Lecture 7-8, Wounds and wound management

Question 1

Skin consists of 2 main layers

Answer 1

Epidermis and dermis

Question 2

Epidermis

Answer 2

• General composition of the outer layer
• Avascular keratinized stratified squamous epithelium
• Protective function
• Thicker in areas with less hair (nose, footpads)

Question 3

Dermis

Answer 3

• Underneath the epidermis
• Thicker, vascular (blood and lymph vessels)
• Tough fibroelastic tissue
• Supportive and nourishing function
• Rests on a layer of loose connective tissue - subcutis (hypodermis)
• Subcutis is composed of adipose tissue, the cutaneous trunci muscle
  and direct cutaneous arteries and veins

Question 4

Blood supply of the skin

Answer 4

• Different from humans (musculocutaneous vessels) → different reconstructive techniques
• Direct cutaneous arteries (dogs and cats – most of the skin)
• Parallel to the skin in the hypodermis
• Arise from perforator arteries
• Musculocutaneous arteries
• Perpendicular to the skin surface
• Supply small portions of the skin
• Subdermal plexus is of major importance

Check the pic!

Question 5

Wound

Answer 5

Injury to the body that results in disruption of the continuity of the body structure

• Can be classified in several ways (clean, contaminated etc.)
• The main principles of wound healing are the same for all types

Question 6

Classification of wounds

Answer 6

Open and closed

Question 7

Types of open wounds

Answer 7

• Surgical incision
• Laceration
• Abrasion
• Avulsion
  
  • Degloving
  • Shearing
• Puncture
  
  • Bite/sting: cat/dog; snake; insect;
    tick
  • Firearm
• Burn: thermal; chemical; electrical;
  radiation
• Pressure sores
• Cast- and bandage-related

Question 8

Types of closed wounds

Answer 8

• Contusion
• Hematoma
• Crush injury
• Hygroma

Question 9

Incisional injuries and lacerations

Answer 9

• Surgical or traumatic
• Edges generally clean and free
  from tissue damage
• Tend not to get infected
  
  • Minimal contamination
  • Sufficient bleeding to decrease
    tissue colonization
  • Rarely significant damage to
    surrounding tissues
• Deep wound – physical
  exploration/imaging!
• Surgical management

Question 10

Abrasions

Answer 10

• Superficial damage not extending
  beyond the dermis
• Frictional forces when moving parallel to a rough surface, usually at speed
• Combination of graze, abrasion and avulsion
• Generally heavily contaminated
• Severe abrasions with ongoing tissue necrosis might become avulsions
• Surgical vs open wound management (usually open)

Question 11

Avulsions (degloving injuries)

Answer 11

• Avulsion - the separation of tissue from their deeper attachments (usually including muscle)
• Degloving - skin and deeper tissues torn from an extremity, just as a glove is removed from the hand
  (mechanical vs physiological)
• Defects often extensive and complex
• May be initially free of bacterial contamination, but without appropriate wound management rapid colonization and infection of necrotic tissue will occur
• Degloved skin should be preserved where possible
• Surgical/open wound management/in combination

Question 12

Avulsions (shearing injuries)

Answer 12

• Usually involve loss of deeper tissues (including skin, tendons,
  muscle, possibly bone)
• The joints of the distal limb frequently exposed
• Heavily contaminated with bacteria and debris
• Extremely prone to infection
• Need for orthopedic surgery?
• Open wound management

Question 13

Puncture wounds

Answer 13

• Caused by any sharp object that pierces the skin to create a relatively
  small deficit or hole
• Bite wounds (also insects/snakes); impalement (full penetration); oropharyngeal; firearm wounds (lead!?)
• Contamination/infection variable
• Damage assessment!
• Risk of abscessation

Question 14

Burns

Answer 14

• Caused by extreme temperature (hot or cold) or by contact with a
  chemical substance, electricity or radiation
• (1st, 2nd, 3rd degree)→ thickness (damage)
• ‘’Rule of nines“? (not accurate in veterinary medicine)
• May require prolonged treatment, monitoring (inpatient)
• Treatment depends on the case

Question 15

Pressure sores

Answer 15

• Caused by pressure typically on the elbows and hocks of large dogs
• Open or closed wounds
• Open sores prone to infection (bones and joints)
• Hygromas (best treated medically)
• Medical/surgical treatment

Question 16

Cast- and bandage-related wounds

Answer 16

• Iatrogenic wounds are common
  
  • Ischemic injury due to overtight
    application of bandaging
  • Inadequate padding of
    vulnerable areas
  • Excessive exercise, allowing
    bandage slippage
  • Wet or dirty bandages (higher
    risk of bacterial strikethrough and
    infection)
• Serious wounds may result in the loss of digits or limbs

Question 17

4 distinctive phases of wound healing

Answer 17

• Acute inflammatory phase
• Debridement phase (breakdown)
• Proliferation phase (reparation)
• Maturation phase (remodelling)
• Depending on the type of wound and its classification, one or several
  phases of wound healing can be accelerated, delayed or complicated
• Several phases at the same time

Question 18

Inflammatory phase of wound healing

Answer 18

• Characterized by (5): redness, pain, heat, swelling, loss of function
• Lasts approximately 5 days
• After wounding:

1. Filling with blood and lymph (from damaged vessels)
2. Immediate vasoconstriction of the damaged vessels (lasts 5-10 min)
3. Vasodilation (dilutes toxic substances, provides nutrients and results in blood clot)
4. Epithelial cells begin to migrate from the wound periphery onto the
   exposed tissue
5. The blood clot dries to form a scab
6. White blood cells leaking into wounds initiate the debridement phase

Question 19

Debridement phase of wound healing

Answer 19

• Approximately 6-12 hours after injury
• Formed inflammatory exudate provides all the necessary phagocytic cells and proteolytic enzymes to deal with the demarcation
• An exudate (of WBC, dead tissue, wound fluid) forms on the wound
• Necrotic tissue impedes wound healing
• Phase ends with the rejection of nonvital tissue
• Sometimes combined with inflammatory phase

Question 20

Proliferation phase of wound healing

Answer 20

• Repair phase
• Approximately 3-5 days after injury
• Signs of inflammation subside
• Neovascularization
• Divided into 3 processes:
  
  • Granulation
  • Wound contraction
  • Epithelialization

Question 21

Proliferative phase (granulation) of wound healing

Answer 21

• Red irregular surface
• Fragile tissue
• Functions as a barrier to infection and a scaffold for migrating
  epithelial cells
• Capillary network occurs through sprout formation of capillary
  endothelial cells on the wound surface
• Granulation tissue formed at each wound edge at a rate of 0.4 to 1
  mm/24h

Question 22

Proliferation phase (wound contraction) of wound healing

Answer 22

• The surface and the cavity of the wound become smaller
• Adjacent skin pulled closer to the centre of the wound
• Especially loose skin
• Begins 5-9 days after wounding
• Stops when edges connected/tension too high
• Risk of contracture
• Thinning of the surrounding skin
  (temporary)

Question 23

Proliferation phase (epithelialization) of wound healing

Answer 23

• Proliferation of basal epithelial cells from the adjacent skin edges and their moving over and adhesion to the surface of the wound
• Prevention of excessive formation of granulation tissue
• Total duration can range from days to weeks
• Surface of the wound that has become epithelialized is known as the epithelial scar (thin and fragile)

Question 24

Maturation phase of wound healing

Answer 24

• Increasing strength of the scar as a result of remodelling of tissue
• The newly formed collagen is arranged parallel to the tension lines of the skin
• Total duration can range from weeks to a year or even longer
• No or insufficient hair follicles, sweat and sebaceous glands, poor
  movability and elasticity and an absence of pigment
• The healed wound will never regain skin’s original strength

Question 25

Acute and chronic wounds

Answer 25

• In chronic wounds there is a lack of orderly progression through the
  four phases of wound healing
• An important cause of chronic wounds is infection, which causes a
  sustained inflammatory phase

Question 26

Factors influencing wound healing

Answer 26

• Malnutrition
• Radiation
• Use of corticosteroids
• Underlying metabolic diseases

Question 27

Differences between dogs and cats

Answer 27

• Intact skin of cats less perfused in comparison to dogs
• Breaking strength of a wound 50% less in cats 7 days after primary
  closure
• Formation of granulation tissue takes longer in cats and first appears only at the wound edges
• Pseudohealing more common in cats

Question 28

Wound management

Answer 28

• Many will heal naturally
• Some need intervention (large, necrotic, infected)

Management:

1) Stabilization of the patient!

1) Stopping the bleeding (pressure; special dressings for minor wounds
[adrenaline-soaked gauzes etc.])

2) Reduction of the level of contamination, clipping the area (ideally up to 4-6 hours after wounding to prevent bacterial infection)