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Acute wounds: an overview of the physiological healing process

VOL: 100, ISSUE: 04, PAGE NO: 50

Marion Richardson, BD, CertEd, RGN, RNT, DipN, is senior lecturer and programme leader, emergency nursing, University of Hertfordshire

When an injury occurs and the skin is damaged, the process of tissue repair begins immediately, but some wounds can take up to two years or more to heal completely. Healing is usually categorised into stages to aid understanding of the complex physiological processes that are occurring.

 

When an injury occurs and the skin is damaged, the process of tissue repair begins immediately, but some wounds can take up to two years or more to heal completely. Healing is usually categorised into stages to aid understanding of the complex physiological processes that are occurring.

 

 

However, it is a continuous process and different parts of a wound may be at different stages of healing at any one time.

 

 

For the purpose of clarity, three distinct phases will be highlighted in this article and the physiological activity within each phase will be explained. A recent article by Richardson (2003) offers a review of the structure and functions of skin.

 

 

The inflammatory phase
This phase begins immediately after injury and lasts between two and five days. It is essential that the body restricts the amount of blood loss from the wound and haemostasis characterises the early part of this phase.

 

 

Immediately after injury, the wound bleeds and histamine and adenosine triphosphate (ATP), released from the damaged tissues, attract white blood cells to the area (Hinchliff, 1996). Blood vessel ends then constrict and the clotting cascade is triggered. The blood in the wound begins to gel as platelets stick together forming a clot (Staiano-Coico et al, 2000). This helps to prevent entry of micro-organisms into the wound.

 

 

During the clotting process a protein, fibrin, forms a mesh within the clot in which blood cells become trapped, forming a stronger clot (Dealey, 1999). Where the clot is exposed to air, the surface dries and a scab is formed, providing a temporary seal to the wound.

 

 

Inflammation also occurs during this phase. Prostaglandins (hormone-like substances that act as mediators in the inflammatory process) are released in response to the trauma (Hinchliff, 1996) and cause local vasodilation.

 

 

This increases the blood supply to the site of injury, and gaps in the endothelium (the layer of cells that line the blood vessels) allow blood cells to pass into the interstitial spaces to clear the debris and begin the process of repair. Neutrophils (a type of white blood cell) invade the site and begin the phagocytic process of engulfing and digesting bacteria and contaminants (Staiano-Coico et al, 2000).

 

 

In the later part of the inflammatory stage, monocytes are transformed into macrophages. The macrophages move along the damaged dermis, consuming debris and microbes. They also secrete growth factors, which are vital for the proliferation stage of healing.

 

 

Basal keratinocytes from the epidermis begin to move along the open edges of the wound to protect the deeper exposed tissues (Staiano-Coico, 2000).

 

 

At this stage the wound is red, hot, swollen and painful. This process of inflammation is an essential part of the healing process and should not be subdued with anti-inflammatory drugs (Holt, 2000).

 

 

The proliferative phase
During days two to 21, there is great activity within a wound. Fibroblasts from the blood move along the fibrin threads (Tortora and Grabowski, 2003) and produce immature collagen, which is laid down in the wound, forming a matrix known as the extracellular matrix (ECM).

 

 

Macrophages promote the formation of new blood vessels (Flanagan, 1998) and new capillaries grow into the ECM bed from the endothelial cells of the damaged blood vessels so that the healing wound now has its own blood (and oxygen) supply.

 

 

Oxygen encourages endothelial cells to divide and replicate (Flanagan, 1998). The resultant granulation tissue is not strong (Staiano-Coico et al, 2000) but increases in strength as the capillaries reduce in number and the clot dissolves.

 

 

Wound contraction begins to occur once the wound is full of granulation tissue. Myofibroblasts are produced, which penetrate the ECM and pull the wound edges together (Ehrlich and Rajaratnam, 1990).

 

 

Epithelial cells proliferate, change shape and begin to migrate across the wound surface to form a new surface of epithelial tissue (Calvin, 1998). These cells can travel from their point of origin until they meet across the wound (Garrett, 1997) and do this most readily across a moist surface (Winter, 1962).

 

 

All of this activity can make the wound feel very itchy but the temptation to scratch should be resisted as it only disrupts the delicate tissues and hinders the regeneration and processes of repair.

 

 

The remodelling phase
Over the next two years, the skin regains its strength. The ECM degrades and is resynthesised (Moore, 1999). Collagen continues to be laid down in the wound but becomes more organised (mature collagen). Its strong fibres increase the tensile strength of the wound. Once the epidermis has reached its normal thickness, the scab sloughs off (Tortora and Grabowski, 2003).

 

 

Scar tissue is only ever about 80 per cent as strong as the original skin - it is fibrous and rather inflexible and contains few blood vessels (Calvin, 1998). Sebaceous and sweat glands, damaged hair follicles, and badly damaged muscles and nerves rarely heal fully and are replaced by fibrous tissue (Martini and Bartholomew, 2003).

 

 

The nurse’s role in the management of acute wounds
The healing process outlined above occurs as long as it is not delayed or arrested. There are a number of ways in which the nurse can expedite this process by ensuring that conditions for healing are optimised. Decisions need to be made about when and whether to close the wound and whether the wound is or is likely to become infected with micro-organisms. Giving patients reasoned information about wound care can enable them to participate in this process.

 

 

Deciding whether and when to close the wound
It would be sensible to assume that the smaller the gap between the tissue surfaces of an acute wound, the faster the healing process would be and that all wounds should therefore be closed, for example with sutures, as soon as possible. But not all wounds are suitable for immediate (or primary) closure and it is worth considering some of the factors that necessitate caution and delay (Box 1).

 

 

As a general rule, infected wounds should not be closed immediately (Gottrup,1999). It could be argued that all wounds other than surgical incisions should be considered contaminated but certainly any wound that has been in contact with saliva (human or animal), faeces or any purulent exudates should be treated with caution and thoroughly cleaned before closure is attempted.

 

 

Infection is much more likely in wounds where patients do not present for treatment until six or more hours after the injury (Edlich and Reddy, 2001). In the case of deep wounds, this may mean that closure is delayed or that antibiotic therapy is necessary. Gottrup (1999) suggests that it is safe to close clean wounds and wounds to the face after the six-hour limit.

 

 

Wounds caused by compression (such as pressure sores or crush injuries) or tension are 100 times more susceptible to infection than those caused by shearing forces (Edlich and Reddy, 2001) because of the concomitant damage to the underlying tissues.

 

 

Wounds caused by crush injuries should be treated with extra care as infection may occur and healing may be delayed or difficult due to the damaged blood supply. The presence of foreign bodies in a wound also increases the risk of infection.

 

 

Wounds where there is considerable tissue loss are not suitable for closure (Miller and Dyson, 1996) as it is not possible to appose the skin edges without causing further trauma to the skin and underlying tissues (Calvin, 1998).

 

 

If the risk of infection is high, wounds that are more than six hours old should be left open and covered with an appropriate dressing after assessment (Dealey, 1999). This is known as healing by secondary intention.

 

 

Superficial wounds will heal perfectly well in this way if kept free from contamination.

 

 

Deeper wounds, or wounds where cosmetic results are important, may be closed once the resistance to infection is established (four days or more after the injury) (Dealey, 1999). This is known as delayed primary closure.

 

 

Deciding whether to give antibiotic and/or antitetanus therapy
Antibiotics Contamination of a wound with micro-organisms may delay healing (Dealey, 1999) and have serious consequences. Part of the process of wound assessment will be deciding whether antibiotic or antitetanus therapy is indicated. Wounds that are particularly prone to infection include:

 

 

- Wounds with a haematoma or devitalised tissue, or where foreign bodies are present;

 

 

- Deep wounds and those that are difficult to clean;

 

 

- Wounds that are not cleaned within six hours of injury (Gottrup, 1999);

 

 

- Wounds caused by human and animal bites because of the large numbers of bacteria present in the mouth.

 

 

Debilitation, chronic illness, diabetes mellitus, high alcohol intake, malignancy, and steroid, cytotoxic and immunosuppressive therapy reduce resistance to infection. Consideration should be given to the prescription of prophylactic antimicrobial therapy for these patients (Dealey, 1999).

 

 

If antibiotics are indicated, broad spectrum oral antibiotics should be used until growth is cultured from a wound swab. Because of concerns about antibiotic resistance there is a debate about the use of prophylactic antibiotics (Hoffman and Adams, 1998). Some authors recommend waiting until signs of infection are present; others believe that prophylactic therapy is warranted in the situations outlined above (Edlich and Reddy, 2001).

 

 

Tetanus - This is an acute and often fatal disease caused by the spores of Clostridium tetani (Department of Health, 2002). The spores are found in soil and in the intestines of many animals, particularly horses and cows. Humans may contract the disease when contaminated soil enters even an apparently trivial wound. The spores germinate in anaerobic conditions and produce toxins including tetanospasmin, which affects the nervous system. Tetanus is characterised by convulsive muscle spasm and rigidity, which usually begins in the jaw and neck (hence the common name ‘lockjaw’) and death occurs when the respiratory muscles are affected (DoH, 2002).

 

 

Prophylactic immunisation against tetanus has been available since 1924 and most people in the UK have received this in childhood. A total of five doses of vaccine at the appropriate intervals is now considered to give lifelong active immunity against the disease (DoH, 2002) and the immunisation is now given in a combined dose with the diphtheria vaccine.

 

 

If the risk of tetanus is particularly high, for example in a wound contaminated with stable manure, the DoH recommends that human tetanus immunoglobulin be given to provide passive immunity.

 

 

Patients who have not received five doses of tetanus toxoid vaccination at appropriate intervals should be given a dose at the time of treatment of their injury and further doses as required to complete the recommended five-dose schedule. Again, human immunoglobulin should be given for wounds when the risk of contamination with tetanus is identified. Full details and guidelines related to tetanus immunisation are available from the DoH (2002).

 

 

Patient education
A vital part of the nurse’s role is giving information and advice to the patient about the ongoing care of his or her wound. Patients who understand their part in the healing process are much more likely to comply with instructions. Simple advice such as not scratching an itchy wound is more likely to be heeded if the patient understands the consequences of disrupting fragile new healing tissues.

 

 

Generally wounds, once cleaned and closed, should be kept clean for five days or more until the surface layers have healed. Larger wounds and wounds to certain parts of the body, for example joints, may require more time to heal.

 

 

A dressing will often be used to cover the wound and this will normally need to remain in place until the wound closures, for example sutures, are removed. Patients should be advised to keep dressings in place as they act as a barrier to dirt and micro-organisms. If the patient’s occupation could cause the wound site to get wet or dirty, then he or she may need to take time off work.

 

 

If exudates ooze through the dressing then it will need to be changed or additional dressings applied to minimise the risk of infection entering the wound.

 

 

If a wound is constantly wet, the skin becomes macerated and friable, the risk of infection is increased and healing is disrupted. In this case, the patient should seek professional advice.

 

 

It may be possible to shower if the dressing is covered appropriately - for example, a wound on the hand can be covered with a plastic bag.

 

 

Patients should be advised of the signs of infection, for example redness, increased pain and purulent discharge. They should be advised to seek help and advice if these occur. This is much more likely to happen if the wound becomes dirty and/or wet or if the blood supply to the wound is restricted (Dealey, 1999).

 

 

A good blood supply is essential to healing (Flanagan, 1998). A poorly perfused wound will not heal well and patients may need advice as to how to optimise the blood supply to their wound (Dealey, 1999) - for example, exercising the feet and ankles to encourage blood flow to a leg wound.

 

 

Nutrition is also important for healing. Many vitamins and minerals are utilised during this time - proteins, carbohydrates, fatty acids, amino acids and other nutrients such as vitamin C, zinc (Casey, 2003), copper and iron (Flanagan, 1997). Patients may appreciate sensible advice on how to optimise or supplement their nutritional intake to encourage wound healing.

 

 

Finally, patients need to know approximately how long their wound will take to heal and when and where to go for removal of the sutures, staples or other closures. It is important to warn them if scarring is likely and to point out that healing continues for up to two years so cosmetic results will improve over time in almost all cases.

 

 

Conclusion
Wound healing and repair are normal physiological processes in which the nurse can play an important role by making appropriate decisions about wound closure and the need for antimicrobial therapy, and by giving patients clear and reasoned advice about their part in the process.

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