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| {{Infobox_Disease |
| | __NOTOC__ |
| Name = {{PAGENAME}} |
| | {| class="infobox" style="float:right;" |
| Image = |
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| Caption = |
| | | [[File:Siren.gif|30px|link=Anaphylaxis resident survival guide]]|| <br> || <br> |
| DiseasesDB = 29153 |
| | | [[Anaphylaxis resident survival guide|'''Resident'''<br>'''Survival'''<br>'''Guide''']] |
| ICD10 = {{ICD10|T|78|2|t|66}} |
| | |} |
| ICD9 = |
| | {{Anaphylaxis}} |
| ICDO = |
| | '''For patient information, click [[Anaphylaxis (patient information)|here]]''' |
| OMIM = |
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| MedlinePlus = |
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| eMedicineSubj = |
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| eMedicineTopic = |
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| MeshID = D000707 |
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| }} | |
| '''For the WikiPatient page for this topic, click [[Anaphylaxis (patient information)|here]]''' | |
| {{SI}}
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| {{CMG}}
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| ==Overview==
| | {{CMG}} {{AE}} [[User:Dushka|Dushka Riaz, MD]] |
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| '''Anaphylaxis''' is an [[acute (medical)|acute]] [[circulation|systemic]] (multi-system) and severe Type I Hypersensitivity [[allergy|allergic]] reaction in humans and other [[mammal]]s. The term comes from the Greek words ''ana'' (against) and ''phylaxis'' (protection).<ref>"Anaphylaxis." Etymology. ''Oxford English Dictionary''. http://dictionary.oed.com.</ref> Anaphylaxis occurs when a person or animal is exposed to a trigger substance, called an ''[[allergen]],'' to which they have already become sensitized. 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.<ref>"Anaphylaxis." Health. 17 January 2002 . AllRefer.com . 29 Jan 2007 <http://health.allrefer.com/health/anaphylaxis-info.html>.</ref>
| | {{SK}} Anaphylactic reaction |
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| '''Anaphylactic shock''', the most severe type of anaphylaxis, occurs when an allergic response triggers a quick release from [[mast cell]]s of large quantities of [[immunology|immunological]] mediators ([[histamine]]s, [[prostaglandin]]s, [[leukotriene]]s) 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.
| | ==[[Anaphylaxis overview|Overview]]== |
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| 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.<ref>Neugut, Alfred, Anita Ghatak and Rachel Miller. "Anaphylaxis in the United States: An Investigation Into Its Epidemiology." Arch Intern Med. 161.108 January 2001 15-21. 29 January 2007 <http://archinte.ama-assn.org/cgi/content/full/161/1/15>.</ref> Anaphylaxis results in fewer than 1,000 deaths per year in the U.S. (compared to 2.4 million deaths from all causes each year in the U.S.[http://www.cdc.gov/nchs/fastats/deaths.htm]). The most common presentation includes sudden cardiovascular collapse (88% of reported cases of severe anaphylaxis).
| | ==[[Anaphylaxis historical perspective|Historical Perspective]]== |
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| Researchers typically distinguish between "'''true anaphylaxis'''" and "'''pseudo-anaphylaxis'''." The symptoms, treatment, and risk of death are identical, but "true" anaphylaxis is always caused directly by [[degranulation]] of [[mast cell]]s or basophils that is mediated by [[immunoglobulin]] E (IgE), and pseudo-anaphylaxis occurs due to all other causes. The distinction is only important for researchers who are studying mechanisms of allergic reactions. Due to the word "pseudo", it may frustrate patients who feel they are being told that a life-threatening allergic reaction isn't "real".
| | ==[[Anaphylaxis classification|Classification]]== |
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| == Differential Diagnosis of Broad Categories of Causes of Anaphylaxis == | | ==[[Anaphylaxis pathophysiology|Pathophysiology]]== |
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| * Blood products
| | ==[[Anaphylaxis causes|Causes]]== |
| * Drugs
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| * Food allergy
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| * Insect bites
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| * Latex allergy
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| * Sterilization agents
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| == Differential Diagnosis of Pseudoanaphylactic Reactions (Conditions that Mimic Anaphylaxis)== | | ==[[Anaphylaxis differential diagnosis|Differentiating Anaphylaxis from other Diseases]]== |
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| First administration of the following drugs or agents:
| | ==[[Anaphylaxis epidemiology and demographics|Epidemiology and Demographics]]== |
| * [[Aspirin]]
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| * Contrast media (first contact)
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| * [[Pentamidine]] (first contact)
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| * [[Polymyxin]] (first contact)
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| Conditions that may mimic anaphylaxis include the following:
| | ==[[Anaphylaxis risk factors|Risk Factors]]== |
| * [[Carcinoid Syndrome]]
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| * Globus hystericus
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| * Hereditary [[angioedema]]
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| * [[Pheochromocytoma]]
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| * [[Pulmonary Embolism]]
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| * [[Scombroid]] intoxication
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| * [[Systemic Mastocytosis]]
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| * [[Vagal]] reactions
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| ==Symptoms== | | ==[[Anaphylaxis natural history, complications and prognosis|Natural History, Complications and Prognosis]]== |
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| Symptoms of anaphylaxis are related to the action of ([[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]] of [[arterioles]] and constriction of [[bronchioles]] in the lungs, also known as [[bronchospasm]] (constriction of the airways).
| | ==Diagnosis== |
| | | [[Anaphylaxis history and symptoms|History and Symptoms]] | [[Anaphylaxis physical examination|Physical Examination]] | [[Anaphylaxis laboratory findings|Laboratory Findings]] | [[Anaphylaxis chest x ray|Chest X Ray]] | [[Anaphylaxis other diagnostic studies|Other Diagnostic Studies]] |
| Symptoms can include the following: | |
| * [[polyuria]]
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| * [[respiratory distress]]
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| * [[hypotension]] (low blood pressure)
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| * [[encephalitis]]
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| * [[fainting]]
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| * [[unconsciousness]]
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| * [[urticaria]] (hives)
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| * flushed appearance
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| * [[angioedema]] (swelling of the lips, face, neck and throat)
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| * [[tears]] (due to [[angioedema]] and stress)
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| * [[vomiting]]
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| * [[itch]]ing
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| * [[diarrhea]]
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| * [[abdominal pain]]
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| * [[anxiety]]
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| 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. <ref>{{cite web |url= http://www.aafa.org/display.cfm?id=9&sub=20&cont=286
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| |title=“Food Allergies” |(March 28, 2007) |publisher=Asthma and Allergy Foundation of America |quote= }}</ref> However, symptoms of anaphylaxis usually appear very quickly once they do begin.
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| ==Treatment== | | ==Treatment== |
| ===Emergency treatment===
| | [[Anaphylaxis medical therapy|Medical Therapy]] | [[Anaphylaxis surgery|Surgery]] | [[Anaphylaxis primary prevention|Primary Prevention]] | [[Anaphylaxis cost-effectiveness of therapy|Cost-Effectiveness of Therapy]] | [[Anaphylaxis future or investigational therapies|Future or Investigational Therapies]] |
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| 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 [[call for help|help]] of advanced medical personnel. [[First aid]] measures for anaphylaxis include rescue breathing (part of [[Cardiopulmonary resuscitation|CPR]]). Rescue breathing may be hindered by the constricted airways, but if the victim 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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| Another 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 receptor]]s in the lung as a powerful [[bronchodilator]] (i.e. it opens the airways), relieving allergic or [[histamine]]-induced acute [[asthma]]tic attack or anaphylaxis. If the patient has previously been diagnosed with anaphylaxis, they may be carrying an [[EpiPen]] (or TWINJECT TM) for immediate administration of epinephrine. However, use of an EpiPen or similar device only provides temporary and limited relief of symptoms.
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| [[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.<ref>http://www.resus.org.uk/pages/reaction.htm</ref> 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.
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| 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.These three injections, taken at the beginning of anaphylaxis, can often bring it under control and avoid a trip to the Emergency Room.
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| ===Clinical care===
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| [[Paramedic]] treatment in the field includes administration of [[epinephrine]] IM (or IV infusion in severe cases), Benadryl IM, steroids such as Decadron, 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.
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| 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 victim.
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| The clinical treatment of anaphylaxis by a [[physician|doctor]] and in the [[hospital]] setting aims to treat the cellular [[hypersensitivity]] reaction as well as the symptoms. [[Antihistamine]] drugs such as Benadryl (which inhibit the effects of histamine at histamine receptors) are continued but are usually not sufficient in anaphylaxis, and high doses of intravenous [[corticosteroid]]s such as Decadron or Solu-Medrol are often required. [[Hypotension]] is treated with [[intravenous fluid]]s 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.
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| 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.
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| The possibility of biphasic reactions (recurrence of anaphylaxis) requires that patients be monitored for four hours after being transported to medical care for anaphylaxis.<ref> Resuscitation Council (UK) 2005 [http://www.resus.org.uk/pages/reaction.htm The Emergency Medical Treatment of Anaphylactic Reactions for First Medical Responders and for Community Nurses]</ref>
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| ===Planning for treatment===
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| 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
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| [http://www.aafa.org/display.cfm?id=4&sub=81&cont=392 "plan"] form anyone can print. Action plans are considered essential to quality emergency care. Many authorities advocate immunotherapy to prevent future episodes of anaphylaxis.[http://www.acaai.org/public/patients/factSheet.htm "allergy fact sheet"] 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. [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=3310714&query_"WHO guidelines"]
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| Beta-blockers may aggravate anaphylactic reactions and interfere with treatment.
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| ===Prevention===
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| 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.
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| ==References==
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| {{reflist|2}}
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| ==External links==
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| *[http://www.aaaai.org/patients/publicedmat/tips/whatisanaphylaxis.stm American Academy of Allergy and Immunology]
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| * [http://www.foodallergy.org The Food Allergy & Anaphylaxis Network]
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| * [http://www.alert4allergy.org alert4allergy.org - a free service for people in Britain with food allergy.]
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| * [http://www.anaphylaxis.org.uk - UK national registered charity and support group for people at risk from anaphylaxis]
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| * [http://www.peanutallergyuk.co.uk A discussion forum for UK peanut anaphylaxis sufferers]
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| * [http://allergy.hyperboards.com/index.php Public discussion forums and support group for allergy/anaphylaxis sufferers]
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| | ==Case Studies== |
| | [[Anaphylaxis case study one|Case #1]] |
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