9.1 Wound healing and repair, 9.2 accidental wound management

4 phases of wound healing and main cells involved

• Coagulation

  • Platelets

• Inflammation

  • Neutrophils

• Migration/proliferation

  • Macrophages

• Remodeling

  • Fibroblasts and lymphocytes

When do neutrophils peak post wounding?

Peak of inflammation = 2 days post wounding

What 3 substances are released upon platelet degranulation?

• TGF-beta (promotes ECM)

• PDGF

• Fibronectin (makes ECM by forming dimers)

Major proinflammatory enzyme for prostaglanding production

COX-2

• Promotes TNF which recruits neutrophils + monocytes

5 roles of macrophages in wound healing

• Phagocytosis of microbes and wound debris (via collagenase/elastase)

• Cell recruitment and activation

• Angiogenesis (VEGF)

• Matrix synthesis regulation (GF, cytokines, enzymes, PGs)

2 types of macrophages and role in wound healing

• M1 → inhibits proliferation with arginine

• M2 → stimulates proliferation with arginine

  • Shifts from M1

Why is wound healing harder in old age? (2)

• Slower epithelial outgrowth from sweat glands

  • Proliferation is unaltered

• Lower keratinocyte cohesion and greater cell spacing

  • Thinner keratinised tissue

3 things produced by the neodermis during the proliferation phase

• ECM

• Growth factors and TNF-a (cytokines)

• Proteases

3 things which are formed when growth factors interact with ECM

• Collagens

• Fibronectin

• Heparin rich proteoglycans (sequester GFs and release them when needed)

Describe how angiogenesis happens in a new wound. (6)

• Pericytes surround endothelial cells

• Nearby cells make FGF/VEGF (from inflammatory phase of hypoxia) → new capillaries sprout

• Endothelial cells make proteases to digest matrix → ‘drill hole’ making way to blood vessels

• Endothelial cells migrate towards stronger concentrations of growth factors (where hypoxia is)

• Leaky angiogenesis tissue changes integrity

  • Initially leaky → therefore granulation tissue is usually oedematous

• Fibrin clot degraded via matrix metalloproteinase

5 roles of fibroblasts

• ECM production (bond intracellular actin)

• Growth factor and cytokine production (EGF, FGF, CTGF, PDGF, activin)

• Angiogenesis (EGF, FGF, activin)

• Protease release

• Trigger migration and proliferation

List 2 factors contributing to proud flesh formation on a horse.

Proud flesh = granulation tissue due to aborted wound healing process

• Constant movement of limbs

• Poor vascularisation → oxidative stress

Therefore cells constantly stuck in angiogenesis and constantly make matrix

8 types of wound aetiology

• Incision = aseptic scalpel blade cut

• Laceration = sharp tearing and cutting

• Abrasion (graze)

• Puncture

• Degloving = skin sheared and stripped from extremity

• Crushing = often delayed effect

• Decubital ulcers = body prominence (shoulder/hip) compresses and necroses tissue

• Burns = systemic stability more worrying

3 classes for wound duration

• Class 1 = <6h (min. contamination of clean laceration)

  • >6h = infection → >10000 bacteria/gram

• Class 2 = 6-12h (significant contamination)

• Class 3 = >12h

2 characteristics of clean surgery

• Surgical wound

• No break in asepsis

3 characteristics of clean contaminated surgery

• Minor break in asepsis

• Little to no associated leakage

• Opening of respiratory, GI, or urogenital system

3 characteristics of contaminated surgery

• GI or urogenital system infectious spillage

• High bacterial burden wound (e.g. mouth or perineum)

• Major break in asepsis

2 characteristics of dirty surgery

• Presence of infection, foreign material or necrosis

• (Accidental) perforation into respiratory, GI or urogenital tracts

  • Deliberate opening = clean contaminated

4 things to do for patient wound stabilisation

• Control haemorrhage with firm pressure

• Temporarily cover wound with sterile dressing and secure with bandage

  • NOT tourniquet

• Systemic antimicrobials

  • If patient stable = do swab first

• Address wound once the CV system is stable

3 ways to clean a wound

• Grossly contaminated = tap

  • Volume > substance

• Isotonic saline

• Hartmans

3 types of wound irrigation solutions

• Prontosan (polyhexamethylene biguanide)

  • Good V biofilm, lingers in wound for lasting effect

• HOCL

  • Free radicals V microbes

• (Chlorhexidine or iodine)

  • Cytotoxic = don’t use even when dilute!

3 nonselective and 3 selective ways of debridement

Nonselective

• Surgical removal

• Irrigation

• Mechanical debridement (wet to dry)

Selective

• Biological (maggots)

• Enzymatic (collagenase)

• Autolytic (use body moisture = used in dressings for smooth degranulation)