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


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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.



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
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withdrawn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, bone
Ohm’s Law- V=IR
• Damage more related to
cross-sectional area which
explains extremity injuries
without trunk injuries.
Electrical Storms/Lightning

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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


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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
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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
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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
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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.
2.
3.
Zone of coagulation - A nonviable area of tissue at the
epicenter of the burn
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
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
Hyperemia
Zone of
Ischemia
Zone of
Coagulation
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
burns
 point
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 –
-
-
-
th
4
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.
th
4
degree Burn
PART 2
Physiologic
Implications
Pathophysiology
Resuscitation
Post-Resuscitation
Board Questions
Physiologic Implications of Burn Injury
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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
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Hypodynamic, with need for close fluid resuscitation monitoring
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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
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Day 3 until 95% wound closure
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Hyperdynamic, febrile, protein catabolic state

Tachycardia can be normal in burn patients
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Blood pressure may be hard to obtain due to circumferential burns
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Release of more inflammatory mediators, cortisol, glucagon,
catecholamines, bacteria from wound
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High risk of infection and pain
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Remove non-viable tissue or close wounds to avoid sepsis
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Nutritional support essential

Maintain and support body temperature with high ambient temps and
humidity
Recovery Period
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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
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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
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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
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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) level
E. 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 furosemide
C. 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 colloidresuscitated patients.
Match the items in two columns
Topical Agents
A. Sodium mafenide
(Sulfamylon)
B. Silver nitrate 0.5%
Solution
C. Silver sulfadiazine
(Silvadene)
Characteristics
A. 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 mucosa
d. 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 patient
a. 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 fullthickness 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.
b.
c.
d.
e.
Depth of tissue injury is related to density and
duration of the current flow.
High-voltage electric injury results in more severe injury to
the trunk than the extremities.
Risk of acute renal failure is relatively high with an
electrical injury due to myoglobinuria and
underestimation of fluid needs.
Incidence of cholelithiasis is high in patients after
electrical injury.
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.
b.
c.
d.
e.
Immediate wound care involves application of a
neutralizing agent.
Acid burns cause liquefaction necrosis.
Alkali burns produce deeper injuries than acid burns.
Hydrofluoric acid burn is treated with local calcium
gluconate gel.
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.