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Skin grafts > Skin grafts > Flashcards

Skin grafts Flashcards

1
Q

What is a skin graft? Hows does it differ from a flap?

A

Segment of dermis and epidermis that is completely removed from the underlying skin and replaced in another site.
Grafts essentially dead and rely on neovascularisation for survival
Flaps are living and have blood/lymphatic supply

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2
Q

Classify skin graft according to different sources from which they are obtained

A

autograft : same anima
allograft : different animal same species
xenograft : different species
isograft : between identical twin or F1 hybrid

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3
Q

Classification of grafts according to thickness

A

full thickness: epidermis and dermis

partial thickness: epidermis and split thickness dermis
further classified as: thin, intermediate,or thick, according to how thick dermal layer is.

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4
Q

what are island grafts?

A

small pieces of skin implanted in large field
-process of coverage differs from sheet grafts in that islands rely mainly on migration of keratinocytes from the edges of islands

also called seed grafts

they include: pich, punch, strip, and stamp grafts

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5
Q

primary indication for grafts in small animals?

A

distal limbs where skin tight so no primary closure or local flaps

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6
Q

most common donor site in small animals

A

most common donor site in small animals

can also use lateral trunk, proximolateral forelimb and lateral hind limb

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7
Q

3 most common causes of graft failure?

A
  1. separation of graft from bed
  2. infection: bacterial enzymes and fluid production
  3. movement
    - -disrupts fibrin bond that attaches bed to recip site
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8
Q

Name 2 bacteria that cause graft breakdown and how does this occur?

A

B hemolytic strept and Pseudomonas produce large amounts of plasmin and proteolytic enzymes which disrupt fibrin attachments

pseudomonas also has elastase which degrades elastin

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9
Q

How often should bandages be changed w/ grafts?

A

Every 12-24hrs to every 2-4days

immediate post op bandage should be left in place for 1-2days in order to facilitate adherence.
some surgeons leave this inital bandage on for 3-5d–tobias authors DO NOT recommend this

bandage changes at least 2-3 weeks post-op,
after that light bandage for another 2 weeks–because process of rennervation of the graft

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10
Q

How long does it take for reenervation of graft? what is significance of this?

A

Sensation tarted to reurn 14 days post op, not complete until day 40. can have parasthesia so prone to self trauma so must be protected.

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11
Q

When does hair regrowth occur?

A

2-3 weeks, best with full thickness and unexpanded mesh grafts

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12
Q

What is a power driven dermatome give example

A

Instruments for graft harvest that control depth and can rapidly create uniform split thickness graft

available in electri and nitrogen driven e.g. browns dermatome

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13
Q

Two ways to mesh a graft?

A

with a blade or a meshing block.

an aluminum block with staggerred parallel rows of cutting blade

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14
Q

Ways to obtain seed graft (5 ways)?

A

suture needle, skin hook, or forceps to elevate skin, then cut with blade, or skin punch

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15
Q

In what two donor sites should grafts be placed?

which is better?

A

Either healthy granulation tissue bed
OR
Acute wound with good blood supply

studies report faster vascularization of grafts on fresh tissue than GT

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16
Q

where will graft not take?

A

relatively avascular areas:

  • stratified squamous epithelial tissues
  • heavily irritated tissues
  • avascular fat
  • poorly vascularized or hypertrophic GT
  • bone
  • cartilage
  • tendon
  • nerve
  • excessice/chronic inflammatory process in bed
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17
Q

when should graft regeneration surpass degeneration?

A

approx 7-8 days

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18
Q

List the 4 main stages of graft take

A

adherence
plasmatic imbibition
inosculation
revascularization

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19
Q

Adherance

Describe the two parts

A

soon after placement fibrin strands develop that contract and pull graft to bed

phase 1: attachment depends on fubrn stands which link collagen and elastin. fibrin polymerization results in increased strength. Greatest gain 8 hours post grafting.

phase 2: begins at 72hrs. fibrinous network invaded by fibroblasts, WBCs, conversion to fibrous adhesion starts. continues until complete fibrous union by day 10.

Maturation then results in contraction

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20
Q

Contraction more in thin or thick grafts?

A

Split thickness/ thin grafts

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21
Q

Describe plasmic imbibition and give a timeline of events that occur during this phase

A

graft vessels spasm and constrict when harvested. fluid builds up between graft and bed as bed vessels leak. soon after placement in bed, graft vessels dilate, pulling fibrinogen-free serum and cells into graft via capillary action. this continues until graft is revascularized.

accumulation of Hb and breakdown products gives graft a cyanotic apearance

absorbed fluid diffuses into interstitium of graft, produces edema.
this peaks 48-72 hours post grafting

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22
Q

Describe Inosculation

A

The anastomosis of the cut ends of graft vessels with recient bed vessels of about same diameter.

can begin around 24 hours post, more commonly noted between 48-72 hours

capillary buds for along fibrin network

many make anastamoses but few survive

connections can be initiated either way (graft to bed, bed to graft)

anastamoses inhibits new capillary bud formation in bed. if separation of graft from bed occurs, this inhibition does not occur, and GT formation in bed continues

initally flow is slow when blood begins to flow into the graft on day 3 or 4 post grafting, but resumes normal velocity by day 6

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23
Q

Describe process of vascular ingrowth. which direction? rate?

A

Growth from bed to graft

new capillary ingrowth at rate of 0.5mm/day

initaially tortuous, then become arterioles

VEGF most elevated 5-7d, peak ingrowth

new lymphatics start day 4-5

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24
Q

Describe the colour changes that occur with graft take

A

initially pale
first 2-3 days: purple/red as inosculation begins
light red by 72-96
by day 7-8 entire graft is pink or red if took

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25
Q

what happens if ontly partial thickness survives?

A

in the case of a partial thikness take, may be darkly discolored becuse of ischemic necrosis of epidermis ,but vascularization of dermis. after epidermis sloughs or is debrided, dermis will re-epithelialize.

final appearance is sparsely haired epithelialised skin

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26
Q

Is rein nervation better in full or partial thickness grafts?

A

Full thickness

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27
Q

Can split thickness be used in cats? explain

A

Cats skin is too thin so cannot use

28
Q

Describe steps in prep of wound bed for grafting

A

chronic GT completely excised, replaced by acute healthy GT bed (day 4-5)

epithelium at wound edge is removed

top of healthy GT bed can be scraped OR 0.5-2mm off top can be sharply excised

defect covered with chlorohex soaked gause while graft developed

let natural hemostasis occur in bed

29
Q

What is a weck knife

A

image in tobias
goulian type uses disposable blade and has guard that slides over blade to fix depth

humby and watson are other types of knives

razor blade can be used

30
Q

good depth for split thickness graft

A

0.35mm same as #11 blade

normally 0.38mm with weck

31
Q

harvesting graft, how can you prepare donor site?

A

Can use sterile saline to tent the skin

32
Q

name 4 good donor sites for grafts

A

lateral thorax
thoracolumbar region
proximolateral forelimb
lateral thigh

33
Q

Give 4 features of when placing the graft what you need to do..

A
  1. so that direction of hairgrowth will be same as surrounding tissues
  2. graft may be cut to exact fit, but many surgeons like it to overlap the edges of wound bed by 1-2 cm. the overlapped portion will necrose and can be excised later
  3. edges should be secured with sutures through graft in underlying skin
  4. additional sutures in center to assure good adherence
34
Q

Apart from shitting yourself with fear of failure what can you do about hematomas under the graft?

A

can be removed with q-tip under graft

thrombin or saline soaked solt to irrigate underneath graft before putitng on bandage

after surgery (days) hematoma can be reomved by making an incision in the graft and milking it out, or q tip

35
Q

How long are immobilisation splint used for?

A

2 weeks

36
Q

Advantages of NPWT in grafts? What pressure is used?

A

Advantages with graft take and increased success

  • Increased adherance
  • Provision of O2 at surface
  • Increased angiogenesis
  • Increased removal of exudate / bact
  • Maintenance of beneficial cytokine environment for healing

Pressure of -75mmHg used for grafts

37
Q

Advantages of split over full thickness grafts explain why

A
  1. better viability
    - study noted 89% survival vs. 58% for full thickness grafts on dog forelimbs
    - greater capillary density
    - less distance for for capillaries to traverse
    - shorter distance for diffusion, better plasmatic imbibition
  2. less wound contraction
    - may be better if contraction would be big problem
    - there is actually expansion of the graft
38
Q

disadvantages of split thickness grafts?

A
  1. less durable
  2. sparse hair growth
  3. scaly appearance, may lack sebaceous glands
  4. may require more specialized equipment
39
Q

4 advantages of full thickness mesh graft?

A

drainage
conformity
flexibility
expansion

40
Q

3 indications for mesh grafting

A
  1. allow drainage from a wound with minor exudate/bleeding
  2. cover large skin defects when insufficient donor skin
  3. reconstruct irregular surfaces
41
Q

preparing the mesh graft

A

after harvesting the skin from donor site (using template for measurements)
place on cardboard sq side up, stretched with hypodermic needles
sq tissue must be removed-“defatting”
meshing done with #11 blade
incisions 1-2cm long, 0.5-2cm apart

42
Q

Mesh expansion explain ways in which you can do it..

A

aluminum block with stainless steel blades, graft placed on block and rolled with teflon or nylon roller

expansion occurs in only one directon depending on orientation of blades.

43
Q

what is the best expansion ratio to use?

A

3:1, 4:1 in dogs and cats

44
Q

hyperbaric O2 therapy good for mesh grafts?

A

dogs study:

  • 13% viable at 10d post grafting with O2
  • concurrent admin of deferoxamine (O2 radical scavenger) improved survival to 65%

still way less than expected

some conflicting results i rats and pigs

currently hyperbaric O2 contraindicated as adjunct therapy for grafts

45
Q

List advantages of mesh grafting…

A
  • excellent viability: 90-100% take when well cared for
  • improved drainage
  • conformability
  • full thickness associated benefits
  • disadvantage: excess gt can grow through the slips and up over the graft
46
Q

What are indications for no post op mesh grafting for full thickness graft?

A

where postgraft contraction might result in contracture (like distal limbs, joint surfaces)

small to moderate sized wounds

wounds with minimal expected drainage/exudate

47
Q

Use of drainage with FTG?

A

yes–small closed suction drains
–use butterfly needle to create drain

–can also do stab incisions, but they tend to clot

48
Q

what is the diff between pinch and punch grafts

A

pinch: small pieces of skin cut free
punch: small pieces of skin cut with a punch biopsy

49
Q

What are the indications for pinch and punch grafts?

A 
small limb wounds
contamnated wounds
low grade infected wounds
areas that dont need major durability 
irregular contour
50
Q

How do you obtain punch grafts describe

A

insert 5mm punch at angle of hair follicles

51
Q

placement of pinch grafts–preparation of recipient bed

A

small slits are made in recipient bed, almost parallel to surface of the wound, openings upward
pockets are 2-4mm deep and 5-7mm apart
apply direct digital pressure to keep it in its pocket

52
Q

placement of punch grafts–preparation of recipient bed

A

cylindrical holes 1-2cm apart

4mm punch used to make the holes. q-tip placed in holes for 5 minutes before graft placement for hemostasis

53
Q

Outcome of pinch grafts

A

thin epithelium, scaly, sparly haired, prone to injury

but take well

54
Q

What are strip grafts?

A

5mm wide strips placed in parallel grooves cut in a GT bed. wounds that are parallel to long access on limb are good for these

55
Q

Describe stamp grafts?

A

chessboard grafs.
square patches-05-2cm per side
no particular indication

disadvantages are that may need to cut depressions into GT to keep the grafts from moving or being disturbed by the bandage, and these may bleed alot because of size of grafts.

56
Q

Paw pad grafts describe

A

small segements of full thickness pad tissue –placed into areas of GT that have formed in an absent metatarsal or metacarpal pad.
after grafter, healing via contraction, epithelialization, and hyperplasia forms a durable weight bearing tissue.

indicated when phalangeal fillet wont work

tough in large breed active dogs
grafts are taken as rectangles from other paw pads, and secured into GT bed by 4-0 suture on the corners

57
Q

How do you manage paw pad in post op period

A

donut to take pressure off pad, two mason metasplints incorporated over cast padding

58
Q

Describe two stage technique for pad grafting

A

-option when paw has sustained severe damage requiring amputation of digits at metacarpaophalangeal joint.

Step 1: pad grafts are harvested and implanted in the lateral thoracic area-each graft is sutured to cutaneous trunci mm. bandaged for 7 days,

Step 2: bipedicle pouch flap containing grafts is elevated and animals paw is wrapped in flap

the advantage of this technique is that SQ layer of graft can replace the fibroelastic pad tissue

59
Q

types of mucosal grafts have been described in small animal medicine

A 
nicititans, 
hypoplastic prepuce, 
conjunctival replacement
nasal passage
urethroplasty
60
Q

Where can mucosal grafts be placed?

A

GT bed,
acute wound bed
dermal side of freshly raised transposition flap

61
Q

How to prepare nasal passage for Mucosal graft?

A

place silicone stents to encourage tubular formation of GT

62
Q

Where do you harvest mucosal grafts from?

A

buccal / sublingual surfaves

63
Q

Describe a conj graft and procedure

A

graft sutured to dermal side of transpoition flap that will be used to reconstruct eyelid. then flap returned to its original position for 4-7 days, then eslevated, transposed, and sutured into defect

64
Q

how do you do a nasal mucosa replacement?

A

10 days after silicone tubes are placed, they are removed.

mucosal grafts are sutured with submucosal side out!! around the tubes, with traction sutures placed.

tube is inserted, and graft and tube are sutured into place. sutures are placed through skin and graft to create new mucocutaneous junction at rostral end. tube acts as stent–removed at 7 days.

65
Q

advantages and disadvantages of mucosal grafts

A

thin, easily vascularized, heal quickly

shrink alot, can shrivel, very delicates, difficult to handle

Skin grafts (1 decks)

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