Ch 80 - Skin Grafts Flashcards
What is the most common donor site for skin grafts?
Cranial lower lateral thoracic area
What are the main causes of graft failure?
- Separation
- Movement
- Infection
Disrupt the fibrin bonds that bind the graft to the bed, impairing neovascularisation and nutrition of the graft
How can infection cause seperation of the graft from the recipient bed?
Bacterial enzymes may cause dissolution of fibrin attachments
- Beta-haemolytic Strep and Pseudomonas produce large amounts of plasmin and proteolytic enzymes
- Pseudomonas also degrade elastin due to production of elastase (elastin facilitates adhesion through its adherence to fibrin)
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
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
- 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 revascularises 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
Define inosculation
The anastomosis of the cut ends of graft vessels with recipient bed vessels of approx the same diameter
- Most commonly seen between 48-72hr
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
What growth factor is elevated in the graft tissue which corresponds with peak vascular ingrowth activity?
VEGF
What growth factor is elevated in the graft tissue which corresponds with peak vascular ingrowth activity?
VEGF
Describe the expected changes 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
List the options for harvesting a split thickness skin graft
- Manual operated graft knife (Goulian-type graft knife, Humby and Watcon graft knife)
- Scapel blade
- Power-driver dermatome
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)
List some advantages and disadvantages of split thickness grafts
Advantages
- Better viability than full thickness (89 vs 58% survival)
- Ingrowing vessels have less distance to travel
- Shorter diffusion distance
- Greater explansion
Disadvantages
- Less durable and more subject to trauma
- Absent or sparse hair regrowth
- Dry appearance due to lack of sebaceous glands
- Expensive equiment
List some benefits of mesh grafts
- Drainage
- Flexibility
- Conformity
- Expansion
What must be done before placement of any full thickness skin graft?
Removal of all subcutaneous tissue from graft
How do you create a mesh graft?
- Use a #11 blade
- parallel rows of staggered incisions
- each incision 1-2cm long and spaced 0.5-2cm apart
ALternatively can use a mesh graft explansion unit
What is the recommended expansion ratio for dogs and cats?
3:1 to 4:1
What is the usual cause of infection of a skin graft?
How is it managed?
- Caused by overgrowth of normal skin organisms on abnormal skin
- Gentle cleaning of surface using 0.05% chlorhexidine with topical broad-spectrum ABx ointment
What are the benefits of hyperbaric oxygen therapy in graft healing?
NONE! Contraindicated
- less granulation tissue production
- More inflammation
- Less percentage viability
- Only 13% graft viability at 10 days
- Reduced vascular ingrowth
What support is there for using NPWT in the acute treatment of skin grafts?
- Earleir appearance of granulation tissue
- More rapid contraction of mesh holes
- Earlier adherence
- Reduced early graft necrosis at day 10 (1% vs 10%)
List advantages and disadvantages of mesh grafts
Advantages
- Excellent viability (90-100% take)
- Improved drainage
- Improved conformability
- Additional stabilisation as granulation tissue grows into holes which also provide a vascular supply to lateral aspect of mesh holes
DIsadvantages:
- Excess granulation may grow through holes and cover top of graft
Should full central sutures be placed in full thickness non-mesh grafts?
Why?
No - may cause haemorrhage and haematoma formation under a graft with limited drainage
List the advantages and disadvantages of a full thickness un-meshed graft
Advantages
- Become pliable and movable
- Resist trauma
- More like normal skin
- Contraction is minimal
- Provide good protection
- No expensive equipment required
Disadvantages
- Do not survive as well as split-thickness grafts in the presence of infection
- Require drainage to survive as well as meshed grafts
What sized biopsy punch is used for punch graft harvesting?
5mm - all SQ tissue must be removed
How are pinch and punch grafts placed into the recipient bed?
- Pinch: Small slits made into granulation bed, approx 2-4mm deep and wide and 5-7mm apart, made at 20-30 degree angle to surface. Each individual graft is tucked deep into a pocket
- Punch - 4mm biopsy punch used to make holes in granulation tissue approx 1-2cm apart in staggered rows. Cotton tipped applicator placed in holes for 5 mins for haemostasis prior to placement of individual punch grafts
List advantages and disadvantages 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
What is a stamp graft?
“Chessboard graft”
Split or full thickness graft cut into squared 0.5-2cm and placed onto recipient bed with 1-10mm space between grafts
What have mucosal grafts been described for?
- Replacement of nictitans membrane
- Extension of hypoplastic prepuce
- Conjunctival replacement
- Reconstruction of nasal passage
- Urethroplasty
Where are mucosal grafts harvested from?
The buccal or sublingual mucosa (avoiding sublingual salivary duct and sublingual vessels)
