Surgical Diathermy

This is the use of electricity to generate heat in tissues. For the surgeon, the heating to be enough to vaporize or coagulate the tissue.

The electricity has to be of high frequency, usually referred to as radio-frequency .This is because it falls into the range of frequencies used for wireless transmissions. One of the main values of the high frequency is that it is too fast to stimulate nervefibers. This means that you don’t get spasm or paralysis of muscle. To avoid these unwanted effects, you need frequencies greater than 100 kHz. Diathermy units use frequencies from 500 kHz (500,000 cycles per second) to 2 MHz (2 million cycles per second).

Types of diathermy

There are two types used in surgery: unipolar and bipolar.

                      Unipolar 

   

this is the type of diathermy that is most often used in surgery, including open, minimally invasive. Follow the wire from the “active electrode” on the diathermy machine.It goes to the device (needle point, scissors, forceps etc.) you will use to apply the diathermy to the patient. Once the device is applied to the patient, the current will flow from the point of contact. It will spread out as it passes through the patient, heading for the “return” pad, which is usually attached to the patient’s thigh. From there it runs back to the diathermy machine, so completing the circuit.

Bipolar       

  

this is a very safe form of diathermy. Usually you use forceps. The current only flows between the tips of the forceps, from the active electrode to the neutral electrode. So there is less risk of stray currents damaging tissues other that those you are aiming to damage.

Effects of diathermy

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

             Coagulation

Produced by interrupted pulses of current  (Square wave-form current).

               Cutting

Produced by continuous current (Sinus wave-form current)

Uses of diathermy current.

There are three main types: cutting, coagulating, and blended.

Cutting current.

Sinus wave-form current at low voltage: 500 – 1,000 volts .The water in the cells is turned to steam, so the cells vaporize giving a cutting effect. The best effect will occur when the current flows through the smallest tissue volume. Obviously, using a clean needle point will produce this. The current flows continuously. In other modalities, the current is applied in bursts

Coagulating current

Square wave-form  current  at high voltage – up to 6,000 volts. The aim of this is to desiccate the tissue, but not to vaporize it. You want to generate lower tissue temperatures than with cutting current. This is done by applying the current in bursts. You are treating bigger volumes of tissue and want the effect to go deeper than with cutting. So a higher voltage is used, usually up to 6,000 volts. Coagulating current provides good hemostasis.

Reference

http://www.drcog-mrcog.info/diathermy.htm

http://www.surgical-tutor.org.uk/default-home.htm?resources.htm~right