Bipolar radio-frequency-induced thermofusion of intestinal tissue – In vivo evaluation of a new fusion technique in an experimental study

Abstract

Purpose: Bipolar radio-frequency-induced thermofusion (BiRTh) of intestinal tissue might replace conventional stapling devices which are associated with technical and functional complications. Previous results of our study group confirmed the feasibility to fuse intestinal tissue using BiRTh-induced thermofusion ex vivo. The aim of this study was now to evaluate the efficacy of fusing intestinal tissue in vivo by BiRTh-induced thermofusion.

Materials and methods: In male Wistar rats a blind bowel originating from the caecum was closed either by BiRTh (n = 24) or conventional suture (n = 16). At 6 h, 48 h, 4 days, and 2 weeks after the procedure caecum bursting pressure was measured to compare both groups.

Results: In total 18 of 21 (85.7%) thermofused and 15 of 16 (93.7%) sutured cecal stumps were primarily tight and leakage-proof (p > 0.05). The operative time was comparable in both groups without significant differences. Both groups showed increases in bursting pressure over the post-operative period. The mean bursting pressure for thermofusion was 47.8, 48.3, 55.2, and 68.0 mmHg, compared to 69.8, 51.5, 70.0 and 71.0 mmHg in the hand-sutured group (p > 0.05) after 6 h, 48 h, 4 days, and 2 weeks, respectively.

Conclusion: These results suggest that BiRTh-induced thermofusion is a safe and feasible method for fusing intestinal tissue in this experimental in vivo model and could be an innovative approach for achieving gastrointestinal anastomoses.

Keywords:

• Intestinal anastomoses
• radio-frequency-induced thermofusion
• radio-frequency surgery
• tissue fusion

Introduction

Anastomotic leakage remains one of the main causes of post-operative morbidity and mortality in gastrointestinal surgery [1,2,3]. Among conventional suturing, stapling devices are mainly used to reconnect intestinal tissue after surgical resection. Furthermore, the use of currently available stapling devices is limited due to relevant costs and technical problems such as complex handling, anastomotic healing, and applicability to all regions of the intestinal tract [4,5,6]. There is great interest in developing alternative stapling devices which may offer the possibility to overcome these problems [7]. Using a bipolar radio-frequency technology to fuse intestinal tissue may be an alternative to complex mechanical components. Previous results of our study group already confirmed the feasibility to fuse intestinal tissue using bipolar radio-frequency-induced thermofusion (BiRTh) ex vivo [8,9].

The aim of the present study was to evaluate the safety and efficacy of fusing intestinal tissue in an in vivo model by BiRTh compared to conventional suture.

Materials and methods

Animals and surgical procedure

Male Wistar rats (n = 40, 250–350 g, Charles River, Sulzfeld, Germany) were cared for in accordance with standards laid down by the German Council on Animal Care, under an approved protocol of the local Animal Welfare Committee. The animals were kept under standard laboratory conditions before operation.

Rats were allocated into two groups: group I (BiRTh, n = 24) and group II (conventional suture, n = 16). Each of these experimental groups was further divided into four subgroups that were sacrificed 6 h, 48 h, 4 days, and 2 weeks after surgery for measuring the bursting pressure. There were six rats per time point in group I, and four rats in group II. Operations were performed under aseptic conditions on a total of 8 days. On each day of surgery, three group I animals and two group II animals underwent surgery alternately according to the scheme: thermofusion – suture – thermofusion – suture – thermofusion.

Animals that underwent surgery on days 1 and 2 were sacrificed 6 h after surgery, animals of days 3 and 4 after 48 h, animals of days 5 and 6 after 4 days (96 h), and animals of days 7 and 8 were sacrificed after 2 weeks. Rats were anaesthetised with isoflurane, followed by an intraperitoneal injection of xylazine hydrochloride (12 mg/kg body weight, Rompun, Bayer, Leverkusen, Germany) and esketamine hydrochloride (40 mg/kg body weight, Ketanest S, Parke-Davis/Pfizer, Karlsruhe, Germany). After abdominal skin was shaved, a 2-cm median laparotomy was performed and the caecum was carefully mobilised. Thereafter, the proximal blind end of the caecum (approximately 1 cm in diameter and 1.5 cm in length) was resected and the cecal stump was closed either by BiRThor by continuous one layer 5/0 poliglecaprone 25 sutures (Monocryl, Ethicon, Germany). For BiRTh a High Frequency (HF) generator (ESG 400©, Olympus Winter & Ibe, Hamburg, Germany) and special sealing instrument (RF device) (Figure 1) were used. A specific modification of the HF generator with a maximum output power of 320 W and 100 V was used. To achieve high temperatures for a successful fusion process heaters are integrated into the jaws of the RF device. Furthermore, the design of our RF device made it possible to preset the compressive pressure by a compression spring. The specific mechanical design enabled a homogenous pressure distribution between the jaws and in the whole fusion area. A preset spring force of 8 N was used at an area of the device’s jaws of 120 mm². This corresponds to a compressive pressure of about 0.0667 N/mm² or 500 mmHg.

Figure 1. Illustration of anastomotic device while fusing a rat caecum.

The fusion process was developed in extensive ex vivo tests [10]. The best results are achieved with a two-tier process [16]. The first part is a 15-s pulsed RF heating process. The pulsed energy emission combined with external cooling with Purisol® (5 °C) reduces the thermal tissue damage. The second part is a 60-s long closed-loop regulated heating process. Therefore the integrated heaters warm the tissue to 180 °C. The temperature profile is shown in Figure 2. To reduce the thermal damage of the surrounding tissue, the cooling is continued for the first 30 s of this heating process. The laparotomy was closed in two layers with a 3-0 absorbable suture (Vicryl, Ethicon, Norderstedt, Germany). The total operating time of each procedure was documented.

Figure 2. Temperature profile during fusion process.

After animal sacrifice, the integrity of the stump, signs of leakage, presence of adhesions, and existence of peritonitis were recorded during post-mortem exploration. The ileocaecal segment was taken out, intestinal contents were removed, and the burst pressure of the stump was measured comparable to established methods [11,12]. For the burst pressure measurement, the ileal segment was opened and a blunt cannula was introduced to the lumen. Both the ends of the bowel were closed by atraumatic clamps. The cannula was fixed to a three-way stopcock connected to a pressure-measuring device (GMH 5130, GHM Messtechnik, Erolzheim, Germany) with pressure sensors (MSD 1 BRE, Measuring range 0–1 Bar, GHM Messtechnik, Erolzheim, Germany) and an infusion pump (Lambda VIT-FIT syringe pump, LAMBDA Laboratory Instruments, Baar, Switzerland), which was infusing saline solution at a constant rate of 200 mL/min. The maximum pressure before bursting was automatically saved and documented.

Statistics

Statistical analyses were performed with SPSS 22.0 (IBM, Armonk NY, USA) software system. Kruskal–Wallis test was utilised for variance analyses. The Mann–Whitney U test was used to calculate the differences between two groups. The statistical significance was set at P less than 0.05 with a confidence rate of 95%.

Results

Surgical technique

In total, 18 of 21 (85.7%) thermofused and 15 of 16 (93.7%) sutured cecal stumps were primarily tight and leakage-proof (p > 0.05). The four remaining animals were excluded from the study due to an anastomotic leak. Three more group I animals were excluded due to anaesthetic-related death. However, no primary seal failure due to technical problems could be recognised. When re-laparotomy was performed, clear intra-abdominal fluid was present in all rats with sufficient cecal stump. Only in cases of anastomotic leaks was faecal material detected. All cecal stumps were found to be surrounded by omentum and/or intestinal segments. No complications, including wound infection, volvulus, intestinal obstruction or abscess, were detected.

The operative time and weight gain were comparable in both groups without significant differences (Table 1).

Table 1. Operative time and weight gain in both groups at 6 h, 48 h, 4 days and 2 weeks after surgery.

	BiRTh group	Hand-sutured group	p-value
Operative time
6 h	0.09 ± 0.01	0.11 ± 0.02	0.259
48 h	0.09 ± 0.03	0.07 ± 0.02	0.181
4 days	0.10 ± 0.03	0.09 ± 0.02	0.446
2 weeks	0.11 ± 0.03	0.13 ± 0.03	0.253
Weight gain (g)
6 h	335.69 ± 96.20	328.29 ± 65.33	0.858
48 h	301.60 ± 11.79	318.00 ± 3.39	0.141
4 days	299.85 ± 62.47	348.67 ± 39.92	0.100
2 weeks	309.63 ± 44.48	317.33 ± 20.74	0.691

BiRTh: bipolar radio-frequency-induced thermofusion.

Bursting pressure

Both groups showed increases in bursting pressure over the post-operative period. The mean bursting pressure for thermofusion was 47.8, 48.3, 55.2, and 68.0 mmHg, compared to 69.8, 51.5, 70.0 and 71.0 mmHg in the hand-sutured group (p > 0.05) after 6, 48, 4 days and 2 weeks, respectively. The burst pressure after BiRTh compared to conventional hand-suture is shown in Figure 3.

Figure 3. Bursting pressure in radio-frequency-induced thermofusion compared to hand-suture at 6 h, 48 h, 4 days, and 2 weeks after surgery (p > 0.05).

Discussion

The aim of this study was to evaluate the efficacy of fusing intestinal tissue in vivo by BiRTh based on our previous ex vivo results [8,9]. For this purpose a device was developed for BiRTh of rat intestine. There were no significant differences regarding leakage rate between thermofusion and conventional hand-suture. Furthermore, the amount of bursting pressure of BiRTh was comparable to the hand-sutured group. However, it must be noted that the statistical power is low, based on the number of tested samples. An interaction analysis of other parameters on bursting pressure such as tissue hardness and thickness or wall shrinkage and desiccation during thermofusion was not possible for the number of tested samples. A search of the literature yielded no prior study examining the effects of tissue hardness, thickness, and compressive pressure for BiRTh of intestinal tissue in vivo. There is likewise no elementary exploration study screening the main effects and interactions on intestinal tissue fusion strength using bipolar radio-frequency energy. However, some previous in vivo and ex vivo studies have shown the feasibility of bipolar radio-frequency energy use for bowel sealing and anastomosis [8,9,11,13,14]. Most of these studies have compared bipolar RF devices compared to other energised or conventional stapling devices showing comparable results of burst pressures ex vivo [14,18]. Furthermore, in the in vivo studies by Shields et al. [15] and Smulders et al. [16], a side-to-side small bowl anastomosis was performed in a small series of 10 anastomoses in five pigs. Except for one anastomosis, all anastomoses were found to be sufficient. In a study by Aslan et al. thermal electro-coagulation with bipolar electrocautery was used to close appendiceal stump in a rat model [13]. The authors demonstrated a bursting pressure of 11.2 ± 2.7 cm H₂O (8.24 ± 1.99 mmHg) 15 days after the first laparotomy. Much higher amounts of bursting pressure were achieved in our study compared to the results by Aslan et al. The mean bursting pressure for thermofusion in this current study was 47.8, 48.3, 55.2, and 68.0 mmHg after 6 h, 48 h, 4 days and 2 weeks, respectively. In contrast, two other studies showed higher bursting pressure values by using a LigaSure™ (Neustadt/Donau, Germany) device for closing the cecal stump [14,17]. Here, the mean bursting pressure was 160.00 ± 26.18 mmHg [14] and 136.1 ± 49 mmHg [17] on post-operative day 7. In addition to BiRTh, there have been also other non-suture modalities described such as laser-assisted tissue fusion [18]. Cilesiz et al. [18] performed laser-welded enterotomies of rat intestine in vivo using an Argon and a Ho:YAG laser. Although the maximum achieved burst pressures in these studies were higher compared to our results, all anastomoses were very weak, with a high rate of anastomotic leaks, especially in the early post-operative period. However, it remains open whether these different results are based solely on the various fusion techniques.

Regarding the current study, there are many limitations that underscore the need for further analyses to determine which parameters mainly affect the quality of intestine tissue fusion, especially histological examinations, so that conclusions can be drawn about the wound healing of thermofused anastomotic tissue.

In summary, our study demonstrated for the first time the efficacy of fusing intestinal tissue in vivo by BiRTh. The stability of the induced thermofusion showed no difference with conventional hand-suture. The results suggests that BiRTh is a safe and feasible method for fusing intestinal tissue in this experimental in vivo model and could be an innovative approach for achieving gastrointestinal anastomoses. However, before application of this technology can be considered in clinical practice, further experiments must be performed before this promising method can be evaluated from a clinical point of view.

Disclosure statement

The authors report no conflicts of interest.