Burns

Burns are injuries to tissue caused by heat, chemicals, and/or radiation. The two factors that influence the severity of a burn are its depth and the surface area involved. Accordingly, burns are classified into four grades based on the depth of tissue involvement. Lund-Browder charts are used to calculate the surface area involved. Massive tissue necrosis, which occurs with severe burns, results in sepsis, shock, and sequential organ failure (see SOFA score for details). In the case of severe burns, patients should be intubated, given supplemental oxygen, and resuscitated with IV fluids. Different formulas exist to calculate initial fluid requirement, but fluids should be adjusted to maintain clinical stability and appropriate urine output. Pulse oximetry, blood gas analysis, and measurement of electrolyte and creatinine levels are important diagnostic procedures for patients with severe burns. In the case of circumferential burns around limbs, peripheral pulses and capillary refill can be used to detect perfusion. Escharotomy should be performed in order to treat compartment syndrome and prevent acute limb ischemia. First and second-degree burns can be treated with antiseptic ointment and dressings. Treatment of third and fourth-degree burns involves debridement of necrotic tissue followed by skin graft or a tissue transfer via flap. Burn wounds tend to become infected and large, severe burns tend to be fatal injuries. The most common causes of death following burns are shock, sepsis, and respiratory failure.

• Thermal injury: scalding, contact with a hot surface, fires
• Non-thermal injury: radiation, chemical burns, electrical burns

Although most burn injuries unintentional, intentional injury must always be suspected in vulnerable population groups, such as children and older adults.

Local effects

• Local changes at the burn site (Jackson model of the burn wound) ^[1]
  • Zone of coagulation: a central zone of irreversible, coagulative necrosis
  • Zone of stasis: surrounds the central zone of coagulation and is comprised of damaged but viable tissue with decreased perfusion
  • Zone of hyperemia: surrounds the zone of stasis and is characterized by inflammation and increased blood flow
• Almost all burns are colonized by bacteria; common pathogens that infect burn wounds include MRSA, Pseudomonas, Klebsiella, Acinetobacter, and Candida
• Eschars can cause constrictive effects.
  • Significant eschar on chest or neck → restriction of chest excursion → asphyxia
  • Circumferential eschars → loss of skin elasticity → impaired blood flow and/or compartment syndrome (caused by an accumulation of fluids) → acute ischemia distal to the eschar

A burn wound is a dynamic wound. If resuscitation and/or wound care are not adequate, the zone of stasis becomes irreversibly damaged and the depth of the burn increases.

Systemic effects ^[2]

• Release of cytokines and other inflammatory mediators → systemic inflammatory response syndrome
  • Increased vascular permeability → extravasation of protein and fluid from the intravascular compartment into interstitial tissue → generalized edema, acute respiratory distress syndrome, and hypovolemic shock with paralytic ileus
  • Disseminated intravascular coagulation (DIC)
• Evaporative fluid loss → hypothermia, dehydration
• Hemolysis, muscle damage → hemoglobinuria and/or myoglobinuria → acute tubular necrosis
• Immunosuppression

Depth of a burn

In cases of severe, deep burns, pain may be absent as a result of damage to sensory nerve endings.

Extent of burns (surface area involved) ^[3]

• Lund-Browder chart
  • Age-specific charts are used to calculate the surface area covered by a burn.
  • Most accurate method for both adults and children
• Palm rule
  • The palm accounts for 1% of the total body area.
  • It is the least reliable method.
• Wallace's rule of nines
  • A quick but reliable method for estimating the surface area covered by burns in the case of adults.
  • The rule of nines is unreliable among children.

• Clinical features of shock ; (e.g., hypotension, poor urine output) and/or ARDS (e.g., dyspnea)
• In case of circumferential burns around limbs:
  • Compartment syndrome
  • Clinical features of acute limb ischemia (e.g., weak/absent pulse, paresthesia, pallor in the affected limb)
• In case of circumferential burns around abdomen:
  • Abdominal compartment syndrome → impaired function of nearly every organ system (e.g., oliguria, acute pulmonary decompensation, hypoperfusion)
  • Signs of increased intraabdominal pressure (e.g., jugular venous distension, hypotension, tachycardia)

In adults, shock sets in if burns involve > 15% of the body surface. Burns that involve 50–70% of the body surface are usually lethal.

In children, signs of shock appear if > 10% of the body surface is involved. Burns that involve 60–80% of the body surface are usually lethal.

Burn severity is based upon clinical history and physical examination, but further testing is conducted to monitor for complications and guide therapy.

• Pulse oximetry
  • Monitor for hypoxemia
  • In circumferential limb wounds at risk for distal ischemia/compartment syndrome assess perfusion with pulse oximetry (> 90% indicates adequate perfusion)
• Blood tests
  • Blood gas analysis: monitor for hypoxemia, metabolic, and/or respiratory acidosis
  • Serum electrolytes: hyperkalemia and hyponatremia occurs in the acute phase following burns; hypernatremia may occur later. ^[4]
  • BUN/creatinine: monitor for acute renal injury
  • Hemoglobin, hematocrit : monitor for hemolysis
  • Serum protein and albumin levels ^[5]
• Wound swab and blood cultures: if wound infection or sepsis is suspected

Immediate measures in case of severe burns

• Airway management: intubation and high flow oxygen therapy is indicated if an inhalation injury is suspected or if burns involve more than 30–40% of the body surface. Do not delay intubation if needed, as fluid resuscitation can increase laryngeal swelling, which will complicate intubation
• Begin initial fluid resuscitation with crystalloids, usually lactated Ringer's solution (RL)
  • In adults and children ≥ age 14
    • Parkland formula was traditionally used to guide initial fluid therapy: the volume of lactated Ringer's solution to be administered within a period of 24 h = 4 mL x % of total body surface involved in 2^nd and 3^rd-degree burns x body weight (in kg)
    • Current recommendations by the ATLS and the American Burn Association: volume of lactated Ringer's solution to be administered within a period of 24 h = 2 mL x % of body surface involved in 2^nd and 3^rd-degree burns x body weight (in kg)
    • Half of this volume should be administered within the first 8 hours and the remaining half within the next 16 hours
  • In children < age 14
    • Volume of lactated Ringer's solution to be administered within a period of 24 h = 3 mL x % of body surface involved in 2^nd and 3^rd-degree burns x body weight (in kg)
    • Infants and small children ≤ 30 kg: initial fluid therapy for a 24 hour period as above + 24 h maintenance fluid requirement of a glucose-containing solution ^[6]
  • Note that this is an INITIAL estimate for fluid requirements: fluid therapy should be modified to achieve a urine output of 0.5 mL/kg/h in adults and 1 mL/kg/h in children (< 30 kg).
• Manage the burn area
  • Remove any burnt clothing
  • Cool the burnt area with cool running water or saline-soaked gauzes. Cover the wound with a sterile dressing.
    • Core body temperature should be monitored for hypothermia; if body temperature < 35°C, warm IV fluids can be given
    • Cool with caution or not at all in patients with burns involving >10% BSA as they are particularly vulnerable to hypothermia.

Because of studies demonstrating serious complications from over-resuscitation (e.g., pleural effusions and compartment syndrome), the ATLS and American Burn Association now recommend only giving half of the fluid resuscitation volume that is calculated by the Parkland formula in adults; i.e., 2 mL x %TBSA x weight (kg) instead of 4 mL). The volume is still given over 24 hours, with one half given in the first 8 hours and the remaining half over the next 16 hours.

Patients with burns who cannot take fluids orally also require maintenance fluids. Parkland formula does not include the daily maintenance fluid requirement.

Because fluid resuscitation can worsen laryngeal edema, intubation should be performed before fluid resuscitation.

Do not use ice or ice water.

Additional measures

• Tetanus prophylaxis
• Analgesia (opiates often necessary)
• Proton pump inhibitors or H2 antagonists: prophylaxis against Curling's ulcers (see stress ulcers and stress ulcer prophylaxis)
• Following resuscitation, the patient should be transported to a special burn unit in the following situations:
  • 2^nd-degree burns involving > 10% of the body surface or 3^rd-degree burns involving > 5% of the body surface
  • Inhalation injury
  • Burns involving specific regions (hands, feet, face, genitalia, joints)
  • Electrical burns and chemical burns
• Prophylactic systemic antibiotic therapy is not routinely recommended.
  • If burn wound infection or sepsis occurs, empirically treat for MRSA until ruled out (e.g. with vancomycin); treat for Pseudomonas (e.g. cefepime) if suspected.

Management based on degree

• 1^st and 2^nd-degree burns
  • Irrigation
  • Topical moisturizers (e.g., calamine lotion) or aloe vera-based gels: relieve symptoms of 1st-degree burns
  • Consider antiseptic ointments (e.g., silver sulfadiazine, mafenide) or topical antibiotics (bacitracin; triple antibiotic ointments are a combination of bacitracin neomycin, polymyxin B)
    • For periorbital or periocular burns, topical antibiotics (e.g., bacitracin, neomycin, or erythromycin) are preferred over silver sulfadiazine, which may be irritating and cause ocular toxicity.
  • Deroofing bullae/vesicles
  • Dressing is indicated in partial thickness (2^nd-degree) burns.
• 3^rd and 4^th-degree burns
  • Early debridement of burnt, necrotic tissue
  • Method of tissue coverage varies depending on the specific burn characteristics. Options include:
    • Free skin grafts (split-thickness or full-thickness)
    • Flap reconstruction with free or pedicled flaps. ^[7]
  • Topical antibiotics (e.g., silver sulfadiazine, bacitracin, neomycin)

Burn eschars: specific measures

• For circumferential burn
  • Perform a doppler test, as well as check the capillary refill time, peripheral pulses, sensations, and pulse oximetry in the limb hourly for 24–48 hours
  • If NO impending vascular/respiratory compromise or compartment syndrome:
    • Elevate the lower limb or torso
    • Perform a range of motion exercises as tolerated
  • If vascular/respiratory compromise or compartment syndrome is impending or has occurred :
    • Escharotomy
    • If compartment syndrome develops: fasciotomy
• For chest/neck eschars:
  • If respiratory compromise impending or has occurred → escharotomy

Small superficial and superficial partial-thickness burns may be treated on an outpatient basis with paraffin gauze, antiseptic ointment, and analgesics.

Chemical burns: specific measures

• Immediate, copious irrigation of all areas of exposure with water, prior to or on the way to the hospital.
  • Once in the hospital, irrigation should be continued until the pH normalizes

References:^[7][8][9]

• ↑ Shock, sepsis, and respiratory failure are the most common causes of death following burns (see “Pathophysiology” above).
  • Common organisms include Staphylococcus aureus (including MRSA), Enterococcus (including VRE), and Pseudomonas.
• Curling ulcers (see stress ulcers)
• Keloid formation, contractures
  • Marjolin ulcer: squamous cell carcinoma that develops in a burn scar
• Complications of chemical burns
  • Cataracts or vision loss if the burn involves the eyes
  • Esophageal strictures if the burn involves the esophagus
  • Systemic poisoning
• Complications of electrical burns: arrhythmias, trauma

We list the most important complications. The selection is not exhaustive.

Inhalation injury

• Definition: damage to the respiratory tract that occurs due to the inhalation of hot smoke and/or noxious gases
• Etiology: inhalation of hot smoke, particles (< 1 μm diameter in size), and/or irritant/noxious gases (e.g., ammonia, chlorine)
• Clinical features
  • Facial burns with singed eyebrows and/or nose hair
  • Evidence of soot on the face or in the airway
• Diagnostics
  • Inhalation injury should be suspected when any of the following are present:
    • History of being trapped in a confined space
    • Facial burns, singed eyebrows and/or nose hair, evidence of soot on the face or in the airway
    • Stridor, dysphonia
    • Extensive burns
  • In case of suspected inhalation injury, the following additional tests should be performed:
    • Bedside respiratory function tests to rule out airway obstruction
    • Chest x-ray in order to rule out ARDS
    • Carboxyhemoglobin levels
    • End-tidal CO₂ (ETCO₂), serum lactate
    • Flexible fiberoptic laryngoscopy: may reveal laryngeal edema
    • Flexible fiberoptic bronchoscopy: mucosal erythema and edema, blistering, ulceration and/or soot deposition
• Treatment: intubation and high flow oxygen therapy
• Complications
  • Airway obstruction due to laryngeal edema
  • Tracheobronchitis
  • Pneumonitis
  • ARDS
  • Arsenic poisoning
  • Carbon monoxide poisoning
  • Cyanide poisoning
• Prognosis: Resolution often occurs spontaneously within 2–3 days.

• Definition: a metabolic phenomenon that can occur in patients with moderate to severe burn injuries and is characterized by an initial hypometabolic phase followed by a hypermetabolic state
• Pathophysiology: An increase in catecholamines, cortisol, and inflammatory cytokines → severe metabolic alterations
  • Elevated resting energy expenditures
  • Insulin resistance
  • ↑ Gluconeogenesis
  • ↑ Lipolysis
  • Protein catabolism
• Clinical features
  • Hypometabolic phase (ebb phase)
    • Onset within 48 hours of the burn injury
    • Decreased cardiac output, oxygen consumption, and metabolic rate
  • Hypermetabolic phase (flow phase)
    • Onset 5–7 days after the injury
    • Can persist for up to ∼ 3 years
    • Hyperdynamic circulation: ↑ blood pressure, ↑ heart rate
    • Muscle wasting, protein loss
    • Significant weight loss
    • Hyperglycemia
    • Increased body temperature
    • Multi-organ dysfunction
• Management
  • Early excision and grafting
  • Analgesia
  • Nutritional support
  • Anabolic steroids
  • Glycemic control with insulin
  • Beta blockers (e.g., propranolol) to decrease resting metabolism

References:^[10][11]