Anaphylaxis Flashcards
What type of hypersensitivity reaction is anaphylaxis
Type 1
What can cause anaphylaxis / Type 1 hypersensitivity reaction
venoms, food (nuts), intravenous drugs, anaesthetics, contrast iodine in x-rays, penicillin
What is an allergy / process of an allergy
an exaggerated immune response. Allergen -> activate B cells, and T-helper cells (Th2 cells) -> causes release of antibodies (immunoglobulins)
Symptoms of anaphylaxis
○ Breathlessness
○ Feeling faint/dizziness; increase in heart rate
○ Organ shock
Skin allergies source and symptoms
plants, bee stings, animal hairs, latex
Symptoms : oedema, redness, itching and rashes
Food allergies causes and symptoms
Fruits, nuts, dairy , gluten , fish , eggs
Symptoms : rashes, vomiting, nausea
Respiratory allergies symptoms and causes
asthma, hayfever -> animal hair, dust, pollen, small particulates
○ Symptoms: breathlessness, coughing, itching,
What types of cell causes symptoms of anaphylaxis
Mast cells: released as a progenitor from bone marrow. Home to connective and mucosal tissues where it matures. Noted for its many granules.
What is the signalling molecule involved in anaphylaxis
Histamines and leukotrines
Where are mast cells located in the body
connective tissue (e.g. under the skin) and in association with epithelial mucosae (e.g. the respiratory and intestinal epithelia).
They contain prominent granules which contain a number of mediators of inflammation, notably histamine and leukotrienes.
How do the inflammatory mediators ( histamine and leukotrines ) released by the mast cells work
The inflammatory mediators released by mast cells act principally on blood vessels and smooth muscle.
In connective tissue histamine causes dilatation of vessels with increased blood flow to the surface and increased movement of fluid out of the blood stream (oedema).
Around mucosae the opposite effect occurs, causing constriction of airways and contraction of the smooth muscle in the walls of the intestines.
What is the name of the specific histamine receptors presented on blood vessels and smooth muscle
GPCRs
Acute allergic reaction symptoms
Wheezing
Uriticaria
Sneezing, rhinorrhea
Conjunctivitis
How does acute allergic reaction work
Allergen specific IgE is pre bound to the FceR1 receptor on mast cells. Circulating allergen binds to the IgE causing receptor cross linking and mast cell degranulation
Chronic allergic reaction symptoms
Further wheezing
Sustained blockage of the nose
Eczema
How does chronic allergic reaction work
Recruitment and activation of allergen specific T cells and other cells by mast cell derived mediators
Which immunoglobulin class is likely to be involved in anaphylaxis
IgE
How does IgE work on first exposure and subsequent exposure to allergen
IgE becomes bound to specific binding sites (IgE-receptors) found on the surface of mast cells, and it is the subsequent stimulation of these cells by exposure to the antigen that causes allergic or anaphylactic responses. An antigen that causes an allergic type of IgE-mediated response is often known as anallergen.
Cross linking by the antigen activates mast cell activation and histamine release from mast cells
What causes the rashes and puffy skin?
In connective tissue, histamine causes dilation of the vessels with increased blood flow to the surface and increased movement of fluid out of the blood stream ( oedema)
Rash ( urticaria) is an acute response to allergen raised lump or wheal
Caused by animal hair , proteins in natural latex , certain chemicals , substances in insect and plant stings
What causes rashes and puffy skin in skin allergy
If the patient has a skin allergy, stimulation of connective tissue mast cells causes vasodilatation leading to the red colour of the skin rash, and oedema leading to its raised appearance. This type of rash is often calledurticariaand is familiar as the pattern of rash caused by stinging nettles. The localised skin reaction is used in allergy testing, where small amounts of possible allergens are injected by pin-prick to see if they cause this kind of localisedwheal-and-flarereaction.
Substances causing skin allergies
animal hair, proteins in natural latex, certain chemicals, substances in insect and plant stings.
hay fever and asthma
the allergen is inhaled, the principal site of action will be mucosal mast cells of the respiratory system. If this is principally in the nasal passages, the effect will be oedema in the epithelia lining the nose and a consequent general irritation including stimulation of mucus secretion. It is the allergic reaction which causes hay fever (allergic rhinitis).
If the allergen reaches the bronchioles of the lungs then there will be contraction of smooth muscle reducing the diameter of the airways, as well as inflammation and increased mucus production. The result is asthma, with difficulty breathing in and (especially) breathing out.
What substances can cause hay fever and asthma
Pollens, faeces of dust mites, and proteins from animal hairs
Food allergies causes
Peanuts and other nuts and legumes ( e.g. soya) , shellfish, milk, eggs , wheat
Food allergies stimulated
If the allergen is ingested, then it will act at mucosal mast cells in the intestinal tract. The stimulation of the associated smooth muscle leads to the vomiting and diarrhoea typical of a food allergy.
If the allergic substance can be absorbed and pass into the blood stream it may also cause skin symptoms (rashes or itching).
What causes the low blood pressure in anaphylaxis
Dilatation of peripheral blood vessels causes symptoms of rashes and oedema, but more importantly it results in a dramatic drop in blood pressure which can affect organ function: this is known asshock.
Constriction of bronchi causes difficulty in breathing.
The patient will respond with an increase in both respiratory and heart rates. There may also be symptoms of nausea, abdominal cramps or diarrhoea from the effects on the intestines.
Why is adrenaline and emergency treatment needed to be given in anaphylaxis
Emergency treatment is aimed initially at the loss of blood pressure (hypotension), and then at the underlying inflammation. The patient is lain down with feet raised in order to improve blood supply to the head and trunk. An injection of adrenaline will act to constrict peripheral blood vessels and redirect blood to the organs.
What sort of drugs might be given to treat anaphylaxis after initial emergency treatment
antihistamines e.g. diphenhydramine
anti-inflammatory corticosteroids e.g. hydrocortisone.
If breathing problems persist, oxygen may be necessary and bronchodilators may be given via an inhaler e.g. salbutamol.
What may be the long term treatment of anaphylaxis
Long term treatment is largely by avoiding known allergens. For those difficult to avoid completely (such as wasp stings, or nuts where small traces may contaminate apparently innocent foods) the patient may be given adrenaline in a self-injection “pen” e.g. EpiPen®, Emerade®.
Why did the patient feel faint?
Due to the dramatic drop in blood pressure (hypotension).
Syncope (fainting) is a temporary loss of consciousness usually related to insufficient blood flow to the brain.
Note that on arrival at A&E, Thomas was initially laid down on a couch with his legs raised to counteract this.
Anaphylactic reactions may also cause bronchoconstriction limiting O2 intake linked to breathlessness
Why was blood pressure monitored in hospital
○ Biggest concern is organ shock (Organ shock
Biphasic anaphylaxis
Monitoring of blood pressure provides a reliable indication of recovery.
Occasionally the symptoms return (usually within hours of the initial reaction).
This is known asbiphasic anaphylaxis.
Patients with moderate respiratory or cardiovascular compromise should be observed for to up to 8-10 hours before discharge
What happens in the connective tissues as a result of release of histamine and leukotrines
○ In connective tissues, it causes vasodilation; in mucosa it causes vasoconstriction.
○ The vasodilation in the connective tissues would present as redness, oedema, warmth
What would the release of histamine and leukotrienes cause in mucosa
○ The vasoconstriction in the mucosa would present as difficulty breathing, nausea, vomiting
