INTRODUCTION

The process of wound healing plays a vital part in the ability of the patient to maintain homeostasis and recover from surgery. An understanding of the principles of wound healing has direct relevance to the choice and use of both dressings and drains. The principles outlined in this chapter apply equally to surgical incisions and minimally invasive techniques, such as cannulation. Essentially, injury may be caused by trauma, outside agents or deliberately, as in surgical incision or puncturing the skin during cannulation.

WHAT IS WOUND HEALING?

Healing is an automatic, self-regulating, natural process that has enabled man to survive disease and trauma. Throughout the ages there have always been healers who through magic, mystery or medicine have sought to speed up this process but generally it is true to say that man healed in spite of them. However, the growth of modern scientific knowledge and technological development within the last 200 years has brought us a health environment in which few wounds are beyond repair and in which most heal quickly and completely.

Healing can be defined as the restoration of the structure and function of diseased or damaged tissues. This process begins as soon as the injury occurs. The body's tissues vary tremendously in their constitution and this variation, together with the type and severity of the wound, is reflected in the way in which that tissue will heal. Thus superficial wounds will regenerate readily and quickly whereas wounds affecting the deeper layers of connective tissue will take longer to repair. Damage to bone, which contains large amounts of inorganic calcium, will heal at an even slower rate.

THE PHYSIOLOGY OF WOUND HEALING

Wounds can be divided into two main types:

1. 1. Closed wounds where no overt tissue loss occurs.

2. 2. Open wounds where there is tissue loss due to excision, trauma, burns or necrosis.

Where there is tissue loss its replacement may be achieved in two ways. First, there may be regeneration of identical tissues from undamaged cells in the area, thus replicating both structure and function. Second, where no undamaged cells remain, repair is achieved with granulation tissue. Granulation tissue is of a fibrous inelastic nature and fills in the defect adequately; it restores neither structure nor function but eventually leaves a raised and uneven scar.