Ch 76 - Open Wounds Flashcards
What are the 4 phases of wound healing?
- Inflammation
- Debridement
- Repair
- Maturation
What are the four ‘steps’ of wound healing
- Formation of fibrin-platelet plug
- Recruitment of WBCs to protect from infection
- Neovascularisation and cellular proliferation
- Tissue remodeling
What are the most common locations of a decubital ulcer?
- Greater trochanter
- Lateral elbow
- Lateral hock
Define contamination, colonisation and infection
- Contamination - The presence of microbes on a surface
- Colonisation - Surface microorganisms are replicating
- Infection - Invasion and replication of microorganisms within the tissue
What microbial burden has been associated with a higher rate of infection? What time does it typically take to reach this level?
10^5 CFU/g
Within 6 hours
What is a more relevant calculation of microbial burden?
Microbial burden = (Number of microorganisms x Virulence) / Host Resistance
How does the production of granulation tissue of cats differ to that of dogs?
- Open wounds in cats produce significantly less granulation tissue and is more likely to have a peripheral, rather than central, distribution
At 21 days after wounding, how does epithelialisation and total healing differ in dogs anc cats?
Dogs: epithelialisation 89%, total healing 98%
Cats: epithelialisation 34%, total healing 84%
What are some potential causes of open wounds which fail to progress towards healing?
- Systemic disease (uraemia, herpatic dz, DM, cushings, FIV)
- Malnutrition
- Local tissue hypoxia and ischaemia (Normovolaemia must be maintained, blood transfusin if anaemic)
- Bacterial colonisation
- Altered cellular and stress response
- Repetitive trauma
- Presence of necrotic tissue
- Tension
What are some options to improve wounds which are incapable of forming granulation tissue?
- Omental flaps
- Muscular flaps
- Vascular skin flap for closure
Is tap water hyper-, iso-, or hypotonic?
Hypotonic
What pressure is generally recommended for high pressure irrigation?
How is this best achieved?
5-8 psi
16-22g needle onto a fluid administration set of a 1L bag of fluids under pressure of 300mmHg
List hyperosmotic wound dressings
- Hypertonic saline (20%)
- Honey
- Sugar
List some hydrophilic dressings
- Hydrogel
- Hydrocolloid
- Alginate
Is saline or a balance electrolyte preparation recommended for initial wound preparation? Why?
Balanced electrolyte prep
- Saline is slightly hypoosmolar and is cytotoxic to fibroblasts
What antiseptics can be used in the wound?
- 0.05-0.1% chlorhexidine
- 0.1 - 0.01% povidone-iodine
No detergents! (Cytotoxic)
Why is debridement important?
Presence of contaminants causes inflammation and devitalised tissue acts as a medium for microbial growth
What are the 2 braod categories of wound debridement?
- En Bloc Debridement (and then primary closure)
- Layered debridement
What tissues are not well vascularised? How is this overcome?
- Cortical bone - forage
- Excess fat - removed
- Intact fascia - debrided to expose underlying muscle and improve vascularization (fasciotomy or fasciectomy)
What substances do most enzymatic debridement agents contain?
- Trypsin
- Collagenase
- Papain
- Urea
How do nonenzymatic debridement dressings work?
What are some examples?
- 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
How is hydrogen peroxide produced by honey? At what concentration?
- Hydrogen peroxide is produced by the action of glucose peroxidase (within the honey) on glucose.
- Forms at a very low concentration of 0.003%
What antimicrobial effects are provided by Honey?
What is the inhibin number of medical grade Honey?
- 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
Other than is antimicrobia properties, what other effects of Honey may enhance wound healing?
- 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
What type of maggots are used for wound debridement?
Maggots of the green blow fly Lucilia Sericata
Can destroy healthy epithelium - MUST be protected
What is the underlying principle of moist wound healing?
Application of a hydrophilic (moisture retentive) dressing to maintain the cellular and cytokine-rich exudate at the wound surface
What is typically included in a triple antibiotic ointment?
- Bacitracin zinc
- Neomycin sulphate
- Polymixin B sulphate
How does incorporation of silver into alginate dressing effect its function?
- Increased antimicrobial activity
- Improved binding affinity for elastase, MMP-2, TNF-a, and IL-8
- Further inhibited production of free radicals
How do bioscaffolds work?
What wounds are they recommended for?
- 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/wounds
What is chitosan?
What are its reported functions?
Chitosan is a lineal copolymer of linked Beta glucosamine and N-acetly-D-glucosamine
Reported functions:
- ENhance the action of inflammatory cells
- Increase production of granulation tissue through upregulation of TGF-B, PDGF, fibroblast production and IL-8 production
List 2 growth factor-containing agents which coulf be used in wound management?
- rhPDGD-BB
- Autologous PRP
What is the recommended porosity of the foam and recommended pressures for negative pressure wound management in small animals?
- 400 - 600 mcm pore foam
- Recommended -125mmHg for foam-based or -80mmHg for gauze based systems
What are the purported benefits of negative pressure wound therapy?
- Improve wound perfusion
- Reduce oedema
- Stimulate granulation tissue formation
- Decrease bacterial colonisation
- Remove exudate
Expression of which growth factors/cytokines may be increases in negative pressure wound therapy?
- VEGF and FGF-2 (experiment on rats)
- IL-8 and VEGF (humans)
How may NPWT be beneficial for skin grafting? Used at what pressure?
Benefits:
- Stibilisation of the graft
- Reduce fluid accumulation under the graft
- Prevent dessication
- Possibly prevent bacterial contaminations
Pressure -65 to -75mmHg
What are the effects of NPWT on bacterial burden?
Unclear….
- Upregulation of IL-8 and IL-1B may trigger accumulation of neutrophils and thus accelerate bacterial clearance
