Environmental
Exposures
Answers
420.The answer is b.(Rosen, pp 1972-1978.)Frostbite usually occurs when
temperatures fall below 0°C (32°F). There are essentially three phases to
the freezing injury cascade. Phase 1 (prefreeze) includes initial skin cooling,
increased blood viscosity, and microvascular leakage which causes localized
edema formation. Phase 2 (freeze-thaw) is when extracellular crystal formation
begins thereby causing intracellular shrinkage and essentially collapse of
the cellular network. Finally, phase 3 (vascular stasis/progressive ischemia)
involves further coagulation, interstitial leakage, and cell death thus resulting
in blister formation, cyanosis, and ultimately mummification of the tissue. The
bullae formed may also have a hemorrhagic appearance. It is important to note
that wind and moisture may increase the freezing rate. Management includes
rapid rewarming with water at a temperature of 37°C to 40°C (98.6°F-104°F)
with care in preventing refreezing. Friction massage, which furthers tissue
loss, should be avoided. Rewarming is a painful procedure that requires
parenteral analgesia. Patients may also have a degree of dehydration and benefit
from crystalloid administration.
(a)Chilblains, also known as pernio, are a condition commonly seen
in the homeless population as a result of chronic dry-cold exposure and
mostly affects the face, hands, and pretibial areas. Trench foot (c),also known
as immersion injury, is common in this population; however, it usually presents
as a loss of sensation with pallor and mottling. (d)Thermal burns may present
with bullae formation but do not elicit cyanosis. (e)Herpes is also unlikely
given the distribution and lack of contacts with similar lesions.
421.The answer is c.(Rosen, p 2002.)This patient is suffering from
miliaria rubra,more commonly known as prickly heat or heat rash.This
is an acute inflammatory disorder of the skin that occurs in tropical climates,
also lending the term “lichen tropicus.” It occurs because of sweat gland
blockage and staphylococcal infection. The acute phase is noted by vesicular
lesions that are caused by obstruction of the sweat glands, which subsequently
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