Info

Electrosurgery

Mains current

No AM radio neuromuscular stimulation

FM radio TV

The human body sends conduction pulses as little electrical currents to the muscles to make them contract. To ensure that electrosurgery does not stimulate the whole body to uncontrolled muscular contractions, alternating current is used with a frequency above the stimulus threshold of the human body. This threshold is at about 10 kHz, i.e. about 10,000 changes of current direction per second. The human body is too inert to react to electrical current above this frequency. This also applies to the heart muscle, so that a high-frequency current through the heart does not cause any damage.

Most high-frequency surgical devices today work with a frequency in a range of about 450-550 kHz (O Fig. 5.4).

Electrosurgical techniques

Surgical effects can be divided into two main groups, depending on the application:

Fig. 5.4. Frequency range for most high-frequency surgical devices

Incision and coagulation. Incision separates the tissue and coagulation dries the tissue out (O Fig. 5.5).

These two surgical effects are in turn broken down into two sub-groups each (O Fig. 5.6): 4 pure or smooth incision with as little lateral haemostatic effect as possible 4 incision with lateral haemostasis by including coagulation shares (mixed current, »blend«, mixing) 4 and contact coagulation (desiccation) and 4 non-contact coagulation (fulguration and spray).

Many users are not familiar with the difference between desiccation and fulguration. But there is a fundamental difference between the two, because if these techniques are used incorrectly, the surgeons can suffer from painful discharges through their gloves.

Coagulation

Incision energy densit

Drying out from heat Coagulated cell

Cell expands by evaporating yded

Fig. 5.5. The two surgical effects are coagulation and incision

5.1.2 Incision

Electrosurgery

Pure cut

During the pure cut, the main aspect is to heat only the tissue at the point of contact very quickly with the active electrode. This is achieved best using an electrode with a small contact surface (e.g. needle electrode) which produces a high current density. This in turn causes »cell explosions« in the tissue. A »micro spark rain« is produced between the electrode and the tissue at high temperatures of more than ioo°C. The continuous supply of energy heats the tissue cells so quickly that they explode. This causes the tissue to separate (incision) (O Fig. 5.7). The supplied heat is dissipated again mainly by means of the evaporated cell liquid. No heat is transferred to the surrounding tissue, producing a smooth cut with a minimum coagulation zone.

Pure (smooth) Blend

Coagulation

Fulguration Desiccation

Pure (smooth) Blend

Fulguration Desiccation

Fig. 5.6. The surgical effects and their subgroups

Fig. 5.6. The surgical effects and their subgroups

Cutting is not possible without micro-sparking.

Cells exploded by heating quickly >100°C

Blend cut

Drying out caused by limited heating below 100°C

Cells exploding by heating quickly below 100°C

Blend cutting

(Incision with coagulation)

For certain incisions, e.g. through parenchymal or capillary tissue, a haemostatic effect is wanted together with the cut. This haemostasis can be produced in various ways:

4 by a cut at low speed, 4 by a cutting electrode with a larger surface 4 and finally by modulating the cutting signal.

This method causes energy and thus warmth to penetrate deeper into the surrounding tissue during the incision, producing the coagulating effect (O Figs. 5.8 and 5.9).

One indication for using blend cutting is an incision through subcutaneous tissue; coagulation is then usually required for only a few vessels so that time is saved in this way.

5.1.3 Coagulation

Desiccation or contact coagulation

The difference between incision and coagulation lies in the large current density, resulting in rapid, local heating of the cell tissue, triggering a cell explosion and causing separation of the tissue.

By contrast, in coagulation the current density is decreased so that the developed heat diffuses through the cell wall into the cell liquid, transforming the protein (visible in the white colouring). This procedure dries the cell out and the cell wall stays intact (O Fig. 5.10). Direct contact with the tissue is a typical feature of desiccation.

At a lower current density, heat penetrates deeper into the tissue so that the tissue dries out to the side of the electrode. The time factor plays a major role: 100 W applied for 0.1 s has a more superficial heating effect on the tissue, whereas 10 W applied for 1 s has a deeper effect and is more likely to produce the required coagulation effect. So a higher power setting does not necessarily result in better or deeper coagulation. On the contrary, if the power

Fig. 5.9. Cutting with coagulation shares

Contact coagulation = desiccation

I Ball electrode

Pmbh

Was this article helpful?

0 0

Post a comment