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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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