Surgical Site Preparation

Preoperative site preparation is important to reduce the incidence of surgical wound infection. An ideal preoperative solution should rapidly decrease the number of microorganisms immediately after the scrub at the surgical site and maintain a residual effect for an extended period. Therefore, self-infection of patients by the transfer of potential pathogens from skin to underlying tissue with a scalpel, needle, or implants is prevented.1,2

Preoperative skin preparation is designed to prevent surgical site infection (SSI).2–4 Although it is not possible to sterilize skin, extremely low numbers of microorganisms at the time of the incision will decrease the chances of infection. The population of microorganisms may be divided in two distinctive categories: resident and transient. Transient microflora are contaminants on the superficial layer of the skin and are characterized by their inability to reproduce on skin.⁵ The pathogens or infectious flora are included in this category. They are efficiently eliminated by preliminary cleaning with soap and water.^6,7 Resident microflora are the normal inhabitants of skin. These flora contribute to the host’s inherent resistance to colonization by potentially pathogenic flora, but these resident flora also are more resistant to hand washing with soap.⁵ Many bacteria reside superficially within the epidermis, and this compromises the efficacy of certain disinfectants.^6,8,9 By using disinfectants, we aim to eliminate transient microflora and significantly decrease resident microflora immediately before a skin incision.^5,6,10

Numerous research studies have been performed to find the best preoperative preparation protocol in humans as well as in dogs.4,11–16 All of those protocols were effective in decreasing the number of microorganisms persisting on skin. Although their environment and skin microflora are quite different, most large animal patient preoperative preparation protocols are extrapolated from other species. Whatever the species, preparation of the surgical site is divided in three basic parts: (1) hair removal, (2) site cleaning, and (3) sterile preparation.

Hair Removal

Clipping or shaving the surgical site improves contact of the disinfectants solution with skin and decreases the population of resident microorganisms more efficiently. In humans, shaving the surgical site has been proven to damage the natural epidermal skin barrier, favoring bacterial growth.17,18 As a consequence, the use of razor blades to shave operative sites has been associated with a higher frequency of surgical wound infection (SWI) compared with depilatory cream or clipping for hair removal. Hair of animals is most often dense, and shaving may be the best hair removal technique to increase the efficacy of disinfectant contact. Lloyd et al. compared the effect of shaving and clipping on bovine epidermal structure. Their conclusion was that shaving as well as clipping removed several cell layers of the stratum corneum and the protective lipid layers.¹⁹ They also reported that a 1-minute scrub on finely clipped skin removed more cell layers than a 2-minute scrub on coarsely clipped skin. In humans, shaving the skull before head surgery is not better for prevention of SWI.^20,21 Bédard compared four protocols of preoperative preparation in cattle.²² Surgical wound infection frequency was the same for cattle undergoing clipping or shaving, although skin reactions occurred more frequently when povidone-iodine and chlorhexidine were used on shaved skin (47.8%) compared with clipping alone (8.7%).

Whatever the hair removal technique used, this should be done immediately before the surgery. Shaving or clipping the previous day has been shown to increase SWI.²³ Instruments used for clipping or shaving should be sharp and lubricated to avoid any skin trauma. A No. 40 clipper blade (Oyster) is routinely used in our clinic. When animals have a thicker winter coat, a larger blade may be used first and followed by the No. 40 blade. The surface to be clipped should be wide enough to account for surgical drape sliding, manipulation around the incision, and lengthening of the incision, if needed. A general rule that has been proposed (D.E. Anderson, personal communication, 2012) is, the width and length of the clipped area should be at least four times wider and two times longer than the primary surgery site. For example, if the primary (exposed skin) area for a laparotomy incision is 10 centimeters (cm) wide by 20 cm long, the clipped and aseptically prepared area should be 40 cm wide by 40 cm long centered on the proposed incision site.

Antiseptics

A distinction needs to be made between antiseptics and disinfectants. Both antiseptics and disinfectants destroy microorganisms by chemical and physical means. However, the term “disinfectant” refers to a substance applied to inanimate objects, whereas an “antiseptic” is applied to living tissue.²⁴ Many antiseptics have been used for the preparation of surgical sites. The most commonly used are povidone-iodine, chlorhexidine gluconate, and alcohol.

Povidone-iodine is a member of the iodine family. Solution of iodine (Lugol and tincture) is one of the oldest antiseptics. These contain elemental iodine, iodine salt (potassium or sodium), and ethanol. Iodine-based antiseptics are efficient and fast acting, but they stain and often irritate skin. Povidone-iodine is a compound composed of polyvinylpyrolidone and iodine, which allows a slow release of iodine, consequently decreasing its irritating and staining effect. Povidone-iodine has a broad spectrum of activity against bacteria and fungi. The mechanism of action is by crossing the cell wall and destroying microbial protein and deoxyribonucleic acid (DNA). Necessary contact time with skin is longer than the time for the iodine solution to be effective.²⁵ Iodophors are partially neutralized by organic material such as blood and sputum, and this is proportional to the amount of organic material present. The minimum contact time is greater than 2 minutes, which can be a disadvantage.^26–28 Addition of alcohol to povidone-iodine improves the efficacy and efficiency and decreases the minimum contact time.¹⁵

Chlorhexidine gluconate has been used more recently for aseptic preparation for surgery. Chlorhexidine gluconate is a cationic molecule and therefore may be incompatible with inorganic ions and some nonionic substances (soaps, detergent, carboxymethyl cellulose iodine compounds). These compounds may inactivate or precipitate the chlorhexidine.²⁷ The mechanism of action of chlorhexidine gluconate is complex and is related to the change of a negatively charged bacterial membrane to a positive charge. This modifies the cytoplasmic membrane exchange, leading to leakage of cytoplasmic contents.²⁷ The major advantages of this disinfectant are a broad range of action and residual effects for up to 6 hours. The residual effect occurs because of protein binding to the stratum corneum and activity in the presence of organic material.^1,2,27 Contamination of chlorhexidine solutions has been reported when the concentration is altered by diluting the product with tap water to less than 1%.²⁷ Bacterial counts after surgical preparation in animals treated with chlorhexidine were lower than those in animals treated with povidone-iodine in both dogs and cattle.^14,29 However, despite significantly lower numbers of bacteria, SWI frequency was the same whichever disinfectant protocol was used. In dogs, skin irritation was significantly more frequent with povidone-iodine than with chlorhexidine.¹⁴ This was not observed in cattle.²⁹

Alcohol is used in many forms, but the most common forms are isopropanol and ethanol. The concentration may vary from 60% to 90%. Alcohol is advantageous because it is effective against most microorganisms, acts by denaturing proteins, and has a fast onset of action. However, its drying effect on skin may be detrimental if frequently used in high concentration. Products designed for hand disinfection include emollients to avoid this side effect, but emollients are undesirable for surgical site preparation. Regrowth of bacteria on skin occurs quickly after use of alcohol-based antiseptics, presumably because of the sublethal effect alcohols have on some of the skin bacteria. For this reason, it is essential to combine alcohol with either chlorhexidine or povidone-iodine in a preoperative skin preparation protocol.²⁶

Recently, a metaanalysis of preoperative antisepsis on clean-contaminated procedures in human patients showed that SWI occurred significantly less often when chlorhexidine was used compared with povidone-iodine.³⁰ Metaanalysis on clean surgical procedures found no difference among different antiseptics for SWI.³¹ Interestingly, chlorhexidine antisepsis has been recommended for preparing the central venous catheter site because CG was associated with a 49% less chance of infection compared with iodine, as recommended by the Centers for Disease Control and Prevention (CDC).^32,33 Blood culture contamination rate was decreased by 30% in a pediatric emergency department when chlorhexidine was used to prepare the puncture site instead of povidone-iodine.³⁴ This may be associated with the shorter preparation time for asepsis before catheter placement and blood sampling as opposed to a surgical procedure. Chlorhexidine has a faster onset of action compared with povidone-iodine and may partially explain the difference.²⁷ This difference may also be explained by the better efficacy of chlorhexidine in the presence of blood, its residual effect, and a 50-fold lower minimum inhibitory concentration needed against nearly all nosocomial bacteria and yeasts.³⁵

A disinfectant protocol combining rapid onset, potency, and residual effect improves efficiency by saving time without adversely influencing efficacy. The most common protocols for surgical site preparation involve alternating the use of chlorhexidine or povidone-iodine and isopropyl alcohol. This allows for the advantages of combining rapid unset of action and residual effect. An iodine compound with 0.7% of free iodine in a solution of 74% isopropyl alcohol has been used for more than 20 years (Dura Prep). Once applied on skin, a waterproof bactericidal film is formed and acts as a physical as well as chemical barrier. The spectrum of action is similar to that of povidone-iodine, although it has a rapid onset of action combined with a residual effect. This preparation does not seem to have a significant advantage compared with more traditional preoperative protocols with regard to the number of colony-forming units (CFUs), frequency of SWI, and skin reaction. The only significant difference was the shorter preparation time required for Dura Prep.15,16,36 Galuppo evaluated two preoperative protocols in horses: (1) a combination of povidone-iodine and alcohol and (2) Dura Prep®.³⁷ As previously mentioned, Dura Prep preparation time was shorter, but no significant differences were found in the number of CFUs perioperatively. Two commercial combinations of chlorhexidine gluconate and alcohol are available: (1) Chlorhexidine gluconate 2% with 70% isopropyl alcohol (Chloraprep) as a preoperative scrubbing agent and (2) a combination of chlorhexidine gluconate 0.5% with 70% isopropyl alcohol (Baxedin PreOp). Studies comparing these different preparation solutions have yielded contradictory results.38,39

Preparation Time for Patient Asepsis

Duration (contact time) of the preparation solution is as important as the disinfectant itself. In 1986, the CDC suggested that the preoperative preparation should last between 3 and 6 minutes for SWI prevention.⁴⁰ Scrubbing times longer than 10 minutes may cause damage to skin and translocation of the superficial epidermal bacteria to the skin surface.²⁶ Povidone-iodine and chlorhexidine gluconate were compared as skin preoperative protocols, and both were similarly efficient in decreasing the number of CFUs on the skin of cattle. This protocol included 5 minutes of a sterile scrub using alternate passages of isopropyl alcohol and povidone-iodine or chlorhexidine gluconate. Chlorhexidine gluconate was more effective in reducing the number of CFUs compared with povidone-iodine, but the SWI rate was similar for both protocols (10.7% and 9.8%)].²⁹ In a study of preoperative methods, four protocols were compared: (1) shaving and chlorhexidine gluconate, (2) clipping and chlorhexidine gluconate, (3) shaving and povidone-iodine, and (4) clipping and povidone-iodine.²² The duration of the preparation was 6 minutes: 3 minutes of cleaning with disinfectant detergent and 3 minutes of sterile scrub using 3 alternate strokes of the selected disinfectant and isopropyl alcohol. The four protocols were similarly effective in decreasing the number of CFUs before surgery, with a bacterial percentage of reduction of 99.7% to 99.9%. The infection rate between the treatment groups was not statistically different, varying from 0% to 8.7%. No residual effect of disinfectants was found in this study, in contrast to previous work in other species.^14,22,27 Time as a factor in protocols for skin preparation was examined in horses before arthrocentesis of the coffin joint.⁴¹ The four povidone-iodine preparation protocols were (1) 10-minute scrub, (2) 5-minute scrub, (3) three 30-second scrubs, and (4) a one-step iodophor commercial surgical solution. They were all equally effective in reducing the number of bacteria at the site of arthrocentesis. Preoperative antiseptics combining either chlorhexidine or povidone-iodine and alcohol have a shorter period of application. It is important to follow the manufacturer’s recommendations for the duration of application.

Aseptic Scrubbing Technique

The scrubbing action itself is quite important to mechanically remove skin debris and decrease microorganisms. Although this fact has been well accepted, recent research on hand washing and scrubbing in human surgery has questioned its validity.42,43 In camelid patients, scrubbing is essential to remove dirt and organic debris on the skin surface.

The first step is to scrub the animal with a soft-bristle brush to avoid damaging the epidermis. It is essential to use the same disinfectant class throughout all steps of surgical preparation. Disinfectants with detergent are used first. The foaming action of detergents keeps debris suspended so that they can be eliminated easily with rinsing. In my opinion, scrubbing should last at least 3 minutes in camelids for the cleaning portion of the preparation, especially for a surgical area as in ventral exploratory laparotomy. After 3 minutes of cleaning, the percentage of reduction of bacteria is between 95.7% and 98%, depending of the preoperative protocol used.²²

The second step is the sterile scrub itself. With a soft-bristle brush or sponge, scrubbing action should start from the center in a circular manner, going progressively toward the periphery of the planned surgical site without ever coming back to the previously scrubbed areas. The surgical site may be divided into three distinctive portions: (1) the portion that is directly on the surgical site (primary field), (2) the area surrounding the planned incision (secondary field), and (3) the junction of the clipped and unclipped hair (boundary zone). On the basis of earlier principles, we start with the first zone followed by the second and finally the third. For each zone, 60 to 90 seconds of scrubbing is performed. After scrubbing, the surgical site is cleaned with alcohol on gauze or with sterile saline.

The last step consists of three alternate passages with isopropyl alcohol and a disinfectant without detergent.²⁵ The alternate passages are performed the same way as described for the sterile scrub. Products combining chlorhexidine gluconate and alcohol may save time, but studies are needed to evaluate safety and efficacy of these products in camelids.