Impact of wound irrigation during laparoscopic appendectomy on surgical site infection in acute appendicitis: a multicenter retrospective analysis

Surgical site infection (SSI) is one of the major complications after appendectomy. Among the many efforts to reduce variable risk factors, subcutaneous wound irrigation has been reported in some abdominal surgeries. However, there are no relevant literatures regarding patients who underwent laparoscopic appendectomy. This study aimed to determine the effect of wound irrigation before skin closure when performing laparoscopic appendectomy. Methods We included patients who had undergone laparoscopic appendectomy due to acute appendicitis from March 2017 to October 2019 from three hospitals. Clinical data of 333 patients were retrospectively collected, and we divided 333 patients into three groups according to the method of wound irrigation: no irrigation (n = 93), saline irrigation (n = 144), and povidone-iodine (PI) (n = 96) groups.


Introduction
Acute appendicitis is a very common in ammatory disease. According to the severity of in ammation or whether it is a perforated appendix or not, the surgical wound can be classi ed as clean-contaminated, contaminated or dirty wound by surgical wound classi cation [1]. Surgical site infection (SSI) is one of the major complications after appendectomy.
The incidence of SSI after appendectomy is reported as 7.0-8.7% [2,3]. As the laparoscopic approach has been introduced, laparoscopic appendectomy reduced the SSI rate as well as minimized the time of operation and produced better cosmetic outcome [4]. Thus, the SSI rate after laparoscopic appendectomy has been reported as 4.2% [5], which is lower than that of open appendectomy. Although some of the known risk factors for SSI cannot be corrected, many efforts to reduce variable risk factors have been performed. The use of a specimen retrieval bag in laparoscopic appendectomy signi cantly decreased SSI [5]. The use of an antibiotic powder before skin closure reduced SSI [6]. To decrease the SSI rate, wound irrigation utilizing various materials are performed. Povidone-iodine (PI) irrigation during spinal surgery signi cantly reduced the SSI rate compared to saline irrigation [7]. In abdominal surgery, subcutaneous wound irrigation with 0.04% polyhexanide solution signi cantly reduced SSI [8]. Moreover, 0.05% chlorhexidine gluconate irrigation reduced SSI after loop ileostomy closure [9]. However, there is lack of studies about the relationship between wound irrigation and SSI in acute appendicitis.
This study focused on the effect of wound irrigation before skin closure in the multicenter setting. We aimed to study the kind of irrigation solution that can in uence the occurrence of SSI during laparoscopic appendectomy in acute appendicitis. In addition, we attempted to determine the risk factors related to SSI after laparoscopic appendectomy.

Patients
We included patients who had undergone laparoscopic appendectomy due to acute appendicitis from March 2017 to October 2019 from three hospitals. All patients were diagnosed with acute appendicitis by abdominopelvic computed tomography (APCT) scan. We excluded patients who needed open appendectomy or open conversion after laparoscopic approach owing to severe in ammation or adhesion during the operation. Patients under 18 years old were also excluded. To minimize the confounding effect derived from different types of skin preparation solution, only patients who underwent skin preparation with PI were included. Laparoscopic appendectomies were performed by four experienced colorectal surgeons. Finally, a total of 333 patients were included in the analysis.
We divided 333 patients into three groups according to the method of wound irrigation during laparoscopic appendectomy: no irrigation (n = 93), saline irrigation (n = 144), and PI (n = 96) groups ( Fig. 1). The suturing technique was adopted according to the surgeon's discretion, i.e., stapler, vertical matrix suture with nylon, or subcuticular suture with absorbable materials. Absorbable sutures were used for approximation of the fascia, and the subcutaneous space was irrigated with saline or PI.
Clinical data were retrospectively collected, such as sex, age, American Society of Anesthesiologists (ASA) physical status classi cation [10], and body mass index (BMI). Preoperative laboratory ndings were reviewed, including white blood cell (WBC) count (⋅10³/µL) and hemoglobin (g/dL), albumin (g/dL), C-reactive protein (CRP) (mg/dL), and erythrocyte sedimentation rate (ESR) (mm/hr) levels. The presence of fever was de ned as body temperature higher than 37.8℃. Both preoperative fever and postoperative fever were recorded. Operative data including operation time, presence of perforated appendicitis, the method of wound irrigation, wound closure, and umbilical skin incision were also collected.
SSIs were de ned according to the criteria of the National Nosocomial Infection Surveillance System (NNIS) by the Centers for Disease Control and Prevention(CDC) [11,12], which can be super cial, deep, and organ/space SSI. Super cial incisional SSI involves only the skin and subcutaneous tissue. Deep incisional SSI involves deep tissues, such as fascial and muscle layers, and organ/space SSI involves any part of the organs' anatomy and spaces that are incised, which were opened or manipulated during operation [13].

Statistical analysis
Categorical variables were analyzed using chi-square or Fisher's exact test. Continuous variables were analyzed using Student's t-test. Data were presented as number (%) or mean ± standard deviation. Univariate logistic regression analysis was done to identify risk factors associated with SSI. P < 0.05 was considered statistically signi cant. Statistical analysis was done using IBM SPSS ver. 20.0 (IBM Co., Armonk, NY, USA).

Patient characteristics and data related to the operation
The demographics of total 333 patients are listed in Table 1. There is no signi cant difference in sex, age, BMI, and the status of preoperative fever (> 37.8℃) between the groups when comparing according to the method of wound irrigation. However, the ASA score differed signi cantly and the ratio of ASA I was higher in the no irrigation group (p < 0.001). In the preoperative laboratory test, hemoglobin and total bilirubin levels were higher in the saline group than that in the other groups (p < 0.001, p = 0.011), and albumin level was signi cantly lower in the PI group (p < 0.005). Although the ratio of perforated appendicitis was higher in the PI group (p < 0.001), there was no signi cant difference in the preoperative fever (> 37.8℃) (p = 0.539), preoperative WBC count (p = 0.921), and CRP levels (p = 0.488) among the groups. In the method of wound closure, most patients in the no irrigation and PI groups underwent skin closure using a stapler or nylon, while patients in the saline group underwent subcuticular suture (p < 0.001). The umbilical skin incision was performed differently, and supraumbilical incision was a substantial portion of the methods in the no irrigation and PI groups (p < 0.001) ( Table 2).    Table 3). In the univariate analysis, none of the factors was associated with SSI (Table 4).

Discussion
In this study, SSI occurred in 15 of 333 patients (4.5%). No deep SSI was observed among these patients.
There was no difference in the SSI rate between groups according to the wound irrigation method. Previous researches on wound irrigation have been conducted to reduce SSI in surgery, not only appendectomy but also other surgeries. Various materials can be used for wound irrigation such as saline, PI, chlorhexidine gluconate, and topical antibiotics. Antiseptic irrigation at the surgical wound can decrease microbial burden and the need for systemic antibiotics [14]. One meta-analysis revealed that irrigation with any solution signi cantly decrease SSI than no irrigation [15]; however, no su cient evidence is available for its acceptance as a standard procedure. Chlorhexidine irrigation in caesarean section did not signi cantly decrease SSI [16]. During spinal surgery, deep SSI was signi cantly reduced after surgery when irrigation was performed with PI at regular intervals during surgery [7]. Topical antibiotics are also applied to the surgical wound to reduce SSI. Topical antibiotics can kill bacteria that cause SSI more effectively than systemic antibiotics because the concentration of antibiotics at the wound is higher than systemic antibiotics [17]. Although there is no su cient evidence that the application of topical antibiotics is bene cial, it is said to be bene cial in abdominal surgery in obese patients [18]. During pancreaticoduodenectomy, intraperitoneal irrigation with antibiotic solution did not signi cantly decrease infectious complications [19]. However, if it has been reported to be meaningful only in some studies, it is not generally accepted as a way to reduce SSI [20].
We attempted to nd the risk factors for SSI by logistic regression analysis using previously known risk factors as variables for analysis. However, there was no signi cant risk factor. Diabetes mellitus and uncontrolled blood glucose are well-known risk factors of SSI [21]. Although the detailed underlying disease could not be known in this study, SSI incidence did not show a signi cant relationship with the ASA score in re ecting the patient's underlying disease and severity. Advanced age is also a known risk factor of SSI [22]. However, advanced age did not affect SSI in this study. Prolonged operation time can increase SSI, but not in this study.
In our study, wound irrigation was performed according to surgeon's preference, not for speci c reasons. In other words, wound irrigation was done not because SSI is expected, but rather as a routine procedure. In this study, selection bias did not occur, which may happen if irrigation was performed considering that SSI was likely to arise. To reduce SSI, various efforts can be made before, during, and after surgery. Various methods before and after surgery have been studied for reducing the SSI rate. Wound irrigation during surgery was considered to be one of the methods used to reduce SSI, and many studies were conducted in various surgeries. To reduce SSI in laparoscopic appendectomy, we tried wound irrigation in previous studies. However, in this study, it was not concluded that wound irrigation using PI and saline reduces SSI.

Conclusions
We tried to gure out the relation between wound irrigation and SSI according to previous known factors for SSI. We could not show any risk factor associated with SSI, and it was not related to wound irrigation.
A large-scale retrospective study or a randomized controlled study is required to determine relevant factors and reduce SSI in the future.

Consent for publication
Not applicable Availability of data and materials The datasets generated and/or analyzed during the current study are not publicly available due to privacy but are available from the corresponding author on reasonable request.