- Created by: BeckiSweet95
- Created on: 17-12-19 12:27
What is Anaphylaxis?
Anaphylaxis is a severe systematic hypersensitivity reaction to an antigen which affects the whole body. It is rapid in onset.
Common allergens include food (eggs, nuts, milk), pollen, bee stings, latex and drugs.
- A uniphasic response is the most common (in 80-90% of people), where a response peaks 30-60 minutes after exposure to the antigen.
- A biphasic response is less common (in 1-23% of people), where the response is firstly uniphasic, and then it returns after an asymptomatic period without exposure to the antigen (8-10 hours later)
Pathophysiology of Anaphylaxis
Anaphylaxis is caused by an IgE mediated response.
- The IgE mediated reaction is initiated by the allergen interacting with the allergen-specific IgE bound to a mast cell.
- When the IgE binds to a mast cell this causes the release of histamine.
- The release of histamine causes systematic vasodilation which causes a drop in blood pressure.
- Also due to histamine, smooth muscle contracts around the body. This can cause breathing difficulties due to constriction on the smooth muscle in the larynx and bronchioles.
- Histamine also causes inflammation of the skin and hives. This inflammation can cause swelling of the mouth and tongue.
- This can progress to death within minutes without emergency medication.
Symptoms of Anaphylaxis
- Generalised flushing of the skin - caused by systematic vasodilation, when blood vessels widen and come closer to the skin.
- Hives anywhere on the body - caused by high levels of histamine being released into the skin.
- Swelling of throat and mouth - caused by constriction of smooth muscle and inflammation.
- Alterations in heart rate - heart rate will increase to compensate for low blood pressure.
- Drop in blood pressure - caused by systematic vasodilation.
- Collapse and unconsciousness - caused by a large drop in blood pressure or lack of oxygen due to inflammation of the airway.
Treatment for Anaphylaxis
- Adrenaline auto-injectors (EpiPen) - adrenaline is a vasoconstrictor which heightens blood pressure and reduces systematic vasodilation.
- Anti-histamines - shut off the work of the histamine.
- IV fluids - given to increase blood pressure.
- Steroids - counteract inflammation.
- Oxygen - given to improve saturations when there is inflammation of the airway.