Anaphylaxis

Causes and Risks:
Anaphylaxis is an acute systemic (whole body) type of allergic reaction . It occurs when a person has become sensitized (that is, the immune system has been triggered to recognize a substance as a threat to the body). On the second or subsequent exposure to the substance, an allergic reaction occurs. This reaction is sudden, severe, and involves the whole body.

The immune system releases antibodies . The tissues release histamine and other substances. This causes muscle contractions and constriction of the airways, resulting in wheezing ; difficulty breathing ; and gastrointestinal symptoms such as abdominal pain , cramps, vomiting , and diarrhea . Histamine causes the blood vessels to dilate (which lowers blood pressure ) and fluid to leak from the bloodstream into the tissues (which lowers the blood volume) resulting in shock . Fluid can leak into the alveoli (air sacs) of the lungs causing pulmonary edema . Hives and angioedema (hives on the lips, eyelids, throat, and so on.) often occur, and angioedema may be severe enough to cause obstruction of the airway. Prolonged anaphylaxis can cause heart arrhythmias .

Some drugs (polymyxin, morphine, X-ray dye, and others) may cause an anaphylactoid reaction (anaphylactic-like reaction) on the first exposure. This is usually from a toxic or idiosyncratic reaction rather than the "immune system" mechanism that occurs with "true" anaphylaxis.

Anaphylaxis can occur in response to any allergen . Common causes include insect bites /stings, horse serum (used in some vaccines), food allergies , and drug allergies . Pollens and other inhaled allergens rarely cause anaphylaxis. Some people have an anaphylactic reaction with no identifiable cause.

Anaphylaxis occurs infrequently. However, it is life threatening and can occur at any time. Risks include prior history of any type of allergic reaction.

Prevention:
Avoid known allergens. Any person experiencing an allergic reaction should be monitored, although monitoring may occur at home in many cases.

Occasionally, people who have a history of drug allergies may safely be given the offending medication after pretreatment with corticosteroids (prednisone), antihistamines (diphenhydramine), and/or epinephrine.

People who have a history of allergy to insect bites /stings may be instructed to carry (and use) an emergency kit consisting of injectable epinephrine and/or an epinephrine inhaler.

Symptoms:

Note: Symptoms develop rapidly, often within seconds or minutes.

Signs and Tests:
Examination of the skin may show hives and angioedema ( swelling of the eyes or face). The skin may be blue ( cyanosis ) from lack of oxygen or may be pale from shock . Angioedema in the throat may be severe enough to block the airway. Listening to the lungs with a stethoscope ( auscultation ) reveals wheezing and may indicate fluid ( pulmonary edema ). The pulse is rapid, and blood pressure may be low. Weakness , pale skin , heart arrhythmias , mental confusion , and other symptoms may indicate shock.

Testing for the specific allergen that caused anaphylaxis (if the cause is not obvious) is postponed until after treatment.

This disease may also alter the results of the following test:



Treatment:
Anaphylaxis is an emergency condition requiring immediate professional medical attention. CPR and other lifesaving measures may be required. This may include placing a tube through the nose or mouth into the airway ( endotracheal intubation ) or emergency surgery to place a tube directly into the trachea ( tracheostomy ).

Epinephrine is given by injection and/or inhalation. This opens the airways and raises the blood pressure by constricting blood vessels.

Treatment for shock includes intravenous fluids and medications that support the actions of the heart and circulatory system.

Antihistamines such as diphenhydramine may be given to further reduce symptoms (after lifesaving measures and epinephrine are administered).

Prognosis:
Anaphylaxis is a severe disorder with a guarded prognosis (expected outcome). Symptoms may resolve with prompt treatment. However, death may occur even with treatment.

Complications:



Call Your Healthcare Provider:
Go to the emergency room or call the local emergency number (such as 911) if any symptoms of anaphylaxis develop!