Steven D. Bines, M.D., Thomas A. Messer, M.D., Stathis J. Poulakidas, M.D., F.A.C.S.
1 Select the true statement regarding the epidemiology of burn injury:
A Most burn injuries occur in occupational environments.
B Young adult men are the most likely to suffer burn injury.
C The most common cause of death after admission for burn injury is airway occlusion.
D Scalding is the most common cause of burns in children younger than 5 years.
E Prevention has not has a significant impact on the incidence or mortality of burn injury.
Ref.: 1-3
Comments
Approximately 1 million injuries are caused by thermal trauma yearly in the United States. The majority of burn injuries occur in the home (43%). In general, 65% of burns occur in non–work-related accidents, 17% in work-related accidents, and 5% each in recreational or in assault or abuse cases. House fires contribute to 75% to 80% of deaths from burns. Burns occur in a bimodal distribution, with increased risk occurring in children younger than 4 years and adults 65 years and older. African Americans and Native Americans are disproportionately affected. Burns occur more frequently in vulnerable populations, including those with epilepsy, those with heavy alcohol use, the poor, and people living in substandard housing. Asphyxiation is a common cause of death at the scene of a fire, but the most common recorded cause of death in burn patients after admission is multiorgan failure. Other causes, in decreasing order of frequency, are shock, trauma, pulmonary failure or sepsis, cardiovascular failure, and burn wound sepsis. Hot-water scald injuries are the most common cause in children younger than 5 years, with flame burns becoming more frequent in those 5 years and older. Ordinances requiring water heaters to be set at no higher than 120° F have decreased the incidence of scald burns. Efforts at prevention have significantly decreased the number of burn injuries occurring in the United States, although disabled or impaired individuals are still at risk.
Answer
D
2 Which of the following regarding burn wound depth is true?
A First-degree burns heal rapidly but contribute significantly to the total body surface area (TBSA) burned in large, mixed-depth wounds.
B Second-degree burns characteristically cause erythema, pain, and blistering.
C Third-degree burns are generally painful and extremely sensitive to touch.
D Fourth-degree burns mandate amputation of the involved extremities.
E Superficial partial-thickness burn is the contemporary term for first-degree burns.
Ref.: 1-3
Comments
Skin consists of two layers: epidermis and dermis. The epidermis is composed of five progressively differentiated layers of keratinocytes, the outermost of which, the stratum corneum, is relatively impermeable. The epidermis provides barrier functions and protects against infection, absorption of toxins, exposure to ultraviolet (UV) light, and fluid and heat loss. The dermis is a cellular and extracellular layer that provides the skin with durability and elasticity. Within the dermis, fibroblasts synthesize mesenchymal proteins, and inflammatory cells are present and contribute to the inflammatory responses to injury. Dermal papillae interdigitate with the epidermal rete ridges to form the dermal-epidermal junction, a site affected by some exfoliative diseases of the skin. Superficial, or first-degree, burns involve only the epidermis and are erythematous and painful. The damaged epidermis will slough off within 3 to 4 days and be replaced by regenerating keratinocytes. Most sunburn is first-degree, and the treatment of superficial burns is similar to that of sunburn. Superficial burns do not contribute significantly to the systemic response to burn injury and are not counted in the percentage of TBSA (%TBSA) burned. Partial-thickness burns (second-degree) involve both the epidermis and dermis and are subdivided into superficial partial thickness and deep partial thickness, depending on the depth of dermal involvement. Superficial partial-thickness burns involve the papillary dermis. Blistering occurs within 24 hours of injury. The exposed underlying dermis is typically pink, blanching, moist, and tender to touch because the nerve endings are preserved. These burns heal within 2 to 3 weeks with little risk of scarring. Deep partial-thickness burns extend to the reticular dermis and may require more than 3 weeks to heal. These wounds blister and reveal mottled pink/white dermis. Sensation may be decreased, and the wounds may dry after initial observation. If deep partial-thickness wounds take longer than 3 weeks to heal, grafting may be required. Full-thickness (third-degree) burns extend through the entire dermis into subcutaneous tissue. Full-thickness burns may be dry, leathery, firm, and insensate. Even if mottled in appearance, they do not blanch and may be hemorrhagic. These wounds require excision of the burn eschar and skin grafting for closure. Intermediate-depth wounds may be difficult to judge by initial appearance. Their potential to heal should be determined with serial observations because the initial evaluation may be inaccurate, even by experienced clinicians. Light reflectance techniques, fluorescein, thermography, and magnetic resonance imaging have not proved useful with respect to serial clinical evaluation. Noncontact laser Doppler imaging can be helpful but has not gained widespread clinical use. Fourth-degree burns extend to muscle, bone, or other deep structures. They are particularly common with electrical injuries or burns with prolonged contact occurring in impaired patients. These very deep burns pose serious reconstructive challenges, and amputation may be required when the extremities or digits are involved.
Answer
B
3 Which of the following statements regarding the zones of injury in a burn wound is true?
A A zone of hyperemia inside a zone of stasis
B A zone of hyperemia superficial to a zone of stasis, with a deeper zone of coagulation beneath
C A zone of coagulation at the surface of a burn wound, a zone of stasis within the injured dermal layer, and a deep zone of hyperemia characterized by vasodilated subcutaneous vessels
D A zone of coagulation, surrounded by a zone of stasis, surrounded by a zone of hyperemia
E A zone of hemorrhagic burn that must be coagulated, a zone of stasis in which the depth of burn injury is already fixed, and a zone of hyperemia that may convert to coagulation
Ref.: 1
Comments
Jackson’s classification of zones of injury in 1953 referred to the varying depth of injury radiating outward from a burn wound and defined the pathophysiology of cutaneous thermal injury. The central zone of coagulation is necrotic and irreversibly damaged; it represents a full-thickness injury that will require excision and grafting. The zone of stasis refers to the surrounding region and is characterized by constricted vessels and hypoxia. Initially viable, this tissue may convert to coagulation or a full-thickness injury as a result of edema, infection, or shock with decreased perfusion. The zone of stasis may remain viable if adequately perfused. In a patient with a large TBSA burn, the viability of this zone may be critical in providing donor sites and reducing the total area that requires grafting. The zone of hyperemia is characterized by vasodilation as a result of inflammatory mediators, and the tissue is viable.
Answer
D
4 Select the most accurate statement regarding burn injury:
A Contact burns occur commonly and rarely require grafting.
B Intoxication is infrequently associated with deep burn injury.
C Circumferential burns on both feet are seen in accidental bathing injuries in children.
D Flash burns are generated by brief, intense heat, and articles of clothing are frequently protective.
E Electrical burns are deeper than they appear because of the high flash temperatures generated by arcing.
Ref.: 1
Comments
The mechanism of burn injury, if known, may aid in assessing wound depth and predicting its capacity to heal. Flash burns are responsible for 50% of admissions to burn centers. Explosions caused by natural gas, propane, and gasoline vapors generate brief, intense heat. If not directly ignited, clothing is protective, with burns affecting only exposed skin. The depth of injury can be variable; many flash burns heal without grafting. Flame burns generally result in deep dermal or full-thickness injury because of the duration of exposure. Structure fires and ignition of bedding or clothing are common causes of flame burns, and burn depth is proportional to the time required to remove the burning or smoldering material from the victim. Intoxication or carbon monoxide (CO) poisoning occurring during a house fire increases the likelihood of deep flame burns. Scald burns are the second most common cause of burns in the United States. The depth of injury is related to water temperature and the duration of contact. At 140° F (60° C), water causes deep dermal injury in 3 seconds. Clothed areas may be scalded more deeply because of prolonged contact with wet fabric before removal. Young children and elderly patients will scald faster and at lower temperatures. If not cautious, diabetic patients may accidentally scald themselves when soaking neuropathic or insensate feet in hot water. These burns are frequently deep partial to full thickness, and such patients are likely to have impaired healing as a result of their comorbid conditions. Hot oil and grease burns tend to be deep partial or full thickness because of the very high temperatures reached while cooking or heating oil. Contact burns result from direct contact with a heat source and often occur in work environments. The hot presses used in industrial applications can cause particularly devastating combined crush/burn injuries that may result in poor functional outcomes. Deep contact burns in domestic environments occur in children or impaired individuals (drugs, alcohol). Palmar or plantar surface burns generally deserve a period of observation because of the propensity of the thicker dermis of these surfaces to heal and generally less optimal results in terms of sensation and function obtained with split-thickness skin grafting in these areas. Electrical injuries may cause deep tissue destruction that belies the surface wound when current flows through the patient, but flash burns from electrical arcing without direct contact are similar to flash burns from other sources.
Answer
D
5 Which of the following patients do not meet the criteria for referral to a burn center?
A A 50-year-old woman with a 1% TBSA partial-thickness burn on her left hand from a cooking accident
B A 30-year-old construction worker with pain and blistering bilaterally on the knees after kneeling in wet cement all afternoon
C A 25-year-old man with 7% TBSA partial-thickness burns on the chest
D A 42-year-old woman with no cutaneous injury, found lying down at the scene of a house fire, and noted to have carbonaceous sputum after intubation in the field
E An 18-year-old man in a motor vehicle collision with 30% TBSA burns on his chest and circumferential burns bilaterally on his arms
Ref.: 4
Comments
The American Burn Association and the American College of Surgeons Committee on Trauma have published guidelines for patient transfer to a burn center for care: (1) partial-thickness burns on greater than 10% of TBSA; (2) burns that involve the face, hands, feet, genitalia, perineum, or major joints; (3) third-degree burns (any size) in any age group; (4) electrical burns, including lightning injury; (5) chemical burns; (6) inhalation injury; (7) burn injury in patients with preexisting medical disorders that could complicate management, prolong recovery, or affect mortality; (8) any patient with burns and concomitant trauma (such as fractures) in which the burn injury poses the greatest risk for morbidity or mortality (in such cases, if the trauma poses the greater immediate risk, the patient’s condition may be stabilized initially in a trauma center before transfer to a burn center); (9) burned children in hospitals without qualified personnel or equipment for the care of children; and (10) burn injury in patients who will require special social, emotional, or rehabilitative intervention. These criteria are not meant to be exclusive, and many centers will treat patients with wounds smaller than those mentioned in the guidelines. Many burn centers care for patients with exfoliative skin disorders, major wounds, necrotizing infections, and other diseases that require significant wound management and critical care.
Answer
C
6 A 6-year-old girl suffers full-thickness flame burns on her forearm after playing with matches. Which of the following is correct regarding wound healing after her skin grafting?
A Capillary leakage results from inadequate cooling of burn wounds after injury.
B Epithelialization signals the end of burn wound healing.
C Diffusion allows skin grafts to survive before neovascularization.
D Routine exposure to UV light may help speed repigmentation of the healing burn wound.
E Epidermolysis is typical of excessive myofibrillar adhesion to the basement membrane.
Ref.: 1
Comments
Burned tissues initially respond with coagulation and constriction of the microvasculature for hemostasis. In the coagulation pathways, including cleavage of fibrinogen by tissue factor, matrix is laid down so that cells can migrate into the wound bed. Inflammatory cells generate plasmin for clot resolution. Vasoconstriction is followed by the vasodilation and capillary leakage seen in the resuscitative phase of injury. Capillary leakage allows migration of cells into the wound but also extravascular leakage, which leads to pulmonary edema, compartment syndromes, and the potential for ischemic injury in tissues with marginal viability (zone of stasis). A great many inflammatory mediators are released, including interleukins, prostaglandins, and neuropeptides, and cause cellular adhesion, chemotaxis, and proliferation. Serotonin, histamine, bradykinin, and arachidonic acid metabolites allow continued vasodilation and vascular permeability. Signals and mediators from cutaneous cells contribute to the inflammation. Neutrophil margination may potentiate ischemia and contribute to reperfusion injury. Inhibition of these pathways is of interest but is currently not clinically useful. Epithelialization of full-thickness wounds occurs from the wound edges, whereas partial-thickness burn wounds heal from the epidermal appendages surviving in the wound bed. Formation of granulation tissue indicates the wound is able to be closed. Skin grafts survive by imbibition (diffusion) of nutrients and oxygen for several days after placement until neovascularization links capillaries in the graft to those in the wound bed (inosculation). Once epithelialized, the barrier functions of the outer skin are restored, and the inflammatory state of the wound may be altered. Basement membrane continues to develop after epithelialization, which explains why blistering and epidermolysis are commonplace early after wound closure. Dermal and subcutaneous fibrogenesis continues along with cellular migration and angiogenesis. Type III and type I collagen are deposited in a mat and result in dermal scar. Cross-linking of type I collagen fibrils increases breaking strength, albeit never to preinjury levels. Matrix metalloproteinases aid remodeling of the matrix and may prevent hypertrophic scar formation. Myofibroblasts aid wound closure by contraction, which may contribute to disability following burn injury. Melanocytes migrate from the wound edges and epidermal appendages after the epithelial cells. Protection from UV rays aids return of pigmentation. Hypertrophic scars have increased sensory nerves, thereby contributing to their sensitivity and pruritus.
Answer
C
7 A 25-year-old man pulled from a house fire has burns on his right arm circumferentially, bilaterally on his legs, and on his perineum. What is the approximate %TBSA burned?
A 28%
B 36%
C 64%
D 46%
E 72%
Ref.: 1
Comments
It is important to estimate the size of a burn initially to guide transfer to definitive care, fluid resuscitation, and caloric needs, as well as for prognostic information. This is generally expressed as the percentage of total body surface area burned. Initial estimation is often performed at facilities without experienced burn personnel. The “rule of nines” may be used to approximate the area of burn involvement before burn care; this rule describes body surface area by anatomic area as follows: head and neck, 9%; each upper extremity (front and back), 9%; anterior trunk, 18%; posterior trunk, 18%; anterior lower extremity (each), 9%; posterior lower extremity (each), 9%; and perineum/genitalia, 1%. More detailed tools, such as the Lund-Browder chart, analyze body surface area more accurately by smaller divisions and are adjusted for age (children have proportionally larger heads and smaller legs). Alternatively, small or scattered patches of burn can be estimated by using the surface of the patient’s palm to represent 1% total body surface area.
Answer
D
8 A 50-kg woman is burned in a house fire and suffers 60% TBSA partial- and full-thickness burn wounds. What is your initial fluid administration plan?
A 1000-mL bolus of lactated Ringer (LR) solution and then 750 mL/h
B 5% dextrose (D5)/LR at 600 mL/h, with titration of fluid administration hourly to a urine output of 0.5 mL/kg/h
C 500-mL LR bolus, repeated as needed to bring central venous pressure (CVP) up to at least 10 cm H2O; maintain fluid rate at 375 mL/h
D LR at 750 mL/h for 8 hours and then 375 mL/h for the following 16 hours
E LR at 800 mL/h for 12 hours and then 400 mL/h for 12 hours
Ref.: 1-3
Comments
The Parkland formula is most commonly used to estimate the fluid resuscitation requirements for the first 24 hours after burn injury. This formula calls for 3 to 4 mL/kg/%TBSA burn to be given over a 24-hour period. Half of the volume should be given over the first 8 hours after injury and the remainder over the following 16 hours. For this 50-kg patient, fluid administration should begin with 4 × 50 kg × 60% TBSA = 12,000 mL crystalloid over the first 24 hours after injury. Half (6000 mL) should be given over the first 8 hours (6000 mL/8 h = 750 mL/h) and the remainder over the following 16 hours (6000 mL/16 h = 375 mL/h). In addition to the calculated resuscitation volumes, children less than 20 kg require maintenance fluids (
) to prevent hypoglycemia. The patient’s response to resuscitation should be monitored and fluid administration adjusted accordingly. The most useful marker of resuscitation is adequate hourly urine output, defined as 30 to 50 mL/h in adult patients and 1 mL/kg/h in children in the absence of myoglobinuria. Crystalloid boluses should be avoided unless required because of hypotensive episodes (mean arterial pressure persistently less than 60 mm Hg) or to resuscitate blood loss from other traumatic injuries. Intravenous fluids are rapidly extravasated as a result of the capillary leakage that occurs in the first 48 hours. Decreased urine output for 1 to 2 hours would require increasing the hourly fluid rate. Adequate or excessive urine output may prompt reduction of fluid administration rates. Many burn centers use algorithm-driven fluid resuscitation protocols, and computer-assisted protocols have been designed. Intravenous fluid administration based on CVP or pulmonary artery catheter monitoring may lead to overresuscitation in many burn patients, but it may be necessary in those with cardiac failure, renal failure, or cardiogenic shock. It is important to decrease fluid administration if not required because the morbidity (abdominal and extremity compartment syndromes, pulmonary edema) from massive volumes of resuscitation fluid is not insignificant. Colloid administration once the capillary leak has closed, 12 to 48 hours after injury, may help restore intravascular volume in patients with persistent low urine output and hypotension despite adequate crystalloid administration. In such cases, 5% albumin (0.3 to 0.5 mL/kg/%TBSA burn) can be administered over a 24-hour period. Plasmapheresis also reduces intravenous fluid requirements in patients who do respond to standard crystalloid resuscitation. Indications for plasmapheresis include a sustained mean arterial pressure of less than 60 mm Hg and urine output of less than 30 mL/h in a patient whose ongoing fluid needs are more than twice the fluid volume estimates. Early plasmapheresis (12 to 24 hours after injury) appears to decrease the incidence of complications from the administration of excessive fluid, such as extremity compartment syndromes, abdominal compartment syndrome, and pulmonary edema.
Answer
D
9 Which of the following is correct regarding inhalation injury in burn patients?
A The admission chest radiograph is useful for ruling out inhalation injury on admission.
B Supraglottic inhalation injury may necessitate intubation even if gas exchange is initially unaffected.
C With proper pulmonary toilet, pneumonia is an unusual complication of smoke inhalation.
D Smoke inhalation is basically just a subset of acute respiratory distress syndrome (ARDS) seen in burn victims.
E Daily bronchoscopy is mandatory to monitor the evolution of inhalation injury.
Ref.: 1, 2
Comments
Inhalation injury occurs in up to a third of major burns and significantly increases mortality in patients when combined with cutaneous burns. Conceptually, inhalation injury can be divided into three types, all of which can coexist within any given patient: CO poisoning (and other toxic inhalation), upper airway thermal injury, and lower airway injury. Upper airway burns occur as a result of thermal injury, as well as the toxic substances in smoke. The capacity for the oropharynx to absorb heat generally prevents thermal injury from extending lower into the airway. Oropharyngeal thermal injury can be diagnosed by direct laryngoscopy and, if significant, is an indication for prophylactic endotracheal intubation to control the airway before life-threatening airway edema develops, particularly after large-volume resuscitation ensues. Endotracheal tubes may be difficult to secure if the patient has facial burns. They are usually tied with cotton tape wrapped around the face in most units. Airway edema is maximal 12 to 24 hours after injury, and if airway protection is required, the patient may remain intubated for 72 hours. Short courses of steroids may be administered to patients without significant burns, but they are contraindicated in those with large burns because of infectious and wound complications. Extubation may be performed when the patient has met weaning parameters. Lower airway inhalation injury results from exposure of the respiratory epithelium to toxic irritants in smoke or steam. Chest x-ray findings on admission are typically normal because infiltrates and lung injury tend to develop in delayed fashion over the days following injury. Damage to the airway leads to inflammation, sloughing of mucosa, and impaired ciliary function, which results in edema, hemorrhage, bronchoconstriction, and bronchial obstruction. Pulmonary edema, acute respiratory distress syndrome, and pneumonia may complicate inhalation injury, with pneumonia occurring in up to 50% of patients. Lower airway inhalation injury is diagnosed most commonly by fiberoptic bronchoscopy, although nuclear medicine ventilation-perfusion scanning has been used. Treatment is primarily supportive and consists of aggressive pulmonary toilet, supplemental oxygen, and endotracheal intubation if required for either airway protection or oxygenation. Bronchoscopy may be used as an adjunct for pulmonary toilet if airway plugging leads to lobar collapse, but it is not always required for management. Aerosolized heparin is administered by some centers to aid mobilization of fibrin-rich casts, which contribute to airway obstruction. Laboratory and clinical research is ongoing for therapies dealing with smoke inhalation injury. Patients with severe inhalation injury may be extremely difficult to ventilate, and ventilatory strategies vary among burn centers. Low–tidal volume ventilation, high-frequency oscillatory ventilation, and even extracorporeal membrane oxygenation (ECMO) have been used by burn units.
Answer
B
10 Select the true statement regarding inhalation of toxic gases.
A Hydrogen cyanide is not a component of smoke in most house fires in the United States.
B Burn-injured patients with significant carboxyhemoglobin levels are best treated at a center with hyperbaric oxygen (HBO) capabilities.
C CO poisoning is best treated with amyl nitrate (available in antidote kits) if administered within 2 hours of injury.
D HBO can be administered via endotracheal tube by a high-pressure ventilator in a general intensive care unit bed at many facilities.
E CO poisoning should be treated until carboxyhemoglobin levels are less than 10% and the patient is asymptomatic.
Ref.: 1, 3
Comments
Many toxic compounds are present in smoke, depending on the materials combusted. Carbon monoxide poisoning is commonly seen in burn victims, as well as in nonburned patients exposed to exhaust in a variety of domestic and occupational environments. CO toxicity correlates with levels of arterial carboxyhemoglobin. Because of the higher affinity of the CO molecule than the oxygen molecule for hemoglobin, CO-bound hemoglobin is not available for oxygen transport to peripheral tissues. Carboxyhemoglobin levels of less than 10% are asymptomatic, levels up to 25% lead to headache and nausea, levels of 30% to 40% cause confusion and weakness, levels above 40% can result in coma, and levels greater than 60% lead to death. The treatment of CO toxicity is 100% oxygen, which shortens the half-life of carboxyhemoglobin from 4 hours to 45 to 60 minutes. Hyperbaric oxygen therapy has been used for isolated patients with CO poisoning and neurologic impairment without other injuries, but it is not generally practical for ventilated or burned patients because HBO chambers are typically small and patients are not accessible during dives. Patients should receive 100% oxygen until carboxyhemoglobin levels have decreased to less than 10%. Hydrogen cyanide is generated by combustion of the nitrogen- and carbon-containing substances found in a number of natural and synthetic household and industrial materials. Its characteristic bitter almond odor is difficult to detect at the scene of a fire. Cyanide hinders cellular respiration by inhibiting cytochrome c oxidase, which results in central nervous system (CNS) and cardiovascular dysfunction, as well as anion gap metabolic acidosis with elevated mixed venous oxygen saturation. Cyanide toxicity may be underappreciated and should be treated presumptively when suspected. Oxygen therapy is beneficial, and antidote kits in the United States contain amyl nitrate, thiosulfate, and sodium nitrite, which are methemoglobin generators. Methemoglobin chelates cyanide and will decrease oxygen-carrying capacity, so these treatments should be used with caution in a critical care setting only.
Answer
E
11 Which of the following is correct regarding ARDS in burn patients?
A Hypercapnia is detrimental to healing of burn wounds.
B ARDS is a frequent cause of mortality from respiratory failure in burn patients.
C ARDS and pulmonary edema are due to massive fluid overload, which leads to left heart failure.
D ARDS is most likely to develop in burn-injured patients with combined cutaneous burns and smoke inhalation.
E ECMO is routinely used for burn-injured patients at risk for ARDS.
Ref.: 1, 2
Comments
Acute respiratory distress syndrome may occur in burn-injured patients with or without inhalation injury and is an independent risk factor for death. Mortality in these cases tends to be due to sepsis and multiple organ failure rather than respiratory failure alone. ARDS is defined by acute onset, bilateral infiltrates on chest radiographs consistent with pulmonary edema, absence of clinical signs of left-sided heart failure (e.g., pulmonary artery wedge pressure of 18 mm Hg or less), and a PaO2/FIO2 ratio of 200 or lower. Clinical manifestations include pulmonary edema, hypoxemia, and altered lung compliance. Microscopic evaluation of the lungs reveals diffuse alveolar damage, microvascular permeability, infiltration of inflammatory cells into the lung parenchyma, interstitial and alveolar edema, and the formation of hyaline membranes. The pathologic changes in the lung eventually end in parenchymal fibrosis. Inflammatory mediators such as platelet-activating factor, interleukin-1 (IL-1), IL-2, IL-6, IL-8, prostaglandin, thromboxane, leukotrienes, hematopoietic growth factors (granulocyte colony-stimulating factor), intercellular adhesion molecules, vascular cell adhesion molecules, and nitric oxide are released locally and systemically after a burn injury. Tumor necrosis factor-α and IL-1 correlate with ARDS severity, and IL-2 promotes multisystem edema, sequestration of neutrophils in the lung, and platelet activation. Reactive oxygen intermediates are generated by macrophages, have been implicated in lung injury and ARDS, and may be exaggerated by combined burn and smoke injuries. One review of burn patients revealed a 73% incidence of respiratory failure and a 20% incidence of ARDS in patients with inhalation injury, as compared with a 5% incidence of respiratory failure and a 2% incidence of ARDS in patients without inhalation injury. ARDS is less likely to develop in patients with inhalation injury but without cutaneous burns. Advanced age is an additional risk factor for ARDS in burn patients. Ventilator management of ARDS in burn-injured patients may result in ventilator-induced lung injury, particularly if normalization of arterial blood gases is pursued. Lung-protective ventilation, as demonstrated by the ARDS Network, has been shown to decrease mortality in ARDS patients by 22% by limiting tidal volumes to 6 mL/kg present body weight (PBW) to maintain mean airway pressure at less than 30 cm H2O. Hypercapnia may be tolerated to low pH values (7.15 to 7.20) to accomplish these goals, and respiratory rates into the 30s may be induced before becoming limited by auto-PEEP (positive end-expiratory pressure). Deep sedation may be required for ventilator synchrony. For patients deemed to be at high risk, implementation of low–tidal volume strategies may be warranted before the development of ARDS. Use of prone positioning, ECMO, high-frequency percussive or oscillatory ventilation (HFPV, HFOV), and nitric oxide has all been reported but has not gained widespread use.
Answer
D
12 Select the true statement regarding infection in burn patients.
A A rim of erythema surrounding the wound signals invasive burn wound infection.
B A scheduled rotation of central line insertion sites significantly decreases the rate of catheter line sepsis.
C Selective decontamination of digestive flora reduces systemic infection.
D Gram-positive organisms are the most significant cause of delayed burn wound infection.
E Invasive infection may convert second-degree burn wounds to full-thickness injury and necessitate skin grafting for closure.
Ref.: 1, 2
Comments
Infection is a frequent source of morbidity and mortality in burn patients and may occur in up to 80% of patients with large burns. Fevers and abnormal white blood cell counts are common in burn patients; physical examination is the most reliable means of diagnosing infections. Tetanus prophylaxis is indicated for burn wounds, as with other traumatic wounds; cases of tetanus are rare in patients who have been immunized in childhood. Though once practiced, the administration of prophylactic systemic antibiotics to patients with burn injuries has been shown to be unnecessary and, in fact, leads to the development of gram-negative and fungal infections. Clinical judgment, laboratory and radiologic examinations, and physical examination are important tools in the diagnosis of infection. Endogenous skin flora are killed by heat similar to skin cells, and an initial swab of burn wounds may be sterile. Bacteria in hair follicles and sebaceous glands may survive (as with epidermal cells), and quantitative skin cultures may reveal 103 bacteria per gram of tissue (normal). A level of 105 bacteria per gram is considered invasive burn wound infection. As bacterial cells increase in number following injury, they erupt from hair follicles and glands and colonize the dermal-subcutaneous boundary. Perivascular growth can result in thrombosis of vessels and necrosis of the remaining dermis, which could result in the conversion of a partial-thickness burns into full-thickness wounds. The infection progresses over days from gram positive to gram negative, and by 21 days after a burn, more than half of the wounds still open are colonized by resistant gram-negative bacteria. Routine burn wound care includes daily washing with soap and water and dressing with topical antimicrobials until wound closure, combined with monitoring of the wound site for signs of wound sepsis. Fever, erythema, increasing pain, and changes in wound drainage or odor may be signs of new infection. Burns seen early typically have a surrounding area of blanching erythema present, but burn wounds initially seen late are more likely to be infected. Significant erythema, swelling, and foul drainage are signs of infection and should be treated. Very superficial infections can be treated with cleansing and topical antimicrobials, but with significant cellulitis, systemic antibiotics are indicated. If deep infection is suspected, wounds should be excised. Burns greater than 20% to 30% TBSA add an immunosuppressive effect to the already significant risk for infection because of the large open skin surface. Early excision and coverage with autograft, homograft, or xenograft help reduce the risk for infection. Large burns initially seen late in the course may require even more aggressive débridement, even to a fascial level at times, in addition to topical agents and systemic antibiotics (in established infection) to gain control of wound sepsis and enable final skin graft closure of wounds. Frequent inspection of the wounds is important to monitor for infection, with changes in color, odor, or quantity of the exudate being suggestive of infection. Dark discoloration may be suggestive of fungal infection—this is best diagnosed on biopsy specimens. If questionable, quantitative tissue cultures may be performed to determine whether the wounds are appropriate for final autografting because graft survival rates may be greater than 90% when colony counts are less than 102/g but only 60% when counts are greater than 105/g. The antibiotic selected for perioperative prophylaxis and treatment of suspected wound infections should include coverage of both gram-positiveand gram-negative organisms, and consideration should be given to highly resistant organisms or fungal infection if the patient does not respond to therapy. Early wound closure is the best preventive measure against sepsis in burn patients. Selective gut decontamination has failed to show benefit. The diagnosis of sepsis in burn patients is not always straightforward because many elements of (SIRS) are present in uninfected burn patients. Intravenous catheter infection is a serious problem in burn-injured patients. Unburned sites are preferred for insertion of peripheral and central venous catheters after initial resuscitation, and scheduled catheter rotation to new sites has not been shown to decrease rates of line sepsis. Current and old intravenous sites should be inspected when evaluating a patient for occult infection, and suppurative thrombophlebitis may require wide excision of infected veins.
Answer
E
13 An 8-year-old girl suffers 18% TBSA, patchy, indeterminate-depth burns as a result of scalding with hot water. Which of the following is most correct regarding the topical antimicrobial agents that may be used?
A Mafenide acetate is an undesirable choice because metabolic alkalosis often contributes to narcotic-induced hypoventilation in pediatric burn patients.
B A 0.5% aqueous solution of silver nitrate may be applied to burn wounds because of its effective antibacterial activity against staphylococci and gram-negative organisms.
C Silver sulfadiazine should be discontinued if neutropenia occurs as a result of its use.
D Silver sulfadiazine is the most commonly used topical agent in U.S. burn centers because of its effective penetration of burn eschar.
E Elemental silver-impregnated dressings must be moistened frequently with normal saline to retain antimicrobial activity.
Ref.: 1
Comments
Systemic antibiotics are not indicated for prophylaxis. Topical antimicrobial agents delay colonization and infection of wounds but have not changed mortality as much as early excision and grafting have. Silver sulfadiazine is the most commonly used agent for burns in the United States. Advantages include a broad spectrum of activity, soothing effect in most patients, and no significant metabolic activity. Silver sulfadiazine does not penetrate eschar, so it does not treat established wound infections. Many providers have implicated it as a cause of early postburn neutropenia, but this neutropenia is typically self-limited, and more current information suggests that it is more likely the result of margination of neutrophils rather than depletion by the topical agent. One other caution is the use of silver sulfadiazine in a sulfa-allergic patient. Mafenide acetate penetrates eschar and is therefore useful for the treatment of burn wound infections; it has broad spectrum of activity against gram-negative organisms. It may be applied as a cream or a solution and is often used after grafting. Mafenide acetate is a carbonic anhydrase inhibitor that may cause metabolic acidosis when used on large areas. It is also painful on application, particularly to partial-thickness burns. Silver nitrate has a broad spectrum of activity and may be used for burn wound dressings. Dressings need to be repeatedly impregnated with aqueous solution to prevent precipitation onto the wound. Concentrated silver nitrate may cause chemical burns and hyponatremia, along with the rare case of methemoglobinemia. Wounds, normal skin, linens, and the patient environment will be stained black by silver nitrate. Ointments of bacitracin, neomycin, and polymyxin B are commonly used for facial burns. Mupirocin has been used against methicillin-resistant Staphylococcus aureus (MRSA). Acticoat (Smith & Nephew, London, England) is a dressing impregnated with elemental silver that may be applied to burn wounds or grafts. Sheets of Acticoat are usually moistened in sterile water before application because sodium chloride will cause precipitation and inactivation of the silver ions. Silver disrupts bacterial cellular respiration, and silver dressings may be left in place for up to 7 days if necessary.
Answer
B
14 Which of the following is not true of nutritional support in burn-injured patients?
A Caloric needs in burn-injured patients may be estimated as 25 kcal/kg/day + 40 kcal/%TBSA burned/day.
B Serum albumin levels provide a useful marker of nutritional status after the patient has recovered from the initial period of burn shock and resuscitation.
C The Harris-Benedict equation can be used but may overestimate caloric requirements.
D Early excision and grafting will decrease caloric requirements after graft closure.
E Urinary nitrogen losses are not generally helpful for assessment of protein loss in burn-injured patients.
Ref.: 1, 2
Comments
Thermal injury causes a hypermetabolic state with an increased basal metabolic rate, increased oxygen consumption, negative nitrogen balance, and weight loss. Administration of increased calories is required for wound healing, immune function, and cellular function. Nitrogen losses are significant after major burns; urinary measurements do not account for losses from the wounds. The Harris-Benedict equation multiplies basal energy expenditure (BEE) by a factor of up to 2 for major burns. The formula for BEE varies by gender: for women, BEE = 65.5 + (9.7 × weight in kilograms) + (1.8 × height in centimeters) − (4.7 × age in years); for men, BEE = 66.5 + (13.8 × weight in kilograms) + (5.0 × height in centimeters) − (6.8 × age in years). Harris-Benedict calculations overestimate caloric needs for patients with moderate burn size. The Curreri formula overestimates needs for large burns and is best used for burns less than 40% TBSA. The Curreri formula to determine the calories needed daily is 25 kcal/kg/day + 40 kcal/%TBSA/day. Indirect calorimetry can be used to quantify oxygen consumption and carbon dioxide production to calculate nutritional requirements: kcal/day = (3.9 × VO2) + (1.1 × VCO2) × 1.44. The Fick equation can be used if the patient has a pulmonary artery catheter in place, but pulmonary artery monitoring is becoming less commonplace. Infection, ARDS, and donor sites increase catabolism. Likewise, healing and skin graft closure of wounds decrease the catabolic state, thus making reevaluation important to ongoing care. Serum albumin levels are not accurate markers of the nutritional state. Prealbumin levels correlate more closely with nutritional and catabolic status and may be monitored over the course of weeks during a patient’s hospitalization. C-reactive protein may be used to monitor the patient’s generalized inflammatory state. A variety of other markers have been investigated for similar purposes. Calories should be provided as oral or enteral feedings in virtually all cases. Inability to feed because of ileus is rare in burn patients; feedings should be instituted early after admission in all patients with large burns and interrupted as infrequently as possible. Interruption of enteral tube feedings occurs frequently as a result of the administration of medications, procedures, and tube occlusion or malposition and may lead to significant decreases in the calories delivered. Small burns generally require oral feedings only, whereas moderate or large burns are more likely to require supplemental enteral feedings in patients who are not intubated. Ventilated patients should have enteral feedings initiated early via nasogastric or nasojejunal tubes. Glucose levels should be monitored. The optimal range for glucose management in burn-injured patients has not yet been fully defined, but it is generally agreed that hyperglycemia should be avoided. Many nutritional and metabolic manipulations are the subject of research and are as yet unproven.
Answer
B
15 A 22-year-old man suffers partial- and full-thickness burns to 45% of TBSA in a gas explosion while at work. Which of the following is most correct regarding surgical management of his wounds?
A Assessment of the depth of injury on admission is accurate enough for definitive surgery to be planned in more than 90% of cases.
B Fascial excision allows grafts to be placed over a healthy muscle bed and is the preferred approach to burns on the hands and dorsal surface of the feet.
C Sheet (unmeshed) grafting is preferred for areas subjected to repeated shear, thus making it the choice for extensive burns on dorsal surfaces.
D The principle of early excision and grafting benefits burned patients by reducing the number of infections and, ultimately, the mortality with severe burns.
E Widely meshed grafts minimize the degree of wound contraction associated with the use of split-thickness grafts.
Ref.: 1, 2
Comments
Early excision plus grafting of burn wounds has led to a significant decrease in mortality in burn patients over the last 30 years. Length of stay, cost, and reconstructive surgeries have also decreased as a result. Excision of deep partial- and full-thickness burn wounds should be done after resuscitation is complete and the patient is stabilized, often by 3 to 4 days. When uneven burns or those of indeterminate depth are present, it is reasonable to delay surgery for 7 to 10 days and observe for healing to avoid grafting to portions of the wounds that will heal. Wounds that are expected to heal within 3 weeks are best treated with antimicrobial dressings, whereas full-thickness burns, as well as deep partial-thickness wounds with delayed healing, require grafting. Fascial excision refers to removal of burned skin and subcutaneous tissue down to the level of the fascia, frequently with electrocautery. This approach provides a bed that readily takes graft and is usually easy to define. However, such deep débridement often results in fragile, aesthetically displeasing grafts. Tangential excision involves sequentially cutting away eschar with a handheld knife with a depth guard until viable dermis or subcutaneous tissue is present as noted by diffuse punctuate bleeding. Experience is important in judging the depth of excision required to support a graft. Hemostasis may be achieved with a combination of electrocautery, suture ligature, thrombin spray, direct pressure, and dilute epinephrine solution in gauze pads. Skin grafts may be full thickness or split thickness, depending on the amount of dermis present when harvested. Harvesting is most commonly done with a dermatome. Thinner grafts will heal with greater contraction, but thicker grafts come at a cost of loss of dermis at the donor site, which leads to prolonged times until healing and increased donor site scarring. Meshing of grafts (ranging from 1 : 1 to 4 : 1) may be used to allow egress of fluid from the wound bed through the graft and to increase the area covered when donor sites are limited. Widely meshed grafts are associated with prolonged healing, increased scarring, and more contraction than are less meshed or sheet grafts. A variety of dressings may be placed over grafted areas, the goal of which is to maintain contact of the graft with the wound bed to allow graft survival, prevent shearing, and facilitate subsequent vascular ingrowth into the graft.
Answer
D
16 Which of the following is correct regarding the skin substitutes used in burn reconstruction?
A Cultured epidermal autografts have dramatically increased survival in patients with nearly 100% TBSA burn injuries.
B Allografting to burn wound sites is limited to temporary closure because of eventual rejection of the graft by the patient.
C Porcine xenograft has the advantage of better early vascularization and engrafting after placement as a result of decreased antigenicity in comparison to most cadaveric human allografts.
D Use of the Integra Dermal Regeneration Template is advantageous because of lower rates of wound infection than with early autografting in heavily colonized burn wounds.
E Vascularization of porcine xenograft may be aided by use of low-dose cyclosporine, provided that the patient is free of infectious complications at the time of placement.
Ref.: 1, 2
Comments
After débridement and excision of burn eschar, closure of the wound with immediate autografting, when possible, is preferred. Full-thickness skin grafts are the best possible cutaneous replacement, but they are not feasible for burns of significant size because the full-thickness donor site must be closed primarily. Meshed split-thickness grafts may be used to cover areas larger than the donor site harvested, but for large burns and patients with limited donor sites, even meshed autografts will not be able to cover all open wounds. Wounds not able to be autografted immediately may be covered with biologic dressings while awaiting donor site healing before reharvesting. Human allograft has been widely used as a temporary biologic dressing. It is usually meshed 1 : 1 to allow drainage of fluid and applied in a similar fashion to other skin grafts. Allograft will vascularize and engraft, provide wound closure for 2 to 4 weeks, and subsequently be rejected and need to be replaced with new allograft or autograft if available. Sheets of allograft may be placed over widely meshed autograft at the time of surgery to protect grafts as the interstices epithelialize. Porcine xenograft is cheaper and more easily stored before use, but it does not vascularize and engraft. It may be used similar to allograft for temporary biologic coverage of burn wounds, as well as for exfoliative diseases of the skin (e.g., toxic epidermal necrolysis). Cultured epidermal autografts grown from patient keratinocytes were initially promising as a skin substitute but have not significantly evolved in burn wound management at this time. Dermal substitutessuch as the Integra Dermal Regeneration Template (Integra Lifesciences, Plainsboro, NJ) have seen more clinical use. The Integra dermal template is a bilaminate composed of an outer silicone film that provides barrier function and an inner layer of type 1 collagen and chondroitin sulfate. This inner layer serves as a template for the ingrowth of autologous fibroblasts, endothelial cells, and other mesenchymal cells. After vascularization of the Integra, the silicone film is removed, and very thin autografts may be applied to the neodermis. Reported advantages include neodermis architecture similar to that of uninjured dermis, which results in improved cosmetic and functional results, as well as rapid healing of thin autograft donor sites. Disadvantages include wound infection and increased length of time and immobilization before final autograft closure.
Answer
B
17 A 27-year-old factory worker has worsening pain and discoloration of the hands after working with an unknown cleaning agent yesterday. Which of the following is true regarding chemical injury?
A The affected hands should be soaked in water for at least 30 minutes to dilute the concentration of the offending agent.
B Phenol is absorbed systemically and may result in CNS toxicity with even small areas of cutaneous involvement.
C Dry powders, such as concrete, should be moistened before removal from affected areas.
D Initial treatment of a chemical burn wound includes the application of a neutralizing agent.
E Alkali burns are frequently worse than acid burns because alkali creates a leathery, impermeable eschar at the surface of the skin.
Ref.: 1, 2
Comments
Many agents used in household and occupational settings have the capacity to cause chemical burns on exposed skin. For virtually all chemicals, the immediate approach to treatment is the same. All affected clothing should be removed immediately to ensure cessation of exposure, and the burns should be flushed with copious amounts of water to dilute away the offending substance. Soaking in a tub or basin is undesirable because the affected body surface will continue to be bathed in the chemical, albeit at lesser concentrations. Dry powders causing chemical burns should be brushed away. Patient referrals are often accompanied by a request for neutralizing agents, but any delay in flushing wounds may result in deepening of the burns, and neutralizing agents may actually cause exothermic reactions and further skin injury. Unlike thermal injury, chemical burns cause progressively deepening damage to skin until the chemicals are inactivated by reaction with tissues or are diluted away by flushing with water. Acid burns are usually more self-limited because the action of acids tans the skin and forms a barrier to deeper penetration of the acid. Alkali (e.g., drain cleaners, cement), in contrast, combines with cutaneous lipids to form soaps that continue to dissolve skin until neutralized. Chemical burns are often seen late in the course because they appear superficial at first and may progress from a mild discoloration to sloughing over a period of days. Treatment of the skin wounds is similar to that for other burns—partial-thickness injuries heal with topical antimicrobials, and full-thickness injuries will require skin grafting. In addition to cutaneous injury, some chemical agents may be absorbed and result in systemic illness. Anhydrous ammonia may cause severe pulmonary injury and ARDS. Chromic acid may result in renal and hepatic failure, as well as anemia, even with small areas of cutaneous exposure. Formic acid causes metabolic acidosis, hemolysis, and hemoglobinuria. Phenol (carbolic acid), a disinfectant, can cause CNS depression, vomiting, respiratory distress, and seizures despite the superficial skin injury. Hydrofluoric acid is unique in that it is a very strong acid that allows fluoride ions to enter tissues and chelate calcium and magnesium, thereby resulting in severe local tissue destruction and the systemic effects of severe hypocalcemia, including cardiac dysrhythmias. Conventional treatment includes the application of calcium gels (often calcium gluconate mixed with water-soluble lubricant) to arrest progress of the agent, as well as monitoring and correction of serum calcium levels. Direct injection of calcium gluconate has been used but should be done cautiously in already edematous tissues, especially the digits. Intraarterial injection of dilute calcium gluconate has been performed with success at some centers. Hot tar burns are seen in roofing workers. These injuries are actually thermal in nature, but adherent tar will continue to burn until cooled and may complicate assessment of wound depth until removed. Citrus-based solvents are effective if available; otherwise, petrolatum-based ointments may be placed over adherent tar to aid in removal.
Answer
B
18 A 22-year-old utility company employee is found down at a job site at the base of the ladder. He has a charred wound in the left temporal region with palpable shards of skull present. His left arm is waxy and fixed in flexion. There are full-thickness burns on his left flank, the lower part of his left leg is firm, and the toes of his left foot are burned and missing. Which of the following is the correct statement regarding electrical injury?
A The cause of the dark, reddish urine noted in the urinary catheter will most likely be revealed by computed tomography of the abdomen.
B Signs concerning for compartment syndrome should prompt urgent escharotomy of the affected limbs.
C Neurologic deficits that develop in a delayed fashion, weeks to months after the injury, have a better prognosis.
D Early fascial decompression of the extremities may be important in preserving limb function.
E Myoglobinuria is addressed by maintaining an hourly urine output of 0.5 mL/kg in adults and 1 mL/kg in children less than 20 kg.
Ref.: 2
Comments
Electrical injuries are classified in the medical literature into low-voltage, high-voltage (>1000 V), and lightning injuries (also termed ultra-high voltage). Patients injured by electricity may, in fact, have injuries by any of three mechanisms: flash burns from the very high temperatures generated when high-voltage current arcs through the air, flame burns because of ignition of clothing, and true electrical injury as a result of conduction of electrical current through the patient’s body. Low-voltage injuries may cause local tissue injury but rarely lead to systemic injury. High-voltage injuries may cause unpredictable patterns of local injury, including deep tissue destruction belied by the small size of the skin wounds, full-thickness cutaneous wounds at entry/exit sites and areas where arcing occurs across joints or flexor surfaces, and musculoskeletal injuries from severe tetanic contractions of the paravertebral and other muscle groups. Patients with electrical injury are at particularly high risk for associated traumatic injuries because electrical exposures frequently occur in occupational settings and may involve falls from a height. In fact, the tetanic muscle contractions caused by alternating current tend to cause “hanging up” by workers who grasp an electrical source and pull themselves in; patients who hang up and survive often do so because they subsequently fall and break contact with the current, but they suffer other injuries as a result. Evaluation of patients suffering high-voltage electrical injury includes full examination for traumatic injury, radiographic studies, electrocardiogram, and bladder catheterization. Patients with no loss of consciousness at the scene, no history of arrhythmias during transport, and a normal admission electrocardiogram do not require cardiac monitoring unless the severity of the injury would otherwise require it. Deep tissue damage secondary to high-voltage current may result in unseen muscle swelling and necrosis. Neurovascular examination should document the extent of disability present at admission, and progressive deterioration in extremity function should prompt consideration of compartment release by fasciotomy. Compartment pressures may be measured if the patient is not likely to need compartment release, but fasciotomy should be prompted by clinical grounds if significant concern exists. Escharotomy refers to the division of bandlike circumferential full-thickness burn eschars through to subcutaneous fat only. Fixed deficits or mummified extremities may not benefit from compartment release. Pigmented urine suggestive of myoglobinuria should be treated by fluid resuscitation sufficient to produce a urine output of 100 mL/h. Fasciotomies or even early débridement or amputation of necrotic muscle can be performed to avoid renal failure. Urine myoglobin assays are often not immediately available, but urine that is heme positive by dipstick with no red blood cells on microscopic examination may be presumed to be myoglobinuria resulting from rhabdomyolysis; hematuria found on urinalysis should additionally prompt reconsideration of occult genitourinary trauma. Toddlers may suffer electrical burns to the mouth from chewing on appliance cords. Full-thickness oral burns are typically treated conservatively with attention to preserving mouth opening, and families should be counseled about the possibility of delayed facial artery bleeding after the eschar softens and falls off. High-voltage injuries may result in progressive demyelinating injury and lead to sensory or motor loss weeks or months after the injury. Early cataract formation has been associated with high-voltage electrical exposure.
Answer
D
References
1 Mulholland MW, Lillemoe KD, Doherty GM, et al, editors. Greenfield’s surgery: scientific principles and practice, ed 4, Philadelphia: Lippincott Williams & Wilkins, 2006.
2 Souba WW, Fink MP, Jurkovich GJ, et al, editors. ACS surgery: principles and practice, ed 6, New York: WebMD, 2007. Available at http://www.acssurgery.com
3 Herndon DN. Total burn care, ed 3. Philadelphia: WB Saunders; 2007.
4 Guidelines for the operation of burn centers. resources for optimal care of the injured patient. http://www.ameriburn.org/Chapter14.pdf, 2006. pp 79-86. Committee on Trauma, American College of Surgeons. Available at