Anaphylactic Reaction

Question 1

What is meant by anaphylaxis

Answer 1

Anaphylaxis is an acute (immediate) type 1 hypersensitivity reaction that can be systemic, and is sometimes so overwhelming that it is life-threatening. It results from an IgE-mediated response to an allergen that is present throughout the body.

Question 2

Describe IgE

Answer 2

The IgE response is thought to be important in defence against certain parasitic infections (nematodes). However, it can occur inappropriately to give rise to allergic reactions.

Question 3

Describe the normal pathway of Lymphocyte activation with IgE

Answer 3

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 secreted is IgM, and this switches IgM, and this switches to IgG as the immune response progresses.

Question 4

What happens in Type 1 hypersensitivity

Answer 4

Activation of CD4+ T helper cells (TH2) causes a switch to IgE production.

Question 5

Describe what happens in the IgE response

Answer 5

IgE becomes bound to specific binding sites (FceR) found on the surface of mast cells, and it is the subsequent stimulation of these cells by exposure of the antigen that causes allergic or anaphylactic response.

Question 6

What happens when the allergen cross-links IgE bound to cells

Answer 6

When allergen cross-links IgE bound to cells by FceR1, cells release the mediators of the early-phase reaction

Question 7

What is meant by an allergen

Answer 7

An antigen that causes an allergic type of IgE-mediated response is often known as an allergen.

Question 8

What are the cardinal signs of inflammation

Answer 8

Rubor- redness
Calor- Heat
Tumor- Swelling
Dolor- pain/ unpleasant sensation (itching).

Question 9

How do we position patients with low BP

Answer 9

Legs up- to pool blood back into the upper body away from the extremities

Question 10

What will be present in a drip

Answer 10

Saline solution to increase blood pressure.

Question 11

Advantages of intravenous and intramuscular injection

Answer 11

Intramuscular- very quick action

Intravenous- systemic action

Question 12

Describe mast cells

Answer 12

Mast cells are widely distributed throughout the body both in connective tissue (under the skin) and in association with the epithelial mucosae (the reparatory and intestinal epithelia). They contain prominent granules which contain a number of mediators of inflammation, notably histamines and leukotrienes. These are secreted following antigen binding to the cell surface IgE.

Question 13

Describe the early phase mediators

Answer 13

During anaphylaxis, mast cells rapidly synthesize prostaglandins and leukotrienes trough the cyclooxygenase and lipoxygenase pathways.
Prostaglandins are also switched on, producing platelet activating factor

Question 14

Describe the actions of these inflammatory mediators

Answer 14

The inflammatory mediators released by mast cells act principally on blood vessels and smooth muscle. In connective tissue histamine causes dilatation of blood 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 the 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.

Question 15

Describe the result of systemic mast cell activation

Answer 15

These mediators cause vasodilation and increase in vascular permeability. In addition, fluid shifts from the vascular space to the extravascular space, and a fall in vascular tone occurs, resulting in a drop in blood pressure.

Question 16

Where is histamine released

Answer 16

By mast cells in the skin.

Question 17

Describe skin allergies

Answer 17

If a 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 called urticaria and is familiar as the type of rash caused by stinging nettles. The localised skin reaction is used in allergy testing, where small amounts of possible allergens and injection by pin-prick to see if they cause this localised wheal-and-flare reaction.

Question 18

List the antigens capable of causing skin allergies

Answer 18

Substances known to cause skin allergies include animal hair, proteins in natural latex. certain chemicals, substances in insect and plant stings. Hay fever and asthma.

Question 19

Describe what happens if the allergen is inhaled

Answer 19

If the allergen is inhaled, the principal site of action will be the mucosal mast cells of the respiratory 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 ( leukotrienes). It is the allergic reaction which causes hay fever (allergic rhinitis). If the allergen reaches the bronchioles of the lungs there will be contraction of smooth muscle reducing the diameter of the airways, as well as inflammation and increased mucous production. The result is asthma, with difficulty breathing in and especially out.

Question 20

What substances can cause hay fever and asthma

Answer 20

Pollens, faeces of dust mites, proteins from animal hairs

Question 21

Describe food allergies

Answer 21

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 vomiting and diarrhoea typical of food allergy. If the allergic substance can be absorbed and pass into the blood stream it may also cause skin symptoms (rashes or itching).

Question 22

Which substances are capable of causing food allergies

Answer 22

Peanuts
Shellfish
Eggs
Milk
Wheat
Soya

Question 23

What causes pain

Answer 23

Activation of sensory nerves- prostaglandins good at this.

Question 24

What can PAF, histamines and leukotrienes cause

Answer 24

vasodilation

Question 25

Describe the effect of histamine son heat

Answer 25

Histamines have very little effect on heat- this must be due to vasodilation.

Question 26

Describe anaphylaxis

Answer 26

Anaphylaxis results from a systemic response to the allergen, causing immediate responses throughout the body. Though not common it is potentially fatal and must be treated as a medical emergency. Dilatation of peripheral blood vessels causes symptoms of rashes and oedema, but more importantly it results in a dramatic drop in BP which can effect organ function: this is known as shock. Constriction of the bronchi causes difficulty breathing.

Question 27

Describe how the patient will respond to anaphylaxis

Answer 27

The patient will respond with an increase in both respiratory and heart rates. There may also be symptoms of nausea, abdominal cramps and diarrhoea from the effects of the intestines.

Question 28

What is emergency treatment for anaphylaxis targeted at

Answer 28

Emergency treatment is aimed initially at 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 the peripheral blood vessels and redirect blood to the organs. An intravenous drip may also be used to control blood pressure. Medications that may be used subsequently include antihistamines and anti-inflammatory corticosteroids. If breathing problems persist oxygen may be necessary and bronchodilators may be given via an inhaler

Question 29

Describe substances that can cause anaphylaxis

Answer 29

Those that can pass freely throughout the body:
penicillin, especially if administered intravenously
Local anaesthetics, X-Ray contrast agents
Venom in bee or wasp stings
Peanuts- the allergen can be absorbed fast enough to cause systemic effects.

Question 30

Describe long term treatment for anaphylaxis

Answer 30

Avoiding known allergens.
For those difficult to avoid completely, the patient may be given an adrenaline self-injection pen in case of an emergency.