Skin Anatomy and Wound Classification

Skin Anatomy

• Skin is the body's largest organ and acts as a barrier against the environment.
• It's composed of three layers: epidermis, dermis, and subcutaneous fat.

Definition of Wound

• A wound is a break in the skin or tissue integrity that disrupts structure and function.

Wound Classifications

Based on Cause of Wound

• Intentional wounds: Result from planned medical procedures (e.g., surgery).
• Unintentional wounds: Result from unexpected events (e.g., accidents, injuries).

Based on Skin Integrity Status

• Open wounds: Visible breaks in the skin's surface.
• Closed wounds: Damage beneath the skin without breaking the surface (e.g., contusions, hematomas).

Types of Closed Wounds

• Contusion/ Bruise: Caused by blunt force trauma, resulting in localized bleeding under the skin.
• Abrasion: Superficial scrapes or scratches.
• Hematoma: Collection of blood under the skin, often from a deep bruise or puncture.

Types of Open Wounds

• Incised Wound: Clean-cut wound from a sharp object (e.g., knife).
• Lacerated Wound: Jagged tear caused by blunt force trauma.
• Avulsion: Tearing away of a flap of skin or tissue.
• Penetrating Wound: A wound that perforates through the skin and underlying tissues (e.g., gunshot, stab wound).

Based on Wound Cleanliness (Berard Wound Classification)

• Clean Wound: Elective, primarily closed surgical wounds with no entrance of normally colonized body cavities.
• Clean-Contaminated Wound: Controlled opening of normally colonized body cavities; minimal risk of infection.
• Contaminated Wound: Acute inflammation, open trauma, or breach of sterile technique within 4 hours of injury.
• Dirty/ Infected Wound: Purulent abscess, traumatic wounds with retained dead tissue, or wounds with ongoing infection.

Based on Skin Thickness Loss

• Superficial Epidermal Wounds: Impact the outer layer of skin but not deeper tissues.
• Partial-Thickness Wounds: Extend through the epidermis into the dermis.
• Full-Thickness Wounds: Involve all skin layers, potentially down to subcutaneous fat, muscle, or bone.

Based on Time Elapsed/ Wound Duration

• Acute Wounds: Show signs of healing within four weeks.
• Chronic Wounds: Fail to heal within an expected timeframe based on their type and location.

Physiology of Wound Healing

• A complex process that restores anatomical and functional integrity to damaged tissue.
• Involves various cells (e.g., neutrophils, macrophages, fibroblasts) and components (e.g., collagen) working together.
• Occurs in four overlapping phases: hemostasis, inflammation, proliferation, and remodeling.

Hemostasis Phase (Seconds to Minutes)

• Constriction of blood vessels.
• Formation of a temporary "platelet plug" to stop bleeding.
• Activation of the coagulation cascade.
• Formation of the final blood clot (fibrin plug).

Inflammatory Phase (Lasts for 72 Hours)

• Mast cells release substances like histamine that trigger inflammation.
• Neutrophils (white blood cells) arrive and fight infection.
• Monocytes migrate and differentiate into macrophages to clean debris.
• Cytokines and growth factors released by these cells stimulate fibroblasts and epithelial cells.

Proliferative Phase (Days 3 to 3-6 Weeks)

• Granulation Tissue Formation: New blood vessels and connective tissue form.
• Extracellular Matrix & Collagen Synthesis: Fibroblasts produce collagen to provide strength and support.
• Angiogenesis: New blood vessels grow to supply the healing tissue.
• Re-epithelialization: Skin cells migrate to re-cover the wound surface.

Remodeling/ Maturation Phase (6 Weeks to 1-2 Years)

• Collagen fibers remodel and reorganize for increased strength.
• Collagen type III transitions to collagen type I, making the scar stronger.
• Blood vessels mature and decrease in number.
• Scar tissue regains approximately 80% of its original tissue strength.

Types of Wound Healing

• Primary Healing (First Intention): Wounds that are closed immediately, typically with sutures, allowing for minimal scar formation.
• Secondary Healing (Second Intention): Wounds left open to heal from the bottom up, resulting in more scar tissue.
• Tertiary Healing (Delayed Primary Closure): Wounds initially left open and then closed later after debridement and infection control are achieved.

Complications of Wound Healing

• Infection: Bacteria enter the wound and multiply, hindering healing.
• Hemorrhage: Bleeding from the wound site, potentially leading to blood loss and shock.
• Fistula: An abnormal connection between two body surfaces (e.g., between a wound and the intestine).
• Wound Dehiscence: Partial or complete opening of the wound edges along the suture line before healing is complete.
• Wound Evisceration: Protrusion of internal organs through a dehisced wound.

Factors Affecting Wound Healing

Local Factors

• Infection: Presence of bacteria delays healing.
• Necrotic Tissue & Foreign Bodies: Dead tissue and foreign objects impede healing processes.
• Tissue Hypoxia: Reduced oxygen supply hampers macrophage and fibroblast activity.
• Venous or Lymph Stasis: Slowed blood or lymph drainage leads to poor nutrient delivery and waste removal.
• Recurrent Trauma: Repeated injury to the healing wound delays healing.

Systemic Factors

• Age: Elderly individuals tend to heal more slowly.
• Smoking: Reduces oxygen delivery, impairs WBCs, and decreases fibroblast function.
• Stress: Suppresses immune responses and wound healing.
• Obesity: Increases wound tension, reduces blood supply, and increases risk of complications.
• Malnutrition: Inadequate intake of proteins, vitamins, and minerals slows wound repair.
• Vitamins and Minerals: Deficiencies in vitamin A, vitamin C, vitamin K, zinc, copper, magnesium, and iron have negative impacts on wound healing.
• Metabolic Diseases (E.g., Diabetes): Impair blood sugar control and immune function, affecting healing.
• Anemia & Hypoxia: Reduced oxygen supply to tissues hinders wound repair.
• Drugs (Steroids, NSAIDs, Chemotherapy): Interfere with various aspects of wound healing.
• Immunocompromised Conditions: Weaken the immune system, making infection more likely.

Wound Assessment

• Site of Wound: Location and surrounding tissues.
• Type of Wound: Incised, lacerated, etc.
• Mode of Injury: How the wound occurred.
• Foreign Body: Presence of any foreign object.
• Severity of Pain & Bleeding: Indicators of the wound's depth and extent of injury.
• Wound Length, Width & Depth: Dimensions of the wound.
• Tissue Viability: Assessment of the health of tissue surrounding the wound (e.g., color, texture, temperature).
• Drainage: Type and amount of fluid draining from the wound (serous, serosanguineous, purulent, sanguineous).
• Wound Drains: Presence of drainage tubes to remove fluids.