Anastomotic leaks remain one of the most dreaded complications in gastrointestinal surgery causing significant morbidity, that negatively affect the patients' quality of life. Experimental studies play an important role in understanding the pathophysiological background of anastomotic healing and there are still many fields that require further investigation. Knowledge drawn from these studies can lead to interventions or techniques that can reduce the risk of anastomotic leak in patients with high-risk features. Despite the advances in experimental protocols and techniques, designing a high-quality study is still challenging for the investigators as there is a plethora of different models used.

To review current state of the art for experimental protocols in high-risk anastomosis in rats.

This systematic review was performed according to The Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. To identify eligible studies, a comprehensive literature search was performed in the electronic databases PubMed (MEDLINE) and Scopus, covering the period from conception until 18 October 2023.

From our search strategy 102 studies were included and were categorized based on the mechanism used to create a high-risk anastomosis. Methods of assessing anastomotic healing were extracted and were individually appraised.

Anastomotic healing studies have evolved over the last decades, but the findings are yet to be translated into human studies. There is a need for high-quality, well-designed studies that will help to the better understanding of the pathophysiology of anastomotic healing and the effects of various interventions.

To investigate the early and late antiadhesive effect and any changes of fibrin matrix regulation enzymes on rat peritoneum, after local administration of bevacizumab.

Rats were subjected to cecal abrasion. Bevacizumab (5 mg/kg) against placebo was given intraperitoneally. On the 2nd, 14th, and 28th postoperative days adhesions were scored, and tissue plasminogen activator (tPA), plasminogen activator inhibitor-1 (PAI-1), matrix metalloproteinase-9 (MMP-9), degree of fibrosis, and angiogenesis were measured in abrased cecum and in intact parietal peritoneum.

Bevacizumab significantly reduced adhesions up to 15% on the 2nd, 52.5% on the 14th, and 55% on the 28th postoperative day, and significantly increased tPA concentrations in peritoneum. PAI-1 was decreased, and a significantly higher tPA/PAI-1 ratio along with an increase of MMP-9 was measured at all time points. Fibrosis and angiogenesis were significantly lower on the 14th and 28th postoperative days.

Local bevacizumab administration has a strong early and late antiadhesive action on rat peritoneum, mediated by changes in the tPA/PAI-1 and MMP balance in favor of fibrinolysis up to 28 days after operations.

Implantation of meshes in a contaminated environment can be complicated by mesh infection and adhesion formation.

The caecal ligation and puncture model was used to induce peritonitis in 144 rats. Seven commercially available meshes were implanted intraperitoneally: six non-absorbable meshes, of which three had an absorbable coating, and one biological mesh. Mesh infection, intra-abdominal abscess formation, adhesion formation, incorporation and shrinkage were evaluated after 28 and 90 days. Histological examination with haematoxylin and eosin and picrosirius red staining was performed.

No mesh infections occurred in Sepramesh(®) , Omyramesh(®) and Strattice(®) . One mesh infection occurred in Parietene(®) and Parietene Composite(®) . Significantly more mesh infections were found in C-Qur(®) (15 of 16; P ≤ 0·006) and Dualmesh(®) (7 of 15; P ≤ 0·035). Sepramesh(®) showed a significant increase in adhesion coverage from 12·5 per cent at 28 days to 60·0 per cent at 90 days (P = 0·010). At 90 days there was no significant difference between median adhesion coverage of Parietene Composite(®) (35·0 per cent), Omyramesh(®) (42·5 per cent), Sepramesh(®) (60·0 per cent) and Parietene(®) (72·5 per cent). After 90 days the adhesion coverage of Strattice(®) was 5·0 per cent, and incorporation (13·4 per cent) was significantly poorer than for other non-infected meshes (P ≤ 0·009). Dualmesh(®) showed shrinkage of 63 per cent after 90 days.

Parietene Composite(®) and Omyramesh(®) performed well in a contaminated environment. Strattice(®) had little adhesion formation and no mesh infection, but poor incorporation. Some synthetic meshes can be as resistant to infection as biological meshes.

Our objective was to evaluate the impact of intraperitoneal pressure (IPP) and duration of a CO(2) pneumoperitoneum on the peritoneal fibrinolytic system during laparoscopic surgery.

Human study: Patients undergoing laparoscopic surgery were divided into two groups: low (8 mmHg, n= 32) or standard (12 mmHg, n= 36) IPP. Normal peritoneum was collected from the parietal wall at the beginning of surgery and every 60 min thereafter. Mouse study: Mice were divided into three groups: low (2 mmHg) or high (8 mmHg) IPP or laparotomy. Peritoneal tissue was collected at 0, 4, 8, 24, 48 and 72 h, and 5 and 7 days after surgery. Real-time RT-PCR was performed in humans and mice to measure the levels of tissue plasminogen activator (tPA) and plasminogen activator inhibitor-1 (PAI-1) mRNA in peritoneal tissues.

Human study: The tPA/PAI-1 mRNA ratio was significantly decreased in the 12 mmHg group at 1 h [P < 0.0001 versus matched initial peritoneal biopsies (MI)]. The tPA/PAI-1 mRNA ratio decreased in both groups at 2 h (P < .0.01 versus MI). Mouse study: The tPA/PAI-1 ratio was decreased at 0 h, and the difference was significant at 4 h in both the laparotomy (P < 0.001 versus controls, 0 h, 5 and 7 days) and high-IPP (P < 0.0001 versus 0, 48 and 72 h, 5 and 7 days) groups. No changes in tPA/PAI-1 ratio were observed in the low-IPP group.

A low IPP and shorter duration of surgery appear to minimally impact the fibrinolytic system during a CO₂ pneumoperitoneum.

This randomized study aimed to compare the reaction of the immune system to the process of postoperative adhesion formation after open and laparoscopic cholecystectomy.

In this study, 20 mongrel dogs were used: 10 each in the laparoscopic and open cholecystectomy groups. Blood and peritoneal lavage samples were taken up to postoperative day 14, followed by second-look laparoscopy and reoperation to detect the rate of adhesion formation. Also, specimens were obtained from the liver bed for histology.

In the open cholecystectomy group, the white blood cell count was higher in blood samples and lower in lavage specimens. Adhesion formation was extensive, and the histologic immune reaction was more intensive in the open cholecystectomy group.

This randomized study proved that laparoscopic cholecystectomy was associated with less immune suppression, less inflammatory reaction, and therefore less adhesion formation than open cholecystectomy.

This study assessed and compared the efficacy of two types of bioresorbable membranes in the prevention of postoperative adhesion under clean contaminated and bacterial peritonitis conditions using a cecal ligation and puncture model in rats.

Wistar albino rats (n = 72) were divided into six groups. Bacterial peritonitis was induced using a cecal ligation and puncture model in groups 2, 4, and 6. Groups 1, 3, and 5 served as controls for clean contaminated procedures in the absence of bacterial peritonitis. Groups 1 and 2 were the untreated clean contaminated and bacterial peritonitis groups and served as controls for the effect of the bioresorbable membranes in each condition. In groups 3 and 4, a 1.5 x 3 cm USP glycerol/sodium hyaluronate/carboxymethylcellulose membrane was wrapped around the cecal resection area and a 2 x 4 cm membrane was left under the incision. The oxidized regenerated cellulose membrane was similarly applied in groups 5 and 6. Four weeks later, the adhesions were evaluated. In addition, fibrosis and inflammation were observed histopathologically.

Adhesion development (P = .008), fibrosis (P = .008), and inflammation (P = .0001) differed among the groups. Both materials increased adhesion formation in the bacterial peritonitis condition. Increased fibrotic activity was detected in all material-applied groups under both conditions. In addition, more inflammation was detected in the groups that received the application of a material, especially in the presence of bacterial peritonitis.

Neither material prevented adhesions in clean contaminated conditions. Moreover, they increased adhesion formation in bacterial peritonitis.

To determine whether the presence of cells of the monocyte-macrophage system affects the fibrinolytic response of peritoneal mesothelial cells to lipopolysaccharide (LPS) in the presence and absence of sodium hyaluronate.

Controlled laboratory experiment.

Cell cultures in an academic laboratory research environment.

Human peritoneal mesothelial cells were harvested from patients undergoing a laparotomy for noninfectious reasons and were cultured in vitro. Co-cultures were formed by adding U-937 human monocyte-like cells to a monolayer of mesothelial cells.

After 24 hours, cultures were treated with 10 ng/mL of LPS, and sodium hyaluronate was added in a final concentration of 0.2%. Controls received medium without sodium hyaluronate.

After 24 hours' incubation, tissue plasminogen activator (tPA), urokinase plasminogen activator (uPA), and plasminogen activator inhibitor-1 (PAI-1) levels were determined in medium and cell lysates by using ELISA techniques.

In medium of co-cultures, tPA and PAI-1 concentrations were statistically significantly increased compared with the case of monocultures, whereas uPA concentration was statistically significantly decreased. In cell lysates of co-cultures, PAI-1 concentration was statistically significantly increased compared with the case of monocultures, whereas tPA and uPA were unaffected. Treatment with sodium hyaluronate statistically significantly decreased PAI-1 and uPA concentrations in medium of monocultures but decreased uPA concentration only in medium of co-cultures, compared with the case of controls.

Cells of the monocyte-macrophage system modulate the fibrinolytic capacity of LPS treated human peritoneal mesothelial cells and interfere in the hyaluronan-associated changes in mesothelial fibrinolytic capacity.

Fibrous adhesions remain a major sequela of abdominal surgery. The proinflammatory peptide substance P (SP), known to participate in inflammatory events, may play a key role in adhesion formation. This hypothesis was tested by using an antagonist, CJ-12,255 (Pfizer), that blocks the binding of SP to the neurokinin 1 receptor (NK-1R). Adhesion formation was surgically induced in the peritoneum of rats receiving daily doses of the NK-1R antagonist (NK-1RA; 5.0 or 10.0 mg/kg per day) or saline. On postoperative day 7, both the low and high doses of NK-1RA significantly (P < 0.05) reduced adhesion formation by 45% and 53%, respectively, compared with controls. Subsequently, the effect of NK-1RA administration on peritoneal fibrinolytic activity was investigated to determine a potential mechanism for SP action in the peritoneum. Samples were collected from nonoperated controls and from animals 24 h postsurgery that were administered either NK-1RA or saline. Fibrinolytic activity in peritoneal fluid was assayed by zymography, and expression of tissue plasminogen activator (tPA) and plasminogen activator inhibitor 1, both regulators of fibrinolytic activity, was assessed in peritoneal tissue and fluid by RT-PCR and bioassay, respectively. NK-1RA administration led to a marked (P < 0.05) increase in tPA mRNA levels in peritoneal tissue compared with nonoperated and saline-administered animals. Likewise, NK-1RA administration significantly (P < 0.05) increased tPA in the peritoneal fluid. These data suggest that activation of the NK-1R promotes peritoneal adhesion formation by limiting fibrinolytic activity in the postoperative peritoneum, thus enabling fibrinous adhesions to persist.

Intra-abdominal adhesions and abscesses cause significant morbidity and mortality. The formation of fibrin in the abdominal cavity is a common pathophysiological pathway for both. The aim of this review was to investigate the pathophysiology of intra-abdominal adhesions and abscesses, and to explore the possible sites of action of hyaluronan.

Data were reviewed from the literature using the Medline database.

Both surgery and peritonitis disturb the equilibrium between coagulation and fibrinolysis in the abdominal cavity in favour of the coagulation system. Hyaluronan-based agents reduce adhesion formation after surgery. Moreover, hyaluronan solution reduces abscess formation in experimental peritonitis. Possible mechanisms of action include mechanical separation of wound surfaces, improvement of peritoneal healing, modulation of the inflammatory response and enhanced fibrinolysis.

Diminished fibrin degradation is a common pathway for the formation of adhesions and abscesses. The potential of hyaluronan-based agents to reduce intra-abdominal adhesions and abscesses in abdominal surgery and sepsis is a promising new concept. Elucidating the mechanisms involved and the clinical application of hyaluronan in peritonitis are challenges for future research.