Wound Healing Flashcards
Why is the panniculus muscle a critically important landmark when performing reconstructive cutaneous surgery?
failure to identify and preserve it will lead to loss of blood supply and wound dehiscence
What blood supply do dogs and cats have that humans don’t?
direct cutaneous arteries that run parallel to the skin and terminate as the deep, middle, and superficial plexuses
Why is the subdermal plexus so important?
provides the major blood supply to the skin and is therefore of most importance with regards to cutaneous surgery; must be preserved when undermining or dissecting skin
What are the 5 stages of wound healing?
- Coagultion: <5 minutes
- Inflammatory stage: 0-24 hrs
- Debridement stage: 2-5 days
- Proliferative or repair stage: 5-21 days
- Maturation stage: 21 days - 2 years
What happens in the coagulation phase?
-
primary coagulation: damaged endothelium exposes neg charged collagen to platelets and vWF, forming the platelet plug
- occurs in < 5 minutes in healthy dog/cat
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secondary coagulation: clotting factors form fibrin meshwork
- intrinsic (12, 11, 9, 8)
- extrinsic (3, 7)
- common (10, 5, 2 ,1)
What happens during the inflammatory stage?
- 0-48 hours
- incr vascular permeability, extravasation of cellular/non-cellular blood components to form stable fibrous plug
- marked by infiltration of neutrophils (incr #s for first 24-48hrs) and macrophages (predominate 2-5d after injury)
Why are macrophages critical for uncomplicated wound healing?
they not only degrade and remove organic material, but also modify the extracellular milieu and synthesize fibronectin, which is important for wound repair
What occurs during the debridement stage?
- 2-5 days
- removal of necrotic tissue and elimination of infection
- carried out by neutrophils and macrophages
- involves: pressure lavage, sharp dissection of necrotic tissue, adherent bandages
- end is characterized by influx of fibroblasts (max # at 7-10d), speeding up formation of granulation tissue and collagen deposition
- period of minimal wound strength - lag phase
What is the phase where the veterinarian has the largest impact on wound healing?
debridement stage
Why is the debridement stage referred to as the lag phase of wound healing?
because the majority of wound strength is provided by the suture material and pattern used to close the defect
What occurs during the proliferative stage?
- 5-21 days
- influx of fibroblasts and rapid accumulation of type-1 collagen and angiogenesis > formulation of granulation tissue
- wound gets tensile strength from type-1 collagen accumulation (14-21d) - log phase
- epithelialization - epithelial cells migrate across wound defect until like cells tough each other (contact inhibition)
What does it mean for a wound to heal by second intention?
- closure occurs by contraction (5-7d after injury) of wound via specialized myofibroblasts (1mm/day)
- this continues until skin edges meet and halts the process
What occurs during the maturation stage?
- 21 days - 2 years
- period of collagen remodeling, reorientation, and cross-linking
- second lag phase of wound healing - relatively minimal increases in tensile strength are accomplished
- collagen fibers reorient in linear fashion parallel to lines of mm and gravitational tension
What are some intrinsic factors influencing wound healing?
- hypoproteinemia - decr fibrous tissue deposition
- anemia and blood loss - limit tissue O2 delivery
- malnutritition - same as hypoproteinemia
- uremia - reduces rate/quality of collagen deposition; down-regulates epithelization
- diabetes mellitus - relative periph tissue ischemia
- hyperadrenocorticism - delayed wound healing
- infection - prolongs debridement stage
- antibiotics
What are extrinsic factors that affect wound healing?
- Type of injury
- Foreign material
- irradiation
- antiseptics
What are the differences between crushing, shearing, and laceration injuries?
Crushing injuries cause severe vascular injury and devitalization and appropriate debridement is critical
Lacerations are precise injuries with little collateral tissue destruction - much less susceptible to infection and significant tissue debridement isn’t typically necessary
T or F: you should almost always close a bite wound upon presentation
False; closure almost always contraindicated and should be avoided
What are the effects of tissue irradation?
increased susceptibility to infection (leukocyte death), sloughing of epithelium (loss of germinal epithelium), and failure of proliferation (fibroblast death)
Why is the use of antiseptics for lavage and wound treatment contraindicated in most cases?
they are lethal to fibroblasts and leukocytes and they inhibit epithelialization and granulation tissue formation
What is the difference between the 3 different classes of wounds (duration classification)?
- Class 1: clean lacerations of 0-6 h duration w/ minimal contamination (most amenable to primary closure)
- Class 2: 6-12 h duration w/ significant contamination (avoid primary closure)
- Class 3: >12 h duration w/ gross contamination (avoid primary closure)
What is the difference between clean, clean-contaminated, contaminated, and dirty wounds?
- Clean: surgical procedures not entering resp or GI tracts, UTI, no contamination or break in sterile technique (e.g. castration, spay); infxn rate - 5%
- Clean-contaminated: sx of the GI (no gross contamination of peritoneal cavity) or resp tracts, or minor break in aseptic technique; infxn rate - 10%
- Contaminated: acute inflammation (no pus/infxn) or gross dumping of ingesta from SI/LI into peritoneal cavity; infx rate - 30%
- Dirty: wound with devitalized tissue, organic material and/or pus representing active infection or chronicity
What are two things you should pay close attention to when evaluating a patient’s wound?
vascularity and neurologic function; if these are absent, healing and return to function may not ever occur and amputation of tissues may be necessary
What are appropriate indications for drain use in wound healing?
abscess, pocketing, vast dead space
Define primary closure
surgical closure of wounds within the golden period (<6 h); typically indicated for clean/sharp wounds e.g. lacerations
- allows wound healing to proceed with a significant reduction in time for all phases of healing
Define delayed primary closure
surgical closure of a wound after the golden period but before the appearance of granulation tissue; for recent traumatic wounds like dogs bites or HBC, decreases likelihood of infection
- reduction in the time necessary for wound contraction and re-epithelialization
Define late secondary closure
- closure of a wound by surgical intervention following the proliferation phase (after granulation tissue is present)
- generally used for wounds that are more contaminated and have greater soft tissue damage
- lower risk of infection than primary/delayed primary closure, but typically results in less mobile skin and greater tension on the suture line
What is second-intention healing?
leaving the wound open to heal without any surgical intervention; depends entirely on neovascularization and matrix remodeling to restore tissue bulk, wound contraction to re-establish normal tissue tension/to reduce scar size
