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Wound Healing Inhibition Factors - Donkey (view source)
Revision as of 11:39, 20 February 2010
, 11:39, 20 February 2010no edit summary
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In clinical practice healing can be achieved in one of three ways:
* Primary or first intention healing.
* Secondary or second intention healing.
* Delayed primary healing.
==Primary or first intention healing==
This is the mechanism that occurs when the edges of a wound can be closely
apposed. Most surgical wounds rely upon this mechanism. In a non-infected
surgical wound, healing is reliably accomplished in a predictably short time
(usually 7 to 14 days).
Elective surgical wounds are probably the current ‘gold standard’ of
wound management, but there are major differences between surgical
wounds and accidental injuries (see Table 1 and Table 2 below) and so there are
almost inevitable differences in healing between the surgical situation and
the accidental wound.
[[Image:Wounds table.jpg|center|thumb|450px|<small><center>(Image courtesy of [http://drupal.thedonkeysanctuary.org.uk The Donkey Sanctuary])</center></small>]]
[[Image:Table healing.jpg|center|thumb|450px|<small><center>(Image courtesy of [http://drupal.thedonkeysanctuary.org.uk The Donkey Sanctuary])</center></small>]]
In primary wound healing, the various tissue structures involved are
managed by suturing to restore very close normal anatomical relations. The
underlying tissues are closed carefully to minimize dead space, provide good
support for the skin wound itself and to restore function as far as possible.
Although in most cases this will involve closure of the wound by sutures
or staples, this is not a prerequisite. Close apposition of the margins of the
wound using adhesive tabs or even simply by bandaging in a suitable fashion
may have the same effect and may indeed be considered to be advantageous
in that there is no foreign matter in the wound. Minimal granulation tissue
formation and epithelial migration are required and so the wound heals
rapidly. Usually within seven to ten days the wound margin is sufficiently
strong to permit removal of skin sutures.
Few accidental/ traumatic wounds are amenable to this approach because
there are almost always some complicating factors. Where it is possible
however to create a ‘surgical’ situation from a traumatic injury, wounds will
heal with an excellent result both functionally and cosmetically.
==Secondary or second intention healing==
Second intention healing is the natural way for a wound to heal. Wounds
too extensive or contaminated to suture, or those in which primary closure
has failed, must heal in this way.
In second intention healing, a '''healthy bed of granulation tissue is
required before epithelialisation can proceed'''. The quality of the granulation
tissue bed and the anatomical site has a strong influence on the rate of
healing of the wound. Because there is a necessary delay in the development
of the granulation tissue bed, there is an inevitable delay in healing.
Major factors in the process of second intention healing are the size of
the wound, the anatomical location and the extent of '''complicating factors''':
* Over 70% of donkey wounds are complicated by failure to heal and chronic inflammation
* 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
* 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
<u>Most traumatic wounds create circumstances that preclude primary
closure</u> and so second intention healing is a major clinical aspect of wound
management in donkeys. Factors that disturb normal corrective processes
inevitably complicate and delay wound healing. Early recognition of healing
difficulties allows prompt correction; ideally factors that will result in
non-healing should be recognized pre-emptively at the time of wounding,
but inevitably some will not be apparent until later and possibly when the
wound has failed to heal.
The owner of a donkey with one or more of these factors can be given
rational advice on the likely prognosis and the time-scale for healing. Most
non-healing wounds are preventable by suitable management in the early
stages after injury and others are understandable or predictable. Failure
to recognize potential reasons for failure of healing in a fresh wound, or
delayed presentation, mean that the wound will become chronically inflamed
and so the healing process will be unnecessarily prolonged.
==Delayed primary healing==
This is a useful procedure that combines the early stages of second intention
healing with a primary intention healing after a few days. It is applicable to
a few wounds but it is a very rewarding process. If closure is delayed for
72 to 96 hours, only a minimal risk of infection exists. The method allows
contaminated wounds in which immediate closure may lead to infection to
heal faster than would be the case for second intention healing.
The wound is '''initially cleaned and debrided, but is not closed'''. After a
variable time (usually two to four days), the wound is '''surgically debrided to
remove any demarcated tissues and closed by suture as for first intention'''
healing. There is an inevitable delay in the healing process but, where it
is applicable, the healing time is usually shorter than second intention
healing.
The '''clinical advantages'' of delayed primary healing are considerable:
* The wound can be assessed for causes of failure of healing at various stages, allowing the best time for closure to be chosen
* 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
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.
==References==
* 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