A comparative computed tomography study of canine laparoscopic abdominal anatomy pre- and post-insufflation

Abstract

Laparoscopy has been shown in human medicine to have a rapid recovery time and less morbidity when compared to open abdominal surgery. It involves the insufflation of carbon dioxide into the peritoneal cavity. This creates a space for the surgeon to work in and manipulate the organs. In the normal abdominal cavity the peritoneal cavity is a potential space obliterated by the serosal contact between all the organs. The insufflation of carbon dioxide turns this potential space into a working space. This allows the introduction of an endoscope, usually through a single port, and then various instruments usually through another port into the peritoneal cavity. Multiple veterinary studies have shown the advantages of laparoscopy to decrease the morbidity of animals post surgery. The visualisation of the organs tends to be enhanced by the increased lighting and magnification provided by the laparoscopic equipment. There are intricate attachments and associations between various abdominal organs that are responsible for maintaining organ position and orientation in the peritoneal cavity. Computed tomography (CT) has been proven in human medicine to show excellent abdominal anatomical resolution. It is the modality of choice to detect free abdominal gas. Logically, if there is a massive insufflation of gas, it would be expected that this will enhance the ability of CT to provide real anatomical likeness to the laparoscopic image. The animals were all subjected to multiple CT scans and the scans were found to be rapid and noninvasive. There was a concern over the amount of radiation that each animal received and this was pre-empted by using a CARE 4D dose. The CT machine detected the thickness of the part of the animal being scanned and only provided the needed kV and mAs to penetrate and create an image. This was a paediatric human modality. Six beagle dogs were used and all assessed prior to the study to be clinically healthy. An abdominal ultrasound was performed to assess that they had normal abdominal anatomy. All animals had eight scans performed, four pre-insufflation (PrI) and four post-insufflation (PoI). The animals were placed in a ventro-dorsal routine (VDR), a ventro-dorsal Trendelenburg (VDT), a left lateral (LL) and a right lateral (RL) position. The scans were performed using a helical dual slice sliding gantry CT machine, Somatom Emotion (Siemens AG, Erlangen, Germany). With the insufflation of carbon dioxide in this study, the attachments and associations change and these were shown to play a role in the movement of the abdominal organs during the manipulations and how the organs come to lie in the abdominal cavity. It was shown that together with the insufflation of carbon dioxide into the abdomen, a very important factor in the movement of the organs was gravity. In certain organs the effect of gravity was found to be the significant factor when the positioning of the animal was changed, more so than the insufflation of the abdomen when PrI and PoI scans were compared. The effects of gravity during the changes in position and the insufflation of the abdomen were compared using a set number of measurements, of organ size and location. The size and location of the organs was compared to set landmarks in the body such as the sternum and certain vertebra, depending on the organ in question. These measurements were compared between the pre- and post-insufflation scans to evaluate the changes that occurred after insufflation with regards to the movement of certain organs and their exposure for a surgical approach. These measurements gave the data an objective value which could then be analysed statistically to determine any significant changes. The p value was set at <0.05 in determining statistical significance using a Kruskal-Wallis one way of variance (ANOVA) and the Tukey-Kramer multiple comparison test. This data was analysed and used to determine the best position to place an animal in order to perform laparoscopic surgery of certain organs. This dissertation showed that the VDR and VDT positions proved much better laparoscopic access to the majority of the parenchymatous organs in the peritoneal cavity than the lateral positions. There were certain organs such as the kidney, the ovaries, the uterine horns and the duodenum that were visualised on CT clear of the rest of the parenchymatous organ mass on the non-dependant part in the respective lateral positions. This indicated that these organs will be easily accessible during laparoscopic surgery in the RL and LL. However no matter what position was used, no position was perfect for every organ of interest, and positions need to be combined for certain procedures. The use of positioning will not remove the need for intra-operative retraction and laparoscopic retractors are an essential part of the surgeon’s arsenal when performing laparoscopic procedures. Copyright