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What are the phases of wound healing?
inflammation--> repair--> maturation
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Describe the extracellular matrix from injury to healing.
injury--> bleeding--> vasoconstriction for 5-10min--> [inflammatory phase] platelet activation--> vasodilation--> increased vascular permeability and transudation--> [repair phase] blood clot and provisional ECM formation of fibrin and fibronectin--> proliferative phase and formation of granulation tissue--> [maturation phase] collagen reorganization for scar formation
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What are the different stages of ECM formation after injury, and what are the components of each?
- provisional matrix: blood clot of fibrin and fibronection
- proliferative phase: granulation tissue of collagen, hyaluronan, laminin, and proteoglycans
- maturation phase: scar with reorganization of collagen (not as strong as original tissue, but better than the first two)
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Describe the inflammatory phase of healing.
- inflammation and debridement by inflammatory cells
- Begins with leukocyte migration promoted by ECM formation; mostly neutrophils at first, then macrophages come to debride and clean up wound
- Macrophages also send signals to fibroblasts to migrate and start repair phase
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__________ are essential players to begin the repair phase of wound healing.
Healthy, functioning macrophages
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What is the lag phase of the inflammatory phase of wound healing?
- when fibrinolysis occurs and breaks down the fibrin clot and fibroblasts are very slowly moving in to produce collagen
- this is most significant in sutured wounds
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When is a wound the weakest during the healing process?
lag phase of the inflammatory phase
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Describe the strength of the wound during the different phases of wound healing.
- lag phase of inflammatory phase- weakest
- repair stage- intermediate strength
- maturation phase- strongest (but never normal)
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Describe the repair phase of wound healing.
Proliferation: angiogenesis and fibroplasia (new blood vessels, recruitment of fibroblasts)--> GRANULATION TISSUE--> epithelialization, wound contraction
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What is angiogenesis?
during the repair phase, the endothelial sprouting, chemotaxis and mitogenic mediators recruit fibroblasts; oxygen tension and lactic acid levels are different in a wound than healthy tissue, which promotes new blood vessels sprouting
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What is fibroplasia?
mesenchymal cells, such a fibroblasts and myofibroblasts, come in to deposit collagen and produce proteoglycan so the wound becomes stronger
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Describe granulation tissue. (5)
- contains myofibroblasts, which cause wound contraction
- capillaries are perpendicular to surface of wound
- fills the tissue defect
- protects wound
- barrier to infection
- scaffold for epithelialization
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Describe epithelialization.
- mobilization and migration of cells on the outside, which proliferate and grow new skin on the surface of the wound
- occurs UNDERNEATH the scab, from the wound edge, inward
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Describe contraction.
- reduction in size of wound by myofibroblasts
- surrounding skin stretches
- in areas of joints, contracture occurs (abnormal function of joint or muscle)
- skin stops growing/ contracting due to contact inhibition (when it touches the other wound edge, it knows the wound is healed)
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What molecules are responsible for the reorganization of the ECM during the maturation phase?
MMPs and TIMP are key in signaling cell death/ stopping the process after adequate wound healing
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Why is wound edge apposition so important?
when wound edges are already apposed, epithelialization can start within 24-48 hours
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Full thickness wounds that are not sutured closed, they heal by...
- wound contraction and epithelialization (second intention and granulation tissue)
- adnexal structures don't regenerate (scars are hairless)
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General differences b/w cats and dogs with wound healing. (3)
Cats heal slower, produce less granulation tissue, when cats finally heal they have faster contraction
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What are the 4 classifications of wounds? Describe each.
- Clean: no hollow viscous entered, atraumatic (incision)
- Clean contaminated: operative wounds of a contaminated organ system, no break in technique
- Contaminated: open traumatic wounds, operative wounds with break in technique
- Dirty: old traumatic wounds, infected wounds, perforated viscera
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What are the classes of duration of contamination?
- Class 1: within 6 hours
- Class 2: within 6-12 hours
- Class 3: >12 hours or gross contamination
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What are the 6 steps to open wound management?
- 1. prevent further contamination
- 2. remove foreign contamination
- 3. debridement
- 4. drainage
- 5. promote vascular bed
- 6. closure selection
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Describe step 1 of open wound management, preventing further contamination. (5)
clean table, cover wound, wear gloves, use aseptic technique, give broad spectrum antibiotics
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Describe step 2 of open wound management, removing foreign contamination. (4)
sterile lube--> shave around wound--> scrub wound--> lavage
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Why is lavaging an open wound important when removing contamination from the wound?
rehydrate necrotic tissue, reduce bacterial numbers, remove debris and foreign contaminants
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What do you lavage an open wound with when removing contamination?
sterile isotonic crystalloids
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What do you sanitize an open wound with after lavage?
DILUTED antiseptic
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Why is step 3 of open wound management, debriding, so important?
- necrotic tissue is a barrier to cell migration, prolongs inflammation, and delays the repair phase
- debridement minimizes infection and promotes wound healing
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What are the different methods of wound debridement? (5)
- surgical (with scalpel)
- enzymatic
- mechanical (wet to dry bandage)
- interactive dressings
- larval (omg gross)
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Describe step 3 of open wound management, debriding. (4)
- use aseptic technique
- obtain deep tissue culture
- remove necrotic tissue
- avoid disrupting subdermal plexus (blood supply to skin)
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What are parameters to keep in mind when determining which tissue is necrotic and needs to be removed? (4)
color, vascularity, warmth, and contractility
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When do you need to provide drainage to a wound?
- pocket, dead space, when you close a wound
- open wounds do not need drains
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How can you achieve step 5 of open wound management, promoting vascular bed?
- appropriate bandaging techniques to remove exudate, debridement, protect surface of open wound, and stimulates healing and formation of granulation tissue
- topical agents
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What are the types of wound repair?
- First intention: primary wound closure by suturing, delayed primary closure (after you let the wound bed get healthier)
- Second intention: granulation tissue, epithelization and contraction
- Third intention: closure after formation of granulation tissue
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How do you decide if/ when to close a wound?
depends on etiology, wound size, location, and condition [when in doubt, leave it open and wait to see]
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What are goals during the inflammation phase? (3)
reduce contamination, prevent infection, cleaning/ debriding
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What are the goals during the repair phase? (3)
- protection
- topical stimulations (moist wound healing)
- epithelialization and contraction (prevent contracture, immobilization of wound area)
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What are the goals of the maturation phase? (1)
protect fragile epidermis (scar is sensitive initially)
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What are the functions of bandaging? (7)
- maintain moist environment
- provide local energy source
- reduce edema
- increase level of growth factors
- increase inflammatory response
- improve oxygen content
- improve blood flow
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What are the types of primary layer of bandages?
- highly absorptive dressings (hypertonic saline, calcium alginate, gauze)
- moisture retentive dressings (hydrocolloid, hydrogel, polyurethane foam)
- nonadherent semiocclusive dressings (telfa, adaptic)
- select dressing based on how effusive wound is and what type of debridement is needed
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Describe hydrocolloids and when they are indicated.
- primary bandage layer with considerable absorption
- indicated for partial and full thickness wounds that are very exudative
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Describe hydrogels and when they are indicated.
- primary bandage layers with minimal absorption and donates fluid to wound
- indicated for minimal to moderately draining wounds
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Describe alginates and what they are indicated.
- primary bandage layer, in which Na+ from the wound and Ca2+ from alginate interact to form a gel
- indicated for moderately heavy exudative wounds early on
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Describe negative pressure wound therapy.
- provide negative pressure to wound to accelerate granulation tissue formation
- fluid/ edema removal improves blood flow, immunomodulation of bad cytokines, bacterial clearance
- provide mechanical stress to cause cells to proliferate
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What are clinical applications of negative pressure wound healing. (5)
- inflammatory or repair phase only
- exposed bone
- moderate exudation
- large wounds
- reconstructive surgery
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