Types of Wound Closures

Wounds that heal following approximation of the wound edges with little or no granulation tissue formation (as in a surgical wound) are said to heal by primary closure or primary intention. An uncontaminated, clean wound bed with wound margins that can be brought together with little tension on the surrounding tissues is required for healing by primary closure. Healing by secondary closure, or secondary intention, occurs when the wound edges cannot be brought together. The process of granulation tissue formation, wound contraction, and epithelialization is required to fill the wound defect. Healing by secondary closure is more complicated, results in more scar tissue formation, and requires more time and energy to achieve closure than does healing by primary intention. In some cases, a traumatic or surgical wound cannot be immediately closed because of contamination or risk of infection. The wound may be cleaned over a period of a few days. When the wound is free of debris, it may be cleaned, surgically debrided and closed. Such a wound is said to heal through delayed primary closure.

Abnormal Wound Healing

A variety of factors may result in failure of an acute wound to move through the inflammatory, proliferative, and maturation phases of healing in a predictable fashion. Wounds may become chronic because of a larger number of proteases and lack of protease inhibitors, leading to a degradation of the extracellular matrix and a larger wound bed. Chronic wounds have higher amounts of inflammatory immunomodulating agents and are less responsive to growth factors. Patients who are immunocompromised or who have arterial insufficiency may be unable to mount the inflammatory response necessary to clean the wound of debris and produce chemotactic cells that signal other cells necessary for the production of granulation tissue in the wounded area. Such wounds may be void of the classic signs of inflammation. In contrast, some wounds may persist in the inflammatory phase, exhibiting debris, rolled, thickened wound edges, and a lack of adherence of the wound edge to the wound bed. Common causes of chronic inflammation include the presence of a foreign body in the wound bed, repetitive trauma (e.g., excessive licking of the wound bed), and the overuse of agents that are cytotoxic to the cells involved in the healing process. Currently there are insufficient data to assess safety, efficacy, and recommendations for use of some topical agents because of inconsistency or lack of verification of equivalent comparisons between in vitro and in vivo studies.⁹ Agents in question include povidone-iodine, hydrogen peroxide, sodium hypochlorite bleach, and chlorhexidine.^10–12

Some wounds may granulate too little (hypogranulate) because of poor support for a granular matrix. A “pothole” wound is formed as epithelial cells pile up at the wound edge and fail to migrate across the wound bed. The wound edges of such pothole wounds should be gently wiped with gauze and the wound cavity should be lightly filled with a dressing to promote the formation of a granular matrix and prevent premature migration of epithelial cells. In contrast, hypergranulation tissue may be formed when a wound defect has been filled, yet the granulation process continues, resulting in granulation tissue that extends well above the wound surface. Hypergranulation tissue, or proud flesh, can be resolved by the application of pressure to the tissue through certain dressing types, such as hydrocolloid dressing, the use of silver nitrate to cauterize the tissue and level the wound bed, hypertonic saline dressings, or surgical excision of excess tissue.

Factors Affecting Wound Healing

Deterrents to expedient wound healing include wound characteristics, local factors, and systemic factors (Table 36-1). Acute wounds and surgically induced wounds tend to heal more quickly than severe traumatic wounds or wounds of insidious onset. Wounds located over bony prominences, in areas with few epidermal appendages, across joints, and in areas of thick skin have slower healing times. Because more cellular activity and rebuilding of tissue are required, larger and full-thickness wounds require more healing time than smaller or more superficial wounds. The close proximity of wound edges results in shorter healing times for linear wounds than for rectangular or circularly shaped wounds. Maintenance of appropriate wound moisture within the wound bed encourages granulation tissue formation and epithelialization. Thus, wound beds and periwound areas that are too dry (desiccated) or too wet (macerated) have prolonged healing times. Devitalized tissue within the wound bed and dry exudate or scabs can slow the migration of epithelial cells across the wound bed, prolong the inflammatory response, and create an environment conducive to infection.^13,14

Important to consider is the fact that all wounds are contaminated. All body surfaces, including skin, and the digestive tract have a normal microflora of bacteria and fungi that include Staphylococcus, Micrococcus, Peptococcus, Streptococcus, Acinetobacter, and yeast. The resident microflora and pH of the skin create a slightly acidic environment, serving a protective function against disease-causing microorganisms.¹⁵ In an open wound the microflora adhere to the surface and replicate, resulting in colonies that do not necessarily adversely affect the host as the normal immune response is activated. However, if the bacteria or fungi continue to replicate, a point of critical colonization is reached in which the microorganisms become a bioburden, adversely affecting the host. When microorganisms multiply to the point of invading viable body tissues, the wound is considered infected. Because of the presence of individual factors in each host, there is no specific threshold for infection, although in general, wounds with a bacterial quantity of greater than 10⁵ microbes per gram of tissue are considered infected.¹⁶ However, the type of microorganism must also be considered because some are more virulent and produce exotoxins that may inactivate or modify host responses, leading to host cell dysfunction or death. Bacterial endotoxins, molecules within the walls of gram-negative bacteria, may induce a strong inflammatory response leading to fever, bleeding, and clotting. In addition interactions among bacteria can lead to a microorganism community called a biofilm that attaches to the wound surface and is encased in a self-developed glycocalyx (which protects the bacteria). The microorganisms encased in the biofilm exhibit increased virulence and resistance, making them less responsive to biological and pharmaceutical intervention.¹⁷ Immunocompromise, malnutrition, and impaired local circulation of the host can also affect resistance to invading organisms.

In general, infection should be suspected when the signs of inflammation are disproportionate to the size and extent of the wound (e.g., drainage is copious, has uncharacteristic color, wound is very painful, periwound area is extremely red or hot, etc.). Wound cultures such as tissue biopsies, swab cultures, or fluid aspirations may be used to identify an offending microorganism. Although tissue biopsy is the gold standard for culturing, properly performed swab cultures are a reliable method to identify and quantify bacteria in a wound.¹⁸ To properly perform a swab culture, the clinician must first debride and thoroughly rinse the wound bed. The swab should then be moved slowly over viable tissue in the wound bed in a crisscross pattern back and forth, moving from top to bottom while rolling the swab and applying enough pressure to express some of the wound bed fluid. Wounds with a small surface area of little granulation tissue should be cultured by swabbing only the small area for 5 seconds while rotating the applicator.¹⁹ Tissue biopsies are preferred for evaluating pressure/decubital ulcers, burns, or wounds with a suspected neoplastic process.

Because endogenous or exogenous microbes can lead to infection, meticulous adherence to infection control procedures must be exhibited. Procedures include hand washing before and after glove use, the use of gloves, which should be changed between procedures on the same patient and promptly after touching contaminated materials, and isolation of patients with antibiotic-resistant infections.

Initial Assessment

Although external bleeding wounds often capture the attention of the owners, the health care worker must be aware that more life-threatening injuries may be present. The initial stabilization includes an examination of the airway with administration of oxygen, as appropriate. In the case of severe head wounds, facial trauma or tracheal damage, rapid induction may be necessary to accomplish intubation and obtain an open airway (Figures 36-3 and 36-4). Puncture wounds or trauma to the chest wall should increase suspicion of a pneumothorax, for which a thoracocentesis or chest tube may be necessary. All vital signs should be obtained to evaluate the need for IV fluids and/or blood products to treat hypovolemic shock.