How do neuromuscular blockade (NMB) and pre-stretching affect abdominal insufflation dynamics, and how can surgical safety and efficiency during minimally access surgery (MAS) improve by novel insufflation techniques and trocar design?
This dissertation presents a series of studies in a porcine model which investigated the effects of NMB and pre-stretching on abdominal insufflation dynamics. For data acquisition and to maintain stable physiological conditions throughout the experiments, specialized tools were developed. A new method, endoscopic oscillometry, was introduced to monitor abdominal compliance in real time. To this respect, a novel fan-based insufflator was developed and tested to determine its ability to perform endoscopic oscillometry and in maintaining stable abdominal pressures compared to conventional systems.
The study found that NMB had minimal impact on abdominal compliance, but pre-stretching using repeated insufflation significantly influenced intra-abdominal compliance and volume. The fan-based insufflator, more specifically a centrifugal fan, demonstrated superior pressure stability, eliminating the pressure peaks observed with conventional insufflators. Additionally, various trocar designs were evaluated, particularly focusing on their performance in preventing air leaks and surgical smoke during MAS. It was found that trocar design played a critical role in air leak performance, with implications for patient safety, particularly concerning surgical smoke evacuation during the COVID-19 pandemic. The research concluded that improved insufflation control, particularly using a fan-based system, could enhance surgical outcomes by providing more stable operating conditions and reducing risks associated with air leaks and surgical smoke. Moreover, the pressure stability enhances respiratory conditions, as the abdomen exerts less upward pressure on the diaphragm. These findings have potential implications in paediatric, bariatric, robotic, and thoracic surgeries, where precise control over abdominal pressure is crucial. Further research, particularly in clinical settings, is needed to validate these findings and adapt the technology for broader use in surgery.

The large intestines, or colon, is the last part of the digestive tract before the rectum. Colorectal cancer is one of the main reasons that patients need a colon resection. A colon resection is a surgery in which the malignant part of the colon is removed. After removal of the tumor, the two ends of the colon need to be reattached, also called anastomosed. This is usually done using sutures or staples. One of the most frequently occurring and major complications is that the anastomosis does not heal correctly. This can cause an anastomotic leakage, which means that fecal matter and fluids with bacteria can flow into the otherwise sterile abdominal cavity. This is a serious complication that can even result in death. Therefore, a solution can be to insert a stent to cover the anastomosis from the inside, preventing feces and fluids from entering the abdominal cavity. Such a stent was developed at the department of Surgery of the Erasmus MC.

This thesis focuses on the redesign of this stent to cover an anastomosis. Two main problems with the stent were stent migration due to insufficient friction between the stent and the colonic wall, and intestinal blockage due to the presence of the stent.

Preliminary research and a literature study showed that the addition of barbs to the stent could increase friction with the colonic wall. Optimal barb dimensions were researched on fresh colon specimens in an experimental setup. Ideal barb parameters were a height of 1.5 mm, diameter of 1.0 mm, an angle of 30 degrees, with a distribution of 3 barbs per cm2. In addition, the ideal stent diameter was explored in an experiment with fresh colon specimens. The stent should expand the colon with 50-60%. To safely insert and extract a stent with barbs in the colon, a patent search was executed to explore the possibilities of barb and colon protection. A stent with a reducible diameter and a tubular protection structure were identified as the most promising methods to safely insert a barbed stent. The second problem of intestinal blockage was analyzed and causes of intestinal blockage were identified. Minimizing the frontal contact surface at the proximal end of the stent was assumed to be the most important factor to reduce intestinal blockage. A minimal frontal contact surface also reduces the force that feces exerts on the stent, thus reducing the chance of stent migration.

The previously mentioned experiments and analysis formed the basis of a list of design requirements for a new prototype stent. The requirements were divided into five categories; fixation, dimensions, materials, delivery method and performance. After analyzing different manufacturing processes and available materials, two concepts were designed and produced. One concept was chosen after careful considerations of both options.

The final prototype consisted of a stent with barbs that was 3D printed. This design was validated on the set of requirements that were set up earlier. The material of the stent is both flexible and stiff. For insertion and extraction of the stent, the diameter can be reduced by longitudinal inward folding, while the stent forms a rigid tube while in a deployed state. The barbs are stiff and strong and can withstand the force that would move the stent. The frontal contact surface of the stent was reduced by more than 18 times compared to the old prototype, to reduce the influence on intestinal blockage. The stent is surrounded by a sheet to protect the barbs and prevent tissue damage during insertion. A validation experiment showed that the stent was improved in fixation compared to the old prototype. Therefore, based on the research executed in this thesis, the final prototype should theoretically migrate less and cause less blockage. However, an ex-vivo experiment should validate the fixation force of the new prototype, and in-vivo experiments on pigs should determine if the prototype actually does not migrate and actually does not cause intestinal blockage.