Anaphylaxis

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Definition:

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

Anaphylaxis is an acute systemic (multi-system) and severe Type I Hypersensitivity allergic reaction in humans and other mammals. The term comes from the Greek words ana (against) and phylaxis (protection). Minute amounts of allergens may cause a life-threatening anaphylactic reaction. Anaphylaxis may occur after ingestion, skin contact, injection of an allergen or, in rare cases, inhalation….CLICK & SEE

Anaphylactic shock, the most severe type of anaphylaxis, occurs when an allergic response triggers a quick release from mast cells of large quantities of immunological mediators (histamines, prostaglandins, leukotrienes) leading to systemic vasodilation (associated with a sudden drop in blood pressure) and edema of bronchial mucosa (resulting in bronchoconstriction and difficulty breathing). Anaphylactic shock can lead to death in a matter of minutes if left untreated.

An estimated 1.24% to 16.8% of the population of the United States is considered “at risk” for having an anaphylactic reaction if they are exposed to one or more allergens, especially penicillin and insect stings. Most of these people successfully avoid their allergens and will never experience anaphylaxis. Of those people who actually experience anaphylaxis, up to 1% may die as a result. Anaphylaxis results in approximately 18 deaths per year in the U.S. (compared to 2.4 million deaths from all causes each year in the U.S.). The most common presentation includes sudden cardiovascular collapse (88% of reported cases of severe anaphylaxis).

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Researchers typically distinguish between “true anaphylaxis” and “pseudo-anaphylaxis or an “anaphylactoid reaction.” The symptoms, treatment, and risk of death are identical, but “true” anaphylaxis is always caused directly by degranulation of mast cells or basophils that is mediated by immunoglobulin E (IgE), and pseudo-anaphylaxis occurs due to all other causes. The distinction is primarily made by those studying mechanisms of allergic reactions.

Causes:-
Anaphylaxis is a severe, whole-body allergic reaction. After an initial exposure (“sensitizing dose”) to a substance like bee sting toxin, the person’s immune system becomes sensitized to that allergen. On a subsequent exposure (“shocking dose”), an allergic reaction occurs. This reaction is sudden, severe, and involves the whole body.

Hives and angioedema (hives on the lips, eyelids, throat, and/or tongue) often occur. Angioedema may be severe enough to block 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 due to a toxic reaction, rather than the immune system mechanism that occurs with “true” anaphylaxis. The symptoms, risk for complications without treatment, and treatment are the same, however, for both types of reactions. Some vaccinations are also known to cause “anaphylactoid” reactions. Antitoxins and antivenins may cause similar reactions.

Anaphylaxis can occur in response to any allergen. Common causes include insect bites/stings, food allergies (peanuts and tree nuts are the most common, though not the only), and drug allergies. Pollens and other inhaled allergens rarely cause anaphylaxis. In opthamology, the dye fluorescein used in some eye exams is a well known trigger. Some people have an anaphylactic reaction with no identifiable cause.
Symptoms:-
Symptoms of anaphylaxis are related to the action of Immunoglobulin E (IgE) and other anaphylatoxins, which act to release histamine and other mediator substances from mast cells (degranulation). In addition to other effects, histamine induces vasodilation of arterioles and constriction of bronchioles in the lungs, also known as bronchospasm (constriction of the airways).

Tissues in different parts of the body release histamine and other substances. This causes 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). These effects result in shock. Fluid can leak into the alveoli (air sacs) of the lungs, causing pulmonary edema.

Symptoms can include the following:

*polyuria
*respiratory distress
*hypotension (low blood pressure)
*encephalitis
*fainting
*unconsciousness
*urticaria (hives)
*flushed appearance
*angioedema (swelling of the lips, face, neck and throat): this can be life threatening
*tears (due to angioedema and stress)
*vomiting
*itching
*diarrhoea
*abdominal pain
*anxiety

The time between ingestion of the allergen and anaphylaxis symptoms can vary for some patients depending on the amount of allergen consumed and their reaction time. Symptoms can appear immediately, or can be delayed by half an hour to several hours after ingestion. However, symptoms of anaphylaxis usually appear very quickly once they do begin.

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.

The time between ingestion of the allergen and anaphylaxis symptoms can vary for some patients depending on the amount of allergen consumed and their reaction time. Symptoms can appear immediately, or can be delayed by half an hour to several hours after ingestion. However, symptoms of anaphylaxis usually appear very quickly once they do begin.

Apart from its clinical features, blood tests for tryptase (released from mast cells) might be useful in diagnosing anaphylaxis.

In some cases, it is unclear from the patient interview what triggered the anaphylaxis. In this setting, skin allergy testing (with or without patch testing) or RAST blood tests can sometimes identify the cause.

You may click to see:->Anaphylaxis Flow Chart

Treatment:-

Emergency Treatment
Anaphylaxis is a life-threatening medical emergency because of rapid constriction of the airway, often within minutes of onset, which can lead to respiratory failure and respiratory arrest. Brain and organ damage rapidly occurs if the patient cannot breathe. Due to the severe nature of the emergency, patients experiencing or about to experience anaphylaxis require the help of advanced medical personnel. First aid measures for anaphylaxis include rescue breathing (part of CPR). Rescue breathing may be hindered by the constricted airways, but if the patient stops breathing on his or her own, it is the only way to get oxygen to him or her until professional help is available.

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.A woman being treated in an emergency department after going into anaphylactic shock

.The primary treatment for anaphylaxis is administration of epinephrine (adrenaline). Epinephrine prevents worsening of the airway constriction, stimulates the heart to continue beating, and may be life-saving. Epinephrine acts on Beta-2 adrenergic receptors in the lung as a powerful bronchodilator (i.e. it opens the airways), relieving allergic or histamine-induced acute asthmatic attack or anaphylaxis. If the patient has previously been diagnosed with anaphylaxis, he or she may be carrying an EpiPen or Twinject for immediate administration of epinephrine. However, use of an EpiPen or similar device only provides temporary and limited relief of symptoms.

Tachycardia (rapid heartbeat) results from stimulation of Beta-1 adrenergic receptors of the heart increasing contractility (positive inotropic effect) and frequency (chronotropic effect) and thus cardiac output.[10] Repetitive administration of epinephrine can cause tachycardia and occasionally ventricular tachycardia with heart rates potentially reaching 240 beats per minute, which itself can be fatal. Extra doses of epinephrine can sometimes cause cardiac arrest. This is why some protocols advise intramuscular injection of only 0.3–0.5mL of a 1:1,000 dilution.

Some patients with severe allergies routinely carry preloaded syringes containing epinephrine, diphenhydramine (Benadryl), and dexamethasone (Decadron) whenever they go to an unknown or uncontrolled environment.

You may click to see:->First Aid for Anaphylaxis
Clinical care
Paramedic treatment in the field includes administration of epinephrine IM; antihistamines IM (such as chlorphenamine or diphenhydramine); steroids, such as hydrocortisone or dexamethasone; IV Fluid administration and in severe cases, pressor agents (which cause the heart to increase its contraction strength) such as dopamine for hypotension, administration of oxygen, and intubation during transport to advanced medical care.

In severe situations with profuse laryngeal edema (swelling of the airway), cricothyrotomy or tracheotomy may be required to maintain oxygenation. In these procedures, an incision is made through the anterior portion of the neck, over the cricoid membrane, and an endotracheal tube is inserted to allow mechanical ventilation of the patient.

The clinical treatment of anaphylaxis by a doctor and in the hospital setting aims to treat the cellular hypersensitivity reaction as well as the symptoms. Antihistamine drugs such as diphenhydramine or chlorphenamine (which inhibit the effects of histamine at histamine receptors) are continued but are usually not sufficient in anaphylaxis, and high doses of intravenous corticosteroids such as dexamethasone or hydrocortisone are often required. Hypotension is treated with intravenous fluids and sometimes vasopressor drugs. For bronchospasm, bronchodilator drugs (e.g. salbutamol, known as Albuterol in the United States) are used. In severe cases, immediate treatment with epinephrine can be lifesaving. Supportive care with mechanical ventilation may be required.

It is also possible to undergo a second reaction prior to medical attention or using an Epipen. It is suggested to seek one to two days of medical care.

The possibility of biphasic reactions (recurrence of anaphylaxis) requires that patients be monitored for four hours after being transported to medical care for anaphylaxis.

Many anaphylactic patients will be sent home or released after the initial reaction is declared over. Yet, rebound reactions are almost always bound to happen. Most people with anaphylaxis have a rebound a few hours after the initial reaction, yet there are cases where a rebound would occur after as much time as a week.
Planning for emergency treatment:-
The Asthma and Allergy Foundation of America advises patients prone to anaphylaxis to have an “allergy action plan” on file at school, home, or in their office to aid others in case of an anaphylactic emergency, and provides a free “plan” form. Action plans are considered essential to quality emergency care. Many authorities advocate immunotherapy to prevent future episodes of anaphylaxis.

Beta-blockers may aggravate anaphylactic reactions and interfere with treatment.

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:-
Immunotherapy with Hymenoptera venoms is especially effective and widely used throughout the world and is accepted as an effective treatment for most patients with allergy to bees, wasps, hornets, yellow jackets, white faced hornets, and fire ants.

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 “Epipen” or “Ana-kit,” which contain an adrenaline dose ready for injection.

The greatest success with prevention of anaphylaxis has been the use of allergy injections to prevent recurrence of sting allergy. The risk to an individual from a particular species of insect depends on complex interactions between likelihood of human contact, insect aggression, efficiency of the venom delivery apparatus, and venom allergenicity. According to most authorities, venom immunotherapy has been demonstrated to reduce the risk of systemic reactions below 1% to 3%. One simple method of venom extraction has been electrical stimulation to obtain venom, instead of dissecting the venom sac. An allergist will then provide venom immunotherapy which is highly efficacious in preventing future episodes of anaphylaxis.

A vaccine has been in the works to prevent anaphylaxis from peanuts and tree nuts. Despite showing significant promise to prevent individuals with the allergy from developing anaphylaxis if eating a small amount of the food, the FDA has not yet approved the vaccine.

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Disclaimer: This information is not meant to be a substitute for professional medical advise or help. It is always best to consult with a Physician about serious health concerns. This information is in no way intended to diagnose or prescribe remedies.This is purely for educational purpose.

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