Burn definition.etilogy of burn in general. Classification of burn based on agent,
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Burns: Definition, Etiology, and Classification by Agent
Definition
A burn is a traumatic injury to the skin and underlying tissues caused by contact with heat, cold, chemicals, electricity, or radiation. The depth of injury is proportional to the temperature and duration of exposure, and also depends on the body region due to differences in skin thickness and blood flow.
- Mulholland and Greenfield's Surgery, 7e
Burns disrupt the skin's core functions: barrier protection against microbes, thermoregulation, fluid impermeability, sensory perception, and structural integrity. When skin is burned, all of these are lost in proportion to the depth and extent of injury.
- Fitzpatrick's Dermatology, Vol. 1 & 2
Etiology of Burns (General)
Burns arise from multiple overlapping causes. According to large epidemiologic data:
| Cause | Proportion of burn injuries |
|---|---|
| Fire / Flame | ~41% |
| Scald (hot liquids) | ~35% |
| Contact with hot object | ~10% |
| Electrical | ~4% |
| Chemical | ~3% |
| Other (radiation, cold, etc.) | remainder |
- Men account for ~67% of all burns; women for ~33%
- Children under 16 make up 26% of total burns - scald burns predominate in those under 5 years
- Adults most commonly suffer flame burns
- Elderly (>60 years) represent 15% of cases but 37% of deaths
- Home is the most common setting for burns across all age groups
- Alcohol and cigarettes (igniting upholstered furniture or bedding) are significant contributors in adults
With modern surgical critical care, over 96% of burn patients survive.
- Mulholland and Greenfield's Surgery, 7e
Classification of Burns by Causative Agent
1. Thermal Burns
a. Flame Burns
The most common burn etiology in adults, accounting for the highest risk of death and complications among all burn types. Flame burns typically result from:
- Flammable liquids
- Motor vehicle crashes
- Cooking fires
- Ignition of clothing or bedding
Most occur at home (64%); work fires and recreational fires account for 12% and 6%, respectively. Smoke inhalation accompanies 17% of flame burns and raises overall mortality from ~4% (without inhalation) to 24% (with inhalation injury).
- Fitzpatrick's Dermatology; Mulholland and Greenfield's Surgery, 7e
b. Scald Burns
The second most common burn type overall, and the most common in children. Caused by hot liquids or steam. Key points:
-
Over 50% are related to food preparation or consumption
-
Grease burns (temp ~400°F / 205°C) almost uniformly cause deep partial- or full-thickness burns
-
Tar and asphalt (>400-500°F) are hazards for industrial workers
-
At 156°F water temperature, only 1 second is needed to cause a full-thickness burn
-
Bathtub immersion scalds are the most frequent cause of intentional burns in child abuse
-
Fitzpatrick's Dermatology; Mulholland and Greenfield's Surgery, 7e
c. Contact Burns
Result from direct contact with hot solid surfaces such as glass, metal, or plastic. Common examples include:
- Hot metal devices (space heaters, curling irons, motorcycle exhaust pipes, vaping devices)
- Injuries to palms (especially toddlers falling with outstretched hands)
Depth depends on heat of the material and duration of contact.
- Mulholland and Greenfield's Surgery, 7e
2. Electrical Burns
Account for ~4% of burn center admissions. They pose the greatest diagnostic, therapeutic, and prognostic challenge because TBSA (total body surface area) is an unreliable indicator of severity - electrical burns cause significant internal tissue damage that is not reflected on the skin.
Classified by voltage:
- Low voltage: <1,000 V
- High voltage: >1,000 V (associated with spine fractures from tetany, cardiac arrhythmias, compartment syndrome)
Key mechanisms of tissue damage:
- Ohmic heating: current flows through tissues with varying resistance. Bone has the highest resistance and generates the most heat, causing severe deep muscle and tendon necrosis
- Electroporation: electrical force drives water into lipid membranes causing cell rupture
- Arc burns: electrical arcs reach temperatures >4,000°C (7,232°F), causing secondary flame burns
- "No let-go" phenomenon: alternating current stimulates both flexors and extensors, but flexors are stronger, prolonging contact time and tissue destruction
Tissue resistance in decreasing order: bone > fat > tendon > skin > muscle > vessel > nerve.
As little as 20 mA can paralyze respiratory muscles, and 100 mA can induce ventricular fibrillation. Complications include massive myoglobinuria, renal failure, arrhythmias, and late-onset cataracts.
- Fitzpatrick's Dermatology; Mulholland and Greenfield's Surgery, 7e
3. Chemical Burns
Account for ~3% of burn center admissions, with equal proportions at home and at work. The key feature distinguishing chemical burns from other types: they continue to progress after the initial insult until the offending agent is completely removed. Immediate field treatment reduces injury severity.
Common agents (per CDC): carbon monoxide, ammonia, chlorine, hydrochloric acid, sulfuric acid.
Mechanism by agent type:
| Type | Mechanism | Characteristics |
|---|---|---|
| Acids | Hydrogen ions bind proteins → coagulative necrosis | Self-limiting - coagulation creates a barrier |
| Alkalis | Hydroxide ions saponify fats → liquefactive necrosis | Deeper and more serious - no barrier to further penetration |
| Hydrofluoric acid | Fluoride ion penetrates deeply, chelates calcium/magnesium | Can cause systemic hypocalcemia; requires calcium gluconate tx |
| Phenol | Protein denaturation + lipid dissolution | Systemic absorption → CNS/cardiac toxicity |
| White phosphorus | Oxidizes on contact with air → thermal + chemical injury | Ignites spontaneously; must be kept moist |
Healthcare personnel must be protected from secondary exposure during treatment.
- Fitzpatrick's Dermatology
4. Radiation Burns
Caused by exposure to ionizing radiation (UV, X-ray, gamma, nuclear) or non-ionizing radiation (infrared). Radiation damages DNA and cellular machinery at depth, often with a delayed presentation. Sunburns are the most common form. High-dose ionizing radiation (e.g., from nuclear events or radiation therapy) can cause:
- Erythema and desquamation (superficial)
- Ulceration and full-thickness necrosis (deep)
- Long-term risk of malignant transformation (e.g., Marjolin ulcer - squamous cell carcinoma developing in chronic burn scars)
5. Cold Burns (Frostbite)
Although less commonly grouped with "burns," cold injuries cause similar zones of tissue destruction and are considered a burn equivalent. Caused by prolonged exposure to freezing temperatures leading to ice crystal formation in cells, vascular damage, and ischemic necrosis.
Summary Table: Classification by Agent
| Agent | Type | Example | Key Feature |
|---|---|---|---|
| Flame/fire | Thermal | House fire, flammable liquids | Most common in adults; highest mortality |
| Scald | Thermal | Hot water, steam, grease | Most common in children |
| Contact | Thermal | Hot metal, glass | Depth proportional to contact time |
| Electrical | Electrical | High-voltage wires, lightning | Internal damage exceeds surface appearance |
| Chemical | Chemical | Acids, alkalis, HF | Progressive injury until agent removed |
| Radiation | Radiation | UV, X-ray, nuclear | Delayed onset; risk of malignancy |
| Cold | Frostbite | Freezing exposure | Ice crystal-mediated cell death |
Sources: Fitzpatrick's Dermatology, Vol. 1 & 2 | Mulholland and Greenfield's Surgery, 7e | Robbins, Cotran & Kumar Pathologic Basis of Disease
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