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Principles of Electrosurgery ElectrosurgeryDiathermy is the use of high density radio frequency electric current to produce heat Electrocautery refers to direct current (electrons flowing in one direction) whereas electrosurgery uses alternating current. During electrocautery, current does not enter the patient’s body. Only the heated wire comes in contact with tissue. In electrosurgery, the patient is included in the circuit and current enters the patient’s body. Electrosurgery Used to either cut or destroy tissue or to produce coagulation Mains electricity is 50-60 Hz but this produces intense muscle and nerve activation Nerve and muscle stimulation cease at 100,000 cycles/second (100 kHz) Electrical frequency used by diathermy is in the range of 300 kHz to 3 MHz (radio frequencies) Circuit consists of 1. electrosurgical generator - source of the electron flow and voltage. 2. active electrode 3. patient 4. patient return electrode (indifferent electrode). Pathways to ground are numerous but may include the OR table, stirrups, staff members, and equipment. With newer isolated electrosurgical systems - electrosurgical current from isolated generators will not recognize grounded objects as pathways to complete the circuit. Isolated electrosurgical energy recognizes the patient return electrode as the preferred pathway back to the generator. Machines do this by measuring impendence at the indifference electrode. The patient’s tissue provides the impedance, producing heat as the electrons overcome the impedance. The only difference between the “active” electrode and the patient return electrode is their size and relative conductivity. To minimise risk: 1. ensure large pad placed over tissues of low impendence as close as possible (well vascularised muscle mass) 2. good contact 3. use lowest currents The function of the patient return electrode is to remove current from the patient safely. A return electrode burn occurs when the heat produced, over time, is not safely dissipated by the size or conductivity of the patient return electrode. Monopolar diathermy Electrical plate is placed on patient and acts as indifferent electrode Current passes between instrument and indifferent electrode As surface area of instrument is an order of magnitude less than that of the plate - The only difference between the “active” electrode and the patient return electrode is their size and relative conductivity. Localised heating is produced at tip of instrument Minimal heating effect produced at indifferent electrode Bipolar diathermy Two electrodes are combined in the instrument (e.g. forceps) Current passes between tips and not through patient Effects of diathermy The only variable that determines whether one waveform vaporizes tissue and another produces a coagulum is the rate at which heat is produced. High heat produced rapidly causes vaporization. Low heat produced more slowly creates a coagulum. Heating effect depends on: 1. the current intensity 2. wave-form used 3. size of electrode - The smaller the electrode, the higher the current concentration 4. duration activated 5. tissue – eschar have more resistance to current 6. distance from tissue – sparking vs direct contact sparking gives more cutting Coagulation 1. Produced by interrupted pulses of current (50-100 per second) – less heat 2. Square wave-form 3. Uses higher voltages thus more thermal spread Cutting 1. Produced by continuous current – produces heat rapidly 2. Sinus wave-form 3. Uses lower voltages – less thermal spread Blend 1. A “blended current” is not a mixture of both cutting and coagulation current but rather a modification of the duty cycle. As you go from Blend 1 to Blend 3 the duty cycle is progressively reduced. A lower duty cycle produces less heat. Consequently, Blend 1 is able to vaporize tissue with minimal hemostasis whereas Blend 3 is less effective at cutting but has maximum hemostasis. Risk and complications Can interfere with pacemaker function Arcing can occur 1. direct coupling - with metal instruments and implants 2. insulation failure 3. capacitance coupling – occurs when 2 conductors separated by a insulator discharges current into surrounding tissues. (endoscopic diathermy) Superficial burns if use spirit based skin preparation Diathermy burns under indifferent electrode Channeling effects if used on viscus with narrow pedicle (e.g. penis or testis) Lower Risks by: * Inspect insulation carefully * Use lowest possible power setting * Use a low voltage waveform (cut) * Use brief intermittent activation vs. prolonged activation * Do not activate in open circuit * Do not activate in close proximity or direct contact with another instrument * Use bipolar electrosurgery when appropriate * Select an all metal cannula system as the safest choice. Do not use hybrid cannula systems that mix metal with plastic. * Utilize available technology, such as a tissue response generator to reduce capacitive coupling or an active electrode monitoring system, to eliminate concerns about insulation failure and capacitive coupling. * should not be used in the presence of flammable agents (i.e., alcohol and/or tincturebased agents)” *avoid oxygen rish environments * The active electrode(s) should be placed in a clean, dry, well-insulated safety holster, when not in use. * Cords not be wrapped around metal instruments Surgical smoke Surgical smoke is created when tissue is heated and cellular fluid is vaporized by the thermal action of an energy source. smoke from electrosurgery is similar in content to that produced by a surgical laser. Viral DNA, bacteria, carcinogens, and irritants are known to be present in electrosurgical smoke. Universal precautions indicate a smoke evacuation system should be used. NIOSH (the National Institute of Occupational Safety and Health) and the CDC (Center for Disease Control) have also studied electrosurgical smoke at length. They state: “Research studies have confirmed that this smoke plume can contain toxic gases and vapors such as benzene, hydrogen cyanide, and formaldehyde, bioaerosols, dead and live cellular material (including blood fragments), and viruses.” Bibliography Aigner N, Fialko C, Fritz A, Winks O, Zoch G. Complications in the use of diathermy. Burns 1997; 23: 256-264. http://www.valleylab.com/