Anaphylaxis is a severe and potentially life-threatening allergic reaction that occurs when the body’s immune system overreacts to a substance (allergen) that a person is allergic to. It can occur suddenly and can progress rapidly, requiring immediate medical attention.
During anaphylaxis, the body releases chemicals, including histamine, which can cause symptoms such as:
SYMPTOMS
- Difficulty breathing: This may be accompanied by a feeling of tightness in the throat, wheezing or a sensation of choking.
- Swelling of the face, lips, tongue, or throat: This can cause difficulty swallowing or speaking.
- Rapid or weak pulse: Anaphylaxis can cause a rapid or weak pulse, or an irregular heartbeat.
- Nausea and vomiting: These symptoms may be accompanied by abdominal pain.
- Hives or rash: Anaphylaxis can cause red, itchy bumps or rash on the skin.
- Chest pain or tightness: This may be accompanied by a feeling of anxiety or a sense of impending doom.
- Lightheadedness or dizziness: Anaphylaxis can cause a drop in blood pressure, leading to lightheadedness or fainting.
Anaphylaxis can also cause a drop in blood pressure (anaphylactic shock), which can lead to shock, a life-threatening condition that can cause organ damage or failure.
Pathophysiology
The underlying pathophysiology of anaphylaxis involves both the immune system and the release of inflammatory mediators.
- Sensitisation: The first step in anaphylaxis is sensitisation to an allergen. This occurs when the immune system is exposed to an allergen for the first time and produces specific IgE antibodies to that allergen.
- Allergen recognition: During a subsequent exposure to the allergen, the allergen binds to IgE antibodies on the surface of mast cells and basophils, causing the cells to become activated.
- Inflammatory mediator release: Activated mast cells and basophils release a variety of inflammatory mediators, including histamine, leukotrienes, prostaglandins, and cytokines.
- Vasodilation and increased permeability of blood vessels: The release of histamine and other mediators causes widespread vasodilation and increased permeability of blood vessels, leading to decreased blood pressure and increased fluid accumulation in tissues.
- Bronchoconstriction: The mediators also cause smooth muscle contraction in the airways, leading to bronchoconstriction and difficulty breathing.
- Tissue swelling: The release of mediators also causes the accumulation of fluid in tissues, leading to swelling, especially in the face, lips, and tongue.
- Other effects: Anaphylaxis can also affect the cardiovascular system, leading to a rapid heartbeat and decreased blood pressure, as well as the nervous system, causing confusion, dizziness, and unconsciousness.
Together, these effects can result in shock, cardiac arrest, and death if left untreated. The severity of anaphylaxis can vary from person to person and can range from mild symptoms to a life-threatening reaction.