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Anaphylaxis is defined as a severe and rapid multi-system allergic reaction that occurs when an individual has been exposed to a triggering substance, called an allergen. An allergen is a mild antigen that is capable of stimulating a hypersensitivity reaction mediated by the immunoglobulin E (IgE). This class of antibodies causes the release of histamine by mast cells through the process known as degranulation due to sensitization. Histamine is a chemical mediator that causes widespread vasodilation (widening of the blood vessel lumen) causing hyperemia or increase blood flow and bronchospasm along the airways. Even small amounts of exposure to allergens may cause a life-threatening anaphylactic reaction that may lead to anaphylactic shock or circulatory collapse which is the most severe type of anaphylaxis. If left untreated, anaphylactic shock will usually lead to sudden death in a few minutes’ time. Anaphylaxis may occur after ingestion, inhalation, skin contact (e.g. insect sting or insect bite) or injection of an allergen.


Symptoms of anaphylaxis can include the following: respiratory distress, low blood pressure or hypotension; syncope or fainting; unconsciousness, skin lesions called urticaria (hives), flushed appearance, angioedema (swelling of the face, neck and throat), tears (due to angioedema and stress), vomiting, itching, and anxiety reaction with a sense of impending doom.

The time interval between ingestion of the allergen and anaphylaxis symptoms can vary for some patients. It will depend on the amount of allergen ingested and sensitivity of the individual to that particular allergen. Symptoms can appear immediately, or can be delayed by 30 minutes to several hours after ingestion. However, most of the time symptoms of anaphylaxis usually appear very quickly once they do begin.

Some of the common causative agents in humans include: foods (e.g. milk, cheese, nuts, peanuts , soybeans and other legumes, fish and shellfish, wheat, fruit, and eggs); drugs (e.g. penicillin, cephalosporins, contrast media (dyes) , Acetyl salicylic acid (ASA) and other non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and diclofenac); latex (in gloves); Hymenoptera stings from insects such as bees, wasps, yellow jackets, hornets, and some ants; exercise and transfusion of incompatible blood products.

Treatment of anaphylaxis depends on the severity of symptoms. For most cases that manifested only as hives or wheals and itching, this can be managed by antihistamines alone because this form is not life threatening. However, in a more serious allergic response particularly the Anaphylactic shock, an aggressive emergency treatment is necessary to prevent sudden death. Because of the rapid narrowing of the airways, often within minutes of onset, an anaphylactic shock is always a medical emergency. Most cases need advanced medical care the soonest possible time therefore, you must seek help immediately if this happen. Vital organs particularly the brain may lead to an irreversible damage rapidly within a few minutes without oxygen supply due to impaired breathing. First aid measures include rescue breathing (if the patient developed respiratory arrest) as part of basic life support in cardiopulmonary resuscitation (CPR) and administration of epinephrine (adrenaline) if available for those trained with ACLS (advanced cardiac life support). Emergency medical services (EMS) or the paramedics treat patients with administration of oxygen therapy and, if necessary, endotracheal intubation along with epinephrine injection during transport to advanced medical care. For those patients with severe angioedema, cricothyroidectomy or tracheotomy may be required to serve as a temporary opening and maintain oxygenation.

Epinephrine belongs to a drug class known as beta-adrenergic agonist. These drugs act on Beta-2 adrenergic receptors in the lung and works as a powerful bronchodilator therefore, relieving histamine-induced airway constriction. However, tachycardia (rapid heartbeat) may also happen as an adverse reaction of repetitive epinephrine administration because of its stimulating effect to Beta-1 adrenergic receptors of the heart increasing contractility (ionotropic effect) and frequency (chronotropic effect) and thus, the cardiac output. Occasionally, an arrhythmia may develop known as ventricular tachycardia with the heart beating at around 240 per minute which can also be fatal. Hence, a protocol has been developed that suggests Intramuscular (IM) injection of only 0.3–0.5mL of a 1:1,000 dilution of epinephrine which is a dilution just enough to prevent worsening of the airway constriction at the same time stimulates the heart to continue beating, and may be life-saving. The goal of clinical treatment of anaphylaxis is to reduce the cellular hypersensitivity reaction and to abolish the symptoms. Antihistamine (anti-pruritic) drugs are given and if not sufficient may need higher doses of intravenous corticosteroids to control symptoms. If the blood pressure drops then intravenous fluids and sometimes vasoconstrictor agents are needed. Bronchodilator drugs (e.g. salbutamol or Albuterol) can also be used to relieve bronchospasms. In severe cases, emergency treatment with epinephrine as earlier mentioned is a lifesaver. Other cases may require mechanical ventilator supportive care.

It is advisable that those patients who are prone to anaphylaxis should have an "allergy action plan" on file at school, home or in their office. This may serve as a guide to aid family members, teacher and colleagues at work in cases of an anaphylactic attack An action plan is considered vital to quality emergency care.

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