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Wound Healing Inhibition Factors - Donkey (view source)

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In clinical practice healing can be achieved in one of three ways:
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* Primary or first intention healing.
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* Secondary or second intention healing.
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* Delayed primary healing.
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==Primary or first intention healing==
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This is the mechanism that occurs when the edges of a wound can be closely
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apposed. Most surgical wounds rely upon this mechanism. In a non-infected
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surgical wound, healing is reliably accomplished in a predictably short time
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(usually 7 to 14 days).
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Elective surgical wounds are probably the current ‘gold standard’ of
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wound management, but there are major differences between surgical
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wounds and accidental injuries (see Table 1 and Table 2 below) and so there are
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almost inevitable differences in healing between the surgical situation and
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the accidental wound.
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[[Image:Wounds table.jpg|center|thumb|450px|<small><center>(Image courtesy of [http://drupal.thedonkeysanctuary.org.uk The Donkey Sanctuary])</center></small>]]
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[[Image:Table healing.jpg|center|thumb|450px|<small><center>(Image courtesy of [http://drupal.thedonkeysanctuary.org.uk The Donkey Sanctuary])</center></small>]]
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In primary wound healing, the various tissue structures involved are
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managed by suturing to restore very close normal anatomical relations. The
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underlying tissues are closed carefully to minimize dead space, provide good
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support for the skin wound itself and to restore function as far as possible.
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Although in most cases this will involve closure of the wound by sutures
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or staples, this is not a prerequisite. Close apposition of the margins of the
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wound using adhesive tabs or even simply by bandaging in a suitable fashion
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may have the same effect and may indeed be considered to be advantageous
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in that there is no foreign matter in the wound. Minimal granulation tissue
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formation and epithelial migration are required and so the wound heals
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rapidly. Usually within seven to ten days the wound margin is sufficiently
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strong to permit removal of skin sutures.
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Few accidental/ traumatic wounds are amenable to this approach because
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there are almost always some complicating factors. Where it is possible
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however to create a ‘surgical’ situation from a traumatic injury, wounds will
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heal with an excellent result both functionally and cosmetically.
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==Secondary or second intention healing==
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Second intention healing is the natural way for a wound to heal. Wounds
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too extensive or contaminated to suture, or those in which primary closure
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has failed, must heal in this way.
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In second intention healing, a '''healthy bed of granulation tissue is
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required before epithelialisation can proceed'''. The quality of the granulation
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tissue bed and the anatomical site has a strong influence on the rate of
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healing of the wound. Because there is a necessary delay in the development
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of the granulation tissue bed, there is an inevitable delay in healing.
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Major factors in the process of second intention healing are the size of
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the wound, the anatomical location and the extent of '''complicating factors''':
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* Over 70% of donkey wounds are complicated by failure to heal and chronic inflammation
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* Second intention healing relies upon the inflammatory response; the longer the wound takes to heal, the greater will be the scar and the possible cosmetic and functional deficits
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* The anticipated problems associated with second intention healing may encourage clinicians to try to close wounds by primary union, although this can be ill-advised
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<u>Most traumatic wounds create circumstances that preclude primary
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closure</u> and so second intention healing is a major clinical aspect of wound
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management in donkeys. Factors that disturb normal corrective processes
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inevitably complicate and delay wound healing. Early recognition of healing
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difficulties allows prompt correction; ideally factors that will result in
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non-healing should be recognized pre-emptively at the time of wounding,
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but inevitably some will not be apparent until later and possibly when the
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wound has failed to heal.
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The owner of a donkey with one or more of these factors can be given
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rational advice on the likely prognosis and the time-scale for healing. Most
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non-healing wounds are preventable by suitable management in the early
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stages after injury and others are understandable or predictable. Failure
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to recognize potential reasons for failure of healing in a fresh wound, or
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delayed presentation, mean that the wound will become chronically inflamed
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and so the healing process will be unnecessarily prolonged.
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==Delayed primary healing==
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This is a useful procedure that combines the early stages of second intention
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healing with a primary intention healing after a few days. It is applicable to
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a few wounds but it is a very rewarding process. If closure is delayed for
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72 to 96 hours, only a minimal risk of infection exists. The method allows
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contaminated wounds in which immediate closure may lead to infection to
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heal faster than would be the case for second intention healing.
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The wound is '''initially cleaned and debrided, but is not closed'''. After a
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variable time (usually two to four days), the wound is '''surgically debrided to
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remove any demarcated tissues and closed by suture as for first intention'''
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healing. There is an inevitable delay in the healing process but, where it
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is applicable, the healing time is usually shorter than second intention
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healing.
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The '''clinical advantages'' of delayed primary healing are considerable:
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* The wound can be assessed for causes of failure of healing at various stages, allowing the best time for closure to be chosen
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* Acute inflammatory responses and natural debridement can take place before it is ‘driven’ towards healing without the development of a difficult and prolonged chronic inflammatory process
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The '''disadvantages''' include the need for repeated procedures and an inevitable increase in scarring when compared to first intention healing, even when the time delay is relatively insignificant.
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==References==
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* Knottenbelt, D. (2008) The principles and practice of wound mamagement In Svendsen, E.D., Duncan, J. and Hadrill, D. (2008) ''The Professional Handbook of the Donkey'', 4th edition, Whittet Books, Chapter 9
     
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Author, Donkey, Bureaucrats, Administrators
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