The formation of postoperative adhesions is a significant clinical problem for the present-day surgery hence there are a diversity of variants how to simulate peritoneal adhesions in a different models which provides reproducible and representative field for new researches. At this moment, investigations in the peritoneal adhesions branch are very exiting field for making an ideal model. Thus the amount of the options how to perform all demands are enormous and even now we have a lot of methods to induce the adhesion formation process in a rat model. However, nothing could be ideal and all the models have some issues, which means that process of invention is still going on [1].
Last year we invent a rat model of postoperative peritoneal adhesions and it shows glorious results even after a year of researches if to compare it with recent models. It shows that our model is stable and durable for time despite other inventions [2]. This year we have analyzed and compared our necrosis model with fixation [2] with three commonly used adhesion models: necrosis model without fixation [3], abrasive model, and dissection model [1].
For developing models in this work, we used 48 male Wistar rats of the same age and mean weight (250-300 g), which were split into five groups of eight rats in each group. Prior to the operation, all rats were quarantined for 3 days in the vivarium and kept in a 12:12-h light-dark cycle with food and water available ad libitum. Then the rats were anesthetized by intramuscular injection of 0.05 ml/kg of Xylazine and 0.5 mg/kg of “Zoletil 50”, their chest hair were removed by shaving and the skin was scrubbed with ethanol. To access the abdominal cavity a 3-cm laparotomy was performed. In the “necrosis with fixation" group, the cecum was delivered and its wall was injured by 1-minute application of a cotton pad soaked in 1 N NaOH and then the cecum wall was fixed to the abdominal wall by a non-absorbable suture to localize adhesion sites. In the “necrosis without fixation” group, the cecum was delivered and its wall was injured by 1 minute application of a cotton pad soaked in 1 N NaOH. After the procedure, the alkaline solution was washed out completely with saline water. In the “abrasive” group, the cecum wall was injured by repeating rubbing with the help of the abrasive material. In the “dissection" group, dissection of the three peritoneal wall sites (5×2 mm) opposite the cecum were prepared. In the control group, only the 3-cm laparotomy was performed. The wound was closed by two layers of continuous sutures. Prophylactic antibiotic (50 mg/kg Tylosin) was injected once daily for 5 days after the surgery. At day 7 after surgery, the animals were euthanized and the abdominal cavity was opened via a U-shaped incision.
Adhesion formation was evaluated by a macroscopic inspection according to the adhesion rating scale from 0 to 5 proposed by Oncel et al. [4]. Grade 0: no adhesions; grade 1: loose filmy adhesions that can be separated by blunt dissection; grade 2: adhesions requiring <50% of sharp dissection for separation; grade 3: adhesions requiring >50% of sharp dissection for separation; grade 4: serosal injury, grade 5: full-thickness injury.
After the implementation of all procedures, severe grade of adhesion for the “necrosis with fixation" group was 2.7 and all the adhesion sites were strictly localized between the cecum and the abdominal wall. In the “necrosis without fixation" group all the rats has 2-grade adhesions. In the “abrasive” group, three rats had 2-grade adhesions, four rats had no adhesions and one rat died before euthanizing process. In the “dissection” group, four rats had 1 grade adhesions, one rat had no adhesions and three rats died before euthanizing process. In the control group, five rats had 1-grade adhesions and three rats had no adhesions. Adhesion sites in all the groups except the “necrosis with fixation" group were localized spontaneously between the cecum and the other parts of the abdominal cavity.
From all this data, we can make a derivation that models with abrasion and dissection are not so convenient because they don't satisfy the demands in reproducibility. Nevertheless, necrosis model without attachment can be used if our main aim are adhesions and not so important were they will be. Also, necrosis model with attachment can be used in some situations too, because despite the huge trauma risk this model is convenient if we want adhesions in determined surface or place. All experiments were carried in compliance with the recommendations of the European Convention on Humane Treatment of Laboratory Animals [5].