Cleaning with a wet sterile gauze significantly reduces contamination of sutures, instruments, and surgical gloves in an ex-vivo pelvic flexure enterotomy model in horses

Abstract

The objective of this study was to investigate whether cleaning surgical materials used to close pelvic flexure enterotomies with a wet sterile gauze will reduce contamination and whether the use of a full thickness appositional suture pattern (F) or a partial thickness inverting (or Cushing) suture pattern (C) would make a difference in the level of contamination. Large colon specimens were assigned to group F or C and divided into subgroups N and G. In group G, a wet sterile gauze was passed over the suture material, another over the instruments, and another over the gloves. In group N, no treatment was applied. The bacterial concentration was measured by optical density (OD) at 24 h. The OD of subgroup CG was lower than that of subgroup CN (P = 0.019). The OD of subgroup FG was lower than that of subgroup FN (P = 0.02). The OD of subgroups CG, CN, FG, and FN was lower than that of the negative control (P < 0.003, P < 0.001, P < 0.001, and P < 0.00). The use of a sterile wet gauze significantly reduced contamination of suture materials. A partial thickness inverting suture pattern did not produce less contamination than a full thickness appositional suture pattern.

Reducing surgical complications is one of the primary aims of surgery. Surgical site infection (SSI) is one of the most common complications encountered in surgery (1). New surgical materials have been created, such as antibiotic-coated suture threads, and surgical procedures have been improved to reduce the risk of surgical site infections and eventually reduce the use of post-operative systemic prophylactic antibiotics (1–4).

Surgical sutures can act as foreign bodies and as a potential nidus for infection, thereby preventing wound healing (5,6). Bacterial adherence to suture materials plays an important role in the development of suture infection (6,7). Thus, in highly contaminated surgical procedures, such as pelvic flexure enterotomy, infections could occur throughout the 2-layer enterotomy closure due to bacterial contamination of the suture. Previous research has shown that monofilament sutures are superior to braided sutures in contaminated wounds because bacteria adhere more tightly to braided sutures, which leads to more infections (6,8). Furthermore, recent studies on incisional infections in humans have established that biofilms occur on suture materials and are responsible for postoperative infections (9). Microorganisms that grow in a biofilm are highly resistant to antibiotic therapy and can be a serious challenge to eradicate (10). It is therefore important to minimize or prevent contamination at an enterotomy site.

The outcome of equine colic surgery can be influenced by different factors, many of which are beyond the surgeon’s control. As treatment modalities, such as preoperative, surgical, and postoperative treatments, are likely to influence outcome, the study of these factors could improve the final result and perhaps increase understanding of some surgical complications. Many aspects of the treatment of surgical colics appear to be influenced by the individual surgeon’s preferences, which may benefit from scientific research to identify the best practice to apply (11). One of these could be the pelvic flexure enterotomy (PFE).

Enterotomy is a routine procedure in abdominal surgery in both humans and animals, with enterotomy of the large colon pelvic flexure being particularly common in horses. Although the risk of surgical complications is low, the procedure may cause contamination and inflammation that could lead to postoperative complications, including peritonitis and adhesions (12), either of which can prove fatal to horses. The use of sterile materials and aseptic procedures is therefore mandatory in order to prevent surgical site infections (13). A 2014 survey of current methods used in pelvic flexure enterotomy closure by the European College of Veterinary Surgeons (ECVS) and the American College of Veterinary Surgeons (ACVS) revealed that 58.3% of surgeons adopt measures to reduce contamination during enterotomy closure (14). The most common approach was to close the second layer of the enterotomy with a new suture strand, which is associated with a simultaneous change in surgical gloves and instruments (14). Although some studies reported the use of 2 suture strands to close enterotomies (15), there is no evidence that this technique significantly reduces contamination.

Our main hypothesis in this study was that cleaning the sutures, gloves, and instruments used to close the first layer of a pelvic flexure enterotomy with a wet sterile gauze would significantly reduce bacterial contamination. Our second hypothesis was that a full thickness first layer suture pattern would have the same affect on the level of contamination as an inverting suture pattern. We compared bacterial contamination of surgical materials before and after cleaning with a wet sterile gauze in an ex-vivo pelvic flexure enterotomy model in horses.

Samples from the left colon, including the pelvic flexure and approximately 100 cm of ventral colon and 100 cm of dorsal colon, were harvested from 36 horses at a local abattoir immediately after slaughter. Pelvic flexures were placed individually in sterile plastic bags and immersed in sterile 0.9% saline solution at room temperature. The neck of the bag was closed with a plastic band. The pelvic flexure was then cut free from the rest of the large colon. All the tests were conducted within 2 h after death. Samples were randomly assigned (www.random.org) to 2 groups: full thickness (F) and Cushing (C), with 18 samples per group. To mimic clinical settings, each pelvic flexure was placed over a sterile drape on a colon tray. An 8-cm-long incision was made on the antimesenteric site and the luminal content was emptied using a water hose fed into the lumen of the colon. The enterotomy site was continuously lavaged during the procedure with sterile fluids (5-L Ringer’s Lactate Solution; SALF SpA, Bergamo, Italy) flushed on the bowel from a standardized height of 30 cm and at a constant rate of 1 L/min. In group F, after the left colon was completely empty, the enterotomy site was closed with a 1-layer, full thickness, simple, continuous pattern suture, whereas in group C, it was closed with a Cushing pattern. All the suture lines were started and ended with a surgeon’s knot. These sutures represented the first of a 2-layer suture pattern, which is usually recommended (15). The same experienced surgeon (MG) closed all enterotomy sites using a 2-0 monofilament suture material (Biosyn 2-0; Covidien, Milano, Italy). A new set of sterile instruments and sterile gloves were used to carry out the surgical procedure for each specimen.

Groups F and C were divided into 2 subgroups: not treated (N) and gauze wipe (G), each consisting of 9 samples. In subgroup N, the first 15 cm of suture material and the needle were collected immediately after completion of the suture line. A sterile swab, moistened by immersing in sterile water for 2 s, was passed over the surgical gloves at the level of the 2 distal phalanges of each finger in a proximodistal direction once, in the center of the palmar surface of the finger. Another sterile swab, moistened as before, was passed over the jaws of the needle holder and the tip of the forceps. Each swab and the suture material were placed in a sterile test tube containing a nutrient broth (Oxoid, Milano, Italy) for growing bacteria cells. In subgroup G, after completion of the suture line, sterile gauze soaked with sterile saline was passed twice over the suture material before culture swabs were collected. Two other sterile, soaked gauzes were used to clean the instruments and the gloves, respectively. Sterile culture swabs were then collected in the same way as for group N. A negative control group was also prepared with 18 samples as for the other groups. Sterile swabs, moistened as reported, were passed over the sterile gloves and instruments before being touched by the surgeon and a new strand of suture material and needle were collected before starting the procedure. As done previously, each swab was placed in a sterile test tube with a nutrient broth.

Collected suture strand and swabs were incubated in nutrient broth at 37°C for 24 h. The bacterial concentration for each sample was then measured by obtaining the optical density (OD) of the broth culture and comparing it to a non-inoculated broth culture (blank/control). Optical density (OD) measurements were taken at 600 nm using the Ultraspec 2000 Spectrophotometer (Pharmacia Biotech, Piscataway, New Jersey, USA).

Statistical power and sample size were calculated using a prefilled Microsoft Excel sheet provided by our statistical department (Microsoft, Redmond, Washington, USA) with the calculated number being 9 per each subgroup. Normal distribution of the data was evaluated with the Shapiro-Wilk test. As this showed that the data were not normally distributed, the Kruskal-Wallis test was used to compare differences in optical density between subgroups for surgical materials. Results were reported as the median (range) and P-values < 0.05 were considered significant. Statistical analysis was done using commercial software (Prism 6.01; GraphPad Software, La Jolla, California, USA).

Results are summarized in Table I. The median OD (min-max) of subgroup CG was 0.054 (0.00 to 0.17) and was significantly lower than subgroup CN, which was 0.1 (0.008 to 0.36; P = 0.019). Additionally, the OD of subgroup FG was 0.049 (0.007 to 0.30) and it was significantly lower than subgroup FN, which was 0.123 (0.015 to 0.27; P = 0.02). The difference between subgroups FN and CN and subgroups FG and CG was not significant (P > 0.999). Furthermore, the differences between subgroup CG, CN, FG, and FN and the negative control, which was 0.007 (0.003 to 0.03), were significant (P < 0.003, P < 0.001, P < 0.001, and P < 0.001, respectively).

Table I.

Optical density (OD) results of different groups

	CG	CN	FG	FN	Negative
OD	0.054 (0.00 to 0.17)a	0.1 (0.008 to 0.36)	0.049 (0.007 to 0.30)b	0.123 (0.015 to 0.27)	0.007 (0.003 to 0.03)c

^aMedian OD of CG is significantly lower than CN.

^bMedian OD of FG is significantly lower than FN.

^cMedian OD of negative group was significantly lower than all subgroups.

Our results demonstrate that after completion of the first layer of pelvic flexure enterotomy closure in horses, wiping with wet sterile gauze ensures a more significant reduction in contamination of suture strand, surgical gloves, and instruments than not wiping. The optical density was similar with a partial thickness inverting (C) or a full thickness appositional (F) pattern of suture. Furthermore, our results demonstrate that a partial thickness inverting suture pattern does not produce significantly less bacterial contamination than a full thickness appositional suture pattern.

It is difficult, if not impossible, to maintain complete asepsis when carrying out a pelvic flexure enterotomy as intraoperative emptying of the colon using a water hose ensures that some ingesta comes in contact with the bowel serosa near the enterotomy site even with aggressive lavage with sterile fluids. Contact between the suture material, gloves, and surgical instruments and the contaminated bowel cannot be avoided when the enterotomy site is closed, which leads to bacterial contamination of the suture material. Therefore, changing the suture material is not sufficient to decrease contamination, as both the instruments and gloves would also have been in contact with the bacteria from the colon (16). The surgeon should assume that the new suture material, instruments, and gloves will likely become contaminated shortly after they come in contact with the area around the enterotomy site. Thus, simply cleaning the suture material, instruments, and gloves with a wet sterile gauze could be effective at reducing the contamination.

An inverting suture pattern does not provide any advantage in terms of contamination of suture material and surgical instruments based on the similar OD values found. The failure to show a difference may result from contact between the surgical material and the highly contaminated edges of the enterotomy site when an inverting pattern is used. An inverting suture pattern may even be detrimental, due to poor bleeding control, poor healing, and excessive inversion of the tissue (15). Hemorrhage control is a crucial factor in the choice of suture pattern, and the full-thickness layer is designed to control bleeding by grasping the mucosa within each needle bite (15).

Although the contamination of suture material and instruments has been reported previously (16,17), only 1 study has evaluated methods to reduce contamination during surgical operations without the use of sterilization or changing suture materials but rather by using isopropyl alcohol (18). The suture material may potentiate the infection at the enterotomy site due to bacterial adherence (17), thus increasing the risk of infection (5,8,17). Inflammation due to suture material increases susceptibility to infection and may cause bacterial biofilm to form, which is difficult to treat and complicates the outcomes of surgical procedures (6,18). This study did not establish that biofilm formation would be decreased or prevented. The fact that the median optical density of the group using gauze (G) was 7 times that of the median optical density of the negative control (N) suggests that a substantial number of bacteria is still present on the suture, instruments, and gloves. It could be speculated that wiping with a gauze may be enough to diminish the biofilm formation, but this cannot be proved with this study. Nevertheless, a surgeon who carries out an enterotomy should always follow good surgical practice to minimize contamination as much as possible. During closure of an equine pelvic flexure enterotomy, if the first layer of the closure is contaminated, then minimizing contamination for the second layer of closure should effectively reduce inflammation and procedural complications.

The present study is limited because it was conducted in an ex-vivo setting, which did not allow us to evaluate all the factors that may contribute to potential complications, including postoperative adhesion formation, in order to assess the effectiveness of our method. However, the conditions of each enterotomy were similar and the health status of the animal or the degree of ischemia of the pelvic flexure were not factors in determining bacterial levels. In this study, although we did not assess the type of bacteria present after suture and swab incubation, we evaluated a method to clear adherent bacteria, independently of their species. Although the study was carried out using the same instruments and conditions as in a surgical theater, it is important to note that different in-vivo factors may contribute to the healing of highly contaminated wounds.

Although we didn’t compare monofilament and multifilament suture materials, we chose a monofilament suture material that withstands contamination better than multifilament sutures (8,17,19–20). Different results may be obtained with different suture materials. The type of sampling used could be seen as another limitation of this study. Results may have been different if the tips of the instruments and the fingers of the gloves were immersed directly in the nutrient broth and incubated instead of using moistened swabs. We decided to consider the contamination of gloves, instruments, and suture material as a total and not differentiate among the contaminations. This situation could be seen as a limitation, but it was decided to assume that, if only one of these materials still presented a contamination risk after the procedure of wiping, all of the materials would immediately become contaminated again, thereby canceling the effect of the sterile gauze.

In conclusion, we can state that a partial thickness inverting suture pattern in the first layer of a pelvic flexure enterotomy does not reduce contamination of suture material, instruments, and gloves compared with a full-thickness pattern. Cleaning the suture material, instruments, and gloves with a wet sterile gauze significantly reduces contamination at the PFE site. Based on the findings of this study, we can speculate that application of this method in a clinical setting should reduce bacterial contamination of pelvic flexure enterotomies in horses.