Discussion

Endoscopic surgeons are becoming aware that such new hemostatic dissecting devices as USADs or BVSs are the key devices for advanced endoscopic operations, which require coagulation and division of many vessels [1-6]. When all vessels have to be ligated and divided by knot tying or clipping, the procedure becomes significantly time-consuming and requires much expertise.

Although these new hemostatic dissecting devices have been widely welcomed by surgeons, there are some drawbacks. As far as USADs are concerned, the risk of the cavitation phenomenon occurring at the tip of the vibrating blade, must be cautioned [7]. This ultrasonic vibration-specific phenomenon has as tissue destructive effect and may result in adjacent organ injury. Besides, ultrasonic vibration generates mist. The ultrasonic vibration breaks the links among water molecules in the tissue and eventually causes the mist. The mist obscures the operation field during endoscopic surgery. Moreover, the mist has potential hazard to transmit infectious material to the atmosphere [8] and to possibly disseminate viable cells [9].

In BVSs designed for endoscopic operations, two actions are needed to achieve coagulation and cutting. After coagulating the vessel one has to slide the cutter to cut the target. Moreover when the cutting function is integrated, the gripper must be straight because a cutter has to slide straight along the gripper. And when the gripper is curved for facilitating tissue dissection, cutting function has to be abandoned. The similar drawback is also pointed out in USADs. The active blade of a USAD must be straight or almost straight to transmit the ultrasonic vibration effectively. Freedom for the shape of the end effecter in these devices is limited.

Reflecting on all those drawbacks associated with the conventional hemostatic dissecting forceps, our main aims in the current development of a new hemo-static dissecting forceps are set: (1) not to have cavitation phenomenon, (2) not to produce mist, and (3) to have freedom in shape. In order to achieve all these goals, we decided not to use ultrasonic vibration or high-frequency electrocautery as its energy source.

The reason why we started to test the metal membrane heating element as an alternative energy is that we thought it would be possible to control the heat by giving the controlled power to this element and to obtain the similar time-versus-temperature curve as in the USAD technique. We have reported that the heat produced by a USAD is considerably milder, and it increases the temperature more gradually than does the heat produced by conventional monopolar elec-trocautery [10]. It was reported that the heat produced by a BVS is also significantly milder than is the conventional monopolar high-frequency technique [11]. As extremely rapid increase in temperature results in boiling the water in the cells, their subsequent explosion and eventually desiccation of tissue, it is not ideal for tissue welding [12]. On the other hand, when the temperatures lower than the boiling point are reached, protein and intracellular water denature into glue-like material.

Our development group has already investigated in previous experiments and reported that the metal membrane heating element made of molybdenum can emit adequate temperatures to seal vessels sufficiently [13]. The basic concept and principle for the current study have not been changed from the previous ones. We brought the same technology into the shape compatible for endoscopic surgery, making necessary parts thinner. As a heating element, molybdenum membrane is again used. The main change in the power controller was to set the program for emitting constant voltage, while in the previous experiments it was driven to obtain the constant temperature. This change was introduced mainly because we found that in the constant temperature setting, the energy given to the tissue is decreased in the latter half of the activating period, when more energy should be needed for cutting the target. Interestingly in the constant voltage setting, we found the time-versus-temperature curve is more similar to those in USAD technique, and energy given to the tissue for the latter half of the activating period is higher.

When compared with previous reports on the ability of a USAD to seal the vessel, the ability of our new device seems equivalent or even higher [14-16]. The minimal burst pressure recorded in our experiment was 897 mmHg, which is much higher than the normal blood pressure of a living animal. In addition, the time required to seal and cut the vessels by our new device was as short as by the USAD technique. Interestingly, the microscopic findings in the artery stump obtained in the current experiments were remarkably similar to those obtained by a USAD in our previous experiments [14].

Advantages of our new device, compared with USADs, were clearly seen in the current experiments. It does produce a little amount of smoke, although it does not significantly disturb the operation, whereas the mist produced by USAD disturbs the procedure frequently. The fact that the cavitation phenomenon is never seen in our new device should make the dissection procedure significantly safer than the USAD procedure.

Like BVSs, the shape of the end effecter in our device can be made as curved as surgeons wish for their utility. And in our device this utility with the curved shape does not have to be compromised by the cutting function. Another advantage of our device is that both functions, sealing and cutting, are achieved in one action, while this utility is not integrated in BVSs. When also compared with the high-frequency techniques, there are advantages seen in our device. From the viewpoint of "electrical security", our device, which emits no electric current, should be safer than the current electrocautery, in which high-frequency electric current is transmitted in the human body, although it occurs only between the two electrodes in the bipolar technique. During tissue dissection near the nerve system, for example, our device is considered to be advantageous. Another unique advantage of our device is that the surface of the blade can be coated with fluo-roplastic to prevent char sticking. The end effecter of the other electric devices cannot be coated because the electric current has to be discharged through the surface of the end effecter.

We are bringing this development to the next stage in order to assess the stability, durability, and feasibility as a commercial good. And the development is also focused on establishing the same system for open sur gery. The endoscopic version as well as the open version is expected to pass further subjects or tests, and to be put into clinical trial in near future.

Acknowledgment

The authors are grateful to all staffs of Therapeutic Products Development Department, Research & Development Division, Olympus Medical Systems Corporation, Tokyo, Japan, for their enthusiastic support of the current experiments.

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