All surgical procedures compromise the physical defensive barrier of the skin, which allows contamination, multiplication and proliferation of micro-organisms. Surgical site infections can be prevented by following strict protocols and aseptic techniques before, during and after surgery. This includes the surgical equipment, instruments, environment and staff (Melekwe et al, 2018). In human medicine, approximately 2% of surgeries result in the development of a surgical site infection; in veterinary medicine the rates are approximately 2.8% in dogs, 1.5% in cats and 1.6% in horses (Burgess, 2019).
This article reviews sterile surgery preparation and aseptic technique in both the human and veterinary field, considering changes which reduce surgical site infection in veterinary practice.
Surgery sites and surgical site infections
Translocation of endogenous microbial flora is the most common route of surgical site infection. Skin preparation and aseptic techniques aim to reduce or eliminate the growth of resident and transient flora at the wound site, thereby reducing the morbidity and mortality rates from surgical site infections (Fossum, 2018). In addition, the clean/clean-contaminated/contaminated/dirty status of the site of surgery is linked to the translocation of resident microbial flora as a result of surgical intervention (Billas et al, 2022).
Clipping
Hair clipping is generally considered to be mandatory for most routine surgeries to reduce the risk of pathogens entering the surgical site (Guzman-Pruneda et al, 2019; Curtis, 2021). This is best performed using clippers with a clean blade and no missing teeth, as the use of razors increases the patient’s risk of infection by producing microscopic cuts of the epidermis which can harbour bacteria (Fletcher et al, 2007). However, hair clipping too soon before surgery, for example the day before, is not recommended as it can increase the pathogen load on the skin (Roberts, 2013).
Traditional recommendations are to clip a large enough area to allow the incision to be extended if required. This should encompass all wound edges, drape movements and drain placements to approximately 20 cm diameter from the incision site (Fossum, 2018). Some studies have shown that sterile surgical fields without hair clipping have no higher risk of development of surgical site infection in humans providing the area is suitably cleaned (Fletcher et al, 2007; Jolivet and Lucet, 2019). This raises a query about whether the preparation of a surgical site with clipping is absolutely necessary, given its potential to lead to a degree of hypothermia for the patient. While veterinary standards often follow regulations set in human medicine, Hague et al (1997) showed that the bacterial flora of the skin was unaffected by clipping in sites where arthrocentesis was carried out in horses, and this is supported by a more recent study in canines (Lavallée et al, 2020). If clipping is required, the length of blade used should be considered carefully, as shorter blades leave less fur behind, but increase skin irritation and degradation of the skin microbiome both immediately and 24 hours later. For this reason a 40 blade is generally recommended, which is either new or freshly cleaned (Messiaen et al, 2019).
Scrub solutions
For humans, a preoperative antibacterial wash is given before planned surgery, to be used both the day before and on the day of surgery (Guzman-Pruneda et al, 2019), which reduces the resident microbial flora before the patient enters the hospital. This is more difficult with veterinary patients, although a polite request for owners to ensure their pets are not excessively dirty is usually appropriate (Fossum, 2018).
Regardless of the choice of surgical scrub, physical dirt must be agitated and removed before surgery using a detergent (Gerrard, 2020). This prevents deactivation of the disinfection solution by organic matter, which includes blood and serum proteins in the case of povidone-iodine (Fletcher et al, 2007).
The most common surgical scrub solutions used in both veterinary and human fields are chlorhexidine gluconate solution and povidone-iodine. The veterinary surgeon most often chooses the antiseptic solution used to prepare the patient before surgery, according to his or her experience, although it is the veterinary nurse who often performs the actual surgical scrub (Rosewell, 2015). The surgical scrub procedure should be completed thoroughly and adequately, and the sites should be rinsed afterwards with alcohol or sterile water to ensure they are free of debris (Melekwe et al, 2018).
Scrub choice is influenced by effectiveness against specific pathogens, contact time and residual action; chlorhexidine gluconate solution has a contact time of 3 minutes (Curtis, 2021) and a residual action of up to 6 hours (Scowcroft, 2012). In contrast, povidone has a 10-minute contact time and a much shorter residual action (Shellim, 2007) of 90 minutes (Melekwe et al, 2018) following the drying time of the solution (Fletcher et al, 2007).
Storage of the solution once mixed is another consideration, as repeated waste of the scrub solution will cost the veterinary practice money and may alter adherence to protocols or choice of solution. Storing solution after dilution past the manufacturers recommended period may allow bacterial growth. Chlorhexidine has been found to be cheaper than povidone-iodine (Lee et al, 2010), although povidone-iodine which has been diluted can be kept for weeks if it is stored in aseptic conditions, sheltered from sunlight and extremes of temperature (Reddan, 2012; Uchida et al, 2014). The reliability of the dilution depends on the original formulation, as a povidone-iodine manufactured at 10% may have anywhere between 85 and 120% of the stated concentration, and up to 20% alcohol, even if this is not labelled (Pelletier et al, 2020).
Chlorhexidine gluconate
Chlorhexidine is a hypochlorite compound that destroys enveloped and non-enveloped viruses as well as fungi, bacteria and algae, but not spores (Roberts, 2013). This class of disinfectant compounds is inactivated by organic matter. They can cause irritation to the ocular, oropharyngeal, oesophageal and gastric tissues (Roberts, 2013; Wild, 2017). Chlorhexidine can cause a more severe skin reaction than povidine-iodine, including irritation (Rao et al, 2021), which tends to reduce its widespread use, although some prefer it as a 1:50 4% chlorhexidine gluconate solution rinse for intraoral surgeries (Curtis, 2021). da Silveira Teixeira et al (2019) found that use of a solution greater than 0.04% results in morphological changes of gingival fibroblasts and inhibition of cell proliferation.
Some studies state that chlorhexidine gluconate is a more effective skin disinfectant across a variety of surgical sites (Lee et al, 2010; Vackar, 2021) than povidone-iodine solutions, while other studies have found chlorhexidine gluconate solution to have similar effectiveness to povi-done-iodine compounds (Belo et al, 2018; Melekwe et al, 2018; Espinel-Rupérez et al, 2019).
Chlorhexidine gluconate is more effective if staff are trained correctly in its use (Scholz et al, 2021) or if it is combined with alcohol (Wade et al, 2021) and if both scrub and paint methods of application are used. This reduces the prevalence of surgical site infections (Kallmeyer, 2020), although for this method to be effective the scrub solution itself must be changed between the scrub and the final paint (Curtis, 2021). Certain methods can reduce the cost of the surgical scrub when using chlorhexidine gluconate instead of alternatives (Lee et al, 2010). Disposable single-use scrub applicator sticks used in human medicine were found to be less effective than using square gauze swabs (Syed et al, 2018), although this was a small study around a shoulder joint. More research is needed looking at different body contours, but in the meantime, the shape of the area being disinfected should be considered during the preparation period.
Povidone-iodine
Iodine is a bactericidal, fungicidal, sporicidal and virucidal compound. It is much less irritant to tissues than chlorhexidine gluconate, but is similarly deactivated by organic material (Wild, 2017). It is most commonly mixed with povidone to increase its stability and provide better sustained disinfectant activity. It acts by penetrating the cell walls of the microorganism and disrupting the synthesis and structure of proteins and nucleic acids.
Some studies, as well as literature reviews, state that the effectiveness of povidone-iodine alcohol solutions is higher than that of chlorhexidine gluconate (Peel et al, 2019; Schacherer, 2021), although povidone-iodine must be allowed to dry to be fully effective (Fletcher et al, 2007). Povidone-iodine is also ototoxic and can cause chemical burns in neonates, as well as being unsuitable for use on mucous membranes (Scowcroft, 2012).
Povidone-iodine is the recommended surgical scrub solution for ocular surfaces, with a dilution rate of 1:50 for the cornea and 1:10 for the surrounding skin (Reddan, 2012; Curtis, 2021), although some studies have reported less corneal irritation using 1% aqueous chlorhexidine gluconate than 5% povidone-iodine (Oakley et al, 2018; Ali et al, 2021). Some authors advise that povidone-iodine remains bactericidal at concentrations as low as 0.001% so its use should still be considered (da Silveira Teixeira et al, 2019) while others showed that reducing concentrations below 5% rendered povidone-iodine ineffective (Gnanasekaran et al, 2019).
In human surgeries the recommended surgical preparation solution is Chloraprep 2%, which contains chlorhexidine gluconate 70% and alcohol. If this is unsuitable or unavailable the second choice is Hibiscrub 4% chlorhexidine gluconate, although the instructions on dilution are unclear. If both chlorhexidine solutions are unsuitable, a povidone-iodine-alcohol 10% solution is recommended, and if this is not possible then the final recommendation is to use povidone-iodine 10% (National Institute for Health and Care Excellence, 2002).
Regardless of the base of chlorhexidine or povidone-iodine, combining either compound with alcohol reduces the occurrence of surgical site infection more than use of either of the compounds alone (Vij et al, 2018). Aqueous solutions of alcohol are more effective than pure alcohol and its use with either chlorhexidine gluconate or povi-done-iodine negates the hazards (including flammability and a lack of residual action) of using surgical spirit alone (Scowcroft, 2012).
Many studies have considered the effectiveness of individual scrub solutions alone. However, two studies found completing initial surgical scrubs with povidone-iodine based scrubs, allowing contact and drying time, then following this with a chlorhexidine gluconate scrub, was the most effective method of skin preparation (Mermel, 2020; Molloy et al, 2022). In this scenario, care must be taken not to mix the two compounds, as chlorhexidine gluconate is inactivated by iodine (Scowcroft, 2012; Roberts, 2013).
Studies in human medicine have found the specific microbial flora on the surface of the skin vary by area. This could indicate that generalised protocols are not ideal (Dockery et al, 2021), but that the choice of surgical scrub solution should be more personalised to the patient and the area of surgery.
Choice of scrub pattern
The popularity of the back and forth scrub pattern has increased, with some studies and companies claiming that this method is more effective (Curtis, 2021). Other studies have found that both concentric circles and the linear method of surgical scrub have the same effectiveness (Swales and Cogan, 2017). Alternatively, the scrub method chosen can be largely contour- and area-dependent for effectiveness, implying that a standard protocol for all surgeries may not be the best way to prevent surgical site infection (Dockery et al, 2021). Other studies have found the scrub pattern to be largely irrelevant and have found no significant drop in asepsis when a non-mechanical (ie soaking rather than scrubbing) method is used (Davids et al, 2015).
Regardless of scrub solution used, the author believes that any scrub pattern should consider the contour of the anatomy, and the pattern of scrub application should cover all surfaces, including irregularities in the epidermis, while never dragging potential contaminants towards the intended incision sites. One way to complete this is to use both clockwise and counterclockwise spirals, with fresh gauze to begin each spiral.
Drapes
The choice of surgical drapes is often also down to the surgeon’s preference, although it is usually a choice between reusable cloth drapes, which can be washed and autoclaved, or sterile single use drapes, that are sometimes impregnated with antiseptic or adhesive layers.
Kieser et al (2018) found no discernible difference between the incidence of surgical site infection in humans when comparing the use of disposable vs reusable drapes, and the same has been seen in the veterinary industry (Vasanthakumar, 2019). Reusable drapes cost significantly less than single use drapes (Cetin and Sonmez, 2021), both financially (with long-term use) and environmentally.
Use of adhesive drapes has been associated with a higher incidence of surgical site infection, which was not affected by impregnation with iodine (Jolivet and Lucet, 2019). A wider literature review found that use of iodine-impregnated drapes reduced the occurrence of surgical site infections, although this study did not specifically consider adhesive drapes (Nicholson et al, 2020).
Liquid antimicrobial skin sealants are sometimes used in human surgeries to reduce migration of bacteria towards the surgical site for several days post surgery. However, they have also been found to have no effect (Jolivet and Lucet, 2019) and so their role in the veterinary industry is unclear.
Antibiotic debate
Antibiotics are given prophylactically in most cases in human medicine (Allen et al, 2018; Hoel et al, 2018; Sarfani et al, 2022) to reduce surgical site infection (Martin et al, 2018). The choice of antibiotic is usually dictated by whether or not the patient has a known penicillin allergy (Sarfani et al, 2022). Studies have highlighted the importance of these being given in a timely manner, before the first surgical incision (Hagen et al, 2020), while other studies have reinforced that this cannot replace safe and sterile surgical practice (Lyssens et al, 2019). In the veterinary industry there has been a considerable drive toward the safe and responsible use of antibiotics. The British Veterinary Association (2019) recommendations on antimicrobial resistance state that prophylactic antimicrobials should never be given as a substitute for good management, and should be avoided unless they can be fully justified by a high level of infection risk. Espinel-Ruperez et al (2019) found no comparable difference in the occurrence of surgical site infection when the use of postoperative antimicrobials was reduced, extended or absent, although the patients were all given preoperative antimicrobials regardless of the clean, clean-contaminated or contaminated assessment of the proposed surgery. If used, the antibiotic chosen should be narrow spectrum, at an adequate dose and interval and, if possible, based on skin cytology testing, unless guidelines advise the prophylactic use of antimicrobials (Burgess, 2019).
Environment
Maintaining a clean surgical theatre is vital (Burgess, 2019). Studies have found that the use of ultraviolet C light is more effective at reducing levels of pathogens than manual cleaning alone (Browne et al, 2021). Contaminants in the immediate postoperative environment, such as the kennel area and the staff that are in contact with the patient, are additional routes of infection and must be clean or reduced where possible (Yakuba and Pilau, 2020). In human medicine, applying a suitable post-surgery wound protection has decreased rates of surgical site infection (Woodruff and Hohler, 2018), although in veterinary practice there are concerns over adherence, intolerance, interference and limited observation. Contamination from the home environment post surgery must also be considered.
Other factors
Some studies place a greater importance on other factors relating to the surgery, such as length of operating time (Stetter et al, 2021), using separate instruments to close a wound, irrigating the wound before closure and changing gloves before skin closure (Lyssens, 2017; Vij et al, 2018). The invasiveness of the procedure itself (Guzman-Pruneda et al, 2019), the provision of non-steroidal anti-inflammatory drugs and preoperative hyperglycaemia (Espinel-Ruperez et al, 2019) may be more important factors in preventing surgical site infection than the preoperative scrub. Nutritional status, the maintenance of normothermia throughout surgery (Woodruff and Hohler, 2018) and reducing the amount of people entering and leaving the theatre environment (Lyssens, 2017) all impact the likelihood of a patient developing a surgical site infection, and should be assessed, with protocols altered wherever possible.
In human surgery, lifestyle factors may increase a patient’s likelihood of developing a surgical site infection. These can include obesity (Guzman-Pruneda et al, 2019), advanced age and diabetes (Bordeianou et al, 2019), all of which are potentially applicable to veterinary patients.
If a wound site is left with a dead space, or the inflammation of local tissues is likely to form a dead space after surgery, postoperative negative pressure at a wound site, if possible, reduces the occurrence of surgical site infection (Javed et al, 2019). The use of closed drains rather than open drains is recommended (Lyssens, 2017) where drainage is required.
No reduction in incidence of surgical site infection has been seen with the use of antimicrobial-impregnated suture material (Thieman Mankin and Cohen, 2020), although the mass, possibly unnecessary, use of these products may have already been affected by the campaign for responsible use of antibiotics in the veterinary industry.
Planning a procedure carefully to reduce surgical time greatly reduces the occurrence of surgical site infection (Hoddinott et al, 2021). Part of this planning requires having equipment and staff ready and fully aware of the surgical requirements of the patient, as well as having the skills and knowledge to avoid unnecessary delays. Another consideration is performing surgeries in increasing order of contamination or decreasing order of cleanliness wherever possible. Edmiston (2018) discussed the use of a ‘champion’ within the practice to challenge, teach and model best practice behaviours for avoiding surgical site infections. This is a highly effective model for ensuring that good practice and training standards do not slip. This role also allows someone to take charge of assessing and assigning each patient a risk scale, according to the factors discussed above, to help decide which surgical scrub is appropriate. The champion can also ensure training is completed for new staff and as regular reviews for established staff, make sure protocols are followed without fail (Burgess, 2019), and check that preoperative antibiotics are given appropriately if deemed suitable.
Conclusions
While the debate around which surgical scrub solution to use is ongoing, providing there are no contraindications or sensitivities of the patient or area to the dilution agent used, potentially a more impactful method for reducing surgical site infection is to integrate a holistic approach to the patient and their commensal pathogens. This practice approach could be team-led to consider the patient’s general health, comorbidities and risk factors, potential for intervention or issue with mobility and drains, as well as the home environment, and any antibiotic culture and sensitivity testing.
Conflicts of interest
The author declares that there are no conflicts of interest.
KEY POINTS
- Surgical site preparation is vital to ensure sterility and reduce the number of cases of surgical site infection.
- Different tools and methods are promoted as being more effective, although little broad scale research encompasses all the variables relevant to the veterinary field.
- Clinical discussions of the patient’s individual case, condition, comorbidities and potentially skin cytology could be considered where appropriate to ensure an appropriate reduction in translocation of microbial skin flora.