Electrosurgical generators used for LEEP are identical to ones used in laparoscopic and urological surgery. The alternating current output ranges between 100 and 4000 KHz. At frequencies of greater than 100 KHz, cellular membrane depolarization does not occur, so there is no associated shock or muscular contraction. Electrical generator features may include:
Isolated circuitry - automatically deactivates the electrosurgical generator if any current that is transmitted to the active electrode is not returned through the patient electrode. Helps prevent "alternate site" burns.
Ground referenced - older type - does not contain isolated circuitry.
Return electrode monitoring (REM) - causes a warning light and/or an audible tone if the return circuit is interrupted. Some units will alarm with only partial loss of grounding.
Most generators allow switching between cutting and coagulation modes, and can blend a cutting effect with a coagulation effect. These blend modes permit concomitant coagulation hemostasis and surgical excision of tissues. For example, a "blend 1" mode may represent a cutting effect of 75% and a coagulation effect of 25%. Blend modes represent a greater proportion of coagulation effect that further minimizes bleeding, but often increases thermal damage to the excised tissue. If a thermal artifact is present, evaluation of the specimen margin to exclude margin involvement becomes difficult.
Most loops have an insulated shaft and crossbar to prevent accidental thermal injury. Common loop sizes range from 1 by 1 cm to 2.0 by 1.5 cm. The stainless steel or tungsten wire of the loop is approximately 0.2 mm thick. Ball electrodes ranging from 3mm to 5mm are used for fulguration. The probe is a monopolar output, and requires the use of a grounding electrode.
Return (patient) electrodes may be adhesive gel pads or a solid "antenna," and may be either disposable or reusable. They should be applied near the operative site, usually on the patient's buttocks or thigh. The pad wire should be connected to the generator and the circuit tested before the procedure to insure that the system is functioning correctly. Poor contact between the dispersive pad and the patient may result in a thermal burn at that site.
A smoke evacuator is essential to remove the "plume" produced during the procedure. It filters airborne particles and co-existing microorganisms present in the plume. The operator usually must activate the smoke evacuator prior to turning on the electrosurgical unit. One manufacturer has combined an electrosurgical unit with a smoke evacuator so that when the generator is activated, the smoke evacuator is automatically activated also. Negative pressures from the smoke evacuator cause an air flow into the vagina, up the fixed tubing in the speculum, and through the evacuator tubing toward the equipment. This minimizes plume spillage into the treatment room. A series of microfilters helps remove the carbon, smell, and viral particles generated. Since human papilloma virus has been isolated from similar laser plumes, clinicians generally wear micro-pore or submicron surgical masks. 18, 19
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