binds to FceRI receptors on mast cells sensitising them to the antigen
if the Allergen/antigen is reintroduced it will react with these IgE antibodies
explain the steps of anaphylaxis (pathophysiology)
- Allergen/antigen reintroduced
- Reacts with specific IgE antibodies on mast cells and basophils
- IgE antibodies bind to high affinity receptors on the surface of mast cells and basophils
4.Triggers rapid release of the stored histamine and the rapid synthesis of newly formed inflammatory mediators
specifically, it is the Cross Linking of IgE antibodies and FceRI receptors on the cell surface causes rapid cellular degranulation and liberation of chemical mediators = (process is known as mast cell degranulation)
- the release of histamine and the mediators cause the symptoms of anaphylaxis
what are the mediators released in degranulation of mast cells during anaphylaxis?
histamine
protease enzymes,
proteoglycans and chemotactic factors.
Platelet activating factor (PAF),
leukotrienes
prostaglandins
what affects do the mediators released in degranulation have?
- Smooth muscle spasm in resp + GI tracts
- Muscle oedema
- shock and asphyxia (deprivation of oxygen).
- Vasodilation & Increased vascular permeability (which causes hypotension and hives)
- Stimulation of sensory nerve endings
- Increased mucous secretion and increased
Smooth muscle contraction in airways - capillary leakage causes cardiac affects (vasodilation, Hypotension, cardiac arrhythmias, syncope and shock)
increased vascular permeability can produce a shift of - fluid shift
what affect does histamine release have in anaphylaxis?
-activates H1 and H2 receptors
-Vasodilation, hypotension, and flushing are mediated by H1 receptors.
- H2 receptors increase atrial and ventricular contractility, atrial chronotropy, and coronary artery vasodilation.
- Histamine is what makes you itchy
what is a biphasic reaction?
two physical phases, or sets of effects that have time in between
eg. second anaphylaxis reaction 12 hours later
list some common triggers of anaphylaxis
Foods: peanuts, pulses, tree nuts (brazil nuts, almond, hazelnuts), fish and shellfish, eggs, milk, sesame
Venom: Bee stings, wasp stings
Drugs: antibiotics, opioids, NSAIDs, muscle relaxants (Baclofen, Diazepam), general anaesthetics
Contrast agents: (used in x-rays) eg. barium
Rubber latex
Non-immunologic (physical stimuli) eg. heat, cold, sunlight
what does ABCDE stand for in the guidelines of treatment for anaphylaxis?
Airway: look for and relieve airway obstruction. Remove any traces of allergen
Breathing: look for a treat bronchospasm and signs of respiratory distress
Circulation: colour, pulse, BP
Disability: assess whether responding or unconscious (AVPU)
Exposure: assess skin with adequate exposure, but avoid excess heat loss
what are the stages in the guidelines of treatment for anaphylaxis?
- ABCDE and decide anaphylaxis
- lay patient flat or sat down to help breathing
- call for help
- administer adrenaline - IM in the anterolateral aspect of the middle third of the thigh (adult dose 0.5mg)
5.give high flow oxygen
- monitor (pulse oximetry, ECG, BP)
- another dose of adrenaline if no affect after 5 mins
- can give antihistamine to stop skin symptoms. can administer IV fluids
how does adrenaline treat anaphylaxis?
Stimulation of beta1-adrenoceptors: positive inotropic (force of heart contraction) and chronotropic (heart rate) effects on the heart
Stimulation of beta2-adrenoceptors: relaxes smooth muscle → reduces oedema and bronchodilators via stimulation of these receptors
decreases further release of mediators from mast cells and basophils by increasing c-AMP(cellular signal induction) and so reducing the release of inflammatory mediators
causes Vasoconstriction – increase in peripheral vascular resistance, increased BP and coronary perfusion. counters the vasodilation
how does IV fluid treat anaphylaxis?
help restore the circulating volume and therefore the stroke volume thus increasing the cardiac output
increases BP
how does Chlorphenamine treat anaphylaxis?
An antihistamine which blocks the Histamine 1 receptor
thus blocking the action of the histamine released during anaphylaxis
Used for skin symptoms
