What are the phases of wound healing?
inflammation--> repair--> maturation
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
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)
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
__________ are essential players to begin the repair phase of wound healing.
Healthy, functioning macrophages
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
When is a wound the weakest during the healing process?
lag phase of the inflammatory phase
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)
Describe the repair phase of wound healing.
Proliferation: angiogenesis and fibroplasia (new blood vessels, recruitment of fibroblasts)--> GRANULATION TISSUE--> epithelialization, wound contraction
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
What is fibroplasia?
mesenchymal cells, such a fibroblasts and myofibroblasts, come in to deposit collagen and produce proteoglycan so the wound becomes stronger
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
- 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
- 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)
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
Why is wound edge apposition so important?
when wound edges are already apposed, epithelialization can start within 24-48 hours
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)
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
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
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
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
Describe step 1 of open wound management, preventing further contamination. (5)
clean table, cover wound, wear gloves, use aseptic technique, give broad spectrum antibiotics
Describe step 2 of open wound management, removing foreign contamination. (4)
sterile lube--> shave around wound--> scrub wound--> lavage
Why is lavaging an open wound important when removing contamination from the wound?
rehydrate necrotic tissue, reduce bacterial numbers, remove debris and foreign contaminants
What do you lavage an open wound with when removing contamination?
sterile isotonic crystalloids
What do you sanitize an open wound with after lavage?
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
What are the different methods of wound debridement? (5)
- surgical (with scalpel)
- mechanical (wet to dry bandage)
- interactive dressings
- larval (omg gross)
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)
What are parameters to keep in mind when determining which tissue is necrotic and needs to be removed? (4)
color, vascularity, warmth, and contractility
When do you need to provide drainage to a wound?
- pocket, dead space, when you close a wound
- open wounds do not need drains
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
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
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]
What are goals during the inflammation phase? (3)
reduce contamination, prevent infection, cleaning/ debriding
What are the goals during the repair phase? (3)
- topical stimulations (moist wound healing)
- epithelialization and contraction (prevent contracture, immobilization of wound area)
What are the goals of the maturation phase? (1)
protect fragile epidermis (scar is sensitive initially)
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
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
Describe hydrocolloids and when they are indicated.
- primary bandage layer with considerable absorption
- indicated for partial and full thickness wounds that are very exudative
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
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
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
What are clinical applications of negative pressure wound healing. (5)
- inflammatory or repair phase only
- exposed bone
- moderate exudation
- large wounds
- reconstructive surgery