Inflammation and Healing

1) INFLAMMATION

Inflammation is the normal reaction of tissue to damage, including physical, chemical and infectious agents, e.g.

Mechanical - bites, RTA's, kicks and other blows to the body, crush injuries.

Chemical - corrosive substances such as acids and alkalis, irritants such as petrol, oil, tar.

Physical - Heat, electric shock, radiation burns.

Infectious - Bacterial or viral invasion e.g. respiratory viruses cause inflammation of the lining of the respiratory tract.

Allergic reactions - e.g. the skin inflammation associated with atopy, Rheumatoid arthritis

Inflammation is recognised by four key elements:

The Cardinal Signs

HEAT - PAIN - REDNESS - SWELLING

What happens in inflammation:

Damage causes the release of chemicals called immune mediators from the injured cells. These cause dilation of blood vessels (Heat and Redness), which then leak lymph into the damaged area (Swelling). The chemicals also stimulate nerve fibres (Pain) to draw the animal's attention to the injury and to encourage it to stop doing whatever caused the injury. Depending on the area involved, there may also be stimulation of secretion of mucus. Blood clotting factors are also stimulated in case there has been sufficient damage to cause haemorrhage. White blood cells are attracted to clean up any infection (hence pus).

Leakage of fluid from the body into an area of inflammation gives rise to a variety of EXUDATES:

Serous - watery lymphatic exudate consisting mostly of serum

Purulent - Containing large numbers of white blood cells

Sanguineous - Containing blood

Mucoid - Containing mucus secreted from the damaged tissue

Fibrinous - containing fibrin - a blood clotting protein which solidifies at sites of trauma

Because inflammation releases so many chemical mediators into the bloodstream, it may cause systemic signs such as fever, tachycardia, tachypnoea.

Treatment of inflammation:

Remove the cause if possible. If trauma has occurred, appropriate first aid will reduce inflammation, e.g. immobilisation, compresses.

Chronic inflammation relies on identifying the cause accurately, e.g. allergies.

2) WOUND HEALING

The idea of inflammation is to lead to healing. After an injury, the aim of treatment is to encourage wounds to heal. There is a significant role to be played by the Veterinary Nurse in this treatment. Wounds can be divided into surgical and non-surgical.

Surgical wounds are clean or clean-contaminated. Clean wounds involve full asepsis with no contamination from the body. Clean-contaminated involve surgery on naturally contaminated body sites, e.g. the alimentary tract.

Traumatic wound are either contaminated - fresh trauma, or infected - old wounds with an established infection. In both cases there was no aseptic technique at the time of injury

Treatment of wounds

1) Cleaning.

In surgical situations, clipping and prepping is the mainstay of aseptic technique. In non-surgical wounds, the amount of cleaning necessary depends on the situation. Physically contaminated wounds benefit from flushing to clean out physical debris (bits of the road), contaminated exudates (pus, fibrin), dead tissue (may need surgical removal).

It is important to remember that flushing solutions can be dangerous in some areas - for instance hibiscrub in ears. It is safest to use sterile saline as a flushing agent. Do not use excessive pressure as this can force contamination deeper into the wound.

2) Dressing

The aims of dressings are to reduce movement of healing surfaces and provide support, prevent contamination, absorb exudates, prevent trauma by the patient, and provide an appropriate environment for healing.

Special dressing types are used in specific cases. In particular, in contaminated wounds or where there is poor skin closure, wet dressings are used to maintain a good environment for healing whilst allowing migration out of the wound of toxins and debris. Current favoured wet dressings are the gel types, which contain lots of moisture. Calcium alginate dressings are sometimes used in heavily exuding areas as they swell and absorb the exudate. These dressings require frequent changing as they will soak the external bandaging, and also they start to smell rather quickly, although this is due to bacteria within the gel not to problems with the wound itself.

Types of Healing

1) First intention

The aim of suturing is to produce first intention healing, in which the wound closes by epithelial migration across the defect, and granulation tissue ( produced by dermal fibroblast cells) is confined to the layers below the epidermis. This leads to minimal scarring.

2) Second intention

Occurs when a wound breaks down or there is no possibility of co-apting the wound edges. Granulation tissue produced by the fibroblasts proliferates and fills the wound. Eventually the epithelium grows across the granulation surface. The granulation tissue then shrinks back causing contraction. This can be a real problem if the wound is in an area which needs a range of skin movement e.g. over joints. Healing by second intention is a less desirable form of wound closure, but some injuries, such as de-gloving RTA's may rely on it. Skin grafting (see below) may follow second intension granulation.

Wound Breakdown (Dehiscence)

Is the commonest problem with surgical (first intention) wounds. Often due to infection, but contributory factors are suture technique, site of wound, post operative care and other health problems - e.g. Cushing's disease (hyperadrenocorticism) causes wound breakdown as it suppresses the inflammatory response.

Post-operative nursing care of a wound is vital, and should include dressing inspection, patient monitoring (pain, fever) and Elizabethan collars or similar where necessary.

Drains

Drains are often necessary in wounds where there is contamination or exudate into a cavity or into surgical dead space.

Closed drains are used to drain a body cavity in which there is no need for communication with the outside world, e.g. chest drains. They may be connected to suction or allowed to drain normally under gravity / pressure.

Open drains are tubes left in wounds to allow drainage to the outside world, either freely or into a dressing, e.g. penrose drains

ADVANTAGES OF DRAINS:

allow dead space to close without the need for suturing

allow exudate to flow away from wound

allow monitoring of flow / secretions

DISADVANTAGES OF DRAINS

Are foreign bodies

May allow retrograde flow into wound

Need to be made of suitable material

3) FISTULAE AND SINUSES

A fistula is a tract connecting two epithelial (or endothelial) surfaces (one of which may be the skin). The subject appears here because fistulae may be a complication of surgery.

A recto-vaginal fistula, for example connects the rectum and vagina. Fistulae are sometimes the result of trauma, such as a fistula which connects the gastrointestinal tract to the outside world after healing of a perforating injury. They require surgical repair of both surfaces.

A sinus is a blind- ending tract which discharges into a body cavity or through the skin, and is almost always the result of a piece of foreign material at the end of the cyst. This may be a foreign body, e.g. twig or grass seed, or it may be related to surgery e.g. a fracture repair screw, or a suture. Cure depends on surgery to remove the offending material.

4) ABSCESSES AND ULCERS 

An abscess is an accumulation of pus at a localised site where there has been invasion of infection within a tissue (cellulitis is like an abscess spread thinly throughout a tissue). The pus is composed of white cells- particularly polymorphs which congregate at the site in response to factors released by damaged tissue. Lots of the polymorphs in pus are dead, after having engulfed harmful bacteria. The toxins released by bacteria in an abscess can cause the animal to be ill with a fever etc. This means it's a good idea to cause the abscess to rupture, releasing the pus and toxins and allowing healing. This is done by lancing or by applying hot compresses. Antibiotics are given to kill the bacteria.

A cold abscess forms when there is pus accumulation in the absence of active infection- either the infection has been cured but pus has formed, or the pus is forming in response to, say, a sterile foreign body. These need draining to remove them.

Ulcers are effectively superficial inflammation and loss of surface (epithelial) tissue, e.g. corneal ulcers, stomach ulcers, skin ulcers. They are often secondarily infected, and treatment means removal of the inciting cause, and appropriate care to allow healing. In the case of skin ulcers this often means dressings.

4) SKIN GRAFTS

Because healing by second intention can lead to excessive scarring and contraction, skin grafting is often used to cover large areas of skin loss.

The main problem with grafting is the establishment of a blood supply to the moved area of skin. There are two ways of doing this:

a) Pedicle grafts. A full piece of skin is cut from an area leaving a connecting strip of skin to the area (the pedicle) which carries blood supply to the graft.. The graft is then sutured over the recipient area. The donor site is chosen to allow enough loose skin to close the hole.

b) Free grafts. A piece of skin is harvested and placed onto a bed of granulation tissue on the wound. Both sites must be clean and healthy. The graft may be taken as Full thickness (including dermis - good tissue, but formation of new blood supply is difficult) or partial thickness (less dermis included- good access to blood supply at the new site, but poorer skin quality.) Partial thickness grafts are taken using a dermatome. Full thickness grafts may not be taken as complete sheets, but may be implanted as pinches of skin or a mesh. THE KEY TO SUCCESSFUL SKIN GRAFTS IS A DRESSING WHICH PREVENTS MOVEMENT AND ABSORBS EXUDATES.

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