Ch 80 - Skin Grafts Flashcards

1
Q

What is the most common donor site for skin grafts?

A

Cranial lower lateral thoracic area

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2
Q

What are the main causes of graft failure?

A
  • Separation
  • Movement
  • Infection

Disrupt the fibrin bonds that bind the graft to the bed, impairing neovascularisation and nutrition of the graft

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3
Q

How can infection cause seperation of the graft from the recipient bed?

A

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)

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4
Q

Which grafts lead to the best cosmetic outcome/best hair regrowth?

A
  • Full thickness sheet grafts
  • Unexpanded mesh grafts
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5
Q

By what time must regeneration overtake degeneration for a graft to survive?

A

By day 7-8

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6
Q

What are the 2 phases of graft adherence?

A
  • 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
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7
Q

What is plasmatic imbibition

A

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

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8
Q

Define inosculation

A

The anastomosis of the cut ends of graft vessels with recipient bed vessels of approx the same diameter
- Most commonly seen between 48-72hr

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9
Q

What is vascular ingrowth?

A

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

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10
Q

What growth factor is elevated in the graft tissue which corresponds with peak vascular ingrowth activity?

A

VEGF

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11
Q

What growth factor is elevated in the graft tissue which corresponds with peak vascular ingrowth activity?

A

VEGF

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12
Q

Describe the expected changes in graft appearance

A
  • 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

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13
Q

List the options for harvesting a split thickness skin graft

A
  • Manual operated graft knife (Goulian-type graft knife, Humby and Watcon graft knife)
  • Scapel blade
  • Power-driver dermatome
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14
Q

How long is splinting required after skin graft placement on a limb?

A

Until the fibrous tissue anchourage is strong enough to withstand shearing strain without capillary rupture (approx 10-14 days)

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15
Q

List some advantages and disadvantages of split thickness grafts

A

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

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16
Q

List some benefits of mesh grafts

A
  • Drainage
  • Flexibility
  • Conformity
  • Expansion
17
Q

What must be done before placement of any full thickness skin graft?

A

Removal of all subcutaneous tissue from graft

18
Q

How do you create a mesh graft?

A
  • 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

19
Q

What is the recommended expansion ratio for dogs and cats?

A

3:1 to 4:1

20
Q

What is the usual cause of infection of a skin graft?
How is it managed?

A
  • Caused by overgrowth of normal skin organisms on abnormal skin
  • Gentle cleaning of surface using 0.05% chlorhexidine with topical broad-spectrum ABx ointment
21
Q

What are the benefits of hyperbaric oxygen therapy in graft healing?

A

NONE! Contraindicated
- less granulation tissue production
- More inflammation
- Less percentage viability
- Only 13% graft viability at 10 days
- Reduced vascular ingrowth

22
Q

What support is there for using NPWT in the acute treatment of skin grafts?

A
  • Earleir appearance of granulation tissue
  • More rapid contraction of mesh holes
  • Earlier adherence
  • Reduced early graft necrosis at day 10 (1% vs 10%)
23
Q

List advantages and disadvantages of mesh grafts

A

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

24
Q

Should full central sutures be placed in full thickness non-mesh grafts?
Why?

A

No - may cause haemorrhage and haematoma formation under a graft with limited drainage

25
Q

List the advantages and disadvantages of a full thickness un-meshed graft

A

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

26
Q

What sized biopsy punch is used for punch graft harvesting?

A

5mm - all SQ tissue must be removed

27
Q

How are pinch and punch grafts placed into the recipient bed?

A
  • 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
28
Q

List advantages and disadvantages of pinch and punch grafts

A

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

29
Q

What is a stamp graft?

A

“Chessboard graft”
Split or full thickness graft cut into squared 0.5-2cm and placed onto recipient bed with 1-10mm space between grafts

30
Q

What have mucosal grafts been described for?

A
  • Replacement of nictitans membrane
  • Extension of hypoplastic prepuce
  • Conjunctival replacement
  • Reconstruction of nasal passage
  • Urethroplasty
31
Q

Where are mucosal grafts harvested from?

A

The buccal or sublingual mucosa (avoiding sublingual salivary duct and sublingual vessels)