1 Modification of Cauterizing Forceps for Microsurgery University of Wisconsin – Madison College of Engineering BME 200/300 October 13, 2001 Team Members: Luke Harris Crystal Marshek Client: Dr. Behnam Badie, M.D. Department of Neurological Surgery Advisor: Wally Block College of Engineering2 Abstract: The problem that the group was presented with involved the modification of a device used during neurological microsurgery. The device used is similar to a standard forceps (Figure 1). When a foot pedal is depressed, activation of a radio frequency causes cauterization, but when released the radio frequency ceases. Cauterization results in the searing of tissue to stop blood flow. The foot pedal currently used is awkward and potentially dangerous due to the use of multiple foot pedals during surgery. A useful innovation would be a switch or button on or near the shaft of the forceps that would allow the surgeon to position the tips and cauterize in one single motion. A button or switch on the forceps is necessary to allow them to be used as a multipurpose tool during surgery. The forceps are used for both tissue manipulation and cauterization when needed. After carefully evaluating the needs of the client, a preliminary design was developed to satisfy these requirements and minimize cost. Figure 1: Radio frequency cauterizing forceps (Valleylab, 2001). Background Information: Microsurgery involves the minute dissection or manipulation of living structures or tissue, such as those found in the brain. During microsurgery the surgeon’s eyes are fixated in a microscope to enhance viewing of neurological components. This limits the surgeon’s ability to make multiple movements. Modifications to the device are needed because the surgeon must look down during the operation to verify that the correct foot pedal is being depressed. This additional movement disrupts the concentration and progression of the surgery. The surgical forceps function in both tissue manipulation and cauterization. In present instrumentation, the surgeon must continuously depress a foot pedal to3 allow cauterization. This causes a radio frequency, of varying amplitude and wavelength, to be sent to the tips of the forceps. This modulated radio frequency results in the cauterization, or closure, of the severed blood vessels. Design Specification: After meeting with the client, Dr. Behnam Badie, important design constraints and motivational factors for a new device were noted. The motivation behind modifying the presently used instrument is to allow cauterizing using one single motion versus the current foot pedal method. The foot pedal causes additional movement. It is inconvenient for the surgeon to look down during the operation to verify that the correct pedal is being depressed. Although the inconveniency of a foot pedal can be solved using a button on the forceps’ shaft, Dr. Badie stressed that the motion to activate such a device must be natural. The use of the surgeon’s other hand is not an option because it is necessary in the transfer of additional surgical equipment. Therefore, control of the button would be ideal if done with one hand, one finger, and with relatively no extra motion. Several constraints were considered when developing the preliminary design. There were a total of five constraints, three focusing on the button and two on safety. The first was the height of the button. If the button is placed on the forceps, the surgeon’s view must not be obstructed. Minimizing the height of the button as well as analyzing its placement on the forceps can solve this. The second constraint was the buttons width, which cannot exceed the width of its location. The third constraint is that the surgeon should not have to exert a large force on the button to cause cauterization. This is the main reason why a switch was decided against. To activate, a switch needs an x and y component of force. The x component will cause horizontal movement of the forceps, possibly changing the location of the forceps during an operation. The button, on the other hand, could be activated using only the y component of force. This would minimize any horizontal motion. Purchasing a button that needs a small amount of pressure to depress can also minimize the vertical motion. One constraint with respect to safety was the need for the forceps and button to be able to withstand sterilization techniques such as autoclaving. Autoclaving is the process of using pressurized steam to destroy microorganisms. Also, modifications made cannot have sharp edges that may puncture latex gloves during surgery. The literature search was futile. The only available articles found pertained to how forceps can be used during surgery, not the specifications of the forceps. Therefore, help was sought help from Professor Burke O’Neal. Professor O’Neal is an expert with electronics and gave insight on how to wire a button placed on the shaft of the forceps. Three wires would be necessary: one for the electrical4 input, another for the switch, and a third for the electrical output. Professor O’Neal also made clear that the button itself was not something that could be easily purchased. Buttons used in medical instrumentation must be manufactured to a high degree of accuracy. Possible Solutions: General Design Due to the many specifications from the client, one main design was developed with several variations. The main design consists of forceps that have an easily depressible “bubble” button for the activation of cauterization. This type of button was chosen because it has a protective “insulation” material. The protective material would cover any cracks or edges where debris or liquids could settle, causing malfunction. The flexible insulation material would also serve as protection for the electrical components. The button would also be brightly colored to indicate its exact location. The button would work similarly to the foot pedal in that when depressed, cauterizing would take place, and upon release, cauterizing would immediately stop. Idea #1 (“Bubble” button on shaft of forceps – Figure 2) In this design, the button would be placed on the top edge of the forceps, approximately where the thumb is placed when squeezing the forceps together. The wiring for the button would include Professor O’Neal’s suggestion for
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