PREP Answers Week of July 24
1. Correct Answer B
The patient described in the vignette has heat stroke, a medical emergency that requires immediate action
to minimize morbidity and mortality. The diagnosis can be made on the basis of classic signs and symptoms:
hyperpyrexia (105.8°F [41°C] or higher), hot dry skin, and severe central nervous system dysfunction. In
most, but not all cases, sweating stops before the onset of heat stroke.
Hyperpyrexia to this degree combined with the usual dehydration that accompanies heat stroke can lead to
end-organ tissue damage due to release of endotoxins and cytokines. Rapid cooling to 101.8°F (38.8°C) is
critical, although further cooling beyond that point is unnecessary and may lead to hypothermia. The best
cooling method is to place ice packs at the neck, groin, and axilla. Iced peritoneal lavage is also highly
efficient. Evaporative techniques using fans and water at 59°F (15°C)in a mist spray may be equally
effective, but there are few data to support this conclusion.
Support of the cardiovascular system also is a high priority. Heat stroke is associated with a marked increase
in cardiac output, marked vasodilation, and low peripheral vascular resistance. If the hyperpyrexia and
hypovolemia are not corrected, a falling cardiac output will ensue, possibly the result of direct thermal injury
to the myocardium. Even after body temperature returns to normal, a high-output state may continue for
several hours.
Nontraumatic rhabdomyolysis may result from heat injury, putting the patient at risk for acute renal failure.
Laboratory evidence of the condition includes an elevated serum creatinine phosphokinase concentration or a
rapidly rising blood urea nitrogen value. Renal function should be monitored carefully.
Dehydration is usually present in heat stroke, but it is not essential to the pathophysiology of this condition.
Due to the altered mental status that accompanies heat stroke, intravenous fluids are preferred over oral
fluids. For less dangerous categories of heat illness, such as heat cramps or heat exhaustion, oral
rehydration is appropriate. PREP 2006 Q 208
2. Correct Answer A
The history of syncope and the physical findings of facial flushing, sweating, and symptoms of nausea and
confusion occurring in association with exertion on a hot day described for the girl in the vignette are most
likely due to heat exhaustion.
Heat exhaustion occurs when the body's heat-dissipating mechanisms are stressed by the heat production of
exercise and heat absorption from the environment; the body temperature is normal or mildly elevated.
Components of environmental heat conditions are temperature, humidity, and wind. During exertion in hot
conditions, the dissipation of heat by vasodilation (convection and radiation to the environment) is limited,
making the evaporation of sweat the most significant heat loss mechanism. Sweating that causes water and
electrolyte loss with resultant intravascular volume depletion and vasodilation (flushing)both contribute to
other signs and symptoms seen with heat exhaustion. These include dizziness, syncope or near-syncope,
weakness, muscle cramps, orthostatic or sustained hypotension, tachycardia, nausea, vomiting, and mental
confusion. Among the factors that can promote the risk of exertional heat-related illness are dehydration,
lack of acclimatization, lack of fitness, obesity, recent febrile illness, sunburn, and a number of drugs (eg,
antihistamines, haloperidol, laxatives, or tricyclic antidepressants).
Heatstroke, a term used when the body's ability to dissipate heat is overwhelmed, is defined by a rectal
temperature that exceeds 104ºF (40ºC) and alteration in consciousness (eg, disorientation, stupor,
hallucinations, convulsions, coma). Sweating, often considered a classic sign, is not always evident. Heat
stroke is a medical emergency; ensuing complications such as shock, organ system compromise, and
consumptive coagulopathy may be fatal or cause long-term sequelae.
Hyperventilation,orthostatic hypotension, seizures, and supraventricular tachycardia, each potential causes
of syncope, also may be associated with heat-related illnesses. However, the constellation of signs and
symptoms in the vignette are more descriptive for heat exhaustion. It is crucial to recognize these signs and
symptoms so as to begin cooling measures and rehydration. PREP 2005 Q 2
3. Correct Answer D
Rapid weight loss, or weight-cutting, prior to the pre-competition weigh-in is practiced by as many as two thirds
of wrestlers. They believe that rapid weight loss will allow them to qualify for competition in a lower weight class
and, as a result, that they will have an advantage against a smaller opponent. To lose weight, most wrestlers
employ a combination of exercise, food or fluid restriction, or methods of dehydration (eg, take prolonged
saunas, wear rubber or plastic suits). Few use pharmacologic agents (eg, cathartics, laxatives, or diuretics) or
induce vomiting. In the brief period between the weigh-in and competition (30 minutes to 20 hours), wrestlers
hope to replenish lost fluids and electrolytes.
Weight-cutting has potential adverse physiologic effects, including possible decreases in muscle strength and
aerobic power capacity, reduced endurance, impaired thermoregulation, and depletion of electrolytes and muscle
glycogen. The American College of Sports Medicine has published a position paper on weight loss in wrestlers that
discourages weight-cutting and offers several recommendations:
•
Educate coaches and wrestlers about the potential risks of rapid weight loss.
•
Discourage the use of weight-cutting practices
•
Schedule weigh-ins immediately prior to competition.
• Schedule daily weigh-ins before and after practice to monitor weight loss and dehydration; weight
loss should not
exceed 2 to 3 lb/wk or 1.5% of body weight.
• Assess the body composition of each wrestler prior to the season and use this data (not ideal body
weight) to
determine the minimum wrestling weight (eg, percent body fat should be ≥7% for males ≥16 years of
age, ≥5% for males ≥16 years of age, and 12% for females).
• Emphasize the importance of proper nutrition.
PREP 2004 Q 26
4. Correct Answer D
The constellation of symptoms appearing so soon after a snake bite in the child in the vignette is most
consistent with severe envenomation from a pit viper (Figure C96A). Pit vipers are so named because of
small heat-sensitive pits located on each side of the head between the nostril and the eye. Further
characteristics of pit vipers include elliptical pupils, two large curved fangs, and a triangular head. These
characteristics help to distinguish pit vipers from nonvenomous snakes. Rattlesnakes, copperheads, and
water moccasins are all pit vipers (crotalids) and together account for 99% of all venomous snake bites in
the United States.
The venom from pit vipers contains a variety of neurotoxins to help halt and kill their prey as well as
enzymes to start the process of digestion from within. These enzymes are largely responsible for both the
local and systemic symptoms of crotalid envenomation. Envenomation is not inevitable after a bite from a pit
viper; up to 20% of rattlesnake bites are "dry" and do not result in envenomation.
When envenomation occurs, local pain develops rapidly (5 to 10 min) and typically is intense. Victims often
complain within minutes of perioral numbness or a metallic taste in their mouths. Progressive swelling
proportional to the inoculum develops over the next 8 hours along with local ecchymoses and vesicles
(Figure C96B). Unless antivenin is administered, the local symptoms progress to necrosis. Cardiovascular,
pulmonary, renal, neuromuscular, and hematologic symptoms also may develop. Initial laboratory
assessment includes complete blood count, coagulation studies, urinalysis, electrolyte measurement, and
blood for typing and cross-matching. Massive hemolysis may make later cross-matching more difficult.
Crotalid antivenin is the definitive therapy but should be reserved for those who have clear and progressive
symptoms of severe envenomation. It should be administered within 4 hours of the bite for maximal benefit;
administration after 24 hours is not indicated. The dose is not calculated on a weight basis but is based on
the potential for morbidity/mortality. A small child requires more antivenin than an adult, and bites from a
copperhead require less antivenin than bites from a rattlesnake. The initial dose should be repeated every 2
hours until progression of swelling has stopped.
Any individual suspected of having been bitten by a pit viper should be transported immediately to a medical
facility that has access to crotalid antivenin. Therefore, further office observation of the child in this vignette
is not appropriate. Incision and suction of the pit viper wound are indicated only if they can be initiated
within 5 to 10 minutes of the bite. Tourniquets and ice should not be used. However, a loosely fitting
constricting band placed 5 to 10 cm proximal to the wound may be helpful to obstruct venous and lymphatic
flow, especially if a significant delay is anticipated in transporting the victim. PREP 2004 Q 96
5. Correct Answer A
The signs and symptoms exhibited by the child in the vignette are most consistent with a bite from a brown
recluse spider. This spider is small (1 to 1.5 cm in length) and has a brown violin-shaped mark on the
dorsum of the body. The bite is generally innocuous and often unnoticed, leading to a delay in seeking care.
The primary symptoms consist of a local reaction that can range from very mild erythema to a severe
ulceration. Mild-to-moderate pain or itching may be noted 2 to 8 hours after the bite and is followed by the
development of erythema with a central blister or pustule. The central area may become necrotic, producing
an ulcerated crater (Figure C80A). Induration of surrounding tissue peaks at 48 to 96 hours. Systemic
symptoms rarely can develop in small children 24 to 48 hours after the bite and may include fever, chills,
malaise, vomiting, joint pain, intravascular hemolysis, and renal failure.
Treatment of most brown recluse spider bites consists of local wound care. There is no antivenin available. If
there is no necrosis or if the area of necrosis is less than 2 cm, as for the child in the vignette, local care and
observation are recommended. Neither steroids nor antibiotics are warranted for prophylaxis. Excision of
tissue surrounding the bite is not indicated in this case. However, if the area of necrosis is larger than 2 cm
within 48 hours, debridement and antibiotic therapy may be indicated. Patients who develop hemolysis may
require alkalinization of their urine to prevent hemoglobin-induced renal failure. Dapsone has been
suggested for severe envenomation in adults, but its use is controversial, and it should not be used in
children.
The leading cause of death from spider bites in the United States is the black widow (Latrodectus sp), the
only other spider in North America that commonly inflicts a medically significant bite. The bite causes no
local symptoms, but the venom can cause a variety of systemic symptoms within hours, most commonly
pain and muscle rigidity. Overall mortality is about 4% to 5%, but it may approach 50% in small children.
Latrodectus antivenin should be administered to patients who have severe symptoms and to children who
weigh less than 40 kg.