Ch 80 SKin grafts Flashcards
What is the most common donor site for skin grafts?
Cranial lower lateral thoracic area
skin graft
- separated from all vascular and nervous supply
- depends on the reestablishment of vascular supply through engraftment
- full thickness: epidermis and the entire dermis,
- split thickness: epidermis and varying partial thicknesses of the dermis
- island grafts rely mainly on keratinocytes that proliferate and migrate from the edge of the islands to cover the recipient site
- 3 causes of graft failure
SIM
- separation of the graft from the bed
- infection
- movement.
- disrupt the fibrin bonds > impairing revascularization and nutrition of the graft.
- Fluid (e.g., seromas, hematomas, or exudation) mechanically separates the graft from its bed.
- Infection > exudate production but also because bacterial enzymes may cause dissolution of fibrin attachments. - β-Hemolytic streptococci and Pseudomonas spp. produce large amounts of plasmin and proteolytic enzymes
Which grafts lead to the best cosmetic outcome/best hair regrowth?
Full thickness sheet grafts
Unexpanded mesh grafts
By what time must regeneration overtake degeneration for a graft to survive
By day 7-8
post-op bandages
- prevention of postoperative trauma to the graft
- left undisturbed for 24 to 48 hours; this helps to facilitate graft adhesion
- if the graft is not examined until the third to fifth postoperative day, its fate is usually unalterable by that time
- wide mesh nonadherent (petrolatum impregnated) cellulose acetate pad can be placed over the graft and stapled to surrounding healthy skin (to reduce being dislodged)
- 2 to 3 weeks
- engraftment) is well established by 14 days, the process of reinnervation of the graft may take several weeks (may experience paresthesia or dysesthesia)
Where Grafts Will Take
- healthy granulation tissue
- acute wound surface that is vascular enough to produce granulation tissue (after tumor resection) > more rapid vascularization was noted for grafts placed on fresh tissue than on grafts placed on a granulation tissue recipient site
- free from infection and debris
Where Grafts Will Not Take
- stratified squamous epithelial surface
- heavily irradiated tissues
- avascular fat
- chronic poorly vascularized or hypertrophic granulation tissue
- bone, cartilage, tendon
- denuded nerve
- infected wounds, crushed tissues, and chronic ulcers are poor recipient sites for grafting
- not appropriate > manage as open wound or use vascularised APF
Process of Engraftment (Graft Take) - 4 phases
- graft begins to degenerate immediately after being detached
- Regeneration initially progresses more slowly than degeneration; for the graft to survive, regeneration must overtake degeneration by 7-8th day.
- Graft survival depends on early reestablishment of sufficient circulation to provide nutrients and to dispose of metabolic waste products
Adherence
plamatic imbibition
inosculation
vascular ingrowth
What are the 2 phases of graft adherence?
Phase I - Attachment largely dependant on fibrin strands, forming links between collagen and elastin on each surface. Greatest gain over the initial 8 hours (fibrin polymerization results in progressive gain in strength)
Phase II - Begins at approx 72hr. Fibrinous network is invaded by fibroblasts, leucocytes and phagocytes which begin the conversion into a fibrous adhesion. Continues to gain strength until a complete fibrous union is formed at day 10
What is plasmatic imbibition
Nourishment of the graft until it revascularised via dilation of graft vessels, pulling fibrinogen-free, serum-like fluid and cells (erythrocytes and neutrophils) which have accumulated between the graft and recipient bed, into the vessels by capillary action
- Absorbed fluid diffuses into interstitial space cause peak oedema at 48-72hr
- hb breakdown products gives a purplish or cyanotic appearance
Define inosculation
leads to reestablishment of early graft blood flow by connecting the native graft vasculature to the sprouting donor bed vasculature.
- anastomosis of the cut ends of graft vessels with recipient bed vessels of approximately the same diameter
- Most commonly seen between 48-72hr
- anastomoses have an inhibitory effect on capillary bud proliferation in the recipient bed > stops granulation tissue proliferation
- Initially perfusion is slow , normalises by day 5-6
What is vascular ingrowth?
Revascularisation of grafts by the ingrowth of new vessles from the bed into the graft
- Grow at approx 0.5mm/day
- Vessel maturation begins within 48hr
- leads to the stable anchoring
- under cytokine control > VEGF days 5 to 7, corresponding with the peak of vascular ingrowth activity
- lymphatic drainage of the graft by the fourth or fifth day
Describe the expected changed in graft appearance
- Initially pale
- First 48hr, inosculation begins and associated oedema and vasc congestion - red to dark purple
- 72-96hr - lighter reddish hue
- 7-8 days - entire graft red-to-pink if survival is complete
- Day 14 - more normal, pale pink colour
Areas of avascular necrosis are persistently pale
Areas of ischaemic necrosis may appear black
Reinnervation
Reinnervation is better in full-thickness grafts than in split-thickness grafts.
- animals show signs of paresthesia as grafts reinnervate > at least 1 month protection (bandage, ecollar) recommended
- Because the skin of a cat is so thin, split-thickness grafts are not indicated
Graft Bed Preparation
- healthy granulation, epithelium at wound edge is removed
- The top of healthy granulation tissue may be lightly scraped or wiped with a gauze sponge
- The defect is covered with a moist surgical sponge while the graft is harvested, ideally with 0.05% chlorhex (aseptically prepared)
- let natural hemostasis occur before applying the graft
split-thinkness graft harvest
- freehand with a manually operated graft knife or scalpel blade.
- power-driven dermatomes
- 0.35 mm = ideal thickness for partial-thickness grafts in dogs.
- Holes may inadvertently be cut > allow drainage from beneath the graft
- Good donor sites: lateral thorax, the thoracolumbar region, the lateral thigh
Graft Placement
- ensure direction of hair growth same
- graft to overlap the edge of the defect by up to 1 to 2 cm. (overlapped > undergo avascular necrosis, excised later)
- edge secured with sutures or staples
- Additional sutures should be placed in the central field of the graft to ensure good contact with the recipient bed
How long is splinting required after skin graft placement on a limb?
Until the fibrous tissue anchourage is strong enough to withstand shearing strain without capillary rupture (approx 10-14 days)
What must be done before placement of any full thickness skin graft?
graft prep
Removal of all subcutaneous tissue from graft (defatting)
- scissors or scalpel
- high-pressure hydrosurgical handpiece
exposed dermis will have a cobblestone appearance
List advantages and diadvantages of pinch and punch grafts
Advantages:
- Simple
- No special equipment
- Take quickly and reliably
- Allow drainage
- Withstand infection well
Disadvantages
- Excessive bleeding may float graft out of recipient pocket or delay revascularisation
- Poor cosmetic appearance - sparce hair coat, dry and scaly
- Delicate and prone to injury
Paw Pad Grafts
- After grafting, healing via contraction, epithelialization, and hyperplasia forms a durable weight-bearing tissue
- indicated when loss of some digits precludes use of a phalangeal fillet
- large active dogs, pad grafts are less likely to be successful
- Single-Stage Technique
- Two-stage technique involving pad grafts and a bipedicle pouch flap has been described for autografting the pads to a paw stump
resurface reconstructed nasal passages
- recipient area must be prepared for the grafts, granulation tissue initally grow around silicone rubber (Silastic) tubes
- ## approximately 10 days after placing the silicone tubes, a mucosal graft is prepared and placed
Preputial Reconstruction
- Because of their thinness, mucosal grafts revascularize and heal quickly
- as soon as the graft is healed in place, which may be as early as 7 to 10 days, the mucosal-lined preputial tube should be constructed
- Bilateral single-pedicle advancement skin flaps will be advanced to cover the mucosal graft lining.
