Wound dressing? ??

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Wound Healing

• A complex integrated sequence of cellular,
  physiologic, and biochemical events initiated by
  the stimulus of injury to tissue

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Healing process

• The same events, in the same order, occur in
  every healing process regardless of the tissue
  type or the inciting injury

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Healing process

• The activation of basic cellular processes of
  inflammation, cell proliferation, and growth as
  well as regulation of these processes once repair
  is complete.

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Healing process

• All repair occurs with an overlapping series of
  orchestrated events to limit the damage and
  restore the function and integrity of the
  structure

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Types of wound closure

• Primary closure
• Delayed primary closure
• Secondary closure
• Closure of partial thickness skin wound

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Primary closure

• First intention closure
• Immediately sealed wounds with simple suturing,
  skin graft placement, or flap closure
• Eg. emergency laceration repair,
• closure of the surgical wound

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Primary closure
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Secondary closure

• No active intent to seal the wound
• The wound is closed by reepithelization and
  contraction with some deposition of scar tissue

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Secondary closure
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Delayed primary closure

• Tertiary intention
• Surgical intervention, such as suturing, skin
  graft replacement, or flap design, after repeated
  debridement and antibiotics therapy

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Delayed primary closure
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Partial thickness wound healing
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TISSUE RESPONSES TO INJURY

• Vascular events
• Cellular events
• Chemical mediators

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Vascular events

• Immediate transient vasoconstriction
• active vasodilatation
• permeability change

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TISSUE RESPONSES TO INJURY

• Vascular events
• Cellular events
• Chemical mediators

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Cellular events

• platelets
• neutrophils
• macrophages
• lymphocytes
• fibroblasts
• endothelial cells

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platelets

• Hemostasis
• Release of platelet granules
• œ- granules
• dense granules
• lysosomes

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Neutrophils

• Protection against infection
• Intracellular products release
• free radicals
• cyclooxygenase products
• lipooxygenase products
• protease, antiprotease
• band2 protein

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Macrophages

• phagocytosis
• initiation of fibroplasia
• release cellular products
• neutral protease, complement factors,
• reactive oxygen metabolites,
• growth factors, fibronectin,
• interleukin 1, enzyme inhibitors

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TISSUE RESPONSES TO INJURY

• Vascular events
• Cellular events
• Chemical mediators

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Chemical mediators

• Vasoactive agents
• Chemotactic factors
• Cytokines

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Vasoactive agents

• Histamin
• Serotonin
• Arachidonic acid

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Cytokines in wound healing

• TGF-ß
• PDGF
• FGF
• EGF
• IGF-1
• Etc. KGF, CTGF, TNF, interleukins

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TGF-ß

• platelets, macrophage. fibroblast?? release??
  healing process? ?? ??? ??? ??.
• ??
• stimulates the deposition of collagen and other
  matrix components
• inhibits collagenase activity
• blocks plasminogen inhibitor
• enhance angiogenesis
• chemotactic for fibroblasts, monocytes, and
  macrophages

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PDGF

• ?? platelets? a-granule?? release?? macrophage,
  endothelial cell, fibroblast??? release
• ??
• attract the neutrophil, macrophage, and
  fibroblast to the wound
• powerful mitogen of the neutrophil, macrophage,
  and fibroblast
• stimulate fibroblasts to synthesize new
  extracellula matrix
• increase the amount of fibroblast-secreted
  collagenase

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FGF

• endothelial cell? macrophage?? production
• ??
• stimulate endothelial cells to divide and form
  new capillaries
• chemoattract endothelial cells and fibroblasts

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EGF

• keratinocytes?? release
• ??
• stimulates mitosis in epidermal cells and
  fibroblasts
• increase the secretion of collagenase by
  fibroblasts

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WOUND HEALING PHASES

• Inflammatory phase
• Proliferative phase
• Maturational phase

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Inflammatory phase

• The bodys defenses are aimed at limiting the
  amount of damage and preventing further injury

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• At the initial time of tissue disruption,
  platelets release coagulation factors and
  cytokines to initiate the healing process

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• Within the first day following tissue injury,
  neutrophils attatch to surrounding vessel walls
  and then move through the vessel walls to migrate
  to the wound site

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Proliferative phase

• angiogenesis
• fibroplasia
• epithelization

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Angiogenesis

• The process of new blood vessel formation to
  support a healing wound environment
• Stimulants
• tissue hypoxia major stimulus
• TNF-a, heparin, VEGF, FGF-1, FGF-2

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• The fibroplasia phase is characterized by
  movement of wound macrophages into the site of
  injury, which in turn attract fibroblasts. The
  fibroblasts then repair the site by producing new
  connective tissue matrix.

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Maturational phase ( remodeling )

• The period of scar contracture with collagen
  cross-linking, shrinking, and a loss of edema

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• The remodeling phase is characterized by an
  equilibrium between collagen synthesis and
  collagen degradation in an effort to reestablish
  the connective tissue matrix.

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MECHANISMS IN WOUND HEALING

• Epithelization
• Contraction
• Connective tissue matrix deposition

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Epithelization

• sealed by clot formation
• epithelial cell migration across the defect
• keratinocytes detatchment, migration,
  proliferation, differentiation, stratification

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MECHANISMS IN WOUND HEALING

• Epithelization
• Contraction
• Connective tissue matrix deposition

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Contraction

• Inward movement of the edges of the
• injured tissue
• Begins between days 8 and 10 after
• injury
• Fibroblast and extracellular matrix
• control the process.

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MECHANISMS IN WOUND HEALING

• Epithelization
• Contraction
• Connective tissue matrix deposition

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Components of extracellular matrix

• Collagen
• Elastin
• Fibronectin
• Laminin
• Proteoglycans
• Hyaluronic acid

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Synthesis of collagen

• Combination of aminoacid to form chains
• Chains associate to form molecules
• Molecules associate to form fibrils
• Fibrils aggregate into fibers or bundles

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FACTORS AFFECTING WOUND HEALING

• Types of injury
• Age
• Medications
• Host disease factors
• Technical factors

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Types of Injury

• Sharp injury
• Crush injury
• Missile injury
• Thermal injury

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Aging

• In vitro decrease in the proliferative
  potential of fibroblasts and epithelial cells
• Clinically heal more slowly with less scarring

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Medications

• Steroids Vitamin A
• Anti-inflammatory agents
• Phenytoin
• Antineoplastic agents
• Anticoagulants
• Vitamin E

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Steroids

• Impairing macrophage migration
• Altering neutrophil function
• Inhibit synthesis of procollagen by fibroblasts

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Vitamin A deficiency

• Impair monocyte activation
• Inhibit fibronectin deposition
• Impairment of TGF-ß receptors
• Vitamin A directly counteracts the effect of
  glucocorticoid

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Host disease factors

• Nutrition
• Infection
• Wound hypoxia
• Diabetes
• Jaundice

• Uremia
• Malignancy
• Irradiation
• Denervation

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Nutrition

• Protein
• Vitamin C decrease in rate and quality of
  collagen production
• Vitamin K
• Minerals zinc, copper

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Infection

• Bacteria
• prolong the inflammatory phase
• interfere with epithelization,
  contraction and
• collagen deposition
• Endotoxin
• collagen degradation and destruction
  of
• surrounding previously normal tissue

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Wound hypoxia

• Oxygen necessary for normal metabolic cellulat
  function
• Tissue oxygen level ? 35mmHg ??? ????neutrophil?
  bacterial killng, fibroblasts? replication? ???
  collagen production? ??? ??.

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Causes of wound ischemia

• Poor arterial flow - atherosclerosis
• Poor venous flow venous stasis
• Smoking
• Radiation
• Edema
• Diabetes mellitus
• Vasculitis
• Pressure

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Diabetes mellitus

• Tissue hypoxia
• artherosclerosis, microvascular abnormality
• Repetitive trauma

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Diabetes mellitus

• Susceptable to infection
• attenuated inflammatory response
• impaired chemotaxis
• inefficient bacterial killing
• Impaired lymphocyte and leukocyte function
• Increased collagen degradation and decreased
  deposition

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Technical Factors

• Surgical technics
• Suture materials
• Wound care

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Surgical technique

• Handle gently
• Adequate hemostasis
• Careful apposition of wound edges

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Surgical technique skin incision

• Direction
• Length
• Location

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Suture materials

• Absorbable sutures
• Non-absorbable sutures

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Principles of wound managementopen wound

• Clean the wound effectively
• Achieve moist wound healing
• Minimize the periwound edema
• Prevent new pressure insult or wound
• soilage
• Maintain adequate tissue oxygenation

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Agents to optimize wound healing

• Dressing
• Antibiotics controversial
• Debriding agents
• Phamacologic agents

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Ideal dressing

• simple, inexpensive, highly absorptive,
  nonadherent
• achieve moist healing and have antibacterial
  properties
• less frequent dressing change
• all-in-one dressing

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Wound-healing products(1)

• Passive products lint
• cotton wool
• plugging and concealing wounds

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Wound-healing products(2)

• New dressings polymeric films,
• polymeric foams,
• hydrogels,
• hydrocolloids
• Classified as interactive dressings, providing a
  microenvironment which is conducive to healing

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Wound-healing products(3)

• Active products which actively stimulate healing
  beyond that of the normal biological maximum.

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