Introduction

Laparoscopic surgery requires the development of fast, effective and reliable learning techniques, that initially it should be practiced outside of the operating room. Laparoscopic surgery has led to the development of techniques for surgeons to improve their skills. Several models for teaching and practice have been used, including inanimate simulators, cadavers (human and animal) and live anaesthetised animals, progressing to finally operating on true patients, which initially should always be under the direct supervision of expert surgeons ^{(Usón et al., 2006)}.

The use of anaesthetised animal models has the advantage of working on living tissue that may bleed, similar to a real situation. But these procedures are expensive and require special equipment and qualified personnel ^{(Reznick et al., 2006)}. However, until technology advances to achieve a high degree of realism with simulation that is cost-effective, surgery with animal models is the most appropriate procedure for surgical learning ^{(Gomez-Fleitas, 2005}; ^{Rodriguez-Garcia et al., 2006)}.

It is necessary to develop animal models realistic for training laparoscopic surgeons, which can simulate the situations experienced in endosurgery. Laparoscopy differs from traditional surgery, because surgeons need to acquire motor coordination for using a new surgical instrument, do not have direct tactile sensation with tissues, and need to guide their maneuvers via a two-dimensional view of a three-dimensional field ^{(Menezes, 2012)}.

The rabbit is currently used as a model for teaching paediatric surgery ^{(Hernández et al., 2012)}. Its size closely resembles surgical conditions of infants ^{(Simforoosh et al., 2011)}.

Paediatric laparoscopy has progressed slowly because the instrumentation is more precise and must be adapted to the size of the paediatric patient. This involves a steep learning curve ^{(Álvarez-Zapico, 2001)}. However, currently about 60% of paediatric surgeries are performed laparoscopically and 80% of paediatric surgeons are familiar with these techniques ^{(Ure et al., 2000)}.

The objective of this study was to establish working ports for the introduction of paediatric laparoscopic equipment to perform Nissen fundoplication in rabbits for experimental and teaching purposes. The goal was to ensure that the surgeon had an excellent view of the surgical field, without interference between the instruments and the lens. The results are not intended for use in paediatric surgery. Instead, this research was performed so that investigators will not need to spend time finding the appropriate location for the ports in future research.

Materials and methods

This study was approved by the Ethics and Animal Welfare of the Universidad Autónoma de Ciudad Juárez (CBE.ICB/001.01-25).

To conduct this study, six New Zealand white rabbit cadavers were used (each weighed 2.5 to 3.5 kg). These cadavers were collected from the surgical practices of the medicine students. Animals were handled and euthanized (Sodium Pentobarbital at 100 or > mg/kg IV) according to the Mexican Official Norm: Technical specifications for the production, care and use of laboratory animals (NOM 062-ZOO 1999). Only rabbits without previous abdominal surgery were included.

A 5 mm trocar was introduced by the Hasson technique, and a laparoscope of 5 mm and 30° attached to a microcamera was inserted through the trocar. The abdomen was insufflated (to a pressure of 6-8 mm Hg). The placement of secondary trocars was conducted with direct visualization. The position of the trocars was established by two veterinary surgeons and one paediatric surgeon with experience in laparoscopy. The model was evaluated by four paediatric surgeons.

To establish the exact location of the ports some factors were considered: 1) the anatomy of the rabbit stomach and esophagus ^{(Rodríguez-Alarcón et al., 2010}; ^{Halabi et al., 2012), 2)} laparoscopic Nissen fundoplication performed in rabbits with traditional laparoscopic instruments, and 3) the length of paediatric laparoscopic instruments.

Several approaches were repeated in order to find an adequate view of the surgical area. As an initial procedure, a telescope trocar was inserted 0.4 cm caudal to the umbilicus. Then we inserted the telescope trocar every 0.4 cm until achieving an adequate image. Once an adequate image was obtained, ports were established. Trocars were inserted 0.5 cm caudal and 0.5 cm lateral to the telescope trocar on each side. This created a space of 0.5 cm both medially and caudally, which allowed for an angle of 45° between the two laparoscopic forceps, therefore establishing adequate distance from the instruments to the surgical site without the instruments crossing in the path of the telescope. Each position of the trocars received a score: one point was scored when the instrumentation was crossed, one point when the organs were too far away to manipulate, and one point when the organs were too close to manipulate. The maximum score was 2 points and the location was considered ideal when a zero value was obtained.

Fleiss Kappa coefficient was used to estimate the level of concordance between observers. The Fleiss Kappa coeffient result must be interpreted as follows: values ≤ 0 indicates no agreement, values ≥ 0.01 ≤ 0.20 indicate none to slight concordance, values ≥ 0.21 ≤ 0.40 indicate fair concordance, values ≥ 0.41 ≤ 0.60 indicate moderate concordance, values ≥ 0.61 ≤ 0.80 indicate a substantial concordance, values ≥ 0.81 ≤ 1.00 indicate a perfect concordance between the observers ^{(McHugh, 2012)}.

Results

In the first two approaches a crossing of instruments occurred and in addition the distance was very close to the surgical field. Therefore a value of 2 points was obtained in the evaluations of pediatric surgeons. However, it was possible to obtain a value of zero in the latter approach. We established that the best trocar location for laparoscopic Nissen fundoplication in rabbits was with the telescope port positioned at midline 1.6 cm caudal to the umbilicus (with insufflation the distance was 2.0 cm) (Figure. 1), and with the secondary ports placed slightly lateral to the third mammary glands. To establish the exact location of these ports a point was established at 1.5 cm caudal to the telescope port. After forming an angle of 90°, 3.3 cm were measured on each side. These last measures were taken with the rabbit model abdomen insufflated (Figure.1).

Figure 1 Establishing the measures for the ports. The middle port is a 5 mm to the telescope. The side ports are a 3mm for laparoscopic forceps. 

In this research, the Fleiss Kappa for 4 raters was 1.00 that means a perfect concordance.

Discussion

This study is the first to describe the position of the ports using only three trocars and laparoscopic paediatric equipment in an insufflated rabbit cadaver. A previous investigation had already described the trocar position for Nissen fundoplication in the rabbit ^{(Luks et al., 1995)}. However, ^{Luks et al (1995)} surgery was different because it was a gasless laparoscopy. Another difference was that, Luks et al., used five trocars and in our model only 3 trocars were used. We used fewer trocars because we did not use a liver retractor, and instead, the liver lobules were separated with the same forceps used for dissection.

Optimal trocar positioning is essential in laparoscopic procedures because this helps achieve an ergonomically correct body position. Incorrect trocar placing could cause fatigue of the wrist joint and lack of space for comfortable movement ^{(Ballesteros et al., 2007}; ^{Marhuenda et al., 2011}; ^{Pérez-Duarte et al., 2012)}.

Actually there is no uniform consensus about port placements for laparoscopic procedures; neither in human surgery nor in animal models. The placement of ports is currently established by the surgeon’s preference based on personal practice. In an adult human, for example, the target organ should be located 15-20 cm from the optical trocar. Generally, the two remaining trocars are placed in the same 15-20 cm arc at 5-7 cm on either side of the optical trocars. This permits the instruments to work at a 60°-90° angle with the target organ and avoids problems from the target organs being too far or too near the ports ^{(Trejo et al., 2007}; ^{Supe et al., 2010)}. To facilitate optimal instrument manipulation along with satisfactory visualization during laparoscopy, trocars are usually placed in a triangular fashion, termed triangulation ^{(Supe et al., 2010)}. In our research, placing the telescope trocar at 1.5 cm from the umbilicus allowed us to comply with these points. In addition, in the present investigation, the ports were introduced keeping in mind the "base-ball diamond" concept previously mentioned in other studies^{19,20(Kaur, 2008}; ^{Modi et al., 2013)}. First, the telescope was fixed in between the working instruments. Second, half of each instrument was placed inside the surgical site and half was kept outside, maintaining an elevation angle of 30°. Third, the manipulation angle was set to 60°, and fourth, the azimuth angle was set 30°. The definition of the diverse angles is listed below, as described by Kaur in 2008:

These ergonomic characteristics should also be followed when using surgical animal models. In this study we described the best trocar placement for laparoscopic Nissen fundoplication in the rabbit, in order to avoid fatigue when investigating or practicing, using rabbit models. In this investigation, the position of the ports allowed an adequate view of the surgical area. Additionally, the port distances described allowed the laparoscopy instruments to arrive adequately at the area of the fundoplication, without crossing of the instruments and interference with the telescope, which allowed the surgery to be performed correctly (Figure 2).

Figure 2 In photography laparoscopic forceps perfectly come into contact with the gastric fundus and esophagus can be observed. We can also observe how instrumental never cross with one another and not have interference with the telescope. 

Conclusion

We established the proper position of trocar ports for laparoscopic Nissen fundoplication in rabbits: The telescope trocar located at midline 1.6 cm caudal to the umbilicus (with insufflation the distance was 2.0 cm). The secondary ports positioned slightly lateral to the third mammary glands. To establish the precise location of these ports a point was established at 1.5 cm caudal to the telescope port. After forming an angle of 90°, 3.3 cm were measured on each side (Figure. 1).

The results of this investigation will help, when using the rabbit as a model for teaching paediatric laparoscopic Nissen fundoplication, as surgeons learning this procedure will not have to take time to find the most appropriate site for placement of trocars and instruments.