Surgical Wounds: Healing at the Cellular Level

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Surgical Wound Healing

By the WoundSource Editors

The number of surgical procedures performed in the United States has been increasing annually by as much as 300% over a 10-year period.1 Although technological advances in surgical procedures have allowed some procedures to be performed using minimally invasive techniques, many operations still require incisions, which require special care to prevent dehiscence and surgical site infections (SSIs). SSIs occur in 2% to 4% of all patients undergoing surgical procedures,2 and they are among the most expensive inpatient harms, adding approximately $30,000 to the total hospital cost per infection.3

Types of Surgical Wound Healing

Understanding how these wounds heal at the cellular level is a crucial component in determining how to optimize the healing environment and promote better outcomes for surgical patients. There are three types of wound healing for surgical incisions, and they are distinguished based on how much skin and tissue has been lost. These are primary intention, secondary intention, and tertiary intention.

Primary Intention
Primary intention healing occurs when tissue surfaces have been approximated or closed. Generally speaking, this type of healing occurs when there has not been much loss of cells and tissue and the incisions have been closed using stitches, staples, tapes, or adhesives. This method of healing can last up to four weeks until scar tissue has matured.

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After the initial injury is repaired, the wound fills with blood that clots to protect the wound against infection and desiccation. Epithelial changes begin to occur when basal cells proliferate and migrate toward the incision. Generally, the wound is covered within 48 hours by a layer of epithelium, which forms a scab to separate the underlying dermis from the fibrin clot above. During the inflammatory stage of healing, polymorphonuclear leukocytes are replaced by macrophages, and fibroblasts invade the wound; this generally occurs on postoperative day three. By the fifth day, new collagen fibrils begin to form, and this process continues until healing is complete and scar tissue has formed.4

Secondary Intention
Healing by secondary intention is indicated in wounds with edges that are not linear or do not approximate or wounds with a large tissue defect. This type of healing is also how chronic wounds such as pressure ulcers heal. This healing method is selected when patients have substantial wound contamination, have overall poor condition (e.g., sepsis), or are at risk for wound dehiscence. The method may also be used when the wound has excessive tension, such as wounds that occur over articulating joints.5

The initial cellular and epithelial changes that occur during secondary intention healing are similar to those found in primary intention healing; however, there is often much more inflammation and granulation tissue formation. Healing of these wounds is often much slower and results in more scarring. Wound contraction may also occur through proliferation of myofibroblasts, resulting in a wound that becomes only approximately one-third of its original size. The presence of infection can further delay the process of healing, although surgical debridement of the necrotic tissue may improve healing conditions.4

Tertiary Intention
Tertiary intention healing is also referred to as delayed primary healing. This type of healing is selected when there is a reason to postpone definitive wound closure, such as when there is poor circulation to the incision area, there is a need to allow for drainage, or there is excessive contamination or infection.5 Injuries such as dog bites, crush injuries, or lacerations with the presence of foreign bodies are frequently treated this way.

Tertiary intention healing allows the provider to clean and observe the wound for several days to ensure that the infection is treated successfully before staged surgical closure. Treatment may also consist of serial surgical debridements or topical antimicrobial agents. After the wound is deemed ready for closure, this may be done through the placement of sutures, skin grafts, or with a flap design. Once the wound is closed, the healing process often consists of a combination of primary and secondary intention healing activities, although these wounds may develop more scar tissue than wounds that heal by secondary intention.6

Conclusion

Despite the type of healing that is selected for a surgical wound, there are a myriad of elements that may have an impact on healing, including the presence or risk of infection or dehiscence, the quality of nutrition, the presence of medications or immunodeficiencies that may hinder healing, lifestyle factors (e.g., smoking, exercise frequency, obesity), functional status, and perfusion rate.

Treatment of these wounds during each healing phase follows standard best practices for general wound care, including regular assessment,, debridement, care of the periwound area, and management of exudate and moisture. Given that many SSIs are preventable, selecting the proper healing modality and caring for the wound appropriately are crucial in minimizing complications and promoting the healing process.

References
1. National Quality Forum. NQF-Endorsed Measures for Surgical Procedures. Washington, DC: National Quality Forum; 2017.
2. Berrios-Torres SI, Umscheid CA, Bratzler DW. Centers for Disease Control and Prevention guideline for the prevention of surgical site infection. JAMA Surg. 2017;152:784-791.
3. Knowles M. SSI adds $30k to patient’s hospital costs, study finds. Becker’s Hospital CFO Report. Chicago, IL: Becker’s Healthcare; 2018. https://www.beckershospitalreview.com/finance/ssi-adds-30k-to-patient-s-.... Accessed August 26, 2019.
4. Wound healing [presentation]. Chandigarh, India: Government Medical College & Hospital, n.d.
5. Harper D, Young A, McNaught CE. The physiology of wound healing. Surgery. 2014;32:445-450.
6. Wound healing [presentation]. Knoxville, TN: University of Tennessee Graduate School of Medicine; n.d.

The views and opinions expressed in this blog are solely those of the author, and do not represent the views of WoundSource, Kestrel Health Information, Inc., its affiliates, or subsidiary companies.

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