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Anaphylactic shock is a severe, potentially life-threatening allergic
reaction. It can occur within seconds or minutes of exposure to
something person is allergic to, such as the venom from a bee sting
or a peanut.
The flood of chemicals released by immune system during
anaphylaxis can cause person to go into shock; blood pressure drops
suddenly and airways narrow, blocking normal breathing. Signs and
symptoms of anaphylaxis include a rapid, weak pulse, skin rash, and
nausea and vomiting. Common triggers of anaphylaxis include
certain foods, some medications, insect venom and latex.
Anaphylaxis requires an immediate trip to the emergency room and
an injection of epinephrine. If anaphylaxis isn't treated right away, it
can lead to unconsciousness or even death.
Pathophysiology
Rapid onset of increased secretion from mucous membranes,
increased bronchial smooth muscle tone, decreased vascular smooth
muscle tone, and increased capillary permeability occur after
exposure to an inciting substance. These effects are produced by the
release of mediators, which include histamine, leukotriene C4,
prostaglandin D2, and tryptase.
In the classic form, mediator release occurs when the antigen
(allergen) binds to antigen-specific immunoglobulin E (IgE) attached
to previously sensitized basophils and mast cells. The mediators are
released almost immediately when the antigen binds. In an
anaphylactoid reaction, exposure to an inciting substance causes
direct release of mediators, a process that is not mediated by IgE.
Increased mucous secretion and increased bronchial smooth
muscle tone, as well as airway edema, contribute to the respiratory

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symptoms observed in anaphylaxis. Cardiovascular effects result
from decreased vascular tone and capillary leakage. Histamine
release in skin causes urticarial skin lesions.
The most common inciting agents in anaphylaxis are parenteral
antibiotics (especially penicillins), IV contrast materials,
Hymenoptera stings, and certain foods (most notably, peanuts). Oral
medications and many other types of exposures also have been
implicated. Anaphylaxis also may be idiopathic.
Causes
Common anaphylaxis triggers include:
- Certain medications, especially penicillin
- Foods such as peanuts, tree nuts (walnuts, pecans), fish,
shellfish, milk and eggs
- Insect stings from bees, yellow jackets, wasps, hornets and fire
ants
Less common causes of anaphylaxis include:
- Latex
- Muscle relaxants used in general anesthesia
- Exercise
Anaphylaxis triggered by exercise varies from person to person. In
some people, aerobic activity such as jogging triggers anaphylaxis. In
others, less intense physical activity such as yard work can trigger a
reaction. Eating certain foods before exercise or exercising when the
weather is hot, cold or humid has also been linked to anaphylaxis in
some people.

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Anaphylaxis symptoms are sometimes caused by aspirin, other
nonsteroidal anti-inflammatory drugs — such as ibuprofen (Advil,
Motrin, others) and naproxen (Aleve, Midol Extended Relief) — and
the intravenous (IV) contrast used in some X-ray imaging tests.
Although similar to allergy-induced anaphylaxis, this type of reaction
isn't triggered by allergy antibodies.
In some cases, the cause of anaphylaxis is never identified. This is
known as idiopathic anaphylaxis
Symptoms- Anaphylactic reactions almost always involve the skin or
mucous membranes, most of the patients have some
combination of urticaria, erythema, pruritus, or angioedema.
The classic skin manifestation is urticaria.
- The upper respiratory tract commonly is involved, with
complaints of nasal congestion, sneezing, or coryza. Cough,
hoarseness, or a sensation of tightness in the throat may
presage significant airway obstruction.
- Eyes may itch and tearing may be noted. Conjunctival injection
may occur
- Dyspnea is present when patients have bronchospasm or upper
airway edema. Hypoxia and hypotension may cause weakness,
dizziness, or syncope. Chest pain may occur due to
bronchospasm or myocardial ischemia (secondary to
hypotension and hypoxia).
- GI symptoms of cramp like abdominal pain with nausea,
vomiting, or diarrhea also occur but are less common, except in
the case of food allergy.

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Signs
- Abormal heart rhythm (arrhythmia)
- Fluid in the lungs (pulmonary edema)
- Hives
- Low blood pressure
- Mental confusion
- Rapid pulse
- Skin that is blue from lack of oxygen or pale from shock
- Swelling (angioedema) in the throat that may be severe enough
to block the airway
- Swelling of the eyes or face
- Wheezing
Diagnosis- diagnosis is mainly based on clinics & medical history
like exposure to allergens
Laboratory Studies- The diagnosis of anaphylaxis is clinical and
does not rely on laboratory testing.
- The only potentially useful test at the time of reaction is
measurement of serum mast cell tryptase, though the test's
availability and slow turn around time greatly limit its clinical
utility. Tryptase is released from mast cells in both
anaphylactic and anaphylactoid reactions. Levels are usually
raised in severe reactions.
Sensitivity testing- Testing for sensitivity to penicillin antibiotics
may be useful when a penicillin or cephalosporin antibiotic is the

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drug of choice for a serious infection in a patient who has a history
of severe allergic reaction.
Specific IgE tests may be preferable to skin prick tests when
investigating patients with a history of anaphylaxis
Treatment- What to do in an emergency - If someone who is
having an allergic reaction and shows signs of shock caused by
anaphylaxis, a quick reaction is essential. Signs and symptoms of
shock caused by anaphylaxis include pale, cool and clammy skin,
weak and rapid pulse, trouble breathing, confusion and loss of
consciousness, take the following steps immediately:
- Call 911 or emergency medical help.
- Check the person's pulse and breathing and, if necessary,
administer CPR or other first aid measures.
- If the person has medications to treat an allergy attack, such as
an epinephrine auto-injector or antihistamines, give them right
away.
Parenteral adrenergic agents- Reverse cardiovascular, cutaneous,
GI, and pulmonary manifestations of anaphylaxis.
Epinephrine- 0.3-1.0 ml 1:1000 solution IM, repeated at 5-10 mins
if initial response is inadequate
Inhaled beta-agonists- Used to treat bronchospasm. Doses are
identical to those used in the treatment of asthma.
Albuterol- Numerous inhaled beta-agonists are used for treatment
of bronchospasm; albuterol is the most commonly used
preparation. 0.5 mL 0.5% soln in 2.5 cc NS nebulized q15min

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Antihistamines- Diphenhydramine(Benadryl)- 25-50 mg IV/IM q46h , 50 mg PO q4-6h
Corticosteroids- Methylprednisolone- 40-250 mg IV/IM q6h,
60 mg PO qd
2-
Antidote, Hypoglycemia- inotropic, chronotropic, and vasoactive
effects, useful in patient who are resistant to epinephrine or other
adrenergic agents. 1-10 mg IV/IM/SC; typically 1-2 mg q5min to
effect

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Antihistamines- Diphenhydramine(Benadryl)- 25-50 mg IV/IM q46h , 50 mg PO q4-6h
Corticosteroids- Methylprednisolone- 40-250 mg IV/IM q6h,
60 mg PO qd
2-
Antidote, Hypoglycemia- inotropic, chronotropic, and vasoactive
effects, useful in patient who are resistant to epinephrine or other
adrenergic agents. 1-10 mg IV/IM/SC; typically 1-2 mg q5min to
effect