ALLERGIES - Medicine for Mountaineering and Other Wilderness Activities - page 328

them. Because the danger of anaphylactic shock is so great, these serums must be admin-
istered onlywhen absolutely essential andmust begiven onlyinahospital where the aller-
gic reaction can be monitored and controlled.
Insect stings are a less common cause of anaphylactic shock but more common in wil-
derness situations. In the United States, deaths due to allergic reactions to insect stings
far outnumber those caused by all other venomous animals, including venomous snakes,
spiders, and scorpions ( Chapter 33: Envenomations ) . Other substances, such as latex, also
cause anaphylaxis, and for a number of reactions no cause can be identified.
Diagnosis
The symptoms of anaphylactic shock usually appear five to fifteen minutes after expos-
ure to the allergen. Occasionally an hour or more may pass before symptoms appear, and
very rarely twentyfour hours can elapse, particularly after oral ingestion of the offending
substance.
The dominant feature of anaphylactic shock is severe respiratory distress that appears
and progresses rapidly. Swelling of the tissues of the upper air passages, particularly in the
larynx where the airway is already narrowed by the vocal cords (laryngeal edema) narrows
the air passages and can produce lethal respiratory obstruction. Narrowing of the bronchi
withinthelungs—bronchospasm—producesrespiratorydifficultythatissimilartoasthma.
The cause, spasm of muscle in the walls of small bronchi that results in severe constric-
tion, is identical. With anaphylaxis the onset is more abrupt and usually develops within
minutes. Sometimes a sense of pressure beneath the sternum is noted.
The skin is the most common organ involved by anaphylaxis. Hives may be present and
are widely distributed. Angioedema, a localized swelling of the skin and subcutaneous tis-
sue, may occur on an extremity or around the eyes or mouth. Such swelling can also in-
volve mucous membranes and produce respiratory obstruction. The skin usually appears
flushed but sometimes is pale. It is rarely normal in appearance.
Involvement of the eyes and nose causes changes that resemble a sudden, severe attack
of hay fever. The eyes are swollen and red, and the flow of tears is increased. A red,
swollen mucosa and mucoid discharge plug the nose. Nausea, vomiting, abdominal pain,
and diarrhea reflect involvement of the gastrointestinal system. Rarely, involvement of the
cardiovascular system can result in shock or a cardiac arrhythmia that can be fatal.
Treatment
Anaphylactic shock is a true medical emergency for which minutes may make a dif-
ference between therapeutic success and failure. Individuals who know they are at risk
for anaphylaxis should wear warning bracelets and carry auto-injectors, which they must
learn how to use before they are needed. Time for reading the directions, which are avail-
able on the patient insert as well as on the Internet, may not be available once a reaction