Single-port access (SPA) laparoscopy has been widely performed in gynecologic disease due to its advantages over conventional laparoscopy (1, 2). SPA requires only one abdominal incision at the umbilicus, unlike conventional laparoscopy, which requires at least two or three incisions. However, the umbilical incision of SPA laparoscopy is larger than that of conventional laparoscopy because insertion of all laparoscopic instruments and specimen retrieval are performed through the umbilicus (3). Therefore, patients treated with SPA laparoscopy can be vulnerable to postoperative pain despite receiving the smallest number of abdominal incisions among minimally invasive surgeries (MISs).

Postoperative pain is one of the major concerns for patients before undergoing surgery (4). Inadequately managed postoperative pain can cause various complications such as impairment of physical function and lengthened hospital stay, increasing socioeconomic costs (5). Therefore, pain management is considered one of the key elements in the Enhanced Recovery after Surgery (ERAS) protocol (6, 7). Various pain control methods such as systemic and regional analgesics have been developed (8). Traditionally, a combination of systemic analgesics based on intravenous patient-controlled analgesia (IV PCA) has been preferred for MIS as a multimodal approach. However, the side effects associated with opioids are a disadvantage of IV PCA (9). The continuous wound infiltration (CWI) system, in which a local anesthetic is continuously applied into the surgical wound, has been demonstrated to have postoperative pain–reducing effects and opioid-sparing effects in various laparotomic wounds (10, 11). However, no study has evaluated the effectiveness of a CWI system to manage postoperative pain for SPA laparoscopy for gynecologic disease, which requires the largest incision among MISs.

Therefore, the purpose of this study was to evaluate whether simultaneous use of the CWI system and IV PCA effectively decreases postoperative surgical site pain compared with IV PCA alone in patients who underwent SPA laparoscopy due to gynecologic adnexal diseases.

During the study period, 431 patients underwent SPA laparoscopy for adnexal disease and received IV PCA or CWI for postoperative pain management. Of these, 60 patients who could not maintain IV PCA until discharge due to side effects were excluded. A total of 371 patients was enrolled in this study, comprising 212 (57.1%) patients who received only IV PCA (PCA group) and 159 (42.9%) patients who received IV PCA and CWI concurrently (combined group) (Figure 1). The patient characteristics and surgical outcomes of each group are summarized in Table 1. There was no significant difference in age, BMI, prior abdominal surgery history, length of umbilical wound before and after surgery, specimen retrieval time, operation time, and pathologic diagnosis between the two groups.

The pain control outcomes according to pain management method are presented in Table 2. The NRS pain score declined gradually with time in both groups (Figure 2). The mean NRS scores assessed at 12 h (combined group vs. PCA group, 1.90 ± 1.11 vs. 2.70 ± 1.08, 95% CI [0.57; 1.03], p < 0.001) and 24 h (1.82 ± 0.82 vs. 2.11 ± 1.44, 95% CI [0.03; 0.55], p = 0.026) after surgery were significantly lower in the combined group compared with PCA group. For the remaining period, the pain intensity of the combined group tended to be lower than that of the PCA group, but it did not show statistical significance. The total amount of fentanyl citrate administered via IV PCA during the entire hospitalization period was significantly less in the combined group than in the PCA group (combined group vs. PCA group, 622.1 ± 105.3 μg vs. 703.1 ± 139.1 μg, 95% CI [56.0; 86.3], p < 0.001). The percentage of patients requiring rescue analgesics after surgery was lower in the combined group than in the PCA group, and in particular, there was a significant difference between 6 and 12 h after surgery (14.5% vs. 23.1%, p = 0.037). In addition, the CWI system significantly reduced the total amount of rescue analgesics administered from 6 to 12 h after surgery (0.23 ± 0.43 ampules vs. 0.35 ± 0.48 ampules, 95% CI [0.05; 0.22], p = 0.008). The use of higher potency rescue analgesics was less frequent in the combined group than the PCA group, but the difference was not significant.

In univariate and multivariate linear regression analyzes of postoperative pain score (Table 3), postoperative wound length, operative time, single-port placement time, and pain control method were associated with pain score at postoperative 6 h. A larger postoperative umbilical wound (β = 2.752, p = 0.001), longer total operative time (β = 0.013, p < 0.001), and longer single-port placement time (β = 0.012, p = 0.002) were related to pain score at postoperative 6 h. However, there was no correlation between these factors and postoperative 12, 24, and 48 h pain scores. Simultaneous use of CWI and IV PCA was an independent postoperative pain-reducing factor during the entire hospitalization period in multivariate analysis.

The incidence of side effects in both patient groups is shown in Table 4. Nausea and vomiting were significantly less frequent in the combined group than the PCA group (combined group vs. PCA group, 15.9% vs. 25.0%, p = 0.027). Wound discharge of the umbilical incision site occurred only in the combined group maintaining CWI (21.4% vs. 0%, p < 0.001). After removal of CWI, wound complications such as infection and hernia were not different between the two groups.

This study evaluated the efficacy of the CWI system for postoperative pain management after SPA laparoscopy in patients with gynecologic adnexal disease. We found that simultaneous use of the CWI system and IV PCA (combined group) significantly reduced the immediate postoperative pain scores and the total amount of IV PCA fentanyl during the entire hospitalization. We also found that the CWI system reduces the use of additional analgesics and the incidence of adverse events such as nausea and vomiting.

Paints with gynecologic adnexal diseases may suffer from disease-specific pain before surgery and surgery-related pain after surgery. For instance, endometriosis is a representative disease that cause sever pelvic pain by creating inflammatory change, activating immune response, and increasing innervation in the affected tissue (13–15). In addition, laparoscopic surgery itself causes various types of pain such as surgical site pain, shoulder pain, and visceral pain (16, 17). MIS is considered the gold standard for benign gynecologic disease due to reduced postoperative pain, better cosmetic results, and faster recovery time compared with open surgery (18, 19). Among MISs, SPA laparoscopy is the least invasive in terms of number of abdominal scars but has the disadvantage of requiring the largest incision. Pain after abdominal surgery is generally known to be caused by the abdominal wall incision (20, 21). In laparoscopy, Ebanga et al. (22) reported that among surgical predictors of pain after laparoscopy, only fascia closure and increased operative time were related to immediate postoperative pain. In this respect, SPA laparoscopy has several potential risk factors that can aggravate surgical site pain. First, during the SPA laparoscopic procedure, at least two 5- to 10-mm laparoscopic instruments must be inserted simultaneously through a single umbilical opening. Collisions between instruments and non-ergonomic position of the surgeon can exert unintended forces on the umbilical incision. Second, unlike conventional laparoscopy, the umbilical wound is subjected to continuous tension from the elastic wound retractor of the single-port system while maintaining the pneumoperitoneum (Supplementary Figure S1B). Third, the retrieval of specimens such as huge ovarian cyst or myoma is performed through the umbilicus using an in-bag tissue removal process (Supplementary Figure S1E). During this procedure, extensive wound traction for a long time can result in enlargement of the umbilical wound. Oh et al. (23) reported that the transumbilical morcellation procedure cause umbilical incision enlargement of approximately 3 mm (from 2.5 to 2.8 cm) after surgery. In our study, wound enlargement of approximately 1 mm was observed after surgery (Table 1). This small extension can be interpreted as the fact that the adnexal tissue was relatively soft to morcellate and the specimen retrieval time was short (<2 min). The umbilical wound of SPA laparoscopy can be vulnerable to pain, for the reasons mentioned above. While previous studies have evaluated postoperative pain outcome after SPA laparoscopy, there is still no consensus on this issue (24–26). Kim et al. (26) reported that SPA surgery is more painful than conventional laparoscopy. Therefore, establishing an effective strategy to reduce pain after SPA surgery is important. Indeed, various pharmacological and technical interventions such as laparoscopic surgery under spinal anesthesia (27, 28) and bupivacaine injection to trocar sites (29) have been developed to reduce pain after laparoscopy.

The ERAS protocols to reduce hospitalization period and morbidity have become the standard for postoperative patient care after gynecologic surgery. Adequate postoperative pain management through combined use of analgesics with a different mechanism of action is a key component of the ERAS pathway. Furthermore, since the pain response to the same surgery and routine postoperative pain management for each patient, it is also important to use an appropriate rescue analgesics tailored to each patient’s characteristics (30). Recently, the 2020 American Association of Gynecologic Laparoscopists (AAGL) guidelines recommended multimodal opioid-sparing analgesia for immediate pain management after MIS (31). Opioid-based IV PCA is the preferred traditional pain control method for controlling breakthrough pain in MIS as well as open surgery. However, systemic side effects related to opioids such as nausea, vomiting, ileus, and respiratory depression are frequently reported, (32) and socio-economic costs increase due to delayed recovery and medication to alleviate these side effects. Jung et al. (33) reported that although fentanyl is an opioid with relatively few side effects, approximately 24% of patients who receive fentanyl-based IV PCA experience nausea and vomiting. In addition, according to one meta-analysis (34), opioid-based epidural PCA does not reduce recovery time compared with ERAS pain control strategy. Choi et al. (35) suggested that opioid-based IV PCA is not an essential pain control method for patients who underwent MIS for colorectal cancer. Therefore, opioid-based PCA may be inconsistent with the main purpose of the ERAS pathway, which is to reduce opioid consumption and accelerate recovery. In our study, 60 patients discontinued IV PCA due to opioid-related systemic side effects, and even in patients who maintained IV PCA until discharge, approximately 21% complained of nausea and vomiting and received additional intervention such as antiemetics. Therefore, there is need to establish an effective strategy to reduce opioid usage and postoperative pain, especially for small wounds.

The CWI system effectively controls pain by directly injecting a local anesthetic agent into the surgical site. The ERAS group also recommended that incisional infiltration has no systemic side effects when used appropriately, and it should be incorporated into other pain control methods as a component of multimodal analgesia (6). Many previous studies have demonstrated the effectiveness of the CWI system for postoperative pain control (10, 11, 36). In particular, systematic review and meta-analysis studies reported that CWI is safe and has postoperative pain reduction and opioid-sparing effects in cesarean section (37–39). However, most of these studies have focused on the large laparotomic wound and not the small laparoscopic wound. Lee et al. (40) reported that wound infiltration with short-acting local anesthetic agents effectively reduced immediate postoperative pain in the SPA laparoscopic wound. However, this one-shot administration method has a limitation in that long-term pain control is difficult due to the short half-life of the local anesthetic agent. The CWI system can be a very attractive method because it can continuously deliver a local anesthetic agent. Only a few studies have been conducted to evaluate the effectiveness of the CWI system for MIS. Oh et al. (41) evaluated the efficacy of the ropivacaine-based CWI system after laparoscopic colorectal surgery and demonstrated that it significantly reduced postoperative pain and has opioid-sparing effects. There has been no study on application of a CWI system to gynecologic SPA laparoscopy, to the best of our knowledge. In our study, simultaneous use of the CWI system and IV PCA (combined group) significantly reduced immediate postoperative pain, total amount of additional analgesia, and total quantity of opioid. In contrast, acute wound complications such as wound discharge (woozing of local anesthetic agent) have been reported only in the combined group, but there was no difference in chronic wound complications such as infection and umbilical hernia between the two groups. Furthermore, the incidence of umbilical hernia in the combined group was similar to previously reported results (0.4%) (42).

Our study demonstrated that combined use of the CWI system and IV PCA may be a safe and effective strategy to manage immediate postoperative pain in patients who underwent SPA laparoscopic adnexal surgery. Large-scale randomized trials are needed to evaluate the effectiveness of CWI in SPA laparoscopy.

To the best of our knowledge, this is the first study to evaluate the efficacy of the CWI system for gynecologic SPA laparoscopy. Another strength of this study is that it was conducted with a relatively large number of patients. However, this study has some limitations. First, this was not a prospective, randomized clinical trial. Second, among various types of pain that may occur after laparoscopic surgery such as gas-induced abdominal pain, shoulder pain, and visceral pain (16, 17), only surgical site pain was evaluated in this study. Third, there was no comparison with a CWI system-only group. Future studies should be performed to compare PCA alone, CWI alone, and a combination strategy.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

J-HK: conceptualization, software, visualization, and writing-original draft. J-HK and KL: data curation, investigation, and project administration. J-HK and EP: formal analysis. J-HK and WK: methodology. EP and YH: validation. KL and YH: resources. EP and WK: supervision. EP, KL, and WK: writing-review and editing. All authors contributed to the article and approved the submitted version.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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