Training Models in Pediatric Minimally Invasive Surgery: Rabbit Model Versus Porcine Model: A Comparative Study

Introduction

Minimally invasive techniques for an ever-growing number of indications in small children and infants are increasing and require highly specialized skills and great experience. ¹ As for open surgery, the operating room is usually the predominant venue for the acquisition of technical skills and experience by surgeons, whereas for minimally invasive surgery (MIS) a training program is strongly indicated.^2,3 Two main models for learning technical skills outside the operating room are available: inanimate trainers (the training box, also called a pelvic trainer) and in vivo animal models. ⁴ The first step of training for pediatric surgeons is to develop basic technical skills, and it is best achieved by training on inanimate models as pelvic trainers.^5,6 The second step is represented by the acquisition of advanced operative skills. Mainly two animal models are used for training in MIS: the rabbit model and the pig model.^7,8 In general, the porcine model is used for training in adult MIS surgery, above all for colorectal, urologic, and gynecological procedures.^9–11 A rabbit model is rarely adopted for MIS training.

In the international literature very few studies have reported the role of animal models for training in pediatric MIS.^12–15

The rabbit model, which is smaller than the pig model, could be helpful for pediatric surgeons, due to a small operative chamber, as it is typically encountered in neonates and small children.

We aimed to compare the efficiency of the rabbit model versus the porcine model for training in pediatric MIS.

Materials and Methods

The Pediatric Surgery Unit of “Federico II” University of Naples, Naples, Italy, and the training center of the Biotechnology Center of Cardarelli Hospital, Naples, have been certified training centers for pediatric MIS since 2003. They organize two or three training courses in MIS per year under the patronage of the main European and Italian societies of pediatric surgery: the European Paediatric Surgeons Association, the European Society of Paediatric Endoscopic Surgeons, the European Society of Paediatric Urology, the Italian Society of Videosurgery in Infancy, the Italian Society of Paediatric Surgery, and the Italian Society of Paediatric Urology.

The pig model has usually been the only animal model adopted for MIS training. In the last 3 years we have started to adopt also a rabbit model for training in pediatric MIS because we received several requests from the attendees of our courses to train on a smaller animal model. For this reason we decided to compare the two models—pig and rabbit—for pediatric laparoscopic training.

We decided to evaluate the performances of 10 pediatric surgeons in training (average age, 29.6 years), coming from several European countries. They had never performed laparoscopic surgery on children. They underwent two training sessions on the rabbit model and two training sessions on the porcine model under the supervision of five experienced laparoscopic pediatric surgeons. The order of animals that the learners operated was random. There were one expert tutor and two trainees per each operative table. The courses lasted 2 days. The first day was dedicated to basic MIS procedures. After a theoretical part, through slides and videos, in which the tutors showed the different procedures performed in children, the attendees had more than 6 hours of practice on live animal models. The second day was dedicated to advanced MIS procedures.

All participants had no previous laparoscopic expertise in humans, and they usually performed an average of 10 hours of training on a pelvic trainer per month. At baseline all participants had to take a test on basic laparoscopic skills, including instrument handling, video eye-to-hand coordination, and basic knotting techniques, to assess their laparoscopic skill level. All passed the basic skill assessment and were included in the study.

We decided to evaluate the results of four laparoscopic techniques (inguinal hernia repair, varicocelectomy [considered as basic procedures], nephrectomy, and fundoplication [considered as advanced procedures]) using a specific form. The tutors used the actual Likert scale to score the overall performance and the different technical skills common to all laparoscopic procedures performed. The score ranged from 0 (unacceptable) to 10 (excellent), and the items evaluated in the surgical performances of the practitioners in both the models were as follows: (1) positioning of trocars; (2) creation of working space; (3) dissection; (4) suturing and knot-tying; (5) tissue handling; and (6) handling of instruments. In addition, the tutors evaluated the average operative time and number and type of intraoperative complications and confidence in treating them. This objective evaluation was performed by blinded evaluators through the visualization of the recorded videos of the surgical performances.

At the end of the training sessions the practitioners also completed a self-evaluation questionnaire. In particular, they were asked to define their level of confidence when performing basic and advanced procedures in both the models intended as their subjective judgment to operate in a comfortable setting or not, in regard to ergonomics, working space, and size of laparoscopic instruments.

From a technical point of view, the surgical procedures were performed on male rabbits with an average body weight of 3.8 kg (range, 3.0–4.5 kg) and on male piglets with an average body weight of 20.2 kg (range, 18–30 kg). All the procedures were performed with the animal under general anesthesia. All animals received a central venous line into the jugular vein and an endotracheal tube for mechanical ventilation. During the procedure, veterinary surgeons and animal surgery staff members monitored the depth of anesthesia and other physiologic parameters.

The laparoscopic procedures were performed using a 5-mm 0° or 30° optic in the rabbits, whereas a 10-mm 0° or 30° optic was adopted in the piglets. The pneumoperitoneum was created by carbon dioxide insufflation with a maximum pressure of 7 mm Hg in the rabbits and 12 mm Hg in the piglets. Three-millimeter and 5-mm laparoscopic instruments were adopted in both models.

The present study was performed with approval by the institutional research ethics board for the experimentation and didactics on animal models.

Statistical analyses were performed using Fisher's exact test and Student's t test.

Results

The practitioners had significantly more “confidence” in their surgical performance in the rabbit model compared with the pig model. This difference was statistically more significant for advanced procedures (P = .03).

The overall surgical performance score (ranging from 0 [unacceptable] to 10 [excellent]) was significantly higher in the rabbit model compared with the pig model (8.1 versus 6.0; P = .01). The most significant scoring differences between the surgical performances of the practitioners in the two models were reported in regard to dissection, suturing and knot-tying, tissue handling, and handling of instruments, and the scores were always higher in the rabbit model compared with the pig model (P = .01) (Table 1).

No difference between the two models was reported in regard to average operative time to perform basic procedures (Table 2). However, the average length of surgery to perform advanced procedures was statistically shorter in the rabbit model compared with the pig model (P = .01).

As for the intraoperative complications that occurred during the surgical sessions (Table 2), no statistical difference was reported between the two models.

In addition, because the trainees started on an animal model at random, we decided to compare the scores of those that started on the porcine model with the scores of those who started on the rabbit model, and we found that only the performances of those who started on the pig had a significantly higher improvement when transitioning to the rabbit compared with those starting on the rabbit and going to the pig for all the evaluated skills (P = .01) except for positioning of trocars (Table 3).

The analysis of self-evaluation questionnaires completed by the trainees demonstrated that 3-mm instruments were preferred to 5-mm instruments in both models.

Ninety percent of the trainees preferred the rabbit model to the pig model for pediatric surgical training. They reported that in the rabbit model it is possible to perform more procedures and to perform them more easily compared with the porcine model.

In addition, all practitioners had previously experienced training on inanimate simulators, and all of them stated that tissue handling in the animals is more real than in inanimate simulators (Table 4).

Discussion

Minimally invasive techniques for an ever-growing number of indications in small children and neonates are increasing and require highly specialized skills and a long learning curve.^1,16,17 Unfortunately, the number of patients requiring such surgery is usually small.^2,3 For this reason, training outside the operating room has become essential to improve the learning curve. Two main models for learning technical skills outside the operating room are available: inanimate trainers (a training box, also called a pelvic trainer) and in vivo animal models. ⁴ The first step of training is the acquisition of basic technical skills, which is best achieved by training on inanimate models.^5,6 The second step is the acquisition and refinement of advanced operative skills. In vivo animal models are often used for this last purpose.^7,8 As suggested by Palter et al., ¹⁸ residents seem to prefer animal models for training rather than a virtual simulator model because animal models most closely resemble operating on a live patient. In addition, they are the only models that can effectively simulate bleeding, tissue handling, and complications. In our survey all of the trainees had previously experienced training on inanimate simulators, and they believed that tissue handling in the animals is more real and gentler than in inanimate simulators.

The porcine model was reported as an ideal animal model for resident training in laparoscopic colorectal, urologic, and gynecological surgery in adults.^9–11

In the international literature very few studies have described the role of animal models for training in pediatric MIS, in particular in neonates and small children.^12–15

Because its weight is between 20 and 40 kg, the piglet is a poor animal model for training in pediatric laparoscopy. A smaller animal model could be more appropriate if it simulates the anatomical situation adequately and if it serves to develop surgical expertise and training in other technical issues that are typically encountered in neonates and small children.

The dimensions of the abdominal cavity of a 3–4-kg rabbit are approximately 15 cm long, 10 cm wide, and 8 cm high. It precisely mimics the dimensions of the abdominal cavity in the newborn baby.

In addition, in regard to the anatomical situation, rabbits have a patent internal inguinal ring with retractile or intraabdominal testes, thanks to the cremaster muscle that completely envelops the scrotum. These anatomic conditions mimic perfectly the pathological setting of inguinal hernia and nonpalpable testes in small children and infants. As well, the rabbit has a naturally gaping hiatus, which makes for a good surgical model of hiatal hernia. In rabbits, the esophagus can be easily dissected because there is little fatty or connective tissue surrounding it. In the pig model esophageal surgery is extremely difficult to perform, due to the presence of a huge and multilobulated liver. In the pig model, cholecystectomy is also difficult to perform for the same reason, and also splenectomy is a demanding procedure to perform due to the excessive length of the spleen. In the pig model it is also very difficult to approach the kidneys via laparoscopy because the intestinal loops are big and distended. In contrast, in rabbits the kidneys are located much more anteriorly than in pigs, and they appear almost intraperitoneal. Because intraabdominal and perirenal fat is also scanty, nephrectomy is an easy procedure to perform in rabbits. ¹⁹ However, the renal vessels are extremely delicate, and their dissection can be challenging. Other laparoscopic procedures can be easily performed also on the bowel, the spleen, and the liver of rabbits such as intestinal anastomosis, splenectomy, and congenital diaphragmatic hernia, among other procedures.

In our study the surgical versatility of the rabbit model in MIS training was demonstrated by the operative times recorded by the practitioners. In fact, the average length of surgery to perform advanced procedures (nephrectomy and fundoplication) was statistically shorter in the rabbit model compared with the pig model (P = .01). In addition, trainees were significantly more confident when performing advanced procedures in the rabbit model compared with the pig model (P = .03).

We decided to evaluate the trainees' performances and to collect the trainees' opinions only in regard to four laparoscopic techniques: inguinal hernia repair and varicocelectomy, considered as basic procedures, and nephrectomy and fundoplication, considered as advanced procedures.

A limitation of our study is that bias could exist on the trainees' part because the trainee is judging whether he or she is more “confident,” which is purely a subjective assessment and cannot be truly measured.

We tried to assess objectively the surgical performances of the practitioners in both the models using the actual Likert scale to score the overall performance and the different technical skills common to all laparoscopic procedures performed. The score ranged from 0 (unacceptable) to 10 (excellent), and the items evaluated in the surgical performances of the practitioners in both the models were as follows: (1) positioning of trocars; (2) creation of working space; (3) dissection; (4) suturing and knot-tying; (5) tissue handling; and (6) handling of instruments.

Our results demonstrated that surgeons did better surgical performances in rabbits compared with pigs, especially in regard to dissection, suturing and knot-tying, tissue handling, and handling of instruments.

In addition, we found that only the performances of those who started on the pig had a significantly greater improvement when transitioning to the rabbit compared with those starting on the rabbit and going to the pig for all evaluated skills (P = .01) except for positioning of trocars. We explained this difference on the basis of the fact that the trainees who have performed laparoscopic procedures first on the pig had the benefit of a larger environment and they acquired more confidence in the creation of working space, dissection, suturing and knot-tying, and handling of tissues and instruments compared with those who operated de novo in a smaller environment like the rabbit. ¹⁰

In the rabbit model laparoscopic surgery can be performed in a real pneumoperitoneum environment with conventional trocars and instruments despite the rabbit's size and weight. Furthermore, the rabbit model permits not only dissection exercises with varying degrees of difficulty, but also the practice of several other laparoscopic tasks such as cutting, coagulation, stitching, and knot-tying. Furthermore, the extra difficulty due to the small space seems an additional advantage for trainees to adapt to the very slow controlled movement of instruments necessary in endoscopic surgery. ¹⁹

We think that it is important to begin in a larger environment like the porcine model to acquire confidence with the basic technical skills in a training facility, as demonstrated in our study by the better performance scores recorded by the trainees who started on the pig model compared with those who started on the rabbit model. But, we also think that repetitive skill training would be useful to have the full benefit of training in a smaller animal like the rabbit that reproduces in a more realistic way the working space found in human infants and children, and it resembles real-life conditions closely in terms of occurrence and control of bleeding. ²⁰

In fact, in our study 90% of the trainees preferred the rabbit model to the porcine model for pediatric MIS training. The main reason was attributed to the possibility of performing more procedures and of performing them more easily in the rabbit model compared with the pig model. The rabbit model permits the easy use of 3-mm laparoscopic instruments, commonly adopted in neonates and children. In fact, the majority of the trainees preferred 3-mm instruments to 5-mm instruments in both the models.

The rabbit model also taught the management of the complications in real time and the best way to avoid them. We recorded 5 cases of bleeding (50%), 1 case of renal vessel damage (10%), and 1 case of intestinal damage (10%). The practitioners also learned how to manage these complications; in fact, they controlled the bleeding and renal vessels damage using clips and special hemostatic devices, and they performed the suture of the intestinal perforation that occurred during the nephrectomy.

Several studies in the United States and Canada have highlighted a lack of training, teaching, and education focusing on laparoscopy.^21,22 At the moment in Europe a standardized training certification for laparoscopy does not exist.

This lack emphasizes the importance of residents learning and practicing advanced laparoscopic skills in the laboratory before going into the operating theater to take maximum advantage of learning opportunities with real patients.^23,24

In conclusion, on the basis of the trainees' feedbacks, rabbits are preferred over pigs as a training model in pediatric MIS. In the rabbit model it is possible to perform more procedures and to perform them more easily compared with the pig model. In an analysis of trainees' performances, surgeons did better surgical performances, and their operative times were statistically shorter above all for advanced procedures in the rabbit model compared with the pig model.

The rabbit model is an ideal animal model for training in pediatric laparoscopic surgery. It provides an easy approach to technical training in both basic and advanced laparoscopic procedures.

Repetitive training in the rabbit is needed because it provides superior skills for live operations. We think that the pig model may have benefit as an introduction to laparoscopic surgery because of the larger environment provided as an advanced step; in fact, some of the challenges described in the pig (lobulations of liver, distention of intestines, length of spleen) may offer a benefit to the learner because they are challenging.

We would suggest the constitution and institution of an European training program for pediatric MIS that integrates simulation (a box trainer) and surgery on in vivo animal rabbit models to gain skills and confidence before risking human safety.