Our results indicate that the monopolar device led to higher postoperative complications than the bipolar device. This study showed that the incidence of all-grade ascites and grade ≥3 intra-abdominal infection was significantly higher after utilizing the monopolar device than after utilizing the bipolar device. Notably, the CCI score was significantly higher in the monopolar group than in the bipolar group.
Previous studies reported that the monopolar device was efficient and safe for decreasing surgical time and surgical bleeding without increasing complications compared with the bipolar device [12, 13]. However, caution concerning the monopolar device was advised when hyperthermia during surgery, widespread burn injury to the remnant liver, and increased postoperative transaminase level became evident. Another point of concern with the monopolar device was delayed-onset postoperative complications possibly caused by burn injury; however, no increase in major complications was observed . The reason for this mismatch has not been proven.
A meta-analysis revealed that perioperative blood transfusion was associated with an elevated risk of death, recurrence, and postoperative complications in patients with hepatocellular carcinoma . These findings emphasize the need for performing surgical techniques meticulously to minimize blood loss. Several methods, such as hepatic transection using the CUSA, Harmonic, LigaSure, and EnSeal sealing vessel systems, vascular occlusion via the Pringle maneuver, and intraoperative low central venous pressure, have been adopted to reduce blood loss and blood transfusion [2–4, 6–8, 10, 23–26]. By contrast, when bleeding occurs from the cut surface of the liver, a hemostatic device is needed. Several hemostatic devices, such as ones providing soft coagulation with a monopolar electrode, a monopolar floating ball (TissueLink; Salient Surgical Technologies, Inc., Portsmouth, NH, USA), a Coolinside device (Apeiron Medical, Valencia, Spain), and the bipolar forceps coagulation, have been used clinically in recent years [3, 15, 18, 27, 28]. Each device has its own advantage; however, to date, there is no consensus on the ideal method for hepatectomy. Therefore, hepatic surgeons select the hemostatic device according to their preference. This study aimed to clarify the advantages or disadvantages of the monopolar and bipolar coagulation devices for hemostasis during hepatectomy and postoperative complications.
We noticed several biases in terms of patient characteristics between the two groups. To minimize bias, PSM was performed according to the background liver disease, preoperative liver functions, and type of surgical procedures. This statistical procedure has been widely applied to analyze groups with different backgrounds [3, 29, 30]. After matching, the monopolar group showed a reduction in blood loss, transfusion volume, and total operative time. This finding indicated that the monopolar hemostatic device provided a stronger and quicker coagulative effect than the bipolar hemostatic device. On the contrary, increases in the level of AST were more frequently observed in the monopolar group than in the bipolar group. The monopolar system uses a computer-controlled low voltage level without electrical discharge, and therefore, heat is transferred to the deeper areas of the liver [12, 13]. By contrast, the bipolar system can cauterize only active bleeding between the forceps without adjacent tissue damage [16, 17]. Moreover, thermal damage to the deep cut surface of the liver can be avoided. As previously reported, when a monopolar system was continuously used during transection, hyperthermic and widespread burn injury to the remnant liver surface occurred, which can increase the postoperative transaminase levels or cause other unexpected liver dysfunctions [12, 13].
Next, we considered the individual complications associated with heat injury. One of the most critical complications after hepatectomy is an intra-abdominal infection. In the present study, a significant increase in severe intra-abdominal infection was observed in the monopolar group. However, no statistical difference in biliary leaks was detected between the two groups. Minor bile duct damage undetectable by the bile leak test may be caused by heat injury. A previous study revealed a significant increase in bile leakage with the use of a monopolar hemostatic device . Another study reported a major bile duct injury caused by prolonged exposure to heat produced by the monopolar device . In a pig model, histological examination revealed that the thermal damage caused by the monopolar device was deeper than 10 mm, whereas the damage caused by the bipolar device was 2–3 mm deep . In our study, the extent of thermal damage to the resected specimens was also greater in the monopolar group than in the bipolar group. Additionally, the incidence rate of intra-abdominal infection was significantly higher in the long thermal damage group.
Another individual complication of concern is ascites. In our study, the rate of ascites was significantly higher in the monopolar group than in the bipolar group. Damage to the remnant liver caused by monopolar devices could delay liver regeneration and prolong alleviation of inflammation, potentially leading to higher incidence rates of ascites. Complications after hepatectomy are complex and are closely related to surgical manipulations, anesthesia technique, preoperative evaluation, and postoperative management . A previous study revealed that ICGR15 >10%, tumor size >10 cm, and red blood cell transfusion were prognostic factors for the prevalence of ascites . In this study, multivariate analysis identified numerous clinical parameters as risk factors for ascites or severe intra-abdominal infection. Surprisingly, the type of hemostatic device used was an independent risk factor for both complications.
Finally, we assessed the overall morbidity using the CCI score, which is calculated based on the complication grading by CD classification and integrates every complication occurring after an intervention . The overall morbidity is rated from 0 (no complication) to 100 (death). CD classification includes only the most serious complications; conversely, the CCI score summarizes the total postoperative complication rate associated with a surgical procedure even when multiple complications occur . The CCI score is considered to be more sensitive than the CD classification when reporting postoperative morbidity in liver surgery . Based on the CCI score, the severity of total complications in the monopolar group was significantly higher than that in the bipolar group.
This study has some potential limitations. First, the historical background was different; a bipolar device was used from 2009 to 2011, whereas a monopolar device was used from 2011 to 2018. A learning curve in the surgical techniques and other confounders may have contributed to the outcomes. Second, the data were derived from a retrospective single-center cohort with a small sample size. Third, because the propensity score is a summary of measured covariates, it cannot eliminate unmeasured confounding factors. It is also difficult to completely eliminate arbitrariness by statistical adjustment. Finally, thermal damage to the resected specimens does not always correspond to damage to the remnant liver. Taking this into consideration, the results of this study should be verified by other large-scale series or multicenter randomized controlled trials. Thus, we are planning to conduct a multicenter randomized controlled trial based on this retrospective cohort study.
The results of this study may elucidate the impact of hemostatic devices and can aid surgeons in properly using surgical devices. Indeed, considering the spread of heat injury, the monopolar system should be carefully used only for pinpoint hemostasis. Furthermore, this device should not be used near the main Glissonean pedicle to prevent intra-abdominal infection or bile leakage.