Using LAP PROTECTOR™ to prevent subcutaneous emphysema after robotic gastrectomy

Subcutaneous emphysema (SE), a complication of robotic gastrectomy (RG), occurs when the gas used to establish pneumoperitoneum escapes and enters the soft tissue. SE typically does not result in major clinical problems, but massive SE can have life-threatening consequences. Hence, developing adequate preventive methods against postoperative SE is essential. We aimed to determine whether an existing protective device, the LAP PROTECTOR™ (LP), can be used to reduce the incidence of SE after RG. We analyzed the data of 194 patients who underwent RG at our hospital between August 2016 and December 2022. Since September 2021 (the 102nd patient), we have used the LP (FF0504; Hakko Medical, Hongo, Tokyo, Japan) at the trocar site, as this was expected to reduce the incidence of SE. The primary endpoint of this study was the efficacy of the LP in reducing the incidence of clinically relevant SE (defined as SE extending into the cervical area) a day after RG. Univariate analysis revealed that sex, body mass index (BMI), and LP usage differed significantly between patients with and without postoperative SE. Logistic regression analysis revealed that male sex (odds ratio [OR]: 0.22, 95% confidence interval [CI]: 0.15–0.72, P < 0.001), high BMI (OR: 0.13, 95% CI: 1.23–4.45, P = 0.009), and LP usage (OR: 0.11, 95% CI: 0.04–0.3, P < 0.001) were preventive factors independently associated with a lower incidence of clinically relevant SE. Placing an LP at the trocar site may be a safe and effective method of preventing SE after RG.


Introduction
Robotic surgery is becoming increasingly popular due to several technical advantages, including three-dimensional high-definition vision controlled by the operators, articulated robotic arms providing better ergonomics, and tremor filtration. The increased availability of robotic surgery has expanded the surgical options available for eligible patients. Subcutaneous emphysema (SE) is a rare complication after robotic surgery that can sometimes have serious consequences. At present, the da Vinci surgical system (Intuitive Surgical, Sunnyvale, CA, USA) is one of the most popular surgical robots available. One of the key features of this system is lifting the abdominal wall using trocars, helping to maintain a wide operative field. However, lifting the abdominal wall in this manner can create a small gap between the abdominal wall and the trocars, allowing the gas used to create pneumoperitoneum to enter the subcutaneous space through this gap, leading to the development of postoperative SE.
SE can cause crepitus, insufflation problems, pneumothorax, pneumomediastinum, hypercarbia, acidosis, changes in lung compliance, cardiac arrhythmia, sinus tachycardia, and hypertension. In some cases, SE can also cause lifethreatening complications, such as abdominal compartment syndrome or CO 2 embolism [1][2][3][4][5][6]. Additionally, patients typically undergo robotic gastrectomy (RG) in the reverse Trendelenburg position, which can cause SE to spread toward the cervical area. SE in the upper chest and neck is extremely uncomfortable for the patient and can lead to severe upper airway obstruction and fatal respiratory failure [7]. Therefore, it is important to develop appropriate methods to reduce the incidence of SE.
Previous studies have identified several operative factors associated with an increased incidence of SE. However, few studies have reported concrete preventive measures to reduce the risk of SE [1,8,9]. Therefore, in this study, we aimed to determine whether protecting the cross-section of the abdominal wall with existing protective devices can reduce the incidence of SE after RG.

Patients
This retrospective cohort study analyzed the data of 194 consecutive patients who underwent RG for gastric cancer at the Department of Gastroenterological Surgery, Ishikawa Prefectural Central Hospital (Ishikawa, Japan) between August 2016 and December 2022. For all recruited patients, we collected the following data: patient characteristics (age, sex, and body mass index [BMI]), clinical stage of gastric cancer, surgical procedure used, usage of the LAP PROTEC-TOR (LP) (FF0504; Hakko Medical, Hongo, Tokyo, Japan), overall surgery duration and surgical console time, usage of drainage tubes, amount of blood loss, and postoperative hospitalization. The chest radiograph on postoperative day 1 was also evaluated for patients who developed SE. SEs that reached the cervical area were considered clinically relevant, and the primary endpoint of this study was the incidence of clinically relevant SE.

Surgical indication and procedures
We performed RGs with appropriate lymph node dissection, depending on the clinical stage of cancer [10]. Gastric cancer at any stage was regarded as an indication for RG. A qualified surgeon from the Japanese Society for Endoscopic Surgery either performed or assisted with the RGs. All RGs were performed with the da Vinci Si or Xi surgical system equipped with four articulating robotic arms: one central arm for a 30° rigid endoscope, a first arm for Maryland bipolar forceps, a second arm for fenestrated bipolar forceps, and a third arm for Cadiere forceps [11,12]. We used a robotic vessel-sealing system equipped with an articulated joint (Vessel Sealer, Intuitive Surgical Inc., Sunnyvale, CA, USA). The patient was positioned with a 12° head-up tilt. To maintain pneumoperitoneum, the valve-less AirSeal® system (SurgiQuest Inc., Milford, CT, USA) was used for insufflation at a relatively low pressure (10 mm Hg).
Starting in September 2021 (the 102 nd patient), we used the aforementioned LP system to protect the abdominal section at the trocar sites. The LP was expected to reduce the occurrence of postoperative SE. This LP was originally developed to protect and extend the incision wound, and the device is equipped with two flexible rings that are covered and connected with a silicone rubber membrane. The inner diameter of the LP is 1-2 cm; therefore, it allows the 8-mm trocar of the da Vinci system to pass through it. We applied a 2-0 silk thread on the intra-abdominal side to pull the LP out through the abdominal wall after the surgery was completed, preventing the LP from falling into the abdominal cavity ( Fig. 1a, b). After creating a route for trocar insertion in the abdomen, we inserted the LP with Pean forceps and placed a trocar (Fig. 2a). The LP was wrapped with a sterilized rubber band, preventing leakage of gas through the gap between the LP and the trocar (Fig. 2b, d).

Statistical analysis
All categorical variables are expressed as numbers (percentages), and continuous variables are expressed as medians (ranges). Differences in categorical and continuous variables were evaluated using Fisher's exact test and the Mann-Whitney U test, as appropriate. Logistic regression analysis was performed to identify independent factors associated with the incidence of SE. Statistical significance was set at Fig. 1 a A 2-0 silk thread was applied on the intra-abdominal side to assist with easy device removal after completion of the intra-abdominal procedure. b Pean forceps were used to introduce the LP into the abdomen P < 0.05. All statistical analyses were performed using the EZR statistical software version 1.55 (Easy R; Saitama Medical Center, Jichi Medical University, Saitama, Japan) based on the R statistical software version 4.1.2 and R commander (R Foundation for Statistical Computing, Vienna, Austria). Table 1 summarizes the characteristics and outcomes of the 194 patients included in this study. The LP was used in 93 cases (48%), and SE extending into the cervical area occurred in 41 cases (21%). We divided the patients into two groups depending on the presence or absence of SE (Table 2). When the patient background and perioperative data for groups that were either positive or negative for SE were compared, we determined no significant differences in age, the American Society of Anesthesiologists physical status (ASA-PS), clinical stage, surgical procedure, surgery time, console time, drain placement, blood loss, postoperative hospitalization, and complications. The Clavien-Dindo (CD) system was used to grade surgical complications, with a grade II or higher set as the positive threshold. Univariate significant between-group differences were detected in the following explanatory variables: sex (P = 0.003), BMI (P < 0.001), and LP usage (P < 0.001). Logistic regression  (Table 3).

Discussion
In this study, male sex, high BMI, and LP usage were all associated with a lower incidence of SE after RG. Placing the LP at the trocar site provided the lowest OR (0.11) and was the most effective factor in reducing SE incidence. Previous studies have reported old age and a long operative duration as risk factors for severe SE; however, these factors were not significantly associated with postoperative SE in our study [1,3,8]. To the best of our knowledge, this is the first study to repurpose existing protective devices to reduce the incidence of SE after RG.
SE is a rare complication of laparoscopic surgery, with an overall incidence of 0.43-2.3% [1]. However, the true incidence may have been considerably underestimated. McAllister et al. [13] reported that the 24-h postoperative computed tomography scans of patients who underwent laparoscopic cholecystectomy revealed grossly undetectable but clinical SE in 56% of cases. Similarly, Worrell, Saggar, and colleagues recognized SE in up to 99% of all laparoscopic cases based on radiographic findings and computed tomography scans [1,9,[13][14][15][16]. The reported life-threatening complications and high incidence of clinically relevant SE (21%), including two abdominal infections caused by SE in our study, indicate that this complication deserves immediate consideration [1][2][3][4][5][6].
SE occurs due to the de novo generation or infiltration of air below the dermal layers [14]. The trocar acts as a fulcrum for the robotic arm to move as a class 1 lever and force multiplier (Fig. 3a). The pivot point acts as the fascial entry site, and the port site can be dilated. When instruments are manipulated during robotic surgery, the surgeon lacks sensation and cannot appreciate the force exerted by the trocar on the abdominal wall. Therefore, a certain degree of blunt dissection may occur at the port site without the surgeon's realization. Furthermore, the da Vinci system allows the abdominal wall to be lifted with trocars during surgery, which increases the pressure at the trocar site. This pressure can cause the gap between the trocars and abdominal wall to yield, allowing the entry of pneumoperitoneal air into the subcutaneous space (Fig. 3b). Therefore, protecting the abdominal wall at the trocar site is crucial for preventing SE after surgery.
The surgical risk factors for SE include the following: high-flow insufflation, high intra-abdominal pressure (> 15 mmHg), multiple attempts at the abdominal entry, lack of a snug fit between the skin/abdominal wall and trocars, use of > 5 trocars, use of the laparoscope as a lever, use of the trocars as a fulcrum, laparoscope with a long arm, structural weakness caused by repetitive movements, improper cannula placement, and prolonged operative time (> 3.5 h) [1]. The da Vinci surgical system not only uses the long arm of the laparoscope as a lever but also uses the trocars as a fulcrum. Therefore, the potential preventive measures for SE include avoiding a high intra-abdominal pressure, avoiding the use of additional trocars, and minimizing surgical time as much as possible. However, reducing the intra-abdominal pressure can often cause difficulties in maintaining a good surgical field. Additionally, it is difficult to complete the RG procedure within 3.5 h, especially  The valve-less insufflation system, AirSeal®, is becoming increasingly popular in robotic surgery because it maintains a stable-pressure pneumoperitoneum and performs continuous smoke evacuation [17,18]. However, the use of this device is also known to increase the risk of SE [15]. In this study, an LP was used in all cases, and the incidence of SE was significantly decreased. Therefore, using an LP at the trocar site is beneficial for decreasing the incidence of SE while using AirSeal®, even in long surgeries.
The LP used in this study was originally developed for protecting and expanding the incision wound. However, we started using an LP in RG because of its protective effects on the abdominal wall. Although LPs are available in several sizes and types, we found the LP to be suitable for the trocars in the da Vinci surgical system. During surgery, the LP is crimped to the cross-section of the abdominal wall and confers a protective effect. Therefore, we hypothesized that it would also prevent leakage of air into the subcutaneous space through the trocar insertion site. However, after introducing the LP to cover the trocar sites, we still noticed air leakage through the gap between the trocars and LP because of a slight difference in diameter between the devices (Fig. 3c). Owing to concerns related to lowered body temperature and increased CO 2 consumption, we wrapped sterilized rubber bands around the LP and trocars to prevent air leakage (Fig. 3d). This practice not only prevented SE but also allowed the LP to effectively protect the incision. In addition, LPs were broken intraoperatively in some cases. If an LP is torn into two pieces, it can easily fall into the abdominal cavity. Therefore, a 2-0 silk thread was applied on the intra-abdominal side to prevent losing a damaged LP into the abdominal cavity. The thread was also useful for LP removal. In seven cases, SE occurred despite using an LP. This may be due to either intraoperative LP breakage or pneumoperitoneum without an LP at the entry site when placing a drainage tube or during reconstruction. However, even including those cases, the effectiveness of the LP for preventing SE remained significant.
This study has a few limitations. First, this was a retrospective single-center study, which limits the generalizability of its findings. Second, the LP device was originally developed for other purposes, and was not intended for use at the trocar site. Consequently, using a device specifically designed for use at the trocar site may be better at reducing the incidence of SE. Nevertheless, we did not experience any unforeseen problems in any of the 93 consecutive cases where we used the LP. Fig. 3 a The trocar acts as a fulcrum for the robotic arm to move as a class 1 lever; blunt dissection occurs at the trocar site. b Blunt dissection and a lifting trocar can yield a gap between the trocars and abdominal wall, thus allowing entry of pneumoperitoneal air into the subcutaneous space. c Air leakage occurred through the gap between the trocars and LP due to a slight difference in diameter between the devices. d Air leakage was prevented by wrapping LP and trocars with sterilized rubber bands In conclusion, placing an LP device at the trocar site can be a safe and effective method for preventing SE after RG. Nevertheless, further studies are needed to evaluate the safety of this procedure.