Principles of surgery

Basic Considerations



1. The affinity of carbon monoxide for hemoglobin is

A. 2-5 times greater than oxygen

B. 20-50 times greater than oxygen

C. 200-250 times greater than oxygen

D. 2000-2500 times greater than oxygen

Answer: C

Another important contributor to early mortality in burns is carbon monoxide (CO) poisoning resulting from smoke inhalation. The affinity of CO for hemoglobin is approximately 200–250 times more than that of oxygen, which decreases the levels of normal oxygenated hemoglobin and can quickly lead to anoxia and death. Unexpected neurologic symptoms should raise the level of suspicion, and an arterial carboxyhemoglobin level must be obtained because pulse oximetry is falsely elevated. (See Schwartz 9th ed., p 198.)

2. A 100-kg patient with a 50% TBSA full thickness burn receives 10 L of 0.9% NaCl solution in transit to the hospital. His laboratory values 6 hours after the injury are likely to reflect which of the following:

A. Acidosis

B. Alkalosis

C. Hypoxia

D. Dilutional anemia

Answer: A

The most commonly used formula, the Parkland or Baxter formula, consists of 3 to 4 ml/kg per percent burned of Lactated Ringer’s, of which half is given during the first 8 hours postburn, and the remaining half over the subsequent 16 hours. Given these large volumes of intravenous resuscitation fluid, Lactated Ringer’s solution is preferred, because 0.9% NaCl results in hypernatremia and more importantly a hyperchloremic acidosis. (See Schwartz 9th ed., p 200.)

3. The topical antimicrobial agent mafenide acetate is most likely to cause which of the following complications:

A. Methemoglobinemia

B. Neutropenia

C. Metabolic acidosis

D. Nephrotoxicity

Answer: C

Mafenide acetate, either in cream or solution form, is an effective topical antimicrobial. It is effective even in the presence of eschar and can be used in both treating and preventing wound infections, and the solution form is an excellent antimicrobial for fresh skin grafts. The use of mafenide acetate may be limited by pain with application to partial-thickness burns. Mafenide is absorbed systemically and a major side effect is metabolic acidosis resulting from carbonic anhydrase inhibition. (See Schwartz 9th ed., p 202.)


1. Which of the following patients should be immediately referred to a burn center?

A. A 20-year-old with a 12% partial thickness burn

B. A 30-year-old with a major liver injury and a 15% partial thickness burn

C. A 2% TBSA partial thickness burn to the anterior leg, crossing the knee

D. A 10-year-old with a 7% partial thickness burn

Answer: A

All patients with a partial thickness burn >10% TBSA should be transferred to a burn center. A patient with a burn and other major trauma can be treated and stabilized in the trauma center first. Burns that involve the entire joint should be transferred to a burn center, but a small burn to the anterior surface of the knee would not necessarily mandate transfer. Children should be transferred if there are no personnel able to care for them, but for a child with a 7% TBSA burn, this would not be mandatory. (See Schwartz 9th ed., p 198; See Table 8-1.)

TABLE 8-1 Guidelines for referral to a burn center

Partial-thickness burns greater than 10% TBSA

Burns involving the face, hands, feet, genitalia, perineum, or major joints

Third-degree burns in any age group

Electrical burns, including lightning injury

Chemical burns

Inhalation injury

Burn injury in patients with complicated pre-existing medical disorders

Patients with burns and concomitant trauma in which the burn is the greatest risk. If the trauma is the greater immediate risk, the patient may be stabilized in a trauma center before transfer to a burn center.

Burned children in hospitals without qualified personnel for the care of children

Burn injury in patients who will require special social, emotional, or rehabilitative intervention

TBSA = total body surface area.

2. Which of the following should prompt immediate, elective intubation in a patient with a major burn?

A. Subjective dyspnea

B. Singed nasal hair

C. Perioral burns

D. Oxygen saturation 96%

Answer: A

Perioral burns and singed nasal hairs are signs that the oral cavity and pharynx should be further evaluated for mucosal injury, but in themselves these physical findings do not indicate an upper airway injury. Signs of impending respiratory compromise may include a hoarse voice, wheezing, or stridor; subjective dyspnea is a particularly concerning symptom, and should trigger prompt elective endotracheal intubation. (See Schwartz 9th ed., p 197.)

3. Which of the following is indicated in a 46-year-old patient with a 22% TBSA partial thickness burn?

A. Prophylactic 1st generation cephalosporin

B. Prophylactic clindamycin

C. Tetanus booster

D. Tetanus toxoid

Answer: C

Patients with acute burn injuries should never receive prophylactic antibiotics. This intervention has been clearly demonstrated to promote development of fungal infections and resistant organisms and was abandoned in the mid-1980s. A tetanus booster should be administered in the emergency room. (See Schwartz 9th ed., p 198.)

4. A 4-year-old patient presents with a diffuse scald wound after being held in a hot tub of water. There are circumferential blisters present over the right leg (from hip to toes) and circumferential blistering over the lower left leg (from knee to toes). The right thigh, abdomen and back below the umbilicus, as well as the buttocks and perineum are red but without blisters. What is the total BSA burn?

A. 25%

B. 36%

C. 46%

D. 54%

Answer: A

The ‘rule of nines’ is a crude but quick and effective method of estimating burn size (Fig. 8-1). In adults, the anterior and posterior trunk each account for 18%, each lower extremity is 18%, each upper extremity is 9%, and the head is 9%. In children younger than 3 years old, the head accounts for a larger relative surface area and should be taken into account when estimating burn size. Diagrams such as the Lund and Browder chart give a more accurate accounting of the true burn size in children. The importance of an accurate burn size assessment cannot be overemphasized. Superficial or first-degree burns should not be included when calculating the percent of TBSA, and thorough cleaning of soot and debris is mandatory to avoid confusing areas of soiling with burns. Examination of referral data suggests that physicians inexperienced with burns tend to overestimate the size of small burns and underestimate the size of large burns, with potentially detrimental effects on pretransfer resuscitation.

If patient in question is over the age of 3; the adult estimates can be used. Only the areas of partial thickness (in this case, blistering) are used to calculate the burn area. The left leg is 18%, and the lower right leg should be slightly less than half of 18% (i.e., approximately 7-8%). (See Schwartz 9th ed., p 198.)


FIG. 8-1. The Rule of Nines can be used as a quick reference for estimating a patient’s burn size by dividing the body into regions to which total body surface area is allocated in multiples of nine.

5. 100% inhaled oxygen decreases the half-life of carbon monoxide from 250 minutes to approximately

A. 200 minutes

B. 150 minutes

C. 100 minutes

D. 50 minutes

Answer: D

Administration of 100% oxygen is the gold standard for treatment of CO poisoning, and reduces the half-life of CO from 250 minutes in room air to 40 to 60 minutes. (See Schwartz 9th ed., p 198.)

6. Which of the following is used to treat severe hydrogen cyanide poisoning?

A. Hydroxocobalamin

B. Methylene blue

C. Dialysis

D. None of the above—there is no effective treatment

Answer: A

Hydrogen cyanide toxicity may also be a component of smoke inhalation injury. Afflicted patients may have a persistent lactic acidosis or S-T elevation on electrocardiogram (ECG). Cyanide inhibits cytochrome oxidase, which in turn inhibits cellular oxygenation. Treatment consists of sodium thiosulfate, hydroxocobalamin, and 100% oxygen. Sodium thiosulfate works by transforming cyanide into a nontoxic thiocyanate derivative; however, it works slowly and is not effective for acute therapy. Hydroxocobalamin quickly complexes with cyanide and is excreted by the kidney, and is recommended for immediate therapy. In the majority of patients, the lactic acidosis will resolve with ventilation and sodium thiosulfate treatment becomes unnecessary. (See Schwartz 9th ed., p 198.)

7. Most chemical burns require large volumes of water to remove the chemical. Which of the following chemical burns should be treated by careful wiping or sweeping of the skin, rather than water?

A. Powdered form of lye

B. Formic acid

C. Hydrofluoric acid

D. Acetic acid

Answer: A

Chemical burns are less common, but potentially are severe burns. The most important components of initial therapy are careful removal of the toxic substance from the patient and irrigation of the affected area with water for a minimum of 30 minutes. An exception to this is in cases of concrete powder or powdered forms of lye, which should be swept from the patient to avoid activating the aluminum hydroxide with water. (See Schwartz 9th ed., p 199.)

8. Formic acid burns are associated with

A. Hemoglobinuria

B. Rhabdomyolosis

C. Hypocalemia

D. Hypokalemia

Answer: A

The offending agents in chemical burns can be systemically absorbed and may cause specific metabolic derangements. Formic acid has been known to cause hemolysis and hemoglobinuria. (See Schwartz 9th ed., p 199.)

9. The agent most effective in treating hydrofluoric acid burns is

A. Calcium

B. Magnesium

C. Vitamin K

D. Vitamin A

Answer: A

Hydrofluoric acid is a particularly common offender due to its widespread industrial uses. Calcium-based therapies are the mainstay of treating hydrofluoric acid burns, with topical calcium gluconate applied to wounds, and subcutaneous or IV infiltration of calcium gluconate for systemic symptoms. Intra-arterial infusion of calcium gluconate may be effective in the most severe cases. Patients undergoing intra-arterial therapy need continuous cardiac monitoring. Persistent electrocardiac abnormalities or refractory hypocalcemia may signal the need for emergent excision of the burned areas. (See Schwartz 9th ed., p 199.)

10. The major improvement in burn survival in the 20th century can be attributed to the introduction of which of the following therapies:

A. Antibiotics

B. Central venous fluid resuscitation

C. Nutritional support

D. Early excision of the burn wound

Answer: D

The strategy of early excision and grafting in burned patients revolutionized survival outcomes in burn care. Not only did it improve mortality, but early excision decreased reconstruction surgery, improved hospital length of stay, and reduced costs of care. After the initial resuscitation is complete and the patient is hemodynamically stable, attention should be turned to excising the burn wound. Burn excision and wound coverage should ideally start within the first several days, and in larger burns, serial excisions can be performed as the patient’s condition allows. (See Schwartz 9th ed., p 204.)