The system developed for the laboratory use includes the recent prototype of dissecting forceps designed for endoscopic operation, a power controller, a connecting cable, and a foot switch (Fig. 13.1)
The prototype forceps used for the current test are designed like the Maryland dissecting forceps commonly used in endoscopic operations (Fig. 13.2a). Its shaft is 5 mm in maximum diameter, to be inserted through a 5-mm port. However, a 10-mm port had to be used instead of a 5-mm one in the current experiment because the lead wires for the electricity have not been installed inside the shaft. The forceps are composed of a pair of grippers at the tip, a shaft, and a pair of ring handles to open and close the grippers. The grippers, made of stainless steel, are curved to facilitate
tissue dissection, mimicking those of the Maryland dissecting forceps. One of the grippers is equipped with a metal blade with a relatively dull edge (Fig. 13.2b). A small heating resistor element is built into the blade. This element, a thin metal membrane, is made of molybdenum. Lead wires connect the heating element to the connecting cable. When electric energy is given to the molybdenum membrane, it produces heat, heating the blade. It is the most unique point of our new device, that the blade produces heat, no matter whether the blade contacts the tissue or not. In contrast, other commonly used devices, such as monopolar high-frequency devices, bipolar vessel sealers, or ultrasonically activated devices, need to contact tissue to generate Joule heat or frictional heat. The surface of the blade is coated with fluoroplastic to prevent char sticking. The opposed gripper is equipped with a tissue pad made of elastic silicone to receive the blade (Fig. 13.2c). When a vessel is clamped between the blade and the tissue pad and the blade is heated, the vessel is closed, welded, and sealed. Then the elasticity of the silicone pad allows the blade to cut into the vessel, and finally, the vessel is divided.
The power controller regulates the electric power to let the heating element emit the desired heat. The time-versus-temperature curve, we presume ideal for hemo-static tissue dissection, is like the one obtained by ultra-sonically activated device. So we set the program of the power controller in order to obtain such time-versus-temperature curve in the tissue, which gradually goes up and exceeds the water boiling point in about several seconds, reaching around 200°C in about 10 s. To obtain such time versus-temperature-curve, the temperature difference between the heating element and the contacting tissue has to be considered. Considering this temperature gradient, we set the maximum temperature of the heating membrane higher than 300°C.
Fig. 13.2 a Closeup of the prototype forceps. The grippers are ideally curved as in the conventional dissecting forceps. b In one of the grippers a heating blade is attached. In the blade a
A female pig weighing 61 kg was given general anesthesia and used for the current experiments. The first experiment was performed to assess the device's performance for tissue dissection in the laparoscopic operation. For this task several portions of the mesenterium, omentum, and the root of the inferior mesenteric vessels were dissected, sealed, and divided. The next experiment was for assessing the ability and security in sealing the small- to medium-sized vessels. This task was performed under laparotomy, and the gastroepiploic arteries measuring 3 to 4 mm in outer diameter were sealed and divided by the new dissecting forceps. Output voltage, current, and time required to seal and cut each artery were measured and recorded. The maximum temperature that the heating element was supposed to reach was theoretically calculated in each session. For the sealing security experiment we harvested each artery segment cut by the heating forceps. The harvested arteries were immediately submitted to the following process. A cannula was inserted into the artery segment through the end opposite the occluded stump. The cannulation site was closed tightly with
heating element, made of molybdenum, is built in. c Closeup of the prototype forceps. In the opposed gripper an elastic tissue pad (black part) is equipped to receive the blade
Fig. 13.2 a Closeup of the prototype forceps. The grippers are ideally curved as in the conventional dissecting forceps. b In one of the grippers a heating blade is attached. In the blade a heating element, made of molybdenum, is built in. c Closeup of the prototype forceps. In the opposed gripper an elastic tissue pad (black part) is equipped to receive the blade clamping forceps. The cannula was connected both to a syringe and a digital manometer. The artery segment, digital manometer, syringe, and the connection tubes were filled with normal saline and sealed off to become a closed system. By slowly pushing the piston of the syringe, the artery's intraluminal pressure was increased until the occluded vessel burst. The time versus-pres-sure-curve was demonstrated on the computer monitor and recorded. The peak of the time-pressure curve was defined as the burst pressure of the artery segment.
In addition, we examined the artery stump by microscope. The artery was fixed in paraffin and stained with hematoxylin and eosin.
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