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The physiology of wound healing: an emergency response

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VOL: 98, ISSUE: 08, PAGE NO: 54

Terry Shipperley, MA, BSc, RGN, PGCHSCE, DPS(DN) is clinical nurse specialist, physical health, South Downs Health NHS Trust, Brighton

Claire Martin, BSc, RGN, PGCHSCE, DipPNS, is wound care specialist nurse, Brighton Healthcare NHS Trust

All nurses involved in wound management need to understand the wound-healing process, as this should underpin their care plans. While treatment options will be influenced by the current stage of healing, it is important to note that the stages can vary in length of time and overlap, which can create difficulties in recognition.

For example, the signs and symptoms of wound infection could be confused with the inflammatory phase, while parts of the wound may be in the destructive phase, with other parts in the proliferative phase. Nevertheless, to recognise that the complex physiological process can be divided into distinct phases from the initial emergency response to injury through a process of repair and regeneration to complete healing helps the nurse in the clinical decision-making process.

We have used the idea of equating different stages in the wound-healing process to occupations as a teaching tool since 1996. More recently we have been working on a section to include in one of the local primary care groups’ wound resource file. While working on this document we felt this information would be useful for a wider audience.

The emergency response

Wound healing can be defined as the physiology by which the body replaces and restores function to damaged tissues (Tortora and Grabowski, 1996). The emergency response to a burning building by the fire brigade and the other professionals involved in restoring it to full occupancy can be used as an analogy to describe the body’s response to trauma and the subsequent sequence of events that leads to wound healing.

There are two ways in which wounds can be encouraged to heal, and their selection depends on the nature of the wound itself, However, the healing process is the same for both types, although the time taken to complete healing may differ.

Primary intention

The edges of wounds healing by primary intention are brought together and held by sutures, clips, staples or strips. These wounds heal quickly.

Secondary intention

If the edges of the wound cannot be drawn together because of extensive tissue loss or large surface areas the wound will be left to heal by secondary intention. These wounds heal slowly through the process of granulation and epithelialisation.

The complicated process of wound healing can be simplified by dividing it into four phases. These overlap, and the time taken to progress from one stage to the next is dependent on a multitude of factors and may vary for each individual.

In this teaching tool, each stage has been illustrated by comparing it to an occupational group involved in a response to an emergency.

The inflammatory phase (zero to three days): the fire brigade

This stage is the body’s emergency response to an injury and can be likened to the fire-fighting phase. Trauma to the skin penetrating through the epidermis to the dermis will result in bleeding (Fig 1).

The damaged ends of the blood vessels constrict and the clotting process is initiated through a complicated cascade of chemical reactions accelerated by platelet aggregation. A fibrin mesh forms over the wound, trapping other blood cells and gradually drying out to form a scab, which closes the wound temporarily. This process stimulates the release of various substances (for instance, prostaglandins and histamine) that cause dilation of blood vessels adjacent to the injured area.

The clinical signs of heat, redness, swelling and pain at this stage should not be confused with infection.

The destructive phase (one to six days): the refuse collector

This is the stage in which the body clears away rubbish from the wound in the same way that debris will be cleared away after the fire-fighters have departed. White cells line the walls of blood vessels and migrate into the tissues ready to destroy invading bacteria (Fig 2).

Initially neutrophils and later monocytes engulf and digest dead and devitalised tissue by phagocytic activity. Formation of new tissue in the wound bed will not occur until macrophages have sufficiently cleansed the area and stimulated the release of growth factors (Robson, 1997).

White cell activity can be compromised in dry and exposed wounds (Morison et al, 1997).

The proliferative phase (three to 24 days): the builders

This is the stage in which active regeneration and construction of new tissue occurs, in the same way that builders will be brought in to repair a damaged building. As monocytes mature, they develop into macrophages and produce a number of substances that stimulate angiogenesis (the development of new blood vessels) and the synthesis of collagen and other connective tissue (Fig 3).

Fibroblasts multiply and form a scaffold of collagen fibres that support fragile capillary loops. This is known as granulation tissue because of its red, granular appearance. New blood capillaries begin to grow into the wound margins. Vitamin C, iron and protein in the diet assist this process.

The maturation phase (21 days to two years): the decorators

In this stage the finishing touches to wound healing occur, in the same way that the repaired building will be redecorated. Myofibroblasts help to bring the wound edges together by contraction, reducing the amount of tissue required to fill the defect (Flanagan, 1997). Epithelial cells from the wound edge, sweat glands and hair follicles migrate over new granulation tissue, eventually meeting to form a complete covering over the wound (Fig 4). A moist wound environment accelerates this process, enabling epithelial cells to migrate more easily (Winter, 1963).

Remodelling of the scar is stimulated by macrophages, resulting in the reorganisation of collagen fibres. This maximises the tensile strength of the scar to about 80% of non-wounded skin (Flanagan, 1997). The scar gradually fades from red to white as it matures.

Conclusion

This article gives only a basic insight into a complicated physiological process, which can be studied in greater depth by reference to other texts (Cherry et al, 1995; Silver, 1985; Torrance 1986; Morison et al, 1999). However, we have found it a useful structure to follow as an introduction to the anatomy and physiology of wound healing.

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