The prevention of postoperative pelvic adhesions: an animal study comparing barrier methods with dextran 70

Barrier materials for prevention of surgical adhesions: systematic review

BACKGROUND

Postoperative surgical adhesions constitute a major health burden internationally. A wide range of materials have been evaluated, but despite constructive efforts and the obvious necessity, there remains no specific barrier widely utilized to prevent postoperative adhesion formation. The aim of this study was to highlight and characterize materials used for prevention of postoperative surgical adhesions in both animal and human studies.

METHODS

A systematic review was performed of all original research articles presenting data related to the prevention of postoperative adhesions using a barrier agent. All available observational studies and randomized trials using animal models or human participants were included, with no restrictions related to type of surgery. PubMed and Embase databases were searched using key terms from inception to August 2019. Standardized data collection forms were used to extract details for each study and assess desirable characteristics of each barrier and success in animal and/or human studies.

RESULTS

A total of 185 articles were identified for inclusion in the review, with a total of 67 unique adhesion barrier agents (37 natural and 30 synthetic materials). Desirable barrier characteristics of an ideal barrier were identified on review of the literature. Ten barriers achieved the primary outcome of reducing the incidence of postoperative adhesions in animal studies followed with positive outputs in human participants. A further 48 materials had successful results from animal studies, but with no human study performed to date.

DISCUSSION

Multiple barriers showed promise in animal studies, with several progressing to success, and fulfilment of desirable qualities, in human trials. No barrier is currently utilized commonly worldwide, but potential barriers have been identified to reduce the burden of postoperative adhesions and associated sequelae.

Liquid Paraffin vs Hyaluronic Acid in Preventing Intraperitoneal Adhesions

Adhesion formation after abdominal and pelvic operations remains a challenging problem. Role of adjuvant barriers have been studied but there is no comparative study between liquid paraffin and hyaluronic acid as a barrier method. Hence, we planned to compare the effectiveness of 0.4 % hyaluronic acid and liquid paraffin in the prevention of postoperative intraperitoneal adhesions in rats. This prospective, randomized and controlled study was conducted in 60 adult Wistar albino rats. Surgical trauma by caecal abrasion and 1 g talcum powder was used in the rat model to induce adhesion formation. After trauma, 3 ml normal saline was instilled in the peritoneal cavity in control group (n = 20), 3 ml liquid paraffin was instilled in experimental group A (n = 20) and 3 ml 0.4 % hyaluronic acid was instilled in experimental group B (n = 20). Two weeks after laparotomy, repeat laparotomy was performed and the adhesions were scored according to Zuhlke classification. Liquid paraffin and hyaluronic acid both reduce the extent and grade of adhesions both macroscopically (p = 0.018, p = 0.017) and microscopically (p = 0.019, p = 0.019) respectively. Although there was significant reduction in adhesions by hyaluronic acid at certain specific sites as compared with liquid paraffin, its overall effectiveness in preventing postoperative intraperitoneal adhesions is not significantly different from liquid paraffin (p = 0.092, p = 0.193) respectively. The presence of liquid paraffin and hyaluronic acid in the peritoneal cavity reduce postoperative intraperitoneal adhesions significantly in rats. However, there is no overall significant difference in the effectiveness of two groups. Dosage and safety of these chemicals in human beings remains to be established.

Biodistribution and pharmacokinetics of EGFR-targeted thiolated gelatin nanoparticles following systemic administration in pancreatic tumor-bearing mice

The objective of this study was to evaluate qualitative and quantitative biodistribution of epidermal growth factor receptor (EGFR)-targeted thiolated type B gelatin nanoparticles in vivo in subcutaneous human pancreatic adenocarcinoma (Panc-1) bearing female SCID Beige mice. EGFR-targeted nanoparticles showed preferential and sustained accumulation in the tumor mass, especially at early time points. Higher blood concentrations and higher tumor accumulations were observed with PEG-modified and EGFR-targeted nanoparticles during the study (AUClast: 17.38 and 19.56%ID/mL·h in blood, 187 and 322%ID/g·h in tumor for PEG-modified and EGFR-targeted nanoparticles, respectively), as compared to control, unmodified particles (AUClast: 10.71%ID/mL·h in blood and 138%ID/g·h in tumor). EGFR-targeted nanoparticles displayed almost twice tumor targeting efficiency than either PEG-modified or the unmodified nanoparticles, highlighting the efficacy of the active targeting strategy. In conclusion, this study shows that EGFR-targeted and PEG-modified nanoparticles were suitable vehicles for specific systemic delivery in subcutaneous Panc-1 tumor xenograft models.

Properties And Prevention of Adhesions Applications of Bioelastic Materials

The origins, syntheses, variable composition and physical properties of bioelastic materials are discussed. The latter includes their capacity to undergo inverse temperature transitions to increased order on raising the temperature and to be designable to interconvert free energies involving the intensive variables of mechanical force, temperature, pressure, chemical potential, electrochemical potential and light.

Bioelastic materials include analogues and other chemical variations of the viscoelastic polypeptide, poly(Val-Pro-Gly-Val-Gly), and cross-linked elastomeric matrices thereof. This parent material has been shown to be remarkably biocompatible; it can be minimally modified to vary the rate of hydrolytic breakdown; it can contain enzymatically reactive sites; and it can have cell attachment sites included which promote excellent cell adhesion, spreading and growth to confluence.

One specific application is in the prevention of postoperative adhesion. There are some 30,000,000 per year surgical procedures in this country and a large portion of these would benefit if a suitable material were available for preventing adhesions. Bioelastic materials have been tested in a contaminated peritoneal model, and promising preliminary studies have been carried out in the rabbit eye model for strabismus surgery. In the peritoneal model, 90% of the 29 control animals exhibited significant adhesions; whereas, only 20% of the 29 animals using gas sterilized matrices had significant adhesions. On the basis of this data, it appears that cross-linked poly(VPGVG) is an effective physical barrier to adhesion formation in a trauma model with resulting hemorrhage and contamination.

The potential use of bioelastic materials as a pericardial substitute following the more than 400,000 open heart surgeries per year in the U.S. is under development beginning with the use of bioelastic matrices to prevent adhesions to the total artificial heart being used as a bridge to heart transplantation such that the site will be less compromised when receiving the donor heart.

A method for the consistent creation and quantitative testing of postoperative pelvic adhesions in a porcine model

INTRODUCTION

The assessment of methods for the prevention of postoperative pelvic adhesions is hampered by the lack of a quantifiable adhesion measurement technique. Currently available methods for adhesion model assessment rely on qualitative grading scales; a quantitative method would have many attendant benefits, including standardized reporting.

METHODS

A technique was developed to generate consistent and significant adhesions in a swine model that are suitable for quantitative assessment using a Material Testing System (MTS) machine platform. In this method, the uterine horns are cannulated and then attached to the pelvic sidewall using loose silk sutures. The underlying sidewall and adjacent uterine serosa are injured with electrocautery. Following a two-week survival the entire complex of uterine horn and sidewall are excised en bloc and prepared for MTS testing.

RESULTS

Extrication of the adhesion, as measured by the MTS platform, generates a quantitative assessment of adhesion strength that can be scaled and analyzed to produce several continuous variable descriptions.

DISCUSSION

This technique represents a novel quantitative method for adhesion assessment in an animal model. This quantitative technique may then be applied to accurately assess a range of adhesion prevention techniques, producing results which can be standardized for comparison.

Prevention of intra-abdominal adhesions using the antiangiogenic COX-2 inhibitor celecoxib

OBJECTIVE

To determine the effects of COX-2 specific inhibitors on postoperative adhesion formation.

SUMMARY AND BACKGROUND DATA

Intra-abdominal adhesions are the major cause of intestinal obstruction and secondary infertility after surgical procedures. Because adhesion synthesis requires angiogenesis, and cyclooxygenase-2 enzyme (COX-2) inhibitors have antiendothelial activity, we tested COX-2 inhibitors in a murine model of intra-abdominal adhesion formation.

METHODS

A silicone patch was secured to the lateral abdominal wall of groups of C57BL/6 mice, followed by cecal abrasion to promote adhesion formation. Beginning on the day of surgery, mice were treated with the selective COX-2 agents, celecoxib or rofecoxib, and the nonspecific COX inhibitors, aspirin, naproxen, ibuprofen, or indomethacin. Animals were treated for 10 days and killed. A second group (celecoxib, rofecoxib, aspirin) was treated for 10 days and observed for an additional 25 days. After treatment, intra-abdominal adhesions were scored using a standard method. The patch was subjected to immunohistochemistry with the endothelial-specific marker, CD31.

RESULTS

Animals treated with selective and nonselective COX-2 inhibitors, except aspirin, had significantly fewer adhesions than control animals. Celecoxib produced a maximal reduction in adhesion formation compared with rofecoxib and the nonselective COX-2 inhibitors at 10 days. After 25 days, celecoxib and rofecoxib, but not aspirin, had fewer adhesions than control mice. Adhesions from mice treated with celecoxib had reduced microvessel density compared with rofecoxib, the nonselective COX inhibitors, and control animals.

CONCLUSIONS

Selective COX-2 inhibitors, in particular celecoxib, provide durable inhibition of intra-abdominal adhesions through an antiangiogenic mechanism.

Pathophysiology of intra-abdominal adhesion and abscess formation, and the effect of hyaluronan

BACKGROUND

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.

METHODS

Data were reviewed from the literature using the Medline database.

RESULTS

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.

CONCLUSION

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.

Mesothelial cells: their structure, function and role in serosal repair

The mesothelium is composed of an extensive monolayer of specialized cells (mesothelial cells) that line the body's serous cavities and internal organs. Traditionally, this layer was thought to be a simple tissue with the sole function of providing a slippery, non-adhesive and protective surface to facilitate intracoelomic movement. However, with the gradual accumulation of information about serosal tissues over the years, the mesothelium is now recognized as a dynamic cellular membrane with many important functions. These include transport and movement of fluid and particulate matter across the serosal cavities, leucocyte migration in response to inflammatory mediators, synthesis of pro-inflammatory cytokines, growth factors and extracellular matrix proteins to aid in serosal repair, release of factors to promote both the deposition and clearance of fibrin, and antigen presentation. Furthermore, the secretion of molecules, such as glycosaminoglycans and lubricants, not only protects tissues from abrasion, but also from infection and possibly tumour dissemination. Mesothelium is also unlike other epithelial-like surfaces because healing appears diffusely across the denuded surface, whereas in true epithelia, healing occurs solely at the wound edges as sheets of cells. Although controversial, recent studies have begun to shed light on the mechanisms involved in mesothelial regeneration. In the present review, the current understanding of the structure and function of the mesothelium and the biology of mesothelial cells is discussed, together with recent insights into the mechanisms regulating its repair.

The impact of adhesions on hospital readmissions over ten years after 8849 open gynaecological operations: an assessment from the Surgical and Clinical Adhesions Research Study

OBJECTIVE

To investigate the epidemiology of, and the clinical burden related to, adhesions following gynaecological surgery.

POPULATION

The Scottish National Health Service Medical Record Linkage Database was used to define a cohort of 8849 women undergoing open gynaecological surgery in 1986.

METHODS

All readmissions for potential adhesion related disease in the subsequent 10 years were reviewed.

MAIN OUTCOME MEASURES

Readmissions and the degree of adhesion involvement gave an indication of clinical burden and workload. The rate of readmission following the initial surgery determined the relative risk of disease related to adhesions.

RESULTS

Two hundred and forty-five (4.5%) of 5433 readmissions following open gynaecological surgery were directly related to adhesions. 34.5% of patients were readmitted, on average 1.9 times, for a problem potentially related to adhesions or for further intra-abdominal surgery that could be complicated by adhesions. Readmissions related to adhesions continued throughout the 10 year period of the study. The overall rate of readmission was 64.0/100 initial operations. For readmissions directly related to adhesions, the rate was 2.9/100 initial operations. Operations on the ovary had the highest rate directly related to adhesions (7.5/100 initial operations), with an overall rate of readmission of 106.4/100 initial operations.

CONCLUSIONS

Despite the conservative approach taken in this study, the clinical burden, workload and relative risk of readmissions related to adhesions following open gynaecological surgery was considerable. Post-operative adhesions have important consequences for patients, surgeons and the healthcare system. These results emphasise the need for more effective strategies to prevent adhesions.

New directions in the prevention of adhesion in laparoscopic surgery

The aim of this review is to appraise critically the literature over the past year with respect to new developments in adhesion prevention strategies. The majority of the work continues to be focused on animal models, and interest continues into the usage of heterologous barriers, which are increasingly derived from or related to hyaluronic acid. The recent trend has been to develop barriers that are not only effective but also technically easy to use for the laparoscopic surgeon--hence the development of barrier gels. It is only through the development of these user-friendly barriers that many laparoscopic surgeons will be willing to incorporate these important preventative measures into their busy daily practice. Routine usage of adhesion prevention measures will ultimately reduce patient morbidity and mortality and relieve the burden on health service provision.

The comparison of gonadotropin-releasing hormone agonist therapy and intraperitoneal Ringer's lactate solution in prevention of postoperative adhesion formation in rat models

OBJECTIVE

To evaluate gonadotropin-releasing hormone agonists (GnRH-a) therapy and intraperitoneal Ringer's lactate solution (RL) for the prevention of postsurgical adhesion formation in rat models.

STUDY DESIGN

Forty rats were randomized into four groups: Group I was the control; in group II, RL was applied at the surgery; group III and IV received preoperative subcutaneous injections of the GNRH-a leuprolide acetate and only the diluent of the GNRH-a respectively. A standard lesion was created over the uterus of each rat. Adhesions were scored at relaparotomy 3 weeks later. Analysis of variance (Kruskal-Wallis) and Mann-Whitney U-tests were used for the statistical evaluation.

RESULTS

The average adhesion scores were 2.7+/-0.26, 1.4+/-0.27, 0.9+/-0.18, and 2.5+/-0.34 in groups I, II, III, and IV respectively. There were significant differences between the scores of groups I and II (P<0.01), groups I and III (P<0.001), groups II and IV (P<0.05), and groups III and IV (P<0.01); but not between the scores of groups II and III, and groups I and IV (P>0.05).

CONCLUSION

GNRH-a was successful in reducing postoperative adhesion formation but was not superior to intraperitoneal RL.

Polyethylene glycol 4000 attenuates adhesion formation in rats by suppression of peritoneal inflammation and collagen incorporation

BACKGROUND

Postoperative separation of the peritoneal surfaces is a promising approach for the prevention of adhesion formation. Instillation of polyethylene glycol 4000 (PEG) was recommended as an appropriate method.

METHODS

In a time-course study in rats, efficacy and mode of action of PEG was investigated. Adhesions were induced by crushing of the cecum. Sixty animals were randomly allocated to three control groups with intraperitoneal instillation of 5 mL 0.9% NaCl and to three therapy groups treated with 5 mL 20% PEG. After 3, 7, and 21 days, adhesion grade, intraperitoneal leukocytes, and collagen incorporation into the adhesion strands were evaluated.

RESULTS

Administration of PEG resulted in a decrease of leukocytes by 43% (days 3 and 7), a reduction of the adhesion score by 85% (day 3), 77% (day 7), and 79% (day 21), and an impairment of collagen deposition by 54% (day 7) and 44% (day 21).

CONCLUSIONS

Coating the peritoneal surfaces with PEG is a highly effective measure to suppress the fatal sequence of posttraumatic inflammation, formation of initial adhesions, and their subsequent organization to strong permanent adhesion strands.

Adhesion reduction as a new treatment innovation

A new treatment option, an antiadhesion device, has proved effective in the reduction of postoperative adhesion formation and is now approved for use in the United States. The device is a thin, filmy membrane composed of two organic substances that are resorbed by the body. The device is inserted intraoperatively between apposing tissue surfaces that are potentially adhesiogenic. It proved effective in reducing the incidence of adhesions after both abdominal and pelvic surgery.

Reduction of surgery-induced peritoneal adhesions by methylene blue

BACKGROUND

The possible involvement of inflammatory mediators such as nitric oxide (NO), and reports of protective effects of antioxidants, led us to test the effectiveness of methylene blue and NO synthesis inhibitor in reducing adhesion formation.

METHODS

Generation of adhesions in rats, by scraping the anterior uterine horn wall, was followed by intraperitoneal administration of saline methylene blue, or N alpha-t-BOC-omega-nitro-L-arginine. Additional rats received identical treatments, but without the serosal damage. Two weeks later, formation of adhesions was quantitatively graded.

RESULTS

Adhesions were found in <5% of the rats with the sham surgery, regardless of treatment. In the experimental group, >95% of the rats treated with saline or NO synthetase inhibitor had severe adhesions, in contrast to 5% of the methylene blue treated rats. Severity of adhesion was lower in the methylene blue group (P <0.001).

CONCLUSIONS

Methylene blue was very effective in preventing formation of peritoneal adhesions. Its activity is probably through inhibition of free-radical generation and not of nitric oxide action.

Effects of physical barriers in prevention of adhesions: an incisional hernia model in rats

BACKGROUND

Adhesion formation between viscera and mesh is almost inevitable following incisional hernia repair with prosthetic mesh. Such adhesions may lead to intestinal obstruction and enterocutaneous fistulae formation and make further laparotomies extremely difficult. Sodium carboxymethylcellulose (SCMC) and Interceed TC7 (oxidized regenerated cellulose) as physical barriers have been shown to be effective in reducing postoperative adhesions.

MATERIALS AND METHODS

To evaluate the effects of SCMC and Interceed TC7, we used an incisional hernia model in rats. A ventral abdominal defect (15 x 25 mm) was created in each of 36 male rats which were then divided into three equal groups. In Group I (control) the defect was repaired with polypropylene mesh (PPM) only; in Group II the defect was repaired after a layer of Interceed TC7 was laid over the viscera with Interceed TC7-covered PPM; in Group III the defect was repaired after a layer of SCMC was laid over the viscera with SCMC-coated PPM. Six of the animals from each group were sacrificed at Postoperative Day 7 and the adhesions were scored. The remaining 6 were sacrificed at Day 30 and histological evaluation was made in addition to the adhesion score.

RESULTS

Animals in the SCMC-treated group developed significantly less adhesions (P = 0.0002) compared with control and Interceed TC7-treated groups. However, histological analysis revealed poor fibroblast proliferation with impaired wound healing in the SCMC group.

CONCLUSION

SCMC prevented adhesion formation but seriously impaired wound healing, and Interceed TC7 was ineffective in preventing adhesion in this model.

Prevention of adhesions

A survey is given on the literature of the prevention of adhesions. Various methods of adhesion prevention are discussed: limitation of peritoneal injury, inhibition of the inflammatory response, prevention of coagulation of fibrinogen, removal of fibrin and mechanical separation of injured mesothelial surfaces.

Contemporary adhesion prevention

OBJECTIVE

To (1) review the events leading to peritoneal adhesion formation; (2) review traditional adhesion prevention adjuvants; (3) overview studies for adhesion prevention barriers including a perspective for their use; and (4) look toward the future of adhesion prevention.

RESULTS

A great deal of effort has been dedicated to reduce adhesion formation because of the morbidity associated with adhesions and the associated economic burden, which considering only hospital costs and surgeons' fees, was $1,180 million in the United States. To understand the role of adhesion barriers in gynecological surgery, an appreciation of the cellular cascade and temporal nature of peritoneal repair is necessary. Evidence indicates that areas denuded of peritoneum will heal satisfactorily and that suturing of the peritoneum may increase adhesion formation. Physical barriers, including both mechanical and viscous solutions, are widely used to prevent adhesion formation by limiting tissue apposition during the critical stages of mesothelial repair. Clinical studies do not support the use of intraperitoneal, dextran for adhesion prevention. Theoretical considerations of peritoneal fluid dynamics indicate that crystalloid instillates should not prevent adhesion formation because of their short intraperitoneal residence. This prediction is consistent with clinical observation. The availability of Interceed (Johnson and Johnson Medical, Inc., Arlington, TX) and Gore-Tex Surgical Membrane (W.L. Gore, Flagstaff, Arizona) barriers provides substantial progress in postsurgical adhesion prevention.

CONCLUSIONS

Although many investigators are incorporating adhesion prevention barriers into their routine clinical situations, physician acceptance is constrained by technical difficulties.

Effects of TC7 associated to 32% dextran 70, heparin and carboxymethylcellulose in adhesion prevention in the rat

Experimental studies on adhesion formation 90 days after laparotomy in the rat were done. Uterine horn adhesions after standardised procedures and trauma in a control group of 10 rats were compared with those obtained in six other 10-rat groups in whom heparin, carboxymethylcellulose (CMC), 32% dextran 70 and the fabric TC7 either alone or in various combinations were used at the time of laparotomy. Dextran 70 and CMC used on their own appeared to reduce adhesion formation but the improvement did not achieve statistical significance when compared with the control group. TC7 used alone had no anti-adhesion effect; when used with CMC or dextran 70, TC7 did not enhance the anti-adhesion benefit conferred by either substance used on its own.

Postoperative adhesion after uterine horn surgery in the rat, with the use of TC7

The influence of TC7 in adhesion prevention was tested on 24, 2.5-month-old Wistar rats. Their right and left uterine horns were homogeneously allotted into four experimental groups, each of 12 horns. The groups were as follows: Group C (n = 12), that underwent cuts along 1 cm in the serosal layer; Group TC (n = 12), where the uterine horn was only surrounded with 3 layers of TC7, 1 x 1 cm in size; Group C+TC (n = 12) in which the serosal cuts were covered with TC7, as in group TC and an untouched control group (n = 12). All uterine horns were kept in uniform contact with the intestinal serosa layer by means of two 8/0 nylon stitches spaced 2 cm apart, so that the adhesion surfaces were the same in all groups. Lengths in mm and severity adhesions (0 = no adhesion to 3 = severe adhesion) were recorded. The injury in group C caused extensive (8.83 +/- 4.77 mm) and dense adhesions (score 2.42 +/- 1.11) in 83.33% of the cases. No significant differences were observed compared with the C+TC group (8.08 +/- 5.45 mm, score 2.25 +/- 1.30; P > 0.05, ANOVA). Significantly, more adhesions were observed on the C and C+TC Groups than in the control (1.00 +/- 2.27 mm, score 0.16 +/- 0.37) and TC (3.08 +/- 3.38 mm, score 1.00 +/- 1.15) groups (P < 0.05, ANOVA). TC7 does not appear to be an effective agent for preventing postoperative adhesions in this animal model.

Effect of phosphatidylcholine on postoperative adhesions after small bowel anastomosis in the rat

The possibility of preventing postoperative adhesions using phosphatidylcholine (PC) was studied in rats. A small bowel anastomosis was created using continuous or interrupted 5/0 silk sutures. Adhesions were measured by recording the maximal length of adhesions around the anastomosis and the number of organs involved in the adhesions. PC was administered intraperitoneally either as a single dose or as three separate doses. Postoperative adhesions developed in all animals; the degree of adhesion was independent of the suture technique used. PC given once at a dose of 20 mg significantly decreased adhesion formation (P less than 0.01). The mechanism underlying this effect may be that the exogenous PC provides a lubricant layer replacing endogenous hydrolysed phospholipid. The result with repeated PC administration was not different from that after a single dose. Increasing the single dose of PC to 40 or 60 mg resulted in anastomotic dehiscence and subsequent peritonitis. It is concluded that PC in a single dose of 20 mg reduces adhesion formation after small bowel anastomosis in the rat.

Comparison of the peritoneal cells elicited by oxidized regenerated cellulose (Interceed) and expanded polytetrafluoroethylene (Gore-Tex Surgical Membrane) in a murine model

OBJECTIVE

The peritoneal fluid cell responses to the available barriers used to prevent postoperative adhesions, oxidized regenerated cellulose (interceed) and expanded polytetrafluoroethylene (Gore-Tex Surgical Membrane), were compared.

STUDY DESIGN

Oxidized regenerated cellulose and expanded polytetrafluoroethylene were inserted into the peritoneal cavity of mice and the peritoneal fluid cell number, differential cell count, morphologic type, adherence to plastic, and phorbol-12,13-myristate acetate-stimulated hydrogen peroxide production evaluated. Peritoneal fluid cell attachment to oxidized regenerated cellulose and expanded polytetrafluoroethylene was evaluated by electron microscopy.

RESULTS

Oxidized regenerated cellulose promptly elicited increased numbers of large, morphologically activated peritoneal fluid macrophages that adhered more rapidly and produced more hydrogen peroxide than controls. Expanded polytetrafluoroethylene gradually increased the number of normal-appearing peritoneal fluid macrophages with increased hydrogen peroxide production but normal adherence. Macrophages rapidly attached to both materials in vivo, with oxidized regenerated cellulose being rapidly degraded.

CONCLUSION

Oxidized regenerated cellulose, to a greater extent than expanded polytetrafluoroethylene, elicits an acute peritoneal fluid inflammatory exudate in the mouse, which may contribute to the oxidized regenerated cellulose-induced peritoneal injury and de novo adhesions observed in this model.

Murine peritoneal injury and de novo adhesion formation caused by oxidized-regenerated cellulose (Interceed [TC7]) but not expanded polytetrafluoroethylene (Gore-Tex Surgical Membrane)

STUDY OBJECTIVE

To evaluate the impact of the materials contained in the available adhesion prevention barriers on the peritoneum. STUDY DESIGN, SETTING, PATIENTS: A murine paradigm was used, placing oxidized-regenerated cellulose (Interceed [TC7]) and expanded polytetrafluoroethylene (PTFE; Gore-Tex Surgical Membrane) in the peritoneal cavity for intervals up to 14 days.

INTERVENTIONS AND MAIN OUTCOME MEASURES

The appearance of the peritoneum on scanning and transmission electron microscopy and the presence of de novo adhesions were the end-points used.

RESULTS

Oxidized-regenerated cellulose caused localized sloughing of the mesothelial cell layer and leukocyte infiltration of the deeper tissue leading to the formation of adhesions to the bowel and liver in 58% of the animals. The surface of the oxidized-regenerated cellulose-injured peritoneum healed in 5 to 7 days. Neither peritoneal injury nor adhesions were noted in sham-operated animals or animals with PTFE.

CONCLUSIONS

Oxidized-regenerated cellulose but not PTFE has a localized injurious effect on the peritoneum of the mouse, resulting in de novo adhesions. The impact of the barrier material itself on normal peritoneum may be an important consideration in designing surgical barriers for the prevention of postoperative adhesions.

Trends in the development of bioresorbable polymers for medical applications

The gradual shift from biostable prostheses to degradable, temporary implants represents one of the most significant trends in biomaterials research. In view of this trend, medical applications of degradable implant materials were reviewed with special emphasis on orthopedic polymeric implants. Among the polymeric implant materials derived from natural sources, collagen, various polysaccharides such as cellulose, and microbial polyesters have been intensively investigated. Among the synthetic, degradable polymers, aliphatic polyesters such as poly(glycolic acid), poly(lactic acid), poly(caprolactone) and polydioxanone, are most commonly investigated. Only recently, several new classes of polymers such as poly(ortho esters), polyanhydrides, and degradable polycarbonates have been introduced as potential implant materials. A particularly versatile group of new biomaterials with promising engineering properties are the "pseudo"-poly(amino acids), amino acid derived polymers in which conventional peptide bonds have been replaced by various chemical linkages.

Peritoneal adhesion formation after lysis: inhibition by polyethylene glycol 4000

Peritoneal adhesions cause much long-term postoperative morbidity. This study evaluates the efficacy of polyethylene glycol (PEG) 4000 in reducing adhesion reformation after lysis. Adhesions were induced, by abrasion, in 111 Sprague-Dawley rats at a first laparotomy. At a second operation, 10 days later, these adhesions were graded and lysed, after which the animals received one of the following solutions intraperitoneally: 5 per cent PEG 4000 (n = 21), 25 per cent PEG 4000 (n = 23), 32 per cent dextran 70 (n = 22) or isotonic saline (n = 25), or were left as an untreated control group (n = 20). When the reformed adhesions were graded after a further 10 days 5 per cent PEG 4000 was found to be the only solution that inhibited adhesion reformation. The adhesions that reformed in the other four test groups were significantly worse than when they were first graded (P less than or equal to 0.033 for all groups). Therefore 5 per cent PEG 4000 may be useful in clinical practice for the reduction of adhesion formation after lysis.

Phosphatidylcholine prevents postoperative peritoneal adhesions: an experimental study in the rat

Phosphatidylcholine (PC) is the main constituent of the surface-active material coating peritoneal mesothelium. It may prevent postoperative adhesion formation through production of a lubricant film on mesothelial defects. We therefore examined the effect of its soluble form on surgically induced intraabdominal adhesions in rats. The adhesions were induced at laparotomy by any of four different operative models. PC was administered intraperitoneally (20 mg/rat) or intravenously (20 mg/rat or 50 mg/rat) at the end of the operation and on the second and third postoperative day. It was found that the degree of postoperative adhesion formation was significantly reduced by the intraperitoneal injection of PC in all 4 models. In contrast, no effect was achieved by the intravenous injection of PC, not even at a very high dose level. Our results suggest that soluble PC administered intraperitoneally might be a potent adjunct in postoperative adhesion prevention.

The use of an amniotic membrane graft to prevent postoperative adhesions

Grafts of trypsin-treated, gamma-irradiated human amniotic membranes were used to cover injured uterine horns of nulliparous female rabbits to prevent adhesions. In this study, the gradual integration of the membranes into the serosal layer of the uterus, together with marked neovascularization, was observed. By the 30th postoperative day, the grafts had been completely integrated, with little evidence of rejection and no evidence of infection at the graft sites. Of 30 uterine horns treated with membrane grafts, only 4 (13.4%) showed any adhesion formation at or among the graft sites. All of the 24 untreated controls showed adhesion formation at the site of injury. Furthermore, whatever adhesions were found in membrane-treated horns could be graded as thin and filmy, accounting for less than 10% of the surface area of the graft, whereas the controls showed dense, thick adhesions covering 50% to 100% of the injured areas. We conclude that these specially prepared amniotic membranes are safe and effective in dramatically reducing postoperative adhesion formation in this animal model.

Reoperation for small intestinal obstruction

Today, intestinal adhesions represent the most frequent etiology for complete or partial intestinal obstruction. Although partial obstruction can be treated nonoperatively with a considerable likelihood of success, intestinal strangulation cannot uniformly be predicted or prevented. Complete intestinal obstruction is associated with a significant incidence of strangulation if not treated by a vigorous surgical approach. Consequently, complete intestinal obstruction secondary to adhesions is still a surgical disease. Attempts at control of the adhesion process include mechanical methods to prevent subsequent obstruction and chemical methods to prevent the adhesion process itself. The invasive mechanical methods appear dated. A variety of agents have been used either systemically or in the peritoneal cavity to prevent the establishment of intra-abdominal adhesions. Agents that do not contribute to subsequent morbidity or impede the native host defense mechanisms should be utilized. High-molecular-weight dextran and nonsteroidal anti-inflammatory agents show some promise of being both safe and effective. As is frequently the case, the bottom line in preventing and treating intra-abdominal adhesions is appropriate surgical technique. Intestinal adhesions can be related clearly to leaving damaged, devitalized, or ischemic tissue in the peritoneal cavity or to excessive roughness in handling of tissues. Steps such as avoidance of excessive suture material and unnecessary handling of the bowel will do much to prevent subsequent adhesion generation. Likewise, the surgical lysis of intraperitoneal adhesions is frequently fraught with complications such as intra-abdominal abscess or postoperative incisional failure. This is again related to surgical technique and most directly to the use of blunt dissection to divide adhesions. Knife dissection in the lysis of adhesions is recommended. This technique, combined with excellent intraoperative hemostasis, can be associated with a marked diminution in the incidence of postoperative fistulas and abscesses.

An appraisal of barrier agents in the reduction of adhesion formation following surgery

Reduction of pelvic adhesion formation and reformation represents a major challenge for the reproductive pelvic surgeon. Recently developed barrier methods appear promising, offering the advantage of nonsystemic therapy. Presented is a review of the literature and appraisal of the evolution of barrier agents. The current state-of-the-art barrier agent Interceed (TC-7) is discussed.

The effect of fibrin glue and peritoneal grafts in the prevention of intraperitoneal adhesions

We studied the effect of fibrin sealant and peritoneal grafts applied by fibrin glue on adhesion formation in the rat. Sealing and patching of ischaemic lesions of the uterus resulted in a significant increase in adhesion formation. We conclude, that fibrin sealant and peritoneal grafts can not be given general approval for prophylaxis of intraperitoneal adhesions.

[Postoperative, intra-abdominal adhesions--a new standardized and objective animal model and testing of substances for the prevention of adhesions]

80 male Sprague Dawley rats were divided in 8 groups of equal size. After median laparotomy defined abrasions of the serosa of abdominal wall, cecum and ileum were performed (400p, abrasive paper 280 grains/cm2, 8 cm2). The control group (I) received no medication. In the treatment groups 5 ml of the following agents were instilled before closure of the abdominal wall: normal saline (II), 16,250 IE Neomycin with 1250 IE Bacitracin (III), 30% dextrose (MW 70,000) (IV), 50,000 IE Streptokinase with 12,500 IE Streptodornase (V), or TCDO in concentrations of 10% (VI), 50% (VII), and 100% (VIII). All animals were relaparotomized on the 7th postoperative day, the adhesions were dissected and their extent was calculated by computer aid. Furthermore specimens were obtained for microscopic studies. Compared to the controls no reduction of adhesions could be achieved by dextrose. Significantly more adhesions were observed after treatment with Neomycin/Bacitracin. A reduction of about 23% was registered with normal saline and TCDO 10%. The greatest reduction of adhesions was seen after application of Streptokinase/Streptodornase as well as TCDO in concentrations of 50% and 100% (63%). The results were significant after evaluation with the t-test. Histologically there was a correlation between the extent of adhesions and the fibrin film. The new animal model has proven to result in reproducible data if used to evaluate substances for prevention of adhesions. Clinical studies with the best of these agents could serve as an approach to solve the problem of adhesion ileus.

Adhesion formation in experimental chronic radiation enteropathy

We have studied the late changes associated with radiation enteropathy in mice over a period of 224 days following single or split doses of gamma radiation delivered to the total abdomen (TAI). We focused on the importance of adhesion formation as a cause of strictures and gut-associated deaths following TAI. Gut-associated peritoneal adhesions were found in mice 2-7 months after receiving 13.5-17.5 Gy TAI and appeared to constitute the most consistent serious late effect of irradiation. There was a good correlation between adhesion formation and death for both the single and split-doses of radiation. Adhesions primarily involved the large gut, normally near the cecum. They appeared to result from serosal breakdown and were the major cause of partial gut obstruction. Submucosal fibrosis was present but seemed to be a comparatively minor cause of strictures. Local lymphoid hyperreactivity was also seen following TAI and may have contributed to the late sequelae. The complexity of the pathogenesis of chronic radiation enteropathy was indicated by finding three successive waves of non-scheduled deaths following TAI. The first wave (28-70 days) was not related to adhesion formation and may have been due to localized failure of mucosa to regenerate after irradiation with consequent ulceration. The second wave (98-140 days) occurred over the period when adhesion formation and fibrosis were most marked. In the third wave (168-224 days), the additional complication of fluid exudation was seen. Further experimentation is obviously needed to better define the complex pathogenesis of radiation enteropathy with dose and time after radiation but our data strongly support a multifactorial causation with an important role for adhesion formation in the disease complex.

An animal study of different treatments to prevent postoperative pelvic adhesions

A study was designed to test various high-molecular-weight solutions in the prevention of postoperative intraabdominal adhesions. The bicornuate rat uterus was used as the surgical model, and 80 mature white female rats underwent surgical injury of the right uterine horn. The rats were randomly divided into 5 groups: groups A, B, and C received 5 ml intraperitoneally of chondroitin sulfate, sodium carboxymethylcellulose, and 32% dextran 70, respectively; group D was treated with microsurgical repair; and group E, the control, received no therapy. The animals were killed postoperatively, and the adhesions were scored. Significantly better results in adhesion prevention were demonstrated in the sodium carboxymethylcellulose group vs. the other groups, except in group A where the difference was not significant.

Semisoluble aminated glucan: long-term efficacy against an intraperitoneal E. coli challenge and its effect on formation of abdominal adhesions

The first part of this study in the rat was designed to assess the immediate and, in particular, the long-term effects of semisoluble aminated glucan (SAG) with regard to an intraperitoneal (i.p.) E. coli challenge and side-effects. The severity of the E. coli peritonitis was evaluated by quantification of the concomitant bacteremia. The animals randomly received either 10 ml normal saline i.p. (controls) or 10 ml (50 mg) SAG i.p. (experimental groups). It was found that SAG had no immediate protective effect against the infectious challenge as no difference was detected in the bacterial clearance between saline- and SAG-treated rats at day 0. However, 2 days after injection of saline/SAG a substantial protection of SAG was noted as no blood-borne bacteria could be detected at 1, 2, 3, 4 and 5 h after the E. coli challenge in SAG-treated animals, whereas by contrast matching blood cultures were positive in all controls. A likewise protective effect against E. coli bacteremia of a single i.p. injection of SAG was demonstrated at 7, 21, and 49 days after the administration of the compound. During the 7-week experimental period no clinical side-effects of SAG were observed. At autopsy (days 0, 2, 7, 21, and 49, respectively) no gross pathologic conditions were found. Lung, spleen, and kidney sections from SAG-treated rats were normal, whereas tiny granulomas were exhibited in liver sections, possibly related to the hyperfunctional macrophage state which SAG induced. The second main object of the study was to evaluate SAG's effect on adhesion formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Localized prevention of postsurgical adhesion formation and reformation with oxidized regenerated cellulose

We evaluated oxidized regenerated cellulose (ORC) in experimental rabbit and dog models to assess its potential for reducing or preventing adhesion formation and reformation. Evaluation was performed in the following anatomical sites: uterine horn trauma; small bowel resection and anastomosis; parietal peritoneum excision; and adhesion reformation in the uterine horn. Ten to 14 days after ORC treatment, adhesion formation was macroscopically and microscopically evaluated. Results demonstrate that ORC produced graded reduction in adhesion formation and significantly prevented adhesion reformation.

A model for sidewall adhesions in the rabbit: reduction by an absorbable barrier

Despite use of surgical adjuvants, pelvic adhesions frequently develop following infertility surgery. Recently a resorbable biocompatible material, TC 7, has been designed to be used as a barrier to reduce adhesion formation. Reproducibly severe sidewall adhesions were only able to be created in one of six models tested. The model consisted of the following steps: excision of a full thickness 2 x 2-cm musculoperitoneal tissue mass, scraping of an adjacent 2-cm length of uterine horn, tamponading of all bleeding, and suturing (6-0 Vicryl) of normal tube and sidewall so as to directly approximate the traumatized tissues. Studies were conducted in 13 rabbits after creation of the bilateral sidewall and horn lesions, each serving as its own control. Choice of control and TC 7 sides was determined randomly. Adhesion formation was examined 2 weeks postoperatively. No residual material was noted at that time. Adhesion scores were the composite total of extent (0-4), type (0-4), and tenacity (0-3) of sidewall adhesions, and were significantly reduced on the TC 7 side as compared with the control side (mean 6.8 +/- 0.4 vs 9.0 +/- 0.3, median 6 vs 9, sign test P = 0.0032). No complications of use of the barrier were noted. It is concluded that use of TC 7, a resorbable biocompatible barrier, was able to significantly reduce postoperative adhesion formation on the rabbit sidewall.

Pathogenesis of adhesion formation/reformation: application to reproductive pelvic surgery

Pelvic adhesions are a major contributing factor to infertility in women with tubal peritoneal disease. Surgical treatment of such adhesions often does not resolve their presence. Such postoperative adhesion formation occurs despite the use of microsurgical techniques in a wide variety of surgical adjuvants. The process of adhesion formation represents a variation of the normal healing process of the peritoneum. However, rather than normal mesothelial healing, the fibrinous mass resulting from the peritoneal defect is infiltrated by fibroblasts with subsequent adhesion formation. A description of the pathophysiology of this process is described. The current understanding of the pathologic/pathophysiologic interaction of the surgical adjuvants with this process is described.

Adhesion prevention by solutions of sodium carboxymethylcellulose in the rat. II

In a rat model, sodium carboxymethylcellulose (SCMC) was compared with normal saline and 32% dextran 70 in the prevention of surgically induced intraperitoneal adhesions. The 32% dextran 70 was similar to normal saline in the initial prevention of adhesions, and both appeared less effective than SCMC. After lysis of the initial adhesions, SCMC was significantly more effective than 32% dextran 70 in the prevention of the reformation of adhesions. Possible mechanisms of action, complications of SCMC, and the need for further research in finding an ideal solution for use in adhesion prevention are discussed.

High-molecular weight dextran in human infertility surgery

The use of intraperitoneal 32% high-molecular weight dextran 70 (Hyskon, Pharmacia Inc.) has been reported to reduce the incidence of surgical adhesions in several species. The present study was undertaken to determine the effect of 32% dextran 70 in human females who underwent major abdominal infertility operations. Adhesions were quantitated by means of standardized objective criteria in 44 women in a prospective, randomized, double-blind study, and reevaluated at second-look laparoscopy approximately 6 weeks later. The mean change in the adhesion score for all patients in the 32% dextran 70 group (n = 23) was -2.57 units (i.e., clinically "improved") versus +2.41 units (i.e., clinically "worsened") in the control group (n = 21), p = 0.016. For the subgroup of patients who underwent lysis of adhesions, the 32% dextran 70 group (n = 17) improved significantly, whereas the control group (n = 12) tended not to improve with careful technique alone (-4.2 units versus +0.3 unit, p less than 0.05). These data indicate that 32% dextran 70 not only significantly reduces the formation of adhesions overall in human infertility operations, but also is highly effective in reducing the reformation of adhesions after lysis.

Effects of intraperitoneal 6% dextran 70 on serum immunoglobulin levels, peripheral cell populations, and lymphocyte subpopulations in women undergoing gynecologic surgery

Twelve women underwent elective major gynecologic surgery for benign, non-pregnancy-related conditions. No perioperative or postoperative "anti-adhesion" adjuvants were used. Serum immunoglobulin levels (IgG, IgM, IgA) and peripheral cell counts, including lymphocyte subpopulations, were measured in each patient during the immediate preoperative and postoperative periods as well as 5 to 8 weeks later. These results were compared to a treatment population of 16 women who underwent similar surgery and received 150 ml 6% dextran 70 intraperitoneally at the conclusion of the procedure. There was a decrease in the level of all serum immunoglobulins measured in the immediate postoperative period in both groups (not statistically different). At 5 to 8 weeks postoperatively there was a greater level of IgM in the control population than in the dextran-treated group (P = 0.03). Alterations in the peripheral cell counts, including lymphocyte subpopulations, were similar in the two groups. The use of intraperitoneal 6% dextran 70 did not result in postoperative alterations in the human immune system different from those induced by the surgical procedure itself.