Anaphylaxis Flashcards
What is anaphylaxis?
An acute (immediate) hypersensitivity reaction that can be systemic, and is sometimes so overwhelming that it is life threatening.
- It results from a response to an allergen that is present throughout the body
What are some substances that can cause anaphylaxis?
Substances which can cause anaphylaxis in susceptible patients are those which can pass freely around the body
- Penicillin, especially if it has previously been given intravenously
- Certain other drugs (e.g. local anaesthetics, x-ray contrast agents)
- Venom in bee or wasp stings
- Peanuts- the allergen can be absorbed fast enough to cause systemic effects
What type of cell causes anaphylactic symptoms?
Mast cells
What binds to mast cells?
IgE
Where do mast cells mature?
they are released as progenitor from the bone marrow, and it homes to connective and mucosal tissues where it matures
How are mast cells distributed in body?
Mast cells are widely distributed throughout the body both in connective tissue (e.g. under the skin) and in association with epithelial mucosae (e.g. the respiratory and intestinal epithelia)
What do mast cells contain?
They contain prominent granules which contain a number of mediators of inflammation, notably histamine and leukotrienes
What are the main signalling molecules involved in anaphylaxis?
Histamines and leukotrienes
What do the inflammatory mediators released by mast cells principally work on?
on blood vessels and smooth muscle
What do histamines do to connective tissue and mucosae?
In connective tissue histamine causes dilation 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
The net effect depends on whether the stimulation is local or systemic
What are the symptoms of acute allergic reactions? (4)
Wheezing, urticaria, sneezing/ rhinorrhea, conjunctivitis
What is an acute allergic reaction?
Allergen specific IgE is pre-bound to the FcR1 receptor on mast cells. Circulating allergen binds the IgE causing receptor cross linking and mast cell degranulation.
What are the symptoms of a chronic allergic reaction? (3)
Further wheezing, sustained blockage of the nose, eczema
What happens in a chronic allergic reaction?
Recruitment and activation of allergen specific T cells and other cells by mast cells derived mediators
How are IgE produced?
The CD4 T helper cells causes a class switch to IgE production
What is an allergen?
An antigen which causes an allergic type IgE-mediated response
What causes rashes and puffy skin seen in anaphylaxis?
Histamine causes vasodilation leading to red skin colour and oedema leading to raised appearance
What is skin rash called?
urticaria
When can the localised skin reaction seen in allergy be useful?
In skin prick tests to see if they caused a wheal-and-flare reaction
What is hay fever called?
Allergic Rhinitis
What causes Allergic Rhinitis?
Odema in the epithelia lining the nose resulting in general irritation and stimulation of mucus secretion
What causes asthma?
When the allergen reaches the bronchioles of the lungs, resulting in contraction of smooth muscles which reduces the diameter of the airways, leads to increased mucus production and difficulty breathing in and out
What causes food allergies?
When an allergen is ingested, it acts on the mucosal mast cells in the intestinal tract - leading to vomiting and diarrhoea
if absorbed into bloodstream, can cause rashes or itching
What occurs in anaphylaxis which can be fatal and affect organ function?
A rapid decrease in blood pressure as the blood vessels dilate
Why is adrenaline (epinephrine) given as an emergency treatment for anaphylaxis?
Epinephrine is a vasoconstrictor and therefore is aimed at trying to stabilize blood pressure
After adrenaline, what medication is given following an anaphylactic shock?
Anti-histamines and anti-inflammatory corticosteroids like hydrocortisone
Why do patients feel faint follow an anaphylactic shock?
Due to the dramatic loss of blood pressure - hypotension
Why is blood pressure carefully measured after a shock?
Provides a reliable indication of recovery
What is biphasic anaphylaxis?
When the symptoms return within hours of the initial reaction
How long should patients with moderate respiratory/cardiovascular compromise should be observed before discharge?
8-10 hours
What immunoglobulin is likely to be involved in anaphilaxys?
- Immunoglobulin E
- Histamine and leukotrienes are secreted following antigen binding to the cell surface IgE
- The IgE response is thought to be important in defence against certain parasitic infections (e.g. nematodes)
- However, it can occur inappropriately to give rise to allergic reactions
- In type I hypersensitivity, activation of CD4+ T helper cells (TH2) causes a switch to IgE production
What causes anaphylaxis?
- 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 an allergen
What is the usual pathway when an antibody attaches to a cell?
- The normal pathway of lymphocyte activation occurs where antigen binds to the surface IgM on lymphocytes to stimulate proliferation and secretion of antibody
- Usually the antibody initially secreted is IgM
- And this switches to IgG as the immune response progresses
What is an oedema?
build up of fluid which causes the affected tissue to swell up
What causes the rashes and puffy skin?
If the patient has a skin allergy, stimulation of connective tissue mast cells causes vasodilation leading to the red colour of the skin rash, and oedema leading to its raised appearance
- This type of rash is often called urticaria and is familiar as the pattern of rash caused by stinging nettles
What can cause skin allergies?
Substances known to be capable of causing skin allergies include animal hair, proteins in natural latex, certain chemicals, substances in insect and plant stings
What causes hay fever and asthma?
If 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 passage, 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 are substances that are known to cause asthma/ hay fever?
Substances known to be capable of causing hay fever and asthma include pollens, faeces of dust mites, and proteins from animal hairs
What causes food allergies?
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 bloodstream it may also cause skin symptoms (rashes or itching)
What substances are known to cause food allergies?
Substances known to be capable of causing food allergies include peanuts and other nuts and legumes (e.g. soya), shellfish, milk, eggs, wheat
What is shock?
a dramatic drop in blood pressure which can affect organ function
How does the patient respond to constriction of bronchi?
Increase in both respiratory and heart rates
There may also be symptoms of nausea, abdominal cramps, or diarrhoea from the effects on the intestine
What is emergency treatment aimed at?
initially at the loss of blood pressure (hypotension)
And then underlying inflammation
What do they do to patient with anaphylaxis?
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
Why does an anaphylactic 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
They are was initially laid down on a couch with his legs raised to counteract this
What is long-term treatment for anaphylaxis/ allergies?
Avoid 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
What happens if a breathing problem persists with anaphylaxis?
oxygen may be necessary and bronchodilators may be given via an inhaler e.g., salbutamol
What is an example of an anti-inflammatory corticosteroid?
hydroxycorticosterone
Why was blood pressure monitored in hospital for the anaphylactic patient?
Monitoring of blood pressure provides a reliable indication of recovery
Occasionally the symptoms return (usually within hours of the initial reaction)
This is known as biphasic anaphylaxis
Patients with moderate respiratory or cardiovascular compromise should be observed for up to 8-10 hours before discharge
