Anaphylaxis

Anaphylaxis 

Definition

Anaphylaxis is a rapidly progressing, life-threatening allergic reaction.

Description

Anaphylaxis is a type of allergic reaction, in which the immune system responds to otherwise harmless substances from the environment. Unlike other allergic reactions, however, anaphylaxis can kill. Reaction may begin within minutes or even seconds of exposure, and rapidly progress to cause airway constriction, skin and intestinal irritation, and altered heart rhythms. In severe cases, it can result in complete airway obstruction, shock, and death.

Causes and symptoms

Causes

Like the majority of other allergic reactions, anaphylaxis is caused by the release of histamine and other chemicals from mast cells. Mast cells are a type of white blood cell and they are found in large numbers in the tissues that regulate exchange with the environment: the airways, digestive system, and skin.

On their surfaces, mast cells display antibodies called IgE (immunoglobulin type E). These antibodies are designed to detect environmental substances to which the immune system is sensitive. Substances from a genuinely threatening source, such as bacteria or viruses, are called antigens. A substance that most people tolerate well, but to which others have an allergic response, is called an allergen. When IgE antibodies bind with allergens, they cause the mast cell to release histamine and other chemicals, which spill out onto neighboring cells.

The interaction of these chemicals with receptors on the surface of blood vessels causes the vessels to leak fluid into surrounding tissues, causing fluid accumulation, redness, and swelling. On the smooth muscle cells of the airways and digestive system, they cause constriction. On nerve endings, they increase sensitivity and cause itching.

In anaphylaxis, the dramatic response is due both to extreme hypersensivity to the allergen and its usually systemic distribution. Allergens are more likely to cause anaphylaxis if they are introduced directly into the circulatory system by injection. However, exposure by ingestion, inhalation, or skin contact can also cause anaphylaxis. In some cases, anaphylaxis may develop over time from less severe allergies.

Anaphylaxis is most often due to allergens in foods, drugs, and insect venom. Specific causes include:

Exposure to cold or exercise can trigger anaphylaxis in some individuals.

Key terms

ACTH — Adrenocorticotropic hormone, a hormone normally produced by the pituitary gland, sometimes taken as a treatment for arthritis and other disorders.

Antibody — An immune system protein which binds to a substance from the environment.

NSAIDs — Non-steroidal antiinflammatory drugs, including aspirin and ibuprofen.

Tracheostomy tube — A tube which is inserted into an incision in the trachea (tracheostomy) to relieve upper airway obstruction.

Symptoms

Symptoms may include:

Not all symptoms may be present.

Diagnosis

Anaphylaxis is diagnosed based on the rapid development of symptoms in response to a suspect allergen. Identification of the culprit may be done with RAST testing, a blood test that identifies IgE reactions to specific allergens. Skin testing may be done for less severe anaphylactic reactions.

Treatment

Emergency treatment of anaphylaxis involves injection of adrenaline (epinephrine) which constricts blood vessels and counteracts the effects of histamine. Oxygen may be given, as well as intravenous replacement fluids. Antihistamines may be used for skin rash, and aminophylline for bronchial constriction. If the upper airway is obstructed, placement of a breathing tube or tracheostomy tube may be needed.

Prognosis

The rapidity of symptom development is an indication of the likely severity of reaction: the faster symptoms develop, the more severe the ultimate reaction. Prompt emergency medical attention and close monitoring reduces the likelihood of death. Nonetheless, death is possible from severe anaphylaxis. For most people who receive rapid treatment, recovery is complete.

Prevention

Avoidance of the allergic trigger is the only reliable method of preventing anaphylaxis. For insect allergies, this requires recognizing likely nest sites. Preventing food allergies requires knowledge of the prepared foods or dishes in which the allergen is likely to occur, and careful questioning about ingredients when dining out. Use of a Medic-Alert tag detailing drug allergies is vital to prevent inadvertent administration during a medical emergency.

People prone to anaphylaxis should carry an "Epi-pen" or "Ana-kit," which contain an adrenaline dose ready for injection.

Resources

Other

The Meck Page. February 20, 1998. http://www.merck.com.

---

anaphylaxis /ana·phy·lax·is/ (-fi-lak´sis) anaphylactic shock; a manifestation of immediate hypersensitivity in which exposure of a sensitized individual to a specific antigen or hapten results in life-threatening respiratory distress, usually followed by vascular collapse and shock and accompanied by urticaria, pruritus, and angioedema.

---

active anaphylaxis  that produced by injection of a foreign protein.

antiserum anaphylaxis  passive a.

local anaphylaxis  that confined to a limited area, e.g., cutaneous anaphylaxis.

passive anaphylaxis  that resulting in a normal person from injection of serum of a sensitized person.

passive cutaneous anaphylaxis  PCA; localized anaphylaxis passively transferred by intradermal injection of an antibody and, after a latent period (about 24 to 72 hours), intravenous injection of the homologous antigen and Evans blue dye; blueing of the skin at the site of the intradermal injection is evidence of the permeability reaction. Used in studies of antibodies causing immediate hypersensitivity reaction.

reverse anaphylaxis  that following injection of antigen, succeeded by injection of antiserum.

---

an·a·phy·lax·is (n-f-lkss)

n. pl. an·a·phy·lax·es (-lksz)

1. Hypersensitivity induced by preliminary exposure to a substance and usually producing a contraction of smooth muscle and a dilation of blood vessels.

2. See anaphylactic shock.

---

ana·phy·lactic (-lktk) adj.

---

anaphylaxis (an´filak´sis),

n a violent allergic reaction characterized by sudden collapse, shock, or respiratory and circulatory failure after injection of an allergen.

---

anaphylaxis

an unusual or exaggerated allergic reaction of an animal to foreign protein or other substances. Anaphylaxis is an immediate or antibody-mediated hypersensitivity reaction (type I) produced by the release of vasoactive agents such as histamine and serotonin. Release is a consequence of the binding of IgE antibodies to Fc receptors on the surface of particularly mast cells and basophils. Antigen binding to two adjacent IgE molecules causes perturbation of the cell membrane leading to the release of vasoactive substances. Anaphylaxis may be localized, usually cutaneous, or generalized. Called also anaphylactic shock.

Substances most likely to produce anaphylaxis include drugs, particularly antibiotics and local anesthetics; drugs prepared from animals, such as insulin, adrenocorticotropic hormone and enzymes; diagnostic agents, such as iodinated x-ray contrast media; biologicals used to provide immunity, such as vaccines, antitoxins and gamma globulin; protein foods; the venom of bees, wasps and hornets; and pollens and molds. See also hypersensitivity, anaphylactic.

---

acquired anaphylaxis

that in which sensitization is known to have been produced by administration of a foreign antigen.

active anaphylaxis

see acquired anaphylaxis (above).

aggregate anaphylaxis

caused by large amounts of antibody-antigen complexes that activate complement and resulting in degranulation of mast cells.

antiserum anaphylaxis

passive anaphylaxis.

cutaneous anaphylaxis

a localized form of anaphylaxis, which follows the injection of antigen into the skin.

cytotoxic anaphylaxis

a form of anaphylaxis triggered by antibodies against self antigens. Blood transfusion reactions and Rh reactions are examples.

cytotropic anaphylaxis

refers to binding of IgE to Fc receptors.

heterologous anaphylaxis

passive anaphylaxis induced by transfer of serum from an animal of a different species.

homologous anaphylaxis

passive anaphylaxis induced by transfer of serum from an animal of the same species.

indirect anaphylaxis

that induced by an animal's own protein modified in some way.

passive anaphylaxis

that resulting in a normal animal from injection of serum of a sensitized animal.

passive cutaneous anaphylaxis (PCA)

localized anaphylaxis passively transferred by intradermal injection of an antibody and, after a latent period (about 24 to 72 hours), intravenous injection of the homologous antigen and Evans blue dye; blueing of the skin at the site of the intradermal injection is evidence of PCA.

reverse passive cutaneous anaphylaxis

antigen is injected first, succeeded by the injection of antiserum.

systemic anaphylaxis

a generalized anaphylactic reaction most often observed when the antigen is injected intravenously but may also be produced after local administration of antigen. The main shock organs in cattle and sheep are the lungs, in the horse, cat and pig the lungs and intestines, and in dogs the liver, specifically the hepatic veins.