Understanding Burns: Skin Layers and Functions

Introduction to Burns

• Burns can range from minor to severe, even causing death.
• Pathophysiology of severe burns involves circulatory failure or shock.
• Severe burns also entail widespread inflammation and immunosuppression.
• Understanding skin layers is important to appreciate tissue damage extent in burns.

Functions of Human Skin

• Acts as a barrier preventing pathogens from entering the body.
• Disruptions or loss of skin integrity allows pathogen entry.
• Temperature regulation is another vital function.
• Provides sensation, known as tactility.
• Prevents water loss from the body.

Layers of the Skin

• Generally, human skin has two main layers: epidermis and dermis.
• Hypodermis is a third adipose layer below the skin, but not strictly part of it.
• Understanding characteristics of each layer is crucial in understanding the clinical changes in burns.

Epidermis

• The outermost, thin layer exposed to the environment.
• Composed of stratified epithelial cells arranged in layers.
• Uppermost layers consist of dead cells that are sloughed off.
• Contains specialized cells called keratinocytes, filled with keratin protein.

Dermis

• Contains vasculature, including capillaries, which is a very important feature.
• Thicker than the epidermis.
• Contains nerve fibers that provide sensation, including pressure and pain.
• Nerve fibers connect to nociceptors, which are receptors for pain.
• Contains cells, including fibroblasts.
• Houses hair follicles, sweat glands, and sebaceous glands.

Hypodermis

• Lies below the dermis and is not technically part of the skin.
• Contains fat cells called adipocytes.

Layers Below Hypodermis

• Below the hypodermis is the muscle fascia layer.
• Below the muscles is bone.

Causes of Burns

• Burns are thermal injuries caused by physical and chemical factors.
• Physical factors include fire, heat sources, electric sources, and certain radiations like ultraviolet rays.
• Chemical factors include acids and caustic/alkaline agents.
• Contact with hot water results in scalding.
• Extreme cold can cause frostbite, also a form of burn injury.

First Degree Burns

• Superficial and only affect the epidermis.
• Heal very quickly.
• Lesions are mostly dry.
• Swelling containing fluid (blisters) may develop 24-48 hours after burn.
• Blister formation is delayed or rare.
• Sunburns are common example.

Second Degree Burns (Partial Thickness)

• Can be categorized into two forms, superficial and deeper, depending on the extent of dermis affected.

Superficial Second-Degree Burns (Superficial Partial Thickness)

• Affect only upper part of the dermis.
• Lesions are red due to remaining vasculature in the dermis.
• Lesion will blanch when pressed.
• Painful due to intact nerve fibers.
• Blisters form immediately.
• Lesion is wet due to leakage of fluid from capillaries.

Deeper Partial Thickness Burns

• Affect major part or entire thickness of the dermis.
• Vasculature is destroyed, lesion appears white.
• Pain is typically absent due to nerve fiber destruction.
• Healing is slower than superficial burns.
• Often leads to scarring.

Third Degree Burns

• Extend beyond the dermis, affecting hypodermis, muscle and fascia.
• No pain due to destroyed nerve fibers.
• No blanching.
• Lesions are whitish or charred/blackish.
• Texture may be leathery.

Diagnosing Severity: Skin Biopsy vs. Clinical Features

• Ideally, skin biopsy determines burn degree.
• Logistically impossible during severe burns when timing is key.
• Instead, clinical features, such as skin blanching, wetness, and pain are assessed.

Wallace Rule of Nines

• Used to calculate the surface area of the body that is burned.
• Clinically important for treatment decisions.
• Burn covering more than 20% of body surface is considered a major burn.
• Values are multiples or factors of nine.

Complications of Burns

• Pathophysiology involves inflammation, immunosuppression, and shock.
• Systemic effects impact multiple organ systems.
• Can cause circulatory failure and death.
• Can cause alterations in fluid balance which effects intravascular to interstitial.
• Fluid shifts cause edema.

Systemic Effects: Fluid Balance

• Fluid shifts cause edema.
• Reduced fluid volume in blood vessels can cause hypovolemic shock.
• Increased capillary permeability results in reduced plasma oncotic pressure due to leakage.

Systemic Effects: Hyperkalemia

• Damaged cells release potassium, leading to hyperkalemia.
• Increased potassium levels can promote arrhythmias.

Systemic Effects: Cardiovascular

• Myocardial depression results in reduced cardiac output.

Systemic Effects: Renal

• Myoglobinuria (myoglobin in urine) occurs due to muscle breakdown.
• Released myoglobin damages renal tubules, potentially causing acute renal failure.
• Can lead to necrosis in the kidneys.
• Renal insufficiency results from decreased perfusion due to hypovolemic shock.

Importance of Urine Output

• Oliguria (decreased urine output) indicates patient is in shock and burn injury is severe.

Systemic Effects: Hormonal and Digestive

• Stress response triggers hormone release (cortisol, catecholamines).
• Presence of stomach ulcers, specifically Curling ulcers.

Systemic Effect: Immunosuppression

• Immunosuppression is characteristic of severe burns.
• Patients are more susceptible to infections.
• Open skin lesions allow easy pathogen entry.

Capillary Seal

• Proper treatment and fluid administration can restore capillary integrity.
• Fluid leakage from capillaries is stopped and urine output is increased.

Capillary Seal and Fluid Dynamics

• During shock, water, albumin, proteins, sodium, potassium leak out.
• Cells leak potassium.
• After 24 hours with proper treatment, reverse occurs.

Systemic Response to Acute Burn Injury

• Systemic response characterized by release of inflammatory mediators.
• Direct tissue injury from heat exposure.
• Increased capillary permeability leads to edema and hypovolemia.

Edema and Hypovolemia Consequences

• Hypovolemia increases blood viscosity.
• Reduced oxygen flow which results with hypovolemia will contribute to tissue and organ ischemia; organ failure
• Tissue ischemia results from decreased organ perfusion.
• Endothelial cell injury occurs.
• Leukocyte recruitment leads to further tissue injury.

Explore the pathophysiology and classification of burns, from minor to severe. Learn about the crucial functions of the skin, including its role as a barrier against pathogens, temperature regulation, and sensation. Investigate the epidermis, dermis, and hypodermis skin layers.