Awound is defined as an injury that causes a break in the normal anatomic structure and function of the skin (Chhabra et al., 2017). Wounds can be acute or chronic, with partial or full thickness. Chronic wounds are costly and can have a devastating impact on patients and healthcare professionals. Approximately 6.5 million patients in the United States are affected by chronic wounds with a cost of over $28 billion annually (Dowsett et al., 2021). Understanding the physiological process of wound healing is essential when caring for a wound especially when a wound fails to progress through the entire process. A holistic approach is required when assessing a wound to identify causative factors as well as those that may impact healing. Wound assessment is also necessary to evaluate the progress of a wound to guide clinical decision making for management.
STAGES OF WOUND HEALING
Once a full-thickness cutaneous injury has been sustained, this sets forth a cascade of overlapping events to follow. This cascade of events, or stages, are physiologic responses that are sequenced to result in wound repair (Figure 1). Wounds that fail to progress through each stage or phase will become a chronic wound. Inflammatory and proliferative phases are the most common stages in which a wound will become stalled. Chronic wounds often have an exaggerated inflammatory response that results in destruction of the extracellular matrix and slows growth factor activity, creating a suboptimal wound healing environment (Dearsley, 2021).
Hemostasis
Hemostasis is the initial stage immediately after the cutaneous injury and is characterized by a vascular response (Thobekile et al., 2021). The main goals of hemostasis are to limit blood loss, establish bacteria control, and seal the wound. This stage is brief, often only lasting hours. Blood vessels surrounding the injured tissue constrict to restrict blood flow to the wound bed. Activated platelets and thrombocytes aggregate within the broken vessels prompting the clotting cascade, which results in a clot formation (Beitz, 2022; Thobekile et al., 2021). The newly formed clot functions as a protective barrier against invading bacteria as well as a temporary scaffold for cell migration (Beitz, 2022).
Inflammatory
The inflammatory phase also begins shortly after the injury with the release of cytokines during hemostasis, which attract leukocytes to the wound bed (Kloc et al., 2018). A primary function of the inflammatory phase is to establish a clean wound bed. Neutrophils are the first of the leukocytes to arrive at the injured site and, through enzymatic activity, will eliminate bacteria. This initial flood of neutrophil activity will decrease as the inflammatory phase progresses. As the amount of neutrophils decreases, macrophages will increase in number with the purpose of removing dead bacteria, neutrophils, and cellular debris (Beitz, 2022). Another key function of macrophages is the release of growth factors to stimulate angiogenesis, fibroblast migration and proliferation, and connective tissue formation (Kloc et al., 2018).
Proliferative
Cellular signaling from macrophages leads to fibroblast migration to the wound bed and begins the proliferative or regenerative phase (Beitz, 2022). The aim of the proliferative phase is to contract the wound edges and establish reepithelialization. New vessels that supply the wound bed with nutrients and oxygen are formed through angiogenesis. Fibroblasts are responsible for the synthesis of Type III collagen, which will serve as a scaffolding for the developing granulation tissue in the wound bed (Beitz, 2022). The continued cellular signaling along with the scaffolding provided by collagen prompts the migration of fibroblasts, extracellular matrix, and endothelial tissue to fill the wound bed with granulation tissue. Once the wound bed is filled with granulation tissue, epithelial cells will migrate from the margins of the wound across the wound bed, resulting in the contraction of wound with eventual closure.
Maturation
Maturation, also known as remodeling, is the final stage in wound repair. This stage can take from several months up to 2 years, resulting in scar formation (Phillips, 2000). As the Type III collagen will be replaced by stronger Type 1 collagen, the cells responsible for collagen synthesis and angiogenesis will undergo apoptosis (Beitz, 2022). This replacement of collagen increases the tensile strength to promote durable healing of scar tissue. However, this newly healed scar tissue will only have approximately 80% of the tensile strength or normal, uninjured soft tissue (Shamsian, 2021).
PARTIAL-THICKNESS WOUNDS
Superficial or partial-thickness wounds involve injury to the epidermal and superficial dermal layers. Common examples of partial-thickness wounds include abrasions and skin graft donor sites. The mechanism of wound healing for partial-thickness wounds differs from full-thickness wounds because of the superficial depth of tissue injury. Granulation tissue formation and wound contraction are not necessary to fill in the wound bed (Beitz, 2022). Partial-thickness wounds heal by reepithelialization through lateral and vertical migration of keratinocytes. Damage to the epidermis signals changes in cell structure and an increase in keratinocyte mitosis, promoting lateral migration of tissue (Beitz, 2022). Lateral migration stops once the wound bed is covered with epithelial tissue, causing vertical migration of keratinocytes to resume and gradually reestablish baseline epidermal thickness (Beitz, 2022).
CLASSIFICATION OF WOUND REPAIR
In the mid-19th century, surgical wounds that healed without complications of pus were described as "healing by first intention" (Salcido, 2017). Wound repair classification of primary, secondary, or tertiary intention is based on the optimal primary surgical closure for all wounds (Figure 2). Some factors contributing to the decision making on closure include condition of the wound bed and presence of devitalized tissue, amount of tissue loss, or size of the overall defect as well as presence or risk of infection.
Primary
Primary intention is the closure of a clean wound with the goal of a durable healed scar. The edges are approximated with sutures, staples, adhesive glues, or clips (Yi et al., 2020). These wounds tend to heal rapidly and with minimal scar formation. Examples of wounds that are closed by primary intention include uncontaminated lacerations, biopsy sites, and clean surgical wounds.
Secondary
Not all surgical wounds and lacerations will heal by primary intention. Wounds that are deliberately left open and allowed to heal by scar formation are classified as healing by secondary intention (Doughty & Sparks, 2016). Because of a need for more granulation tissue to fill in the wound, these wounds will heal at a slower pace and with more scar formation than wounds healing by primary intention. Advanced wound dressings can help promote the growth of granulation tissue required for repair. Large wounds with more tissue loss may need to heal by secondary intention as the reparative process becomes more complicated (Chhabra et al., 2017). Wounds at risk for infection or at a high risk for dehiscence may also be left to heal by secondary intention (Yi et al., 2020). Dehiscence may result because of excess tension at wound margins and can occur over joints with significant range of motion or at sites where edema and inflammation are present.
Tertiary
Tertiary intention, also known as delayed primary closure, occurs when a wound is initially left open and is closed at a later time. Infected wounds requiring debridement may undergo delayed closure once the infection is resolved or the devitalized tissue has been removed. Closure methods, such as free flaps and rotational flaps, may be used to provide soft tissue coverage for larger wounds (Salcido, 2017).
FACTORS THAT IMPACT WOUND HEALING
Multiple factors can impact a wound's ability to complete all stages of wound healing effectively. These can be intrinsic and extrinsic factors. Intrinsic factors have genetic and pathophysiologic characteristics. Examples include age; immunosuppression; chronic disease, such as peripheral vascular disease; diabetes; Chronic Obstructive Respiratory Disease; renal failure; liver failure; and pain (Mitchell, 2020). Extrinsic factors include environmental and lifestyle influences, such as smoking, nutrition, and immobility, and medications such as steroids and anticoagulants (Mitchell, 2020). Identification of underlying factors that impact wound healing is important in developing a plan of care in wound management. For example, blood glucose control and smoking cessation should be incorporated into the plan of care for a patient with a chronic wound.
ACUTE VS. CHRONIC WOUNDS
Wounds can be categorized as acute or chronic. Most wounds are considered acute as they will heal rapidly in an organized and predictable manner. Common causes for acute wounds include trauma and surgical. On occasion, a wound will fail to complete all necessary steps toward healing and, as a result, will become a chronic wound. Inflammation, vascular compromise, or repetitive insults to the healing tissue are often associated with the development of a chronic wound (Doughty & Sparks, 2016). Although acute wounds tend to heal in a more rapid manner, timing is less of a factor in the development of chronic wounds because of the failure to progress through all stages in wound healing (Beitz, 2022). Some examples of commonly encountered chronic wound types include venous ulcers, arterial ulcers, pressure injuries, malignant ulcers, and neuropathic ulcers.
ASSESSMENT
Wound assessment should not focus solely on the wound itself and instead should include a holistic assessment. Completing a holistic assessment will aid in identifying factors that can impact wound healing, including those previously discussed intrinsic and extrinsic factors. A patient history should include assessment of past medical history, allergy, medication, family, and psychosocial history to assess for nutrition status, tobacco usage, or comorbidities, which can impact wound healing. Further diagnostic studies may be required. For example, vascular studies including an ankle-brachial index and pulse volume recording should be completed on a patient with a history of hyperlipidemia and tobacco use who presents with a nonhealing lower extremity wound. A comprehensive assessment will guide the development of a treatment plan. Routine reassessments of the wound should be completed to determine if continuation or changes in the treatment plan are appropriate. Inspection and palpation are components of the physical examination. Evaluation of the wound should include location, measurements, exudate, and odor as well as the conditions of the wound bed, edges, and surrounding tissue.
Location and Measurements
Location and measurements are important components of a wound assessment. Location of the wound can provide a suggestion of the etiology of the wound. Wounds located over bony prominences are often consistent with pressure-related injuries. Arterial disease should be considered as a differential diagnosis for ulcerations found at the distal foot or tips of a patient's toes as well as within the toe web spaces. Location should be identified using correct anatomical terms.
Measurements of the wound will help show if a wound is improving or worsening. Objective units of measurement, such as centimeters or millimeters, should be used. The size of the wound can be determined by measuring length (head to toe or using a clock face, 12 o'clock and 6 o'clock) by width (shoulder to shoulder or 3 o'clock and 9 o'clock). Using the same reference points will improve the reliability and meaningfulness of the measurements as well as give a more objective indication of the wound's progress (Bates-Jensen, 2022). Depth can be measured by placing a cotton-tipped applicator vertically at the deepest part of the wound while holding the device at skin level and then comparing with a ruler (Bates-Jensen, 2022). Areas of undermining or tunneling should be measured. A clock face should be used to describe the locations of any undermining or tunneling.
Wound Bed Description
An accurate description of the wound bed can provide an illustration to the overall condition of the wound. Tissue present in the wound bed can range from healthy, red granulating tissue and newly healed pink epithelial tissue to devitalized tissues, such as yellow slough and black eschar (Figure 3). Percentages may be used with wounds that have multiple types of tissue to report the amount of each tissue type present. A clock face may be used to describe the locations of each type of tissue found in the wound bed.
Edges
In normal, healing wounds, new tissue migrates from the edges, causing the wound to contract. Assessment of edges in chronic wounds is key as it can reveal the likelihood a wound will contract. Examine and palpate the edges of the wound. Ideal edges of the wound should be flat, or even with the skin surface and wound bed, and attached. Determine the demarcation of the wound. Well-demarcated wounds have distinct edges of normal tissue and wound bed. Poorly demarcated wounds cause difficultly determining wound margins and often pose a challenge in measuring. Epibole describes edges of chronic wounds that become thickened and rolled under (Figure 3; Bates-Jensen, 2022).
Exudate
Exudate can aid wound healing by preventing the wound bed from drying out and fostering the migration of cells to repair tissue, provides nutrients needed for cell metabolism, and allows the diffusion of immune and growth factors as well as promotes autolysis of devitalized tissue (Chhabra et al., 2017). Wound exudate may also provide clues to the condition of the wound, its etiology, and efficacy of current treatment or of any systemic underlying conditions affecting wound healing. For example, clear, amber exudate is often considered normal, whereas green drainage may be indicative of bacterial infection. High amounts of clear wound exudate accompanied by surrounding tissue edema in a lower extremity wound may be a sign of venous insufficiency. Appropriately managing exudate is a key principle in wound management. Dressings should be selected to maintain a moisture balance optimal for wound healing. Wounds with little to no exudate may become dry appearing or desiccated and can further impair the healing process. It is important to document the color, characteristic, and amount of exudate present in the wound or on the wound dressing. Presence or absence of odor should also be noted. Dressings holding drainage can be a false indicator of a presence of odor and therefore should be discarded before assessing for odor.
Condition of Surrounding Tissue
Surrounding tissues should be regularly assessed as they are often the first to show signs of the deteriorating condition of a wound (Bates-Jensen, 2022). Erythema, edema, induration, maceration, and denudement should all be noted. Erythema may be a sign of inflammation or infection. Deep purple or nonblanching erythema may show an impending extension of the wound because of ischemic changes (Bates-Jensen, 2022). Palpate the tissue to determine if edema, induration, new onset of pain/tenderness, or fluctuance is present, all of which can indicate infection. Tissue maceration is a key sign the dressing is not effectively managing the wound exudate and a new treatment plan is needed.
CONCLUSION
The process of wound healing follows a predictable sequence of events. However, when a wound does not progress through each sequence as expected, it becomes a chronic wound. Multiple factors, both intrinsic and extrinsic, can affect a wound's ability to progress through each stage of healing. Understanding those factors along with the physiological process of wound healing is important in patient care. A holistic approach to assessing the wound is required and will guide in the development of a plan of care.
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