Chapter 76: Open Wounds

Question 1

What are the 4 phases of wound healing?

Answer 1

• Inflammation
• Debridement
• Repair
• Maturation

Question 2

What are the four ‘steps’ of wound healing?

Answer 2

• Formation of fibrin-platelet plug
• Recruitment of WBCs to protect from infection
• Neovascularisation and cellular proliferation
• Tissue remodeling

Question 3

What are the most common locations of a decubital ulcer?

Answer 3

• Greater trochanter
• Lateral elbow
• Lateral hock

Question 4

Define contamination, colonization and infection:

Answer 4

Contamination - The presence of microbes on a surface
Colonization - Surface microorganisms are replicating
Infection - Invasion and replication of microorganisms within the tissue

Question 5

What microbial burden has been associated with a higher rate of infection? What time does it typically take to reach this level?

Answer 5

10^5 CFU/g
Within 6 hours

Question 6

What is a more relevant calculation of microbial burden?

Answer 6

Microbial burden = (Number of microorganisms x Virulence) / Host Resistance

Question 7

How does the production of granulation tissue differ between cats and dogs?

Answer 7

• Open wounds in cats produce significantly less granulation tissue and are more likely to have a peripheral, rather than central, distribution of it

Question 8

At 21 days after wounding, how does epithelialization and total healing differ in dogs and cats?

Answer 8

Dogs: epithelialization 89%, total healing 98%
Cats: epithelialization 34%, total healing 84%

Question 9

What are some (8) potential causes of open wounds which fail to progress towards healing?

Answer 9

• Systemic disease (uremia, hepatic disease, Diabetes, Cushings, FIV)
• Malnutrition
• Local tissue hypoxia and ischemia (Normovolemia must be maintained, blood transfusion if anemic)
• Bacterial colonization
• Altered cellular and stress response
• Repetitive trauma
• Presence of necrotic tissue
• Tension

Question 10

What are some options to improve wounds which are incapable of forming granulation tissue?

Answer 10

• Omental flaps
• Muscular flaps
• Vascular skin flap for closure

Question 11

Is tap water hyper-, iso-, or hypotonic?

Answer 11

Hypotonic

Question 12

What pressure is generally recommended for high pressure irrigation?
How is this best achieved?

Answer 12

16-22g needle onto a fluid administration set of a 1L bag of fluids under pressure of 300mmHg

Gives you 7-8 psi

Question 13

List hyperosmotic wound dressings:

Answer 13

• Hypertonic saline (20%)
• Honey
• Sugar

Question 14

List some hydrophilic wound dressings:

Answer 14

• Hydrogel
• Hydrocolloid
• Alginate

Question 15

Should you use saline or should you use a balanced electrolyte preparation for initial wound preparation? Why?

Answer 15

Balanced electrolyte prep
- Saline is slightly hypotonic and is cytotoxic to fibroblasts

Question 16

What antiseptics can be used in the wound?

Answer 16

0.05 - 0.1% chlorhexidine
0.1 - 0.01% povidone-iodine

No detergents! (Cytotoxic)

Question 17

Why is debridement important?

Answer 17

Presence of contaminants causes inflammation and devitalised tissue acts as a medium for microbial growth

Question 18

What are the categories of wound debridement?

Answer 18

• En Bloc (and then primary closure)
• Layered debridement
  -Nonsurgical (autolytic)

Question 19

What tissues are not well vascularized? How is this overcome?

Answer 19

Cortical bone - forage
Excess fat - removed
Intact fascia - debrided to expose underlying muscle

Question 20

What substances do most enzymatic debridement agents contain?

Answer 20

• Trypsin
• Collagenase
• Papain
• Urea

Question 21

How do nonenzymatic debridement dressings work?
What are some examples?

Answer 21

• Draw exudate and accompanying debris out of the wound
• Dehydrate microorganisms and have a cidal and inhibitory effect

Hypertonic saline dressings. Sugar-, Honey- and Dextran-soaked dressings

Question 22

How is hydrogen peroxide produced by honey? At what concentration?

Answer 22

• Hydrogen peroxide is produced by the action of glucose peroxidase (within the honey) on glucose.
• Forms at a very low concentration of 0.003%

Question 23

What antimicrobial effects are provided by Honey?
What is the inhibin number of medical grade Honey?

Answer 23

• Hydrogen peroxide production
• Oxygen-derived free radicals
• Phytochemicals (phenols and organic acids)
• Acidic pH (3.2 - 4.5)

The inhibin number is the amount of dilution to which the honey will retain its antibacterial activity

Question 24

Other than is antimicrobial properties, what other effects of honey may enhance wound healing?

Answer 24

Reduction of inflammation due to anti-oxidant content
Stimulation of B- and T-lymphocyte proliferation
Stimulation of phagocytic activity
Stimulation of cytokine release from monocytes

Question 25

What type of maggots are used for wound debridement?

Answer 25

Maggots of the green blow fly Lucilia Sericata

Can destroy healthy epithelium - MUST be protected

Question 26

What is the underlying prinicple of moist wound healing?

Answer 26

Application of a hydrophilic (moisture retentive) dressing to maintain the cellular and cytokine-rich exudate at the wound surface
This facilitates debridement, granulation, and epithelialization

Question 27

What is typically included in a triple antibiotic ointment?

Answer 27

• Bacitracin zinc
• Neomycin sulfate
• Polymyxin B sulfate

Question 28

How does incorporation of silver into alginate dressing effect its function?

Answer 28

• Increased antimicrobial activity
• Improved binding affinity for elastase, MMP-2, TNF-a, and IL-8
• Further inhibited production of free radicals

Question 29

How do bioscaffolds work?
What wounds are they recommended for?

Answer 29

• Provides a substrate for extracellular matrix formation
• Stimulates matrix deposition, angiogenesis and epithelialisation due to collagenous and growth factor content

Recommended for use with chronic, indolent ulcers

Question 30

What is chitosan?
What are its reported functions?

Answer 30

Chitosan is a lineal copolymer of glucosamine

Reported functions:
- Enhances the action of inflammatory cells
- Increase production of granulation tissue through upregulation of TGF-B, PDGF, fibroblast production and IL-8 production
*works best with silver

Question 31

What is the recommended porosity of the foam and recommended pressures for negative pressure wound management in small animals?

Answer 31

400 - 600 um pore foam
Recommended -125mmHg for foam-based or -80mmHg for gauze based systems

Question 32

What are the purported benefits of negative pressure wound therapy?

Answer 32

• Improve wound perfusion
• Reduce edema
• Stimulate granulation tissue formation
• Decrease bacterial colonization
• Remove exudate

Question 33

Expression of which growth factors/cytokines may be increased in negative pressure wound therapy?

Answer 33

• VEGF and FGF-2 (experiment on rats)
• IL-8 and VEGF (humans)

Question 34

How may NPWT be beneficial for skin grafting? Used at what pressure?

Answer 34

Benefits:
- Stabilization of the graft
- Reduce fluid accumulation under the graft
- Prevent desiccation
- Possibly prevent bacterial contaminations

Pressure -65 to -75mmHg

Question 35

What are the effects of NPWT on bacterial burden?

Answer 35

Unclear….
- Upregulation of IL-8 and IL-1B may trigger accumulation of neutrophils and thus accelerate bacterial clearance