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Diathermy involves the passage of high frequency alternating current through body tissue. Where the current is locally concentrated heat is produced (1000 deg. C).

Diathermy involves current frequencies between 400KHz to 10MHz, thus allowing currents of 500mA to safely pass through patient (100mA at a household frequency of 50Hz will cause electrocution & ventricular fibrillation).

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

  • 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 effects of diathermy depends on the current intensity and wave-form used

  • Coagulation

    • Produced by interrupted pulses of current (50-100 per second)

    • Square wave-form

    • dessication & sealing of blood vessels,

  • Cutting

    • Produced by continuous current

    • Sinus wave-form

    • cell water is vaporized

  • Blend

    • combination of cutting & coagulation waveforms to increase the degree of haemostasis during cutting.

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