In medicine, is a severe and rapid systemic
Allergic reaction.
The word is from
New Latin (derived from
Greek ἀνα-/''ana'', meaning "up, again, back, against") + φύλαξις/''phylaxis'', meaning "guarding, protection"—cf.
Prophylaxis .)
Anaphylaxis occurs when a person is exposed to a trigger substance, called an ''
Allergen ,'' to which they have become sensitized. Minute amounts of allergens may cause a life-threatening anaphylactic reaction. Anaphylaxis may occur after ingestion, inhalation, skin contact or injection of an allergen. The most severe type of anaphylaxis—''anaphylactic shock''—will usually lead to death in minutes if left untreated.
Anaphylactic shock is a life-threatening medical
Emergency because of rapid constriction of the
Airway , often within minutes of onset.
Calling For Help immediately is important, as brain damage occurs rapidly without oxygen. Anaphylactic shock requires advanced medical care immediately; but other
First Aid measures include rescue breathing (part of
CPR ) and administration of
Epinephrine . Rescue breathing may be hindered by the constricted airways but can help if the victim stops breathing on their own. If the patient has previously been diagnosed with anaphylaxis, they may be carrying an
EpiPen (or similar device) for immediate administration of
Epinephrine (adrenaline) by a layperson to help keep open the airway. Repetitive administration can cause
Tachycardia (rapid heartbeat) and occasionally
Ventricular Tachycardia with heart rates up to 240 beats per minute, but is only dangerous when done in rapid succession. Nevertheless, if epinephrine prevents worsening of the airway constriction, it may still be life-saving.
Symptoms of anaphylaxis are related to the action of
Immunoglobulin E (IgE) and other
Anaphylatoxin s, which act to release
Histamine and other mediator substances from
Mast Cell s (degranulation). In addition to other effects, histamine induces
Vasodilation and
Bronchospasm (constriction of the airways).
Symptoms can include the following:
- Respiratory Distress ,
- Hypotension (low blood pressure),
- Fainting ,
- Unconsciousness ,
- Urticaria (hives),
- Flushed Appearance ,
- Angioedema (swelling of the face, neck and throat),
- Tears (due to angioedema and stress),
- Vomiting ,
- Itch ing, and
- Anxiety , including a sense of impending doom
The time between ingestion of the allergen and anaphylaxis symptoms can vary for some patients depending on the amount of allergen ingested and sensitivity. 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.
Common causative agents in humans include:
- Foods (e.g. Milk , Cheese , Nut s, Peanuts , Soybeans and other Legumes , Fish and Shellfish , Wheat and Eggs );
- Drugs (e.g. Penicillin and other Cephalosporins , Contrast Media , ASA and other NSAID s such as Ibuprofen and Diclofenac );
- Latex ;
- Hymenoptera stings from insects such as Bee s, Wasp s, Yellow Jacket s, Hornet s, and some stinging Ants ; and
- Exercise (see Exercise-induced Anaphylaxis ).
Transfusion of incompatible Blood products may lead to extremely similar symptoms, albeit for substantially different biochemical reasons.
Paramedic treatment in the field may include injection with
Epinephrine , administration of
Oxygen therapy and, if necessary,
Intubation during transport to advanced medical care. In profuse
Angioedema ,
Tracheotomy may be required to maintain oxygenation.
The clinical treatment of anaphylaxis by a
Doctor and in the
Hospital setting aims to treat the cellular
Hypersensitivity reaction as well as at the symptoms.
Antihistamine drugs (which inhibit the effects of histamine at histamine receptors) are given but are usually not sufficient in anaphylaxis, and high doses of intravenous
Corticosteroid s are often required. Hypotension is treated with intravenous fluids and sometimes vasoconstrictor drugs. For bronchospasm,
Bronchodilator drugs (e.g.
Salbutamol ) are used. In severe cases, immediate treatment with
Epinephrine can be lifesaving. Supportive care with
Mechanical Ventilation may be required.
Patients must be monitored for four hours after being transported to medical care for the possibility of biphasic reactions (recurrence of anaphylaxis)
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