Wound Healing Flashcards
Stages of wound healing
haemostasis, inflammation, proliferation, and remodelling.
Primary Intention
Healing by primary intention occurs in wounds with dermal edges that are close together (e.g a scalpel incision). It is usually faster than by secondary intention, and occurs in four stages:
Haemostasis – the action of platelets and cytokines forms a haematoma and causes vasoconstriction, limiting blood loss at the affected area
The close proximity of the wound edges allows for ease of clot formation and prevents infection by forming a scab
Inflammation – a cellular inflammatory response acts to remove any cell debris and pathogens present
Proliferation – cytokines released by inflammatory cells drive the proliferation of the fibroblasts and the formation of granulation tissue
Angiogenesis is promoted by the presence of growth mediators (e.g VEGF), allowing for further maturation of the granulation tissue; the production of collagen by fibroblasts allows for closure of the wound after around a week
Remodelling – collagen fibres are deposited within the wound to provide strength in the region, with the fibroblasts subsequently undergoing apoptosis
The end result of healing by primary intention is (in most cases) a complete return to function, with minimal scarring and loss of skin appendages.
Secondary Intention
Healing by secondary intention occurs when the sides of the wound are not opposed, therefore healing must occur from the bottom of the wound upwards.
It occurs in the same four stages as primary intention:
Haemostasis – a large fibrin mesh forms, which fills the wound
Inflammation – an inflammatory response acts to remove any cell debris and pathogens present
There is a larger amount of cell debris present, and the inflammatory reaction tends to be more intense than in primary intention
Proliferation – granulation tissue forms at the bottom of the wound
This is an important step, as the epithelia can only proliferate and regenerate once granulation tissue fills the wound to the level of the original epithelium; once the granulation tissue reaches this level, the epithelia can completely cover the wound
Remodelling – the inflammatory response begins to resolve, and wound contraction can occur
Myofibroblasts are vital cells in secondary intention. They are modified smooth muscle cells that contain actin and myosin, and act to contract the wound; decreasing the space between the dermal edges. They also can deposit collagen for scar healing.
Keloid scarring
An uncommon complication from wound healing (particularly in people with darker skin), are keloid scars, whereby there is excessive collagen production, leading to extensive scarring. Outside the wound edges.
This can occur in both primary and secondary intention healing.
Factors affecting wound healing
Local factors:
Type, size, location of wound.
Local blood supply
Infection
Foreign material or contamination
Radiation damage
Systemic factors:
Age
Co-morbidities (DM, CVD)
Nutritional deficiency (vit c)
Obesity
Four classes of contamination
Clean
Clean-Contaminated
Contaminated
Dirty
Clean wound
Elective, non-emergency, non-traumatic, and primarily closed, with GI, biliary, and GU tracts remaining intact
Infection rate 2.1%
Clean - Contaminated wound
Urgent or emergency case that is otherwise clean
Elective opening of respiratory, GI, biliary, or GU tract with minimal spillage and not encountering infected urine or bile
3.3% infection rate
Contaminated wound
Gross spillage from GI tract or entry into biliary or GU tract (in the presence of infected bile or urine)
Penetrating trauma <4 hours old or a chronic open wound to be grafted or covered
6.4% infection rate
Dirty wound
Purulent inflammation (e.g. abscess)
Preoperative perforation of respiratory, gastrointestinal, biliary, or genitourinary tract, or a penetrating trauma >4 hours old
7.1% infection rate
