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USMLE Step 2 CK λ Surgery

71.A 41-year-old man presents to the ED reporting that he slipped in the shower and injured his penis. Examination reveals a large penile shaft hematoma with normal appearing glans.

What is it? A classic description of fracture of the tunica albuginea (fracture of the corpora cavernosa)—including the usual cover story given by the patient. These always happen during sexual intercourse, usually with woman on top—but the patient is too embarrassed to explain the true details.

Management. This is a urologic emergency. Prompt surgical repair is needed.

Injury to the Extremities

72.A 25-year-old man is shot with a .22-caliber revolver. The entrance wound is in the anteriolateral aspect of his thigh, and the bullet is seen by x-rays to be embedded in the muscles, posterolateral to the femur.

73.A 25-year-old man is shot with a .22-caliber revolver. The entrance wound is in the anteromedial aspect of his upper thigh, and the exit wound is in the posterolateral aspect of the thigh. He has normal pulses in the leg, and no hematoma at the entrance site. X-rays show the femur to be intact.

74.A 25-year-old man is shot with a .22-caliber revolver. The entrance wound is in the anteromedial aspect of his upper thigh, and the exit wound is in the posterolateral aspect of the thigh. He has a large, expanding hematoma in the upper, inner thigh. The bone is intact.

Apart from the obvious need to fix a bone that might have been shattered by a bullet, the issue in low-velocity gunshot wounds (or stab wounds) of the extremities is the possibility of injury to major vessels. In the first vignette, the anatomy precludes that possibility. Thus that patient only needs cleaning of the wound and tetanus prophylaxis. The bullet can be left where it is.

In the second patient, the anatomy of the area makes vascular injury very likely, and lack of symptoms does not exclude that possibility. At one time, all of these would have been surgically explored. Arteriogram then became the preferred diagnostic modality, and, currently CTAis a highly sensitive non-invasive alternative.

In the third example, it is clinically obvious that there is a vascular injury. Surgical exploration is in order. Arteriogram preceding surgical exploration is done only in parts of the body where the very specific site of the vascular injury dictates the use of a particular incision versus another (for instance at the base of the neck and thoracic outlet).

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75.A young man is shot through the arm with a .38-caliber revolver. The path of the bullet goes right across the extremity, from medial to lateral sides. He has a large hematoma in the inner aspect of the arm, no distal pulses, radial nerve palsy, and a shattered humerus.

That he will need surgery is clear, but the issue here is what to do first. A very delicate vascular repair, and an even more fragile nerve reanastomosis, would be at risk of disruption when the orthopedic surgeons start manipulating, hammering, and screwing the bone. Thus the usual sequence begins with fracture stabilization, then vascular repair (both artery and vein if possible), and last nerve repair. The unavoidable delay in restoring circulation will make a fasciotomy mandatory. Temporary shunting the arterial injury to allow distal perfusion is a good solution if offered as a choice, but is easier said than done in real life.

76.In a hunting accident, a young man is shot in the leg with a high-powered, big-game hunting rifle. He has an entrance wound in the upper outer thigh that is 1 cm in diameter, and an exit wound in the posteromedial aspect of the thigh that is 8 cm in diameter. The femur is shattered.

Even though the major vessels are not in the path of this bullet, this young man will need to go to the OR to have extensive debridement of the injured tissues. High-velocity bullets (military weapons and big-game hunting rifles) produce a cone of destruction.

77.A 6-year-old girl has her hand, forearm, and lower part of the arm crushed in a car accident. The entire upper extremity looks bruised and battered, although pulses are normal and the bones are not broken.

In addition to possible hyperkalemia, crushing injuries lead to two concerns; the myoglo- binemia–myoglobinuria–acute renal failure issue, and the delayed swelling that may lead to a compartment syndrome. For the first, plenty of fluids, osmotic diuretics (mannitol), and alkalinization of the urine help protect the kidney. For the latter, fasciotomy is the answer.

BURNS

1.You get a phone call from a frantic mother. Her 7-year-old girl spilled Drano all over her arms and legs. You can hear the girl screaming in pain in the background.

Management. The point of this question is that chemical injuries—particularly alkalis—need copious, immediate, profuse irrigation. Instruct the mother to do so right at home with tap water, for at least 30 minutes before rushing the girl to the ED. Do not pick an option where you would be “playing chemist,” i.e., soak an alkaline burn with an acid or vice versa.

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2.While trying to hook up illegally to cable TV, an unfortunate man comes in contact with a high-tension electrical power line. He has an entrance burn wound in the upper outer thigh, and an exit burn lower on the same side.

Management. The issue here is that electrical burns are always much bigger than they appear to be. There is deep tissue destruction. The patient will require extensive surgical debridement, but there is also another item (more likely to be the point of the question): myoglobinemia, leading to myoglobinuria and to renal failure. Patient needs lots of IV fluids, diuretics (osmotic if given that choice, i.e., mannitol), perhaps alkalinization of the urine.

If asked about other injuries to rule out, they include posterior dislocation of the shoulder and compression fractures of vertebral bodies (from the violent muscle contractions), and late development of cataracts and demyelinization syndromes.

3.A man is rescued by firemen from a burning building. On admission it is noted that he has burns around the mouth and nose, and the inside of his mouth and throat look like the inside of a chimney.

What is it? There are two issues here: carbon monoxide poisoning and respiratory burns, i.e., smoke inhalation producing a chemical burn of the tracheobronchial tree. Both will happen with flame burns in an enclosed space. The burns in the face are an additional clue that most patients rarely have in real life but will be mentioned on the exam to point you in that direction.

For the first issue we determine blood levels of carboxyhemoglobin, and put the patient on 100% oxygen (oxygen therapy will shorten the half-life of carboxyhemoglobin). For the second issue, diagnosis can be made with bronchoscopy, but the actual degree of damage—and the need for supportive therapy—is more likely to be revealed by monitoring of blood gases.

Management. Revolves around respiratory support, with intubation and use of a respirator, if needed.

4.A patient has suffered third-degree burns to both of his arms when his shirt caught on fire while lighting the backyard barbecue. The burned areas are dry, white, leathery, anesthetic, and circumferential all around arms and forearms.

What is it? You are meant to recognize the problem posed by circumferential burns: the leathery eschar will not expand, while the area under the burn will develop massive edema, thus circulation will be cut off. (Or in the case of circumferential burns of the chest, breathing

will be compromised.) Note that if the fire was in the open space of the backyard, respiratory burn is not an issue.

Management. Compulsive monitoring of Doppler signals of the peripheral pulses and capillary filling. Escharotomies at the bedside at the first sign of compromised circulation. In deeper burns, fasciotomy may also be needed. If the chest wall is involved and respiration impaired, emergent escharotomy is necessary.

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5.A toddler is brought to the ED with burns on both of his buttocks. The areas are moist, have blisters, and are exquisitely painful to touch. The parents report that the child accidentally pulled a pot of boiling water over himself.

What is it? Burns, of course. There are several issues. First: how deep. The description is classic for second-degree burns. (Note that in kids third-degree burn is deep bright red, rather than white leathery as in the adult.) How did it really happen? Scalding burns in kids always brings up the possibility of child abuse, particularly if they have the distribution that you would expect if you grabbed the kid by the arms and legs and dunked him in a pot of boiling water.

Management. For the burn is Silvadene (silver sulfadiazine) cream. Management for the social problem requires reporting to authorities for child abuse.

6.An adult man who weighs x kilograms sustains secondand third-degree burns over—whatever. The burns will be depicted in a front-and-back drawing, indicating what is second-degree (moist, blisters, painful) and what is third-degree (white, leathery, anesthetic). The question will be about fluid resuscitation.

The first order of business will be to figure out the percentage of body surface burned. The rule of nines is used. In the adult, the head is 9% of body surface, each arm is 9%, each leg has two 9%s, and the trunk has 4 9%s.

7.An adult who weighs x kilograms has third-degree burns over… (the calculated surface turns out to be >20%). Fluid administration should be started at a rate of what?

If you are simply asked how fast should the infusion start, rather than what is the calculated total for the whole day, the answer is Ringer’s lactate (without sugar) at 1,000 ml/h.

8.An adult man who weighs x kilograms has third-degree burns over… (a set of drawings provides the area). How much is the estimated amount of fluid that will be needed for resuscitation?

If asked this way, remember the old Parkland formula:

4 ml of Ringer’s lactate (without sugar) per kilogram of body weight, per percentage of burned area (up to 50%) “for the burn,” plus about 2L of 5% dextrose in water (D5W) for maintenance

Give one half in the first 8 hours, the second half in the next 16 hours. Day 2 requires about one half of that calculated amount, and is the time when colloids should be given if one elects to use them. By day 3 there should be a brisk diuresis, and no need for further fluid.

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Remember that these amounts are only a guess, to be fine-tuned by the actual response of the patient (primarily hourly urinary output). Higher amounts are needed in patients who have respiratory burn, electrical burns, or recent escharotomies.

The use of the formulas is now less frequently done, since physicians typically end up adjusting the rate of fluid administration on the basis of the urinary output after initial resuscitation.

9.After suitable calculations have been made, a 70-kg adult with extensive third degree burns is receiving Ringer’s lactate at the calculated rate. In the first 3 hours his urinary output is 15, 22, and 18 ml.

Most experts aim for an hourly urinary output of at least 0.5 ml/kg, or preferably 1 ml/kg body weight per hour. For patients with electrical burns the flow should be even higher (1 to 2 ml/kg per hour); thus by any criteria this patient needs more fluid.

10.After suitable calculations have been made, a 70-kg adult with extensive third degree burns is receiving Ringer’s lactate at the calculated rate. In the first 3 hours his urinary output is 325, 240, and 270 ml.

The opposite of the previous vignette. Somebody is trying to drown this poor guy. The calculation was too generous; the rate of administration has to be scaled back.

11.During the first 48 hours after a major burn, a 70-kg patient received vigorous fluid resuscitation and maintained a urinary output between 45 and 110 ml/h. On postburn day 3—after IV fluids have been discontinued—urinary output reaches 270 to 350 ml/h.

This is the expected. Fluid is coming back from the burn area into the circulation. He does not need more IV fluids to replace these losses.

12.An 8-month-old baby who weighs x kilograms is burned over…areas (depicted in a front-and-back drawing). Second-degree burn will look the same as in the adult; third-degree burn will look deep bright red.

In babies the head is bigger and the legs are smaller, thus the head has two 9%s, whereas both legs add up to 3 (rather than 4) 9%s. Proportionally, fluid needs are greater in children than in adults. Therefore:

•If asked for the rate in the first hour, it should be 20 ml/kg.

•If asked for 24-hour calculations, the formula calls for 4 to 6 ml/kg/%.

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13.A patient with secondand third-degree burns over 65% of his body surface is undergoing proper fluid resuscitation. The question asks about management for the burned areas, and other supportive care.

First of all, tetanus prophylaxis. Then suitable cleaning, and use of topical agents. The standard one is silver sulfadiazine. If deep penetration is desired (thick eschar, cartilage), mafenide acetate is the choice (do not use everywhere; it hurts and can produce acidosis). Burns near the eyes are covered with triple antibiotic ointment. Pain medication is given IV.

After about 2–3 weeks, grafts will be done to the areas that did not regenerate. After an initial day or two of NG suction, intensive nutritional support is needed (via the gut, high calorie/ high nitrogen). Rehabilitation starts on day 1.

14.A 42-year-old woman drops her hot iron on her lap while doing the laundry. She comes in with the shape of the iron clearly delineated on her upper thigh. The area is white, dry, leathery, anesthetic.

What is the issue? A current favorite of burn treatment is the concept of early excision and grafting. After fluid resuscitation, the typical patient with extensive burns spends 2–3 weeks in the hospital consuming thousands of dollars of health care every day, getting topical treatment to the burn areas and intensive nutritional support in preparation for skin grafting.

In very extensive burns there is no alternative. However, less extensive burns can be taken to the OR and excised and grafted on day 1, saving tons of money. You will not be asked on the exam to provide the fine judgment call for the borderline case that might be managed that way (the experts are routinely doing it in burns under 20% and daring to include patients with as much as 40%), but the vignette is a classic one in which the decision is easy: very small and clearly third-degree.

Management. Early excision and grafting.

BITES AND STINGS

1.A 6-year-old child tries to pet a domestic dog while the dog is eating, and the child’s hand is bitten by the dog.

This is considered a provoked attack, and as far as rabies is concerned, only observation of the pet is required (for development of signs of rabies). Tetanus prophylaxis and standard wound care is all that is needed for the child. Had the bite been to the face, and thus near the brain, treatment should be started and then discontinued if it is proven to be not necessary.

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2.During a hunting trip, a young man is bitten on the leg by a coyote. The animal is captured and brought to the authorities alive.

Observation of a wild animal for behavioral signs of rabies is impractical. But having the animal available will allow it to be killed and the brain examined for signs of rabies, thus hopefully sparing the hunter the necessity of getting vaccinated. Had the bite been to the face, and thus near the brain, treatment should be started and then discontinued if it is proven to be not necessary.

3.While exploring caves in the Texas hill country, a young man is bitten by bats (that promptly fly away).

Now we do not have the animal to examine. Rabies prophylaxis is mandatory (immunoglobulin plus vaccine).

4.During a hunting trip a hunter is bitten in the leg by a snake. His companion, who is an expert outdoorsman, reports that the snake had elliptical eyes, pits behind the nostrils, big fangs, and rattlers in the tail. The patient arrives at the hospital 1 hour after the bite took place. Physical examination shows 2 fang marks about 2 cm apart, and there is no local pain, swelling, or discoloration.

The description of the snake is indeed that of a poisonous rattlesnake, but even when bitten by a poisonous snake, up to 30% of patients are not envenomated. The most reliable signs of envenomation are excruciating local pain, swelling, and discoloration (usually fully developed within 30 minutes)—none of which this man has. Continued observation (about 12 hours) is all that is needed, plus the standard wound care (including tetanus prophylaxis).

5.During a hunting trip, a hunter is bitten in the leg by a snake. His companion, who is an expert outdoorsman, reports that the snake had elliptical eyes, pits behind the nostrils, big fangs, and rattlers in the tail. The patient arrives at the hospital 1 hour after the bite took place. Physical examination shows two fang marks about 2 cm apart, as well as local edema and ecchymotic discoloration. The area is very painful and tender to palpation.

This patient is envenomated. Blood should be drawn for typing and crossmatch, coagulation studies, and renal and liver function. The mainstay of therapy is antivenin, of which several vials have to be given. The product currently preferred is CroFab. Surgical excision of the bite site and fasciotomy are only needed in extremely severe cases.

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6.While playing in the backyard of her south Texas home, a 6-year-old girl is bitten by a rattlesnake. At the time of hospital admission she has severe signs of envenomation.

The point of this vignette is to remind you that snake antivenin is one of the very few medicines for which the dose is not calculated on the basis of the size of the patient. The dose of antivenin depends on the amount of venom injected, regardless of the size and age of the victim.

7.During a picnic outing, a young girl inadvertently bumps into a beehive and is stung repeatedly by angry bees. She is seen 20 minutes later and found to be wheezing, hypotensive, and madly scratching an urticarial rash.

Epinephrine is the drug of choice (0.3 to 0.5 ml of 1:1000 solution). The stingers have to be carefully removed.

8.While rummaging around her attic, a woman is bitten by a spider that she describes as black, with a red hourglass mark in her belly. The patient has nausea and vomiting and severe generalized muscle cramps.

Black widow spider bite. The antidote is IV calcium gluconate. Muscle relaxants also help.

9.A patient seeks help for a very painful ulceration that he discovered in his forearm on arising this morning. Yesterday he spent several hours cleaning up the attic, and he thinks he may have been “bitten by a bug.” The ulcer is 1 cm in diameter, with a necrotic center with a surrounding halo of erythema.

Probably a brown recluse spider bite. Dapsone will help. Local excision and skin grafting may be needed. All necrotic tissue must be debrided/excised.

10.A 22-year-old gang leader comes to the ED with a small, 1-cm deep sharp cut over the knuckle of the right middle finger. He says he cut himself with a screwdriver while fixing his car.

What is it? The description is classic for a human bite. No, nobody actually bit him—he did it by punching someone in the mouth and getting cut with the teeth that were smashed by his fist. The imaginative cover story usually comes with this kind of lesion. The point of management is that human bites are bacteriologically the dirtiest that one can get and antibiotics are given. Rabies shots will not be needed, but surgical exploration by an orthopedic surgeon will be required as well as antibiotics.

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