Anaphylaxis

Anaphylaxis is a rare but severe allergic reaction that can affect the skin, lungs, nose, throat, gastrointestinal tract and heart. Roughly 30 out of 100,000 people will experience anaphylaxis. It is a systemic (involving more than one body system) allergic reaction that occurs after a person has been sensitized to a particular allergen, and subsequently encounters that allergen at a later time.

Because anaphylaxis is an allergic reaction, a person usually does not experience an attack the first time they encounter the allergen. An initial encounter creates the opportunity for sensitization, in which the immune system mistakenly recognizes the allergen as a harmful substance and creates immunoglobulin E (IgE) antibodies. These antibodies trigger the allergic reaction the next time the individual encounters the allergen. Frequently, an individual is unaware of the sensitization process as it is taking place and may not remember having been exposed to the allergen prior to an episode of anaphylaxis.



During an allergic reaction, the body recognizes the allergen as an antigen, or foreign invader. IgE antibodies that had been created during sensitization, and had attached themselves to cells in the body called mast cells and basophils, now go into action. When IgE comes into contact with the antigen, it signals the cells to which it is attached to release chemical mediators such as histamine.

These chemical mediators cause inflammation, a protective response of the immune system designed to help drive the antigen out of the body. In addition, the chemicals trigger other responses in the tissues that lead to other symptoms of an allergic reaction.

In a typical allergic reaction, only certain cells in a section of the body react. In anaphylaxis, two or more body systems undergo an allergic reaction. As the tissues of the body release histamine and other substances, the airways constrict. Blood vessels dilate, lowering blood pressure severely and causing lightheadedness. Fluid leaks from the bloodstream into the tissues, resulting in lower blood volume. Bronchial tissues swell, causing breathing difficulties.

These changes lead to anaphylactic shock. As blood pressure plummets, the heart stops pumping blood to the tissues, a condition known as cardiovascular collapse. Tissues and organs fail to get the fluids and oxygen they need to survive. Sometimes fluid leaks into the alveoli (air sacs) of the lungs, causing pulmonary edema (fluid and swelling in the lungs).

An immediate epinephrine injection is necessary to reverse these symptoms. Without it, anaphylactic shock can be fatal. Anyone who suspects they are having an anaphylactic reaction should take epinephrine immediately and call an ambulance for additional medical attention.

There are five primary types of triggers for anaphylaxis:

• Food allergies
• Drug allergies
• Latex allergies
• Insect stings
• Idiopathic triggers

Occasionally, an individual will suffer symptoms that mimic those of anaphylaxis, but which have not been caused by allergies. This is called an anaphylactoid reaction, and it occurs even though there was no previous exposure or sensitization to an allergen. Immunoglobulin E (IgE) antibodies are not involved in this condition. Instead, mast cells and basophils are directly stimulated to react without IgE stimulation.

A typical example of anaphylactoid reaction occurs when an individual shows symptoms after receiving radiographic contrast material, the dye injected into the arteries and veins before an x-ray procedure. Other drugs known to trigger an anaphylactoid reaction include polymyxin (an antibiotic) and morphine (a painkiller).

Anaphylactoid reactions respond well to the same treatment used for treating anaphylaxis. A person should immediately take epinephrine regardless of whether they believe they are having an anaphylactic or anaphylactoid reaction.

Anaphylaxis is caused by an extreme immune system reaction. Allergens that trigger anaphylaxis can be introduced to the body in several ways, including:

Symptoms of anaphylaxis generally occur immediately after exposure to the allergen to which the person is sensitive. However, it can take as long as several hours after exposure before signs of anaphylaxis appear. The more rapidly symptoms appear, the more severe they are likely to become.

Symptoms of an anaphylactic reaction can affect many different parts of the body. Early signs and symptoms include:

Anaphylaxis is a condition that cannot be diagnosed ahead of time. It becomes apparent only after an individual has suffered an allergic reaction, and is diagnosed solely on the basis of the symptoms experienced and their severity.

However, a physician may recommend allergy skin testing to determine the risks to an individual of exposure to certain allergens. For example, a physician treating an individual who has experienced anaphylaxis in reaction to penicillin may use a skin test to try out alternative antibiotics. Such testing must be done with great care, as there is a chance the procedure could provoke anaphylaxis.

An allergy blood test is another option that can help a physician pinpoint allergens that may trigger a reaction. Blood tests are often used for patients who are not good candidates for skin testing, such as infants or individuals with skin disorders (e.g., eczema). They may also be useful to help confirm or rule out diagnoses.

The most commonly used blood test for allergy-related conditions is the radioallergosorbent test (RAST). This test looks for the presence of allergy-specific immunoglobulin E (IgE) in the bloodstream. During an allergic reaction, the body produces IgE antibodies to protect against what it mistakenly perceives to be a dangerous substance. The RAST test measures the amount of specific IgE produced to an individual allergen in a sample of blood. The level of IgE correlates to the sensitivity a patient has to the allergen. Related tests include MAST (multiple-antigen simultaneous testing) and PRIST (paper radioimmunosorbent test).

Anaphylaxis is a medical emergency that requires immediate treatment. Epinephrine is the most common drug used to reverse the symptoms of anaphylaxis. It constricts the blood vessels, prevents fluid leakage, opens the airways and raises blood pressure. It also quickly relieves the itching and skin flushing that is part of most episodes of anaphylaxis. Epinephrine usually is injected in the thigh.

Physicians may direct patients with a history of severe reactions to carry their own epinephrine injection kit to treat themselves in an emergency. This epinephrine is delivered through a device known as an auto-injector. The epinephrine that comes with the auto-injector allergy kit usually is good for 18 months. The kit is only available by prescription.

A patient must be trained to properly use the syringe, as injecting epinephrine into the wrong place in the body can have dangerous consequences. Patients can practice by using a training device. It is also a good idea to make sure a patient’s family, friends and coworkers know how to administer the epinephrine in an emergency situation. Parents should alert the staff at their child's school about their child's risk for anaphylaxis and confirm that staff members know how to administer epinephrine.

Epinephrine should be taken at the first sign of anaphylaxis because a reaction that is treated quickly is less likely to become severe. An ambulance should then be called to provide additional medical treatment. When epinephrine is not available, medical attention should be immediately sought, either through calling an ambulance or driving the patient to a hospital.

Though epinephrine is highly effective in treating anaphylaxis symptoms, its effect can be diminished by beta blockers or angiotensin-converting enzyme (ACE) inhibitors (which prevent blood vessel constriction). These drugs are prescribed to treat high blood pressure and some heart conditions. Patients who use these drugs should make sure a physician knows of their use. The physician may recommend alternative medications for treating heart or blood pressure conditions for patients at risk of severe allergic reactions.

Additional treatment may follow the epinephrine dose. Physicians may instruct patients in advance to take an antihistamine following the injection, if the person is able to swallow without difficulty. These patients may benefit from keeping an antihistamine in their allergy kit. This drug does not stop the reaction, but it can reduce the severity of symptoms.

Cardiopulmonary resuscitation (CPR) from a bystander may be required if a person becomes unconscious and stops breathing or does not have a pulse. Those who have suffered shock are likely to receive intravenous fluids and other medications to help support the actions of the circulatory system, including heart function. In rare cases, emergency personnel may perform a procedure to open an airway.

In about 10 percent of all cases, anaphylactic symptoms recur within four to 12 hours. This is known as a bi-phasic reaction. Antihistamines and corticosteroids may be prescribed to help reduce the chance of additional symptoms. Those who experience anaphylaxis should stay under medical supervision for a minimum of four to six hours after the attack subsides.

Prevention of anaphylaxis is critical for those who have displayed symptoms in the past. As with all allergies, the best prevention method is to avoid the allergen altogether. For example, patients who are severely allergic to penicillin can use an alternative antibiotic to treat infections. A physician is likely to use an allergy skin test to ensure that these alternatives do not also trigger anaphylaxis.

Sometimes, advising a patient to simply avoid an allergen is not always practical. In such cases, additional safeguards may be prudent.

Allergy shot treatment (immunotherapy) is extremely effective in preventing some cases of anaphylaxis. The goal of immunotherapy is to build up a patient’s tolerance to the allergen. For example, patients at risk from insect stings would receive very low-dose injections of the insect venom until they build up a tolerance to it. Once the tolerance has been established, the likelihood of suffering an allergic reaction to a sting plummets. Some allergies do not respond well to immunotherapy, including food allergies and drug allergies.

Patients who have a history of anaphylaxis need to inform all healthcare providers – including dentists – of this history before undergoing medical care. Many experts also suggest patients wear a medical alert bracelet or pendant or carry a card that identifies allergies. This could save a patient’s life if he or she is unable to communicate during an anaphylactic episode.

Patients can also take commonsense measures to reduce the risk of anaphylaxis. Such steps include: