Definition

Anaphylaxis, or anaphylactic shock, is an allergic reaction that can be fatal within minutes, either through swelling that shuts off airways or through a dramatic drop in blood pressure.

Anaphylaxis occurs in individuals when they are exposed to an allergen to which they are allergic. An allergen is almost always a protein that is treated by the immune system as a foreign substance. Contact with, or ingestion of this allergen will set off a chain reaction in a person's immune system that may lead to swelling of the airways, loss of blood pressure, and loss of consciousness, resulting in anaphylactic shock.

The function of the immune system is to protect the body from foreign invaders.

Some anaphylactic reactions involve only one organ system, such as the respiratory tract or skin. However, in anaphylaxis, multiple systems are usually affected simultaneously. This includes the upper and lower respiratory tracts, cardiovascular system, and gastrointestinal tract.

The respiratory tract begins with the nose and ends with the lungs. It is responsible for bringing fresh oxygen into the blood and expelling the body's waste, carbon dioxide.

The cardiovascular system consists of the heart and many blood vessels called veins and arteries. This system pumps blood throughout the body, delivering fresh oxygen and removing waste products.

The gastrointestinal tract extends from the mouth to the anus. It is responsible for receiving food, digesting it into nutrients, absorbing the nutrients into the bloodstream, and also eliminating waste products from the body.

In essence, the immune systems of individuals with allergies perceive allergens (e.g., food proteins, medications, insect venom, latex rubber) as foreign substances to which their bodies are primed or sensitized to react against. More specifically, the part of the immune system that is usually involved in fighting foreign organisms forms proteins called IgE antibodies that sit on the surface of specialized mast cells. Mast cells are filled with chemicals called mediators, such as histamines and leukotrienes, which are released when the allergenic protein reacts with the IgE antibody.

The release of these IgE mediators causes:

• Contraction of smooth muscle found in the respiratory and gastrointestinal tracts, which can produce wheezing and gastrointestinal symptoms (cramps, vomiting, nausea, or diarrhoea)
• Vascular dilation that can cause swelling (angioedema), hives (urticaria), and a decrease in the fluid volume of blood that can lead to shock

Fortunately, effective treatment is available, so death from anaphylaxis can be prevented in most cases. Still, needless deaths occur every day because the symptoms of anaphylaxis go unrecognized or because treatment is not prompt enough.

Symptoms

The most distinctive symptoms of anaphylaxis include:

• Hives
• Swelling of the throat, lips, tongue, or around the eyes
• Difficulty breathing or swallowing

Other common symptoms of anaphylaxis may include:

• Metallic taste or itching in the mouth
• Generalized flushing, itching, or redness of the skin
• Abdominal cramps, nausea, vomiting, or diarrhoea
• Increased heart rate
• Sudden decrease in blood pressure (and accompanying paleness)
• Sudden feeling of weakness
• Anxiety or an overwhelming sense of doom
• Collapse
• Loss of consciousness

Speed of potentially fatal anaphylaxis

• It takes only 1 to 2 minutes for a mild allergic reaction to escalate to anaphylaxis.²⁴
• The faster the onset of an anaphylactic reaction, the greater the likelihood that it will be severe.