PATHOPHYSIOLOGY OF BURNS

Dr. Shiara Ortiz-Pujols

Burn Fellow

NC Jaycee Burn Center

Objectives

PART 1 Anatomy

Overview Causes of Burns Estimating Burns

(Depth & %) Categories &

Zones

PART 2 Physiologic

Implications Pathophysiology Resuscitation Post-Resuscitation Board Questions

Anatomy

Adult skin surface 1.5-2.0 m2 (0.2-0.3 in newborns); largest organ

Skin thickness 1-2 mm; peaks age 30-40; M> F

Functions include: protection from external environment maintenance of fluid/electrolyte homeostasis Thermoregulation immunologic function sensation Metabolic organ (i.e., Vit D synthesis)

Causes of Burns

Usually caused by heat, electricity, chemicals, radiation, and friction

Thermal burns are caused by steam, fire, hot objects or hot liquids. Most common burns for children and the

elderly Electrical burns are the result of direct contact

with electricity or lightning Chemical burns occur when the skin comes in

contact with household or industrial chemicals Radiation burns are caused by over-exposure

to the sun, tanning booths, sun lamps, X-rays or radiation from cancer treatments

Friction burns occur when skin rubs against a hard surface, e.g. carpet, gym floor, concrete or a treadmill

Effect of Heat

Temporal and quantitative 40-44C, enzymes malfunction,

proteins denature and pumps fail

> 44C, damage occurs faster than repair mechanisms can keep up with

Damage continues even when the source is withdrawn

Effect of Electricity

• Effects of current depend on several factors

- Type of circuit- Voltage- Resistance of

body- Amperage- Pathway of

current- Duration of

contact

• High voltage (>1000V) causes underlying tissue damage. Deep tissues act as insulators and continue to be injured.

• Resistance of various tissues from L→H: nerve, vessels, muscle, skin, tendon, fat, boneOhm’s Law- V=IR

• Damage more related to cross-sectional area which explains extremity injuries without trunk injuries.

Electrical Storms/Lightning

Burns are characteristically superficial and present as a spidery or arborescent pattern.

Cardiopulmonary arrest is common following lightning injury.

Coma and neurologic defects are also common but usually clear in a few hours or days.

Watch for tympanic membrane rupture

Usually lethal in 1/3 of patients.

World record for surviving lightning strikes is Roy C. Sullivan who was a park ranger from VA. Roy was struck 7 times from 1942-1977.

Electrical “Pruning”

Effect of Chemicals

Acids and alkalis cause injury via different mechanisms.

Petroleum products can cause delipidation and depth of wound 2° tendency to adhere to skin

Acids: coagulation necrosis

denaturing proteins upon tissue contact

area of coagulation is formed and limits extension of injury

exception is hydrofluoric acid, which produces a liquefaction necrosis similar to alkalis.

Acid damaged skin can look tanned and smooth; do not mistake for a suntan.

Alkalis: liquefaction necrosis potentially more

dangerous than acid burns liquefy tissue by

denaturation of proteins and saponification of fats

In contrast to acids, whose tissue penetration is limited by the formation of a coagulum, alkalis can continue to penetrate very deeply into tissue

Can cause severe precipitous airway edema or obstruction.

Inhalation Injury

Heat dispersed in upper airways leads to edema

Cooled smoke and toxins carried distally Increased blood flow to bronchial arteries

causes edema Increased lung neutrophils –

mediators of lung damage – release proteases and oxygen free radicals (ROS)

Exudate in upper airways – formation of fibrin casts

Stages of Inhalation Injury

Stage 1 – acute pulmonary insufficiency Signs of pulmonary failure at presentation

Stage 2 – 72-96 hrs after presentation (ARDS picture) extravasation of water Hypoxemia Lobar infiltrates

Stage 3 – bronchopneumonia Early – Staph pneumonia (frequently PCN

resistant) Late - Pseudomonas

Inhalation Injury

Bronchoscopy:- erythema- intraglottic soot- ulceration

Grading of Burn Wounds

Mild: < 5% TBSA Moderate: 5-15% TBSA Severe: > 15% (95% of burns seen) May require Burn Unit care because of

potential for disability despite small TBSA (face, hands, feet, perineum)

Area of Burn – “Rule of 9s”

Note that a patient's palm is approximately 1% TBSA and can be used for estimating patchy areas.

Area of Burns - Pediatric

Estimation of Burn Wound Depth Initial assessment is often unreliable Ignore mild erythema when calculating

fluid requirements Pink areas that blanch are usually

superficial Deeper wounds are dark red, mottled or

pale and waxy Insensate areas are usually deep (3rd

degree or greater)

Factors Influencing Wound Depth Temperature and duration Thickness of skin (thin on eyelids, thick on

back) Age (children and elderly have

proportionally thinner skin in comparison to adults)

Vascularity Agent – oil vs water; acidic vs alkalotic Time to definitive care

Burn Zones

Circumferential zones radiating from primarily burned tissues, as follows: 1. Zone of coagulation - A nonviable area of tissue at the

epicenter of the burn

2. Zone of ischemia or stasis - Surrounding tissues (both deep and peripheral) to the coagulated areas, which are not devitalized initially but, 2° microvascular insult, can progress irreversibly to necrosis over several days if not resuscitated properly

3. Zone of hyperemia - Peripheral tissues that undergo vasodilatory changes due to neighboring inflammatory mediator release but are not injured thermally and remain viable

Zone of Coagulation

Zone of Ischemia

Zone of Hyperemia

Layers of the Skin

Categories of Burns – First degree

Burns are divided into 4 categories, depending on the depth of the injury, as follows: First-degree burns are limited to the epidermis. A typical sunburn is a first-degree burn. Painful, but self-limiting. First-degree burns do not lead to scarring and require

only local wound care.

First degree Burn

Categories of Burns – Second degree

Second-degree burnspoint of injury extends into the dermis,

with some residual dermis remaining viable

Partial thickness or Full thickness those requiring surgery vs those which do

not

Superficial Second degree Burn

Deep Second degree Burn

Categories of Burns – Third degree

Third-degree or full-thickness burns involve destruction of the entire dermis, leaving only subcutaneous tissue exposed.

Third degree Burn

Escharatomy Sites

Preferred sites for escharotomy incisions. Dotted lines indicate the escharotomy sites. Bold lines indicate areas where caution is required because vascular structures and nerves may be damaged by escharotomy incisions. (From Davis JH, Drucker WR, Foster RS, et al: Clinical Surgery. St. Louis, CV Mosby, 1987.)

Categories of Burns – 4th degree

- Fourth-degree burn is usually associated with lethal injury.

- Extend beyond the subcutaneous tissue, involving the muscle, fascia, and bone.

- Occasionally termed transmural burns, these injuries often are associated with complete transection of an extremity.

4th degree Burn

PART 2

Physiologic Implications Pathophysiology Resuscitation Post-Resuscitation Board Questions

Physiologic Implications of Burn Injury Predictable changes Related to period of injury Can be anticipated

Pathophysiology of Burns

• Cell damage and death causes vasoactive mediator release:

• Histamines• Thromboxanes• Cytokines• Increasing capillary permeability causes edema,

third spacing and dehydration• Possible obstruction to circulation (compartment

syndrome) and/or airway

Resuscitation Period

“early ebb with late flow”; days 0-3 Hypodynamic, with need for close fluid resuscitation monitoring Massive, diffuse capillary leak 2° to inflammatory mediators;

abates 18-24 hrs after injury and volume requirements abruptly decline

leak can be seen in those with delayed resuscitation 2° systemic release of O2 radicals upon reperfusion

Extravascular extravasation of fluid, lytes, colloid molecules Other variables affect resuscitation: preexisting fluid deficits, delay

until treatment, inhalation injury, depth of wound Must reevaluate resuscitation progress and endpoints frequently;

do not just use a formula

Resuscitation Guidelines

Postresuscitation Period

Day 3 until 95% wound closure Hyperdynamic, febrile, protein catabolic state Tachycardia can be normal in burn patients Blood pressure may be hard to obtain due to

circumferential burns Release of more inflammatory mediators, cortisol,

glucagon, catecholamines, bacteria from wound High risk of infection and pain Remove non-viable tissue or close wounds to avoid sepsis Nutritional support essential Maintain and support body temperature with high ambient

temps and humidity

Recovery Period

95% wound closure until 1 year post-injury

Continued catabolism and risk of non-healing wound

Anticipate septic events, treat complications, and continue nutritional support

Pathophysiology of Electrical Burns Small cutaneous lesions may overlie extensive areas of

damaged muscle → myoglobin ARF. Monitor for at least 48 hours after injury for cardiopulmonary arrest May see vertebral compression fractures from tetanic

contractions or other fractures from a fall. Visceral injury is rare but liver necrosis, GI perforation, focal

pancreatic necrosis and gallbladder necrosis have been reported. Look for motor and sensory deficits—motor nerves are affected

more than sensory nerves. Thrombosis of nutrient vessels of the nerve trunks or spinal cord

can cause late onset deficits. Early deficits are direct neuronal injury.

Delayed hemorrhage can occur from affected vessels Cataracts may form up to 3 or more years after electrical injury Microwave radiation damages tissues via a heating effect.

Subcutaneous fatty tissue is often spared given its lower water content.

Burn Edema and Inflammation Generalized edema found in burns >

30% TBSA Heat directly damages vessels and

causes permeability Heat activates complement histamine

release and more permeability thrombosis and coagulation systems

+

Systemic Response to Burn Injury Accelerated fluid loss 2° leaky capillaries Host resistance to infection Multisystem Organ Failure Infections in burns <20% TBSA are well

tolerated. > 40% TBSA with infection has very low

survival rate Initially CO, subsequent hypermetabolic

state w/ doubling of CO in 24 – 48 hours

OR Pictures

Burn Questions

Select the true statements regarding the epidemiology of a burn injury

a. Scald burns are the most frequent forms of

burn injury.

b. Flame burns are the most frequent forms of burn injury admitted to burn centers.

c. Burn injuries are most common among adults

d. About 15% of pediatric burn injuries are attributed to abuse or neglect.

e. Burn-related deaths are highest among adults.

Select the true statements regarding the depth of burn

a. First-degree burns are physiologically important and therefore considered when calculating TBSA.

b. Second-degree burns always affect the epidermis and dermis of the skin.

c. Third-degree burns are very painful.

d. All first-degree burns heal within 2 to 3 days.

A 50 year-old man sustains a flame burn involving the entire upper left extremity, entire anterior trunk, genital area, and half of the left lower extremity. Approximately what percentage of the total body surface area is burned?

a. 24%b. 28%c. 37%d. 45%e. 30%

According to American Burn Association criteria, which of the following patients

should be referred to a burn center?

A. Second- and third-degree burns involving more than 20% of the total body surface area (TBSA) in patients younger than 10 or older than 50 years of age.B. Full-Thickness burns that involve 2% of the TBSA in patients of any age.C. Significant burns of the face, hands, feet, genitalia, perineum, or skin overlying major joints.D. Burn Injury in children with suspected or actual child abuse or neglect.E. Acute massive skin loss syndromes (e.g., Stevens-Johnson syndrome/toxic epidermal necrolysis, large traumatic de-gloving injuries)

All of the following are true regarding the Pathophysiology of thermal injury,

except?

A. Increased capillary permeability is due to direct

effect of heat and the liberation of vasoactive

mediators.B. Increased pulmonary vascular

resistance occurs during the immediate postburn period.C. Elevated thyronine (T3) and thyroxine

(T4) levels.D. Elevated interleukin-6 (IL-6) levelE. Decreased immoglobulin G (IgG) level

A 60-year-old, 80-kg man has sustained a second-

degree burn to 40% TBSA with a significant inhalation injury. He was admitted to the burn unit 30 minutes after the accident. According to the Parkland formula, resuscitation was started with lactated Ringer’s solution at 800 ml/hr. Six hours later the patient was found to be oliguric. What should be the next step in resuscitation of this patient?

A. Swan-Ganz catheter placement and measurement of pulmonary

wedge pressure.B. Trial of small dose of furosemideC. Low does of dopamine (2-3 ug/kg/min).D. Increase in volume of the lactated Ringer’s

solution infusion.E. Bolus of colloid solution

Which of the following statements is/are true regarding resuscitation of patients

with burn injury during the first 24 hours?

a. Parkland formula uses a balanced electrolyte solution & the fluid requirement is calculated as 3 ml/kg body weight per %TBSA burned.

b. Patients with 15% or more TBSA burn require intravenous fluid resuscitation.c. Adequate urine output implies hemodynamic

stability and adequate organ perfusion.d. Crystalloid resuscitation restores cardiac output

more rapidly than colloid alone.

e. Late pulmonary morbidity and mortality are higher in colloid-

resuscitated patients.

Match the items in two columns

Topical AgentsA. Sodium mafenide(Sulfamylon)

B. Silver nitrate 0.5%Solution

C. Silver sulfadiazine(Silvadene)

CharacteristicsA. Limited eschar

penetration, resistant organisms neutropenia, thrombocytopenia

B. Painful application, hyperchloremic reactions good eschar penetration

C. Hyponatremia, hypokalemia, hypocalcemia, methemoglobinemia

Which of the following statements is/are true regarding metabolism in

the burn patient?

a. Postburn hypermetabolism is mediated by catecholamine

release.b. IL-1 and IL-6 are elevated in burn injuries and enhance

the hypermetabolic response by increasing oxygen consumption.

c. Elevated core and skin temperature and lower core-to-skin

heat transfer are manifested in postburn hypermetabolism.

d. Increased blood flow to the muscles in the burned limb.e. The burn wound preferentially utilizes glucose by anaerobic glycolytic pathways despite increased blood flow to the wound.

Which of the following can minimize metabolic expenditure in burn

patients?A. Nursing the patients at ambient

temperature below 30oC.B. Adequate analgesia and sedation.C. Early excision of the burn and complete

wound closure.D. Early diagnosis and treatment of

infection.E. Use of B-adrenergic blockers.

Select the correct statements regarding nutrition in burn patients.

a. The optimal calorie/nitrogen ratio varies between 150:1 & 160:1.b. Fat is the best source of non-

protein calorie.c. Glutamine deficiency results in

atrophy of gut mucosad. Long-chain triglycerides for

maintaining lean body mass.e. Overfeeding is associated with

hyperventilation.

Which of the following statements is/are true for invasive burn wound

infection?

a. Common in burns larger than 30% total body surface area.

b. Characterized by conversion of a partial-thickness burn to full-thickness burn.

c. Definitive diagnosis can be made if quantitative culture of the biopsy recovers more than 105 organisms per gram on tissue.

d. Incidence of Candida wound infection has increased owing to topical antimicrobial chemotherapy.

e. Topical antimicrobial agents have markedly decreased the incidence of invasive burn

wound infection.

Select the true statements regarding infection in the burn

patienta. Infection if the most frequent cause of

death in the burn patients.b. Cell-mediated immunity is not altered

in major burn injuries.c. Hematogenous pneumonia is the most

common pulmonary infection in burn patients.

d. Diminished granulocyte chemotaxis is an important factor in burn infection.

e. Suppurative thrombophlebitis can be a major source of sepsis.

Which of the following statements is/are true regarding administration of

antibiotics to burn patients?

a. Prophylactic systemic antibiotics are indicated in patients with extensive burns.b. With invasive burn wound sepsis,

systemic antibiotics should not be instituted before culture and sensitivity results are available.

c. Positive wound cultures should be treated with systemic antibiotics.

d. Antibiotics effective against anaerobic organisms are always indicated for burn wound sepsis.

e. Subtherpeutic serum antibiotic levels are common in burn patients.

Which of the following statements is/are true regarding burn wound

excision?

A. Excision is indicated for deep partial-thickness and full- thickness burn wounds.

B. Early excision and closure of burn wounds has been shown to reduce the incidence in invasive burn wound infection, shorten the hospital stay, reduce pain, and improve functional recovery.

C. Excision should be performed after successful fluid resuscitation.

D. Tangential excision involves sequential excision of the eschar down to bleeding, viable tissue.

E. Excision of more than 10% of TBSA single procedure is associated with significantly morbidity.

Which of the following statements is/are true regarding burn wound

closure?A. Split-thickness autograft is

contraindicated if wound culture is positive B-hemolytic streptococci.

B. Xenograft is the most frequently used and effective biologic dressing when an autograft is not available.

C. Allograft dressings promote bacterial proliferation.

D. Cultured autologous keratinocyte sheets can be used for permanent wound coverage with good results.

E. Dermal substitutes provide better temporary wound

coverage that biologic dressings.

Select the true statements regarding inhalation injury.

A. Presence of carbonaceous sputum is a specific sign of inhalation injury.

B Normal carbon monoxide level on admission excludes inhalation injury.

C. Chest radiography is sensitive for diagnosing inhalation injury.

D. Combined fiberoptic bronschosocpy and 133 Xe ventilation-perfusion lung scan has a diagnostic accuracy of more than 96%

E. Pulmonary infection is the most frequent cause of morbidity and mortality with inhalation injury.

Select the correct statements regarding electrical injury.

a. Depth of tissue injury is related to density and duration of the current flow.

b. High-voltage electric injury results in more severe injury to the trunk than the extremities.

c. Risk of acute renal failure is relatively high with an electrical injury due to myoglobinuria and underestimation of fluid needs.

d. Incidence of cholelithiasis is high in patients after electrical injury.

e. With a lightening injury cardiopulmonary arrest is common, and burns are characteristically superficial.

Which of the following statements is/are true regarding chemical

injuries?

a. Immediate wound care involves application of a neutralizing agent.

b. Acid burns cause liquefaction necrosis.

c. Alkali burns produce deeper injuries than acid burns.

d. Hydrofluoric acid burn is treated with local calcium gluconate gel.

e. Coal tar burn is best treated with immediate application of a petroleum-based ointment.

Select the true statements regarding post burn sequelae

A. All second & third degree burns produce permanent scarring.

B. The incidence of hypertrophic scar formation is less after excision and skin grafting than with wounds that heal spontaneously.

C. Hypertrophic scars are best treated by early excision and wound closure.

D. Basal cell carcinoma is the most common carcinoma in an old burn scar.