ELECTROSURGERY UNIT

Typical Number in Hospital: 14

Cost Bands: 4

References: 3,4

This is a surgical diathermy apparatus. Most surgical operations utilize electrosurgery to create a bloodless entry into the body, to treat or remove lesions from inside the body, to remove unwanted hair and to control bleeding. An electrosurgery unit provides a high power (50-400 W) source of high-frequency alternating current at between 0.5 and 3 MHz. The unit may also provide current for endoscopy lamps and for electrocautery.

The apparatus may be unipolar, delivering current between a small active electrode and a large indifferent (or dispersive) electrode, or it may be bipolar in which case the current is delivered between the two arms of a special forceps with insulated handles. There are two main functions, cutting and coagulating. In the case of cutting, a continuous sinusoidal current is delivered to a pointed or sharp electrode to yield clean cutting as the cellular water is rapidly volatized at the point of contact with the probe (active electrode). In coagulation a larger active electrode (e.g. ball-tipped) provides short pulses of high voltage which cause desiccation and fulguration of tissue by an electric arc which coagulates the tissue and arrests blood flow.

Diathermy is not a proper description for the technique, since little heat is generated within the bulk of the tissue between the two electrodes; most is generated at the point of contact between the active electrode and the tissues being treated. The waveform is important in providing current suitable for cutting or coagulating, but these may be blended to provide power suitable for both. More important is the shape of the active electrode.

Modern electrosurgery machines have transistor current generators, but many valve (tube) types are in use, some with spark-gap generators. Transistor circuits have shown difficulty in the past in generating the high voltages required for coagulation. With unipolar electrosurgery the indifferent plate used to be connected to earth. This created a risk of electrocution by earthing the patient, and so later types were not earthed but included a ground reference capacitor which limited the path to earth for low-frequency (e.g. 50 Hz) currents. There is still a risk of diathermy burns with ground referenced systems if the indifferent electrode is poorly fitted or disconnected. Later types are earth free except for a route provided by stray capacitance between the machine, the patient, and earth. These types often include a sensing circuit to recognize detrimental changes in the earth reference arrangement.

Special loop electrodes are also used, particularly during intra-cavity surgery, such as prostatectomy, endoscopic electrosurgery in the rectum, vagina or abdominal cavity, which can be used to cut conical sections from diseased tissue.