Neurosurgical Electrocautery Forceps Mid-Semester Design Report Biomedical Engineering 200/300 Advisor: Wally Block Nick Kortan Andrea Rozmenoski Mike Wells October 18, 20012Abstract Electrosurgical instruments date back to 1891, when doctors first harnessed the ability to use electricity to coagulate blood and cut tissue during surgery. The “bovie” was the first electrically charged metallic instrument in clinics back then. Crude and unreliable in its ways, doctors and nurses were often subject to shock and electrocution risks in the operating room. These conditions are incomprehensible by today’s standards, and that is why we see a radically different instrument today. One that does not heat up to cauterize, but instead passes radio frequency between the tips to do the cauterizing or coagulating work. Cauterization is a procedure performed often used to remove lesions or control bleeding and may be performed thermally, electrically, or by laser. Introduction Neurosurgery is a precise practice, with exceptionally fine tools, and steady surgeons. Dr. Behnam Badie, MD, felt his instruments were compromising his technique, and came to the biomedical engineering program to search for an answer. The instrument he has ideas for is an electocautery forceps, also known as bipolar, foot controlled, coagulating forceps. An electrocautery forceps currently consists of hand-held forceps connected to a radio frequency generator. The forceps design is commonly called “micro bayonet” due to its curved, bayonet-style structure. The generator is activated using a foot pedal, usually located on the floor beneath the operating table(some common designs of foot pedals can be found in Figure 1). When the pedal is not depressed, the forceps can be used to grab and pierce tissue. When the pedal is depressed, it activates a flow of radio frequency between the two tips of the forceps, and acting similar to a microwave by heating up and coagulating any blood in between the tips of the forceps.3Figure 1 One problem with the foot pedal is that the surgeon sometimes needs to pause his procedure during the surgery in order to find and depress the foot pedal. A second, more prevalent problem is that there is often multiple foot pedals for other various instruments beneath the operating table. This has led to the activation of the incorrect devices and failure to activate the correct device in time. To avoid this, Dr. Badie would like to see a new design that allows the forceps to be activated from some mechanism on the forceps themselves. He feels this improvement will allow him to grab tissue, coagulate any blood, and release in one fluid movement. In order to maintain the precision and accuracy with a new design, some limitations were made clear. The switch must be relatively small, or placed correctly in order to give the surgeon full view of what he is operating on. The switch should be accessed ideally with only one finger, preferably the forefinger, and without requiring the surgeon to move his hand position. In order to avoid any extra movements, the switch should be activated by light pressure. Any switch used cannot have any sharp edges that4could catch on the surgeon’s gloves, clothes, gauze, etc. Since the current design runs off a generator powered by a wall outlet, any change in the generator must also be powered by a wall outlet. Finally, it is preferable that a new instrument should not have to be made for each surgery, and therefore the design should be resistant to the sterilization process (i.e. – steam at 250°F for 15-20 minutes, gas, or autoclave). There is, however, still information needed. New design ideas have been produced and one of the main deciding factors in choosing which one will be pursued is the comfort of the surgeon’s hand on the instrument. The design ideas will need to be taken to Dr. Badie to determine which is to his liking. Another deciding factor is the dimensions of the forceps, where again comfort of the surgeon comes into play. Since forceps come in many different shapes and sizes, we will need to obtain a model that we can take actual measurements from. Background In the design of any new device, the necessary background research must be performed first. During our research, both a better understanding of the instrument and new concepts were sought out. Searches for existing tools related to ours were done over the Internet and at the libraries. We found a variety of supply companies that carried forceps similar to what we are studying. ASSI (Accurate Surgical & Scientific Instruments), Conmed, and Vallylabs were companies that had forceps most similar to Dr. Badie’s. Bipolar cautery uses high frequency (radio frequency) electric energy to melt and coagulate tissue placed between two directly apposed electrodes. Because the electrodes are closely approximated, low voltages of electricity are adequate. It is highly effective for use in hemostatic ligation of small vessels and vascular tissue, and can be preformed quickly. Electrosurgery units are used to cut or coagulate tissue, or a combination of the two. The surgical outcome depends on the waveform generated by the ESU. A pure cut waveform is continuous, undamped and sinusoidal in shape. The fluid in the cell heats to the vaporization state resulting in the cell exploding. Coagulation, known as the coag mode, occurs when the cell fluid is allowed to cool between heating, as explained by a Bio-Tek Instruments, Inc. article. The waveform consists of a dampened cut wave that oscillates on and off, similar to the defrost mode on your microwave. This heats the cell fluid, but allows it to cool in between, thus avoiding cell rupture and only causing blood to coagulate, or clump. Bipolar electrocautery eliminates the need for a patient grounding pad, which is what is currently used in monopolar electrocauteriztion. Bipolar cautery exceeds monopolar cautery further because the current does not pass through the entire body, thus eliminating the danger of burns distant to the site of the forceps tips. Because of these characteristics of bipolar cautery, its depth of injury to surrounding tissue is minimal and it produces little smoke. Design Ideas Button Prior to Split5One design produced by the group is to place a circular button enclosed by a “bubble” at the base of the tweezers, just before the forceps divide(Fig 2). While watching
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