Comparison of the C-REX LapAid and Circular Stapled Colorectal Anastomoses in an Experimental Model

Intestinal anastomotic leakage (AL) is a dreaded surgical adverse event following colorectal surgery and is a major cause of postoperative morbidity and mortality [1‒4]. AL following colorectal cancer surgery is associated with higher frequency of local recurrence and lower long-term survival [3, 5‒11]. Despite refinements in anastomotic techniques, the rate of AL has remained unchanged for the last decades, with leak rates as high as 20% in the lower third of the rectum [12‒15].

A potential risk factor for AL is a foreign body reaction, which can cause pathological inflammation in the anastomosis and endanger the anastomotic healing process. Most foreign materials induce inflammatory reactions in tissues, and sutures and staples are no exception. Studies on sutured and stapled anastomoses have demonstrated foreign body reactions in the anastomotic line [16, 17], eliciting additional collagenase activity. The limitations of current anastomotic methods have generated an interest in alternative techniques, such as compression anastomosis, which does not leave foreign bodies in anastomoses.

In 1826, Felix-Nicholas Denans introduced a compression-based anastomotic technique using metallic rings that applied a constant pressure across the bowel wall, inducing a healing area between the intestinal ends and an adjacent ischemic collar with subsequent necrosis and detachment of the rings into the fecal stream [18‒21]. Since then, various compression devices have been designed and used to create colorectal anastomoses, such as Murphy’s button, AKA-2, the BAR and the Nitinol-based devices [18‒21]. However, these instruments have been cumbersome to use and have mostly been abandoned, although the compression method is theoretically appealing. These devices probably didn’t separate sufficiently the ischemic tissue collar from the healing area of the anastomotic line, where the necrotic tissue could theoretically interfere with the healing area by prolonging the lag phase of the healing process, risking AL.

A novel sutureless anastomotic compression device called CARP has been developed and tested with promising results in experimental and human settings [22, 23]. CARP has a predetermined width between the anastomotic rings after they are locked in position with the compressed bowel ends, reducing the risk of too much tissue pressure and premature release of the rings. The CARP rings were designed to have a more ovular shape compared to the previously used devices, intended to separate the ischemic collar more efficiently from the healing area. With this design, a gradual pressure gradient reduction is accomplished, from the area of highest compression to the area of lower compression as approaching the well vascularized anastomotic healing area. However, CARP is limited to open surgery and colonic anastomosis but has now been modified for usage in minimally invasive procedures and transanal rectal anastomosis. This refined CARP device is called C-REX and has four built-in catheters enabling intraoperative measurement of the anastomotic contact pressure and postoperative radiological examination of the anastomotic integrity. The C-REX method includes two devices, LapAid and RectoAid, which are used in pairs when forming an anastomosis. Two LapAid devices are used when constructing colonic anastomosis at and above the sacral promontory, whereas one LapAid and one transanal RectoAid are used when performing rectal anastomosis. C-REX has been tested by the authors with promising results in preclinical studies and in patients [24].

Experimental studies comparing conventional and compression anastomoses have demonstrated more favorable healing in compression anastomoses [19, 25]. A comparative experimental study showed that the histological healing process of compression anastomoses, assessed at postoperative days 3, 7, 30, and 90, progressed faster and with less granulation formation compared to the circular stapled anastomoses constructed 20 cm from the anal verge [25]. The compression anastomoses demonstrated less scarring, narrower anastomotic lines and lesser foreign body reactions. The authors have demonstrated favorable histological anastomotic healing following resection of the sigmoid colon with low CARP colonic anastomosis in an experimental model [22].

Bursting pressure is commonly used as a parameter for mechanical strength for assessing anastomotic healing in experimental models. This method is considered to resemble the physiological strain of an anastomosis and is defined as the maximum intraluminal pressure needed to rupture an anastomosed bowel segment when inflating it with air [26‒29]. Bursting pressure reflects the weakest site of an intestinal segment, which is usually in the anastomotic line during the first postoperative days [27]. However, experimental studies have demonstrated that the use of bursting pressure should be limited to the first postoperative week [27].

The clinical presentation of AL usually develops within the first postoperative week. The mechanical property of an anastomosis is probably important during the early phase of the anastomotic healing, before collagen metabolism shifts to more collagen being synthesized than degradated, marking the beginning of the anastomotic proliferative healing phase. The aim of this experimental study was to compare the early mechanical strength of colorectal anastomoses created with the C-REX LapAid device and traditional circular stapling device in a porcine model.

An experimental study on 48 pigs undergoing open sigmoid colon resection with an end-to-end colorectal anastomosis 15 cm above the anal verge. Twenty-one pigs were anastomosed with traditional circular staplers and twenty-seven with the C-REX LapAid device.

This experimental study was approved by the Regional Ethical Committee for Animal Experimentation at Gothenburg University, Sweden.

A total of 48 pigs weighing 30–62 kg were used. All animals were housed under standard laboratory conditions with free access to water and food.

C-REX LapAid is a compression anastomotic instrument designed for open and laparoscopic colonic anastomosis, thus limited for usage in and above the upper rectum. The anastomotic rings are available in three sizes (26, 29, and 32 mm).

The C-REX LapAid device is used to place the anastomotic rings into the proximal and distal intestinal ends after bowel resection. The rings anchor the transected intestinal ends, where after the C-REX LapAid anastomosis is formed by a snap-locking the rings together. In detail, the C-REX LapAid features a detachable anvil with a pre-assembled LapAn ring (Fig. 1). This ring is placed into the proximal end of the intestine and secured by a purse-string suture (Fig. 2). In similarity to ordinary stapler devices, a concealed trocar is positioned in the head of the C-REX LapAid and by rotating an adjusting knob on the base of the handle, the trocar becomes visible and allowing subsequent joining of the anvil and the trocar. The adjusting knob is turned clockwise to close the gap between the anvil and the head of the instrument just like handling a conventional stapling device. On the top of the head, there is a “first” sectioned ring, whereas the “second” sectioned ring is located on the anvil with the attached silicone O-ring (Fig. 1). When the two sectional rings are clamped together by firing the instrument, the intestinal end is squeezed in between, and 24 pins anchor the first and second ring together. Simultaneously, a circular knife cuts a central donut from the free end of the intestine. The same procedure is repeated on the distal end of the transected intestine, where after the intestinal ends are connected with a coupling segment (Fig. 3). The intergraded catheter system now enables the anastomosis to be validated through the connected catheters protruding through the anus. The circular staplers (Touchstone Brown CSC 29) were purchased on the market and used in the control group.

The animals were premedicated with intramuscular Zoletil and Domitor before transportation to the operating room. Anesthesia was induced with Propofol and maintained with Isoflurane. All animals were intubated and ventilated using the Siemens-Elema Servo Ventilator 900B (MPN: SESV900B). A single dose of prophylactic antibiotics, Synulox, was administered intravenously after the induction of anesthesia. During the surgical procedure, animals received intravenous crystalloids.

Laparotomy was performed through a midline incision and a portion of the sigmoid colon was resected. An end-to-end anastomosis was constructed 15 cm above the anal verge, using either the C-REX LapAid instrument or the circular stapler device. The abdomen was closed in layers using continuous sutures.

Animals in both groups were sacrificed at set time intervals after the surgical procedure to evaluate the bursting pressure of the anastomosed bowel segment, i.e., after 1 h, 6 h, 12 h, 24 h, 48 h, 72 h, and 7 days. The bursting pressure test was performed by infusing compressed air through an attached anal plug, while the oral part of the bowel was clamped by a standard bowel clamp 10 cm above the anastomosis. The abdominal cavity was filled with saline and intraluminal pressure was increased with a continuous air flow rate of 50 mL/min into the closed intestinal segment containing the anastomosis. The bursting pressure was defined as a macroscopic air leakage from an intestinal rupture in combination with a drop in intraluminal pressure (Fig. 4).

The early histological appearance of the C-REX LapAid anastomotic tissue was assessed in animals sacrificed at time intervals 6–24 h after the surgical procedure. This was achieved by staining for the transmembrane glycoprotein CD31, which is a specific marker for vascular endothelium, and with Masson Trichrome staining to demonstrate collagen.

Data was analyzed by non-parametric statistical methods and presented as medians and range. The Mann-Whitney U test was used to compare the difference between bursting pressure values in the stapled anastomotic group and the C-REX LapAid anastomotic group. A p value of < 0.05 was considered significant.

All 48 pigs recovered uneventfully after the surgical procedure and no animal was excluded due to surgical complications. All the end-to-end anastomoses were created 15 cm from the anal verge and were easy to perform in both groups (Fig. 4). Macroscopic examination after sacrifice revealed intact anastomoses in all animals without signs of pathological inflammation, adhesions or stenosis in both groups.

The median bursting pressure 1 h after surgery was 195 mbar (range 180–240) in the C-REX LapAid group compared to 36 mbar (range 28–64) in the stapled group (p < 0.001) (Fig. 5). At 6–12 h, the median bursting pressure was 180 mbar (range 160–220) in the C-REX LapAid group compared to 77 mbar (range 43–185) in the stapled group (p = 0.044) (Fig. 5). At 24 h −7 days, the median bursting pressure was 225 mbar (range 160-260) in the C-REX LapAid group compared to 215 mbar (range 190–240) in the stapled group (p = 0.558) (Fig. 5).

The early microscopic histological architecture of the anastomotic tissue assessed 6 and 24 h after the surgical procedure by the CD31 and Masson Trichrome staining, showed very little change in vascularization and no evident collagen formation in the healing granulation tissue in the anastomotic gap between the C-REX LapAid rings (Fig. 6).

This experimental study showed that the median bursting pressure in colorectal anastomoses constructed with the C-REX LapAid device remained high, i.e., over 180 mbar throughout the study period of 7 days. In contrast, anastomoses by traditional circular staplers showed significantly lower median bursting pressure in the earliest phase, being under 50 mbar. A higher bursting pressure in the early phase of the anastomotic healing might entail an advantage by improved integrity of the anastomoses, by preventing early subclinical leakages with secondary pericolic inflammation, possibly leading to disturbances in the healing process during the lag phase with a subsequent risk of a later AL. However, this theoretical advantage must be evaluated in the clinical setting, although supported by our previous safety study on 21 patients operated with sigmoid resection and C-REX anastomoses, with only one case of AL where the anastomotic rings were not fully closed [24]. In any case, a robust anastomotic integrity throughout the whole postoperative period can hardly be negative.

Colorectal AL remains one of the most feared postoperative adverse events and is a significant challenge, with reported leakage rates up to 20% in anastomoses in the lower rectum [12‒15]. AL is a major cause of postoperative morbidity and mortality [1‒4], impaired anorectal function [30, 31] and is associated with a higher risk of local recurrence and poor prognosis in colorectal cancer surgery [5, 6, 32, 33]. Hence, developing new techniques to improve anastomotic healing and diminish the risk of leakage is of paramount importance. Compression anastomoses have theoretical advantages over hand sutured and mechanical stapled anastomosis, by providing a uniformly distributed force in the anastomotic line and without deposing of any foreign material. The principle of compression anastomosis in gastrointestinal surgery was developed in the 19th century, in which the intestinal ends were compressed together without the need of sutures or staples. Murphy’s button, Valtrac BAR ring, and NiTi rings are representative products of compression anastomotic devices. However, these instruments have been cumbersome to use and have mostly been abandoned.

The novel compression anastomotic method C-REX has been developed to circumvent these practical problems by construction of a device which mimics the function of traditional stapling instruments. The instrument also enables intraoperative measurement of anastomotic contact pressure during the surgical procedure, giving the surgeon direct feedback on the integrity of the anastomosis. In this study, the C-REX LapAid anastomoses demonstrated more than 5-fold higher median bursting pressure 1 h after the anastomoses formation compared to the traditional circular stapling technique. During the period of 6–12 h after the procedure, the median bursting pressure was more than 2-fold higher in the C-REX LapAid anastomoses compared to the stapled anastomoses. After 24 h and up to 7 days, there was no difference in median bursting pressure between the groups. The number of animals used during this period was, however, low, as the focus of the present study was on the first 24 h of the anastomotic strength. However, our previous C-REX RectoAid results in the transanal approach in a porcine model, have demonstrated a median bursting pressure of 200 mbar after 24 h (range 180–220), 220 mbar after 48 h (range 210–240), 220 mbar after 72 h (range 180–240), and 220 mbar after 7 days with range 200–230 mbar (unpublished data).

In line with our previous study on anastomotic healing [22], early histological appearance 24 h after the C-REX LapAid anastomosis formation demonstrated very little tissue reaction in terms of vascular CD31 or collagen formation, suggesting that the mechanical properties of the anastomoses are probably important in the early phase of anastomotic healing.

The authors have now operated 35 patients with a resection of the sigmoid colon or high anterior resection due to colorectal cancer with low colonic or colorectal end-to-end anastomoses with the CARP and C-REX methods with only one AL (2.9%), where the cause of the leakage was related to inadequate manual closure of the device with the LapAid method [24]. Furthermore, no AL was observed clinically or endoscopically in 15 patients operated with high anterior resection and an end-to-end C-REX RectoAid colorectal anastomosis 10–12 cm from the anal verge.

In summary, the novel C-REX LapAid method showed efficiency in constructing colonic anastomoses in a porcine model, providing strong mechanical resistance throughout the study period including the early phase, in contrast to traditional stapled anastomoses. These results encourage further studies in patients undergoing colorectal resection. The authors are planning a safety study evaluating the efficacy of the C-REX RectoAid device in performing minimal invasive transanal end-to-end colorectal anastomoses following low anterior resection of the rectum in 20 patients with rectal cancer, where the frequency of AL is the highest. In addition, the local inflammatory responses in the anastomotic wound (pro-inflammatory cytokines, neutrophil activity and growth factors) will be analyzed by collecting fluid samples directly from the anastomotic gap through the catheter-based system of the C-REX anastomosis. Furthermore, the fluid samples will be sent for bacterial cultures during the third postoperative day for mapping the bacterial flora in the anastomotic wound.

This study protocol was reviewed and approved by the Regional Ethical Committee for Animal Experimentation at Gothenburg University Sweden, Approval No. GBG 128-2014.

Anders Grönberg is the inventor of all C-REX devices. Henrik Thorlacius and Anders Grönberg are founders of CarpoNovum, and hold shares in CarpoNovum A.B.

This research was supported by CarpoNovum A.B.

Anders Grönberg, Dadi Vilhjalmsson, Henrik Thorlacius, and Ingvar Syk designed the study. Anders Grönberg and Dadi Vilhjalmsson performed the operations, and Anders Grönberg managed the postoperative surgical care and follow-up. Dadi Vilhjalmsson wrote the main manuscript and prepared all the figures. All authors reviewed the manuscript before submission.

The data presented in this experimental study are available on request from the corresponding author (D.T.V). The data are not publicly available for privacy reasons.