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Surgical Wounds - Part 1: Wound classification, healing intention and risk factors for complications

Wound classification, healing intention and risk f
Photo: Wound classification, healing intention and risk f
Surgical wound complications including surgical site infections (SSIs) occur in an arena where an aging population with chronic co-morbidities and high acuity severely compromise the playing field.  This article, the first of a two part series, will focus on types of surgical wounds and their healing intention, and factors that influence healing. Part 2 will consider surgical site infections, common wound complications and their management.

Surgical wounds, also known as incisions, are wounds made by a cutting instrument such as a scalpel or laser, ideally in a sterile environment where many variables can be controlled such as bacteria, size, location and the nature of the wound itself. Surgical wounds are classified as acute wounds with closure generally occurring by primary intention i.e. clean wounds where the wound edges are able to be closely aligned and secured with sutures, staples or adhesives and where the healing cascade is naturally activated. Little or no tissue is lost from the wound. Simple enough one might say? Think again! Some wounds are unable to be closed in this manner. Traumatic, contaminated or infected wounds or wounds with large tissue defects may need to be left open until such times as the wound can be safely closed either by surgical approximation and securing of the wound edges or grafting. Called delayed primary closure (or tertiary closure), the wound is left open for serial debridement, to allow drainage and/or granulation. Closure usually occurs within 5 days of the initial surgery unless there are ongoing complications or reconstruction is required. Other wounds, for example, chronic wounds (leg ulcers, diabetic foot ulcers and pressure injuries) as well as some surgical wounds, such as toe or forefoot amputation or dehisced wounds, may need to heal by secondary intention, i.e. the wound is left to granulate and epithelialise due to the fact that the skin edges cannot be easily approximated and healed by primary intention.
Accordingly, surgical wounds are classified relative to the degree of complexity – clean, clean-contaminated, contaminated and dirty. The risk of SSI and other complications increases with the type of surgery. Clean wounds generally heal without complications, however they too are not without risk. Abscess formation or dead space (fluid collection) below the surgical incision can often necessitate unplanned readmission to hospital requiring further surgery with or without drain insertion, the need for antibiotics and increased length of hospital stay. Clean surgical wounds often result from elective or planned surgery, under aseptic conditions, and where the viscera are not opened. These wounds involve incision of normal non-inflamed tissue with closed drainage systems (if required) and are closed primarily. Infection rates are generally low. Examples are hemiarthroplasty, open reduction of fractures with or without pin and plate, stabilisation of fractures with external fixators, endoscopy and surgical removal of skin lesions.

Clean contaminated wounds are wounds that are otherwise clean but created as a result of the need for emergency surgery or re-surgery through a previous clean incision site within a short period of time (usually within 7 days), viscera are opened with no spillage of gut contents, or there is a minor break in aseptic technique. Hemicolectomy, division of adhesions and cholecystectomy are examples.

Moving along the continuum, contaminated wounds are wounds that have been left open and include penetrating trauma less than 4 hours old, opened viscera with spillage of gut contents or infection, for example, appendectomy or where there has been a major break in aseptic technique. Dirty wounds are classified as such in the presence of pus, intraperitoneal abscess formation or visceral perforation (for example abscess formation around a recent appendectomy site) or penetrating trauma greater than 4 hours old. As one might conclude, infection rates and the potential for other wound complications post-surgery increase with the degree of complexity, the nature of the surgery and the manner in which it is performed (surgical technique).

Risk factors for wound complication in addition to infection also need to be considered, where possible, prior to surgery or anticipated post-surgery and management plans developed to minimise risk. Surgical and anaesthetic considerations as well as patient-related factors should be taken into account when ascertaining risk. Many factors impair perfusion and wound healing. Intra-operatively, the surgical classification, skin preparation, site, duration and complexity of surgery, pre-existing infection (local or systemic) and mechanical stressors on the wound impact wound healing capacity. Peri-operatively, time to surgery, body temperature, blood loss, hydration status, perfusion, pain, oxygenation and pre-operative nutritional status all influence wound healing outcomes. Patient-related factors are numerous: age; smoking; alcohol consumption; any co-morbidity that impairs the delivery of oxygen to the periphery (peripheral arterial and other cardiovascular disease, asthma, emphysema, chronic obstructive pulmonary disease, renal failure and anaemia); malignant disease; diabetes; BMI; poor general health; medications; previous history of chemo and/or radiotherapy; and immunosuppression. 

Decreased tissue perfusion and collagen synthesis and deposition decrease wound tensile strength while immunocompromised patients have reduced wound healing capacity due to impaired neutrophil activity. Collectively these factors increase the risk of wound infection and breakdown with poor healing outcomes. Wound complications are costly to the health system and may be associated with an increased risk for further surgery, significant pain and suffering psychosocially for the patient, and may prolong postoperative length of stay or necessitate unplanned early re-admission. Thinking about the potential risks of particular surgeries, identifying those most likely to be at risk early, and timely implementation of interventions to minimise risk may mitigate much of these sequelae. To coin a phrase... A stitch in time saves nine.

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Bonnie Fraser

A mother to three girls, previously Bonnie was an educator in the NSW secondary school system for 20 years before retraining to become a registered nurse. Bonnie has a Bachelor of Science with a Graduate Diploma in Education from the University of New England; and several certificates from TAFE NSW including Certificate IV in Workplace Training and Assessment and a Graduate Diploma in Management Communication. In 2009 Bonnie  attained a Bachelor of Nursing from Newcastle University, and is currently undertaking a Masters Degree in Wound Care though Monash University, this being her final year.  Currently Bonnie is employed as a registered nurse at the Port Macquarie Base Hospital located on the mid north coast of NSW. During her time as an RN she has worked in the areas of orthopaedic and general surgical nursing and fulfilled the roles of both clinical nurse educator for new and transitioning nurses and clinical nurse specialist wound management.