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Wound healing DSilverberg

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Wound healing  DSilverberg Powered By Docstoc
					Wound healing

Danny Silverberg M.D.
            Phases of healing
•   Early
•   Intermediate
•   Late
•   Terminal
      Early wound healing events

• Hemostasis
  –   Platelet aggregation
  –   Intrinsic and extrinsic coagulation cascade
  –   Thrombin, fibrin
  –   Vasoconstriction
    Early wound healing events

• Inflammation
Vasodilatation
Increase in vascular permeability
Chemotaxis
Cellular response
      Early wound healing events

•   Homeostasis
•   Neutrophils
•   48-72h- macrophages
•   5-7 days- few inflammatory cells.
   Intermediate wound healing
             events
• Mesenchymal cell chemotaxis and
  proliferation
• Angiogenesis
• Epithelisation

• 2-4 days after injury
• Mediated by cytokines
             Intermediate wound healing events

Mesenchymal cell chemotaxis and
  proliferation
• Fibroblasts- migration and proliferation
• Smooth muscle

Angiogenesis- reconstruction of vasculature
• Stimulate: High lactate, acidic Ph, low O2
  tension
• Endothelial cell migration and proliferation
            Intermediate wound healing events

Epithelisation
• Partial thickness- Cells derived from wound edges
  and epithelial appendages.
• Incisional wound: cellular migration over less then
  1 mm. Wound sealed in 24-48h.

•   Cellular detachment
•   Migration
•   Proliferartion
•   differentiation
     Late wound healing events
Collagen synthesis
• 3 helical polypeptide chains
• Lysine and proline hydroxylation
Required for cross-linking
     Late wound healing events
Collagen synthesis
• 3-5 days post injury
• Primarily by fibroblasts
• Maximum synthesis rate 2-4 weeks
• Declines after 4 weeks
• Type 1 collagen most common ( 80-90% of skin
  collagen)
• Type 3- seen in early phases of wound healing
          Wound contraction
• Centripetal movement of the wound edges toward
  the center. ( 0.6-0.7 mm/day)
• Begins at 4-5 days
• Maximal contraction 12-15 days
• Trivial component in closed incisional wounds,
  significant for closure of open wounds
• Rate- depends on tissue
• Circular wounds- slower closure but avoid
  stenosis
                        Wound contraction
• Mechanism- cell mediated processes, not
  requiring collagen synthesis
• Myofibroblasts- fibroblasts with
  myofilaments in cytoplasm
• Appear in wound day 3-21
• Located in periphery- pull wound edges
  together.
• Contractures- contraction across joint
  surface
 Terminal wound healing events
• Remodeling- turnover of collagen. Type 3
  replaced by type 1
• Day 21- net accumulation of wound collagen
  becomes stable
• Wound bursting strength- 15% of normal.
• Week 3-6- greatest rate of increase
• 6 weeks- 80-90% of eventual strength.
• 6 months maximum strength ( 90% ). Process
  continues for 12 months
    Cytokines and growth factors
•   Primary mediators in wound healing.
•   Endo, para, auto, intracrine function
•   EGF
•   FGF
•   PDGF
•   TGF
Growth factors in wound healing
        Which of the following is primarily
    responsible for tensile strength in a healing
            wound 4 days after injury?


•   Collagen
•   Elastin
•
•
•
    Fibrin
    Fibronectin
    Hyaluronic acid
                                          ?
        Which of the following is primarily
    responsible for tensile strength in a healing
           wound 6 weeks after injury?


•   Myofibroblasts
•   Fibrin
•
•
•
    Fibronectin
    Collagen
    Collagen cross linking
                                        ?
        Local factors affecting wound healing

Infection
• foreign body/ necrotic tissue, hematomas
• local/ systemic factors
• type of surgery
            Local factors affecting wound healing



Hypoxia and smoking
• O2 delivery necessary for cellular
  respiration and hydroxylation of proline and
  lysine
• Smoking- vasoconstriction, atherosclerosis,
  carboxyhemoglobin.
          Local factors affecting wound healing



Radiation
• Collagen synthesized to abnormal degree-
  fibrosis
• Fibrosis of vessels- (media)-occlusion
• Thinned epidermis, pigmentation
• Limited access of inflammatory cells and
  cytokines- impaired healing
• Damage to fibrocytes and keratinocytes.
             Systemic factors
Malnutrition
• Limited AA supply for collagen synthesis
• Consumption of proteins d/t CHD and fat
  deficiency.
• Vit C deficiency- diminished hydroxylation of
  lysine and proline,
• Vit D- impaired bone healing
• Zinc- inhibition in cellular proliferation and
  defficient granulation tissur formation
    Normal healing is accelerated by which
              of the following?
•   VitC
•
•
•
•
    VitA
    Zinc
    Increased local oxygen tension
    Scarlet red
                                       ?
                        Systemic factors



Cancer
• Cachexia, anorexia
• Altered host metabolism.
• Protein catabolism
• Abnormal inflammatory cell response
                       Systemic factors



Old Age

Diabetes
• Impaired healing ( decreased chemotaxis
  and phagocyte function )
• Risk of infection
                          Systemic factors
Steroids, immunsuppression
• Inhibits all aspects of healing process
• Impaired cellular function, deficiency in
  inflammatory cell function, cytokine
  production, fibroblast proliferation
• All effects ( except contraction ) reversed
  by Vit A.
      Hypertrophic scars and kelloids

• Excessive healing processes- increase in net
  collagen synthesis raised thickened scar
• Keloid- Extension beyond wound margin,
  familial, may develop up to 1 year, rarely subside
• Hypertrophic scar- Confined to wound margin,
  light skinned, early after injury, may subside,
  cause contractures
• Tx- excision, steroid injection, pressure garments,
  radiation tx
      Types of wound closure


Primary closure
• Approximation of acutely disrupted tissue
  with sutures, staples or tape
                    Types of wound closure


Delayed primary closure
• Approximation of wound margin delayed
  for several days
• Prevents wound infection in cases of
  contamination/foreign bodies/tissue trauma
• Less bacterial colonization in open wound
• Normal healing progress occurs
                 Types of wound closure

Secondary wound closure
• Open wound margins approximate by
  biologic contraction
• If a patient requires reoperation 1 month after a
  midline abdominal incision which of the following
  promotes the most rapid gain in strength of the
  new incision

•
•
•
•
    Separate transverse incision
    Midline scar is excised with a 1 cm margin
                                                   ?
    Midline incision reopended without scar excision
    Rate of strength ganed is not effected by incision
    technique

				
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posted:4/15/2008
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