4.8 - Anaphylaxis Flashcards
1
Q
What is anaphylaxis?
A
- acute (immediate) type I hypersensitivity reaction that can be systemic, and is sometimes so overwhelming it is life-threatening
- results from a response to an allergen that is present throughout the body
- substances which cause anaphylaxis in susceptible patients are those which can pass freely around the body e.g:
- penicillin - especially if given intravenously
- certain other drugs e.g. oral anaesthetics, X-ray contrast agents
- venom in bee/wasp stings
- peanuts - the allergen can be absorbed fast enough to cause systemic effects
2
Q
What type of cell causes these symptoms?
A
- mast cells
- released as a progenitor from bone marrow
- home to connective and mucosal tissues where it matures
- noted for its many granules
3
Q
What is the signalling molecule involved?
A
- histamine
- mast cells are widely distributed throughout the body in both connective tissue (e.g. under skin) and in association with epithelial mucosae (e.g. the respiratory and intestinal epithelia)
- mast cell granules contain several inflammatory mediators, notably histamine and leukotrienes
- inflammatory mediators act principally on blood vessels and smooth muscle which express specific histamine receptors (GPCRs)
- in connective tissue, histamine causes dilatation of vessels with increased blood flow to the surface and increased movement of fluid out of the bloodstream (oedema)
- around mucosae, the opposite occurs, causing constriction of airways and contraction of smooth muscles in the walls of the intestine
- net effect depends on whether the stimulation is local or systemic
4
Q
What immunoglobulin class is likely to be involved?
A
- IgE binds with high affinity to Fc receptors of mast cells
- present at extremely low levels in the blood
- produced in response to parasitic infections and in allergic diseases
- cross-linking by antigen to IgE triggers mast cell activation and histamine release
5
Q
What causes the rashes and puffy skin?
A
- in connective tissue, histamine causes dilatation of vessels with increased blood flow to the surface and increased movement of fluid out of the bloodstream (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
6
Q
How does hay fever and asthma work?
A
- if allergen inhaled, 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 inluding stimulus of mucus secretion
- it is the allergic reaction which causes hay fever (rhinitis)
- if allergen reaches bronchioles, there will be contraction of smooth muscles = reduced diameter of airways, inflammation and increased mucus production –> asthma
- substances known to be capable of causing hay fever and asthma include pollens, faeces of dust mites, and proteins from animal hairs
7
Q
How do food allergies work?
A
- if allergen is ingested, then it will act at mucosal mast cells in the intestinal tract
- stimulation of associated smooth muscle leads to the vomiting and diarrhoea typical of a food allergy
- if allergen can be absorbed and passed into bloodstream, it may also cause skin symptoms (rashes / itching)
- substances known to be capable of causing food allergies include peanuts and other nuts and legumes (e.g. soya), shellfish, milk, eggs and wheat
8
Q
Why should adrenaline have been given?
A
- anaphylaxis results from a systemic response to the allergen
- dilatation of peripheral blood vessels results in a dramatic drop in blood pressure (hypotension) which can affect organ function due to reduced blood flow - known as shock
- constriction of bronchi = difficulty breathing
- patient responds with increase in respiratory and heart rates; there may also be symptoms of nausea, abdominal cramps or diarrhoea (from effects on intestines)
- an injection of adrenaline will act to constrict peripheral blood vessels and redirect blood to organs
- patient lain down with feet raised in order to improve blood supply to head and trunk
9
Q
What sorts of drugs might have been in the subsequent injections?
A
- in mucosal tissues of the lung, histamine release causes constriction of bronchi –> breathing difficulties = patient responds with increase in respiratory and heart rates etc
- anti-histamines e.g. diphenydramine
- corticosteroids e.g. hydrocortisone
- if breathing problems persist, oxygen may be necessary and bronchodilators may be given via an inhaler e.g. salbutamol
- long term treatment - avoiding allergens, adrenaline in a self-injection pen e.g. EpiPen
10
Q
Why did the patient feel faint?
A
- due to dramatic drop in blood pressure (hypotension)
- syncope (fainting) is a temporary loss of consciousness usually related to insufficient blood flow to the brain
- legs raised counteracts this
11
Q
Why was blood pressure monitored in hospital?
A
- monitoring of BP provides a reliable indication of recovery
- occasionally the symptoms return (usually within hours of initial reaction) - known as biphasic anaphylaxis
- patients with moderate respiratory / cardiovascular compromise should be observed for 8-10 hours before discharge