with the electrode. This effect is preferably used when sealing tissue over a large surface. In order to generate the necessary sparking effect, high momentary voltage peaks are required.
The advantage of fulguration is that the sparks are sprayed or »jump« to the tissue. Current seeks the way of least resistance (physical principle) so that it is easy to imagine how these sparks »seek« bleeding vessels and coagulate them because they have better conductive properties (O Fig. 5.12).
This naturally also happens in situations in which blood vessels are not visible. Suitable areas of application therefore include for example surgery to the liver, coagulation of the sternum, coagulation of not visibly open veins during transurethral resection and generally widespread, diffuse bleeding.
Fulguration always causes a flat, flexible necrosis at the sparking point. These points are then also less conductive for heat, so that deep coagulation is not possible.
Spray coagulation. Spray coagulation is high-intensity fulguration. This means that a spark jumps already at a very early stage so that widespread coagulation can be performed more easily and faster.
It is not only the power setting and mode which influence the effect on the tissue: the surgical effect is in fact the sum of the following factors. 4 Power setting:
A high power setting causes more tissue damage than a lower power setting 4 Type:
Incision has a different effect on the tissue from coagulation
A smooth cut (pure cut) generates less lateral haemos-tasis than a blend cut. Contact coagulation generates deeper protein denaturation than fulguration or spray coagulation which is more superficial.
4 Shape of the electrode:
A needle electrode concentrates the power on a small contact surface, producing higher power density for an easier cut. A ball electrode or forceps generate larger contact to the tissue: the power density decreases and with it the temperature generated in the tissue, resulting in coagulation.
4 Incision speed:
With the incision speed through the tissue, the user has a direct influence on the degree of haemostasis to the side of the cut: more energy can be emitted laterally at a lower speed, generating more haemostasis than at a fast incision speed.
4 Kind of tissue:
Fat or glandular tissue has higher electrical resistance than muscular tissue, for example. The user therefore feels higher mechanical resistance during the incision at the interface between muscular and fat tissue. The power setting of the HF surgical device is then usually increased.
4 Distance between active electrode and neutral electrode
The distance between the site and the positioned neutral electrode also influences the quality of the surgical result. The reason for this is that the electrical resistance increases with the distance of the neutral electrode to the site. This means that part of the power emitted by the HF surgical device can be lost by higher body resistance (7 see also Sect. 5.2).
5.2 Neutral electrode
REM monitor current
The root »neutral« in the word »neutral electrode« implies a certain safety. But this impression is false in view of the fact that the same power which passes through the electrode handle also penetrates the neutral electrode and corresponding connection cable.
The function of the neutral electrode is to close the alternating current circuit from the high-frequency surgery device - electrode handle - patient - neutral electrode - high-frequency surgery device with the lowest possible current density at the contact surface. Which is quite the reverse of the »active« electrode, where a high current density is required for the surgical effect.
As far as the contact surface and size of the neutral electrode are concerned, the physical rule applies: the larger the contact surface of the neutral electrode, the better for the patient because the current density is smaller.
But if this contact surface is too small, the neutral electrode comes loose or was not applied completely, this can result in serious burns because of the high current density, with the »neutral electrode« also becoming an »active electrode« (7 see also Sect. 5.2.4).
Current high-frequency surgery devices come with monitoring systems which notice a decrease in the contact surface (when the neutral electrode works loose) and draw the user's attention to the situation with an alarm and by stopping the power, before the patient can be harmed.
This function is best illustrated by the example of the monitoring system make Valleylab.
The »Return Electrode Monitoring« (REM) system was developed to avoid burns under the neutral electrode. This neutral electrode monitoring measures the quality of the contact surface between the neutral electrode and the patient all the time, also while the device is activated, and registers every change during the entire surgical procedure.
A visible and audible alarm is generated when the quality of the contact surface is inadequate and the power is switched off immediately to prevent any dangerous situation.
The REM system consists of an electronic monitoring system, a divided neutral electrode and a two-wire connection cable.
The electronic control unit in the generator emits high-frequency alternating current as measuring current; this flows across one-half of the neutral electrode through the patient's tissue and back across the other half of the neutral electrode: the generated electrical resis-
D Fig. 5.13. Measuring current at the divided neutral electrode tance is a dimension of the contact quality of the neutral electrode (D Fig. 5.13).
So the neutral electrode and thus the patient are always integrated in the monitoring of the REM system. The properties of the skin (hair growth, circulation, fat, temperature) differ in every patient, the personal limit value is ascertained individually for each patient and monitored during the entire operation (adaptive REM system).
The alignment of the neutral electrode to the site is irrelevant with this system, because an electronic feature ensures that the high-frequency current always flows symmetrically across the divided neutral electrode
The effectiveness of this safety system depends crucially on how the characteristics of its components interact. These are the inert resistance of the used neutral electrode and the used connection cable, and the resistance value of the patient's skin.
The electronic control unit of the REM system is ideally adapted to the corresponding neutral electrodes and connection cables.
5.2.3 The neutral electrode - Which, where, how?
In spite of all technical possibilities and different versions, there are a few general rules for using the neutral electrode.
4 Positioning as close as possible to the site:
This ensures that the procedure can be carried out with the lowest possible power setting, reducing the risk of alternative currents in the body. 4 Positioning on tissue with good circulation:
Tissue with good circulation has lower transition resistance, making it easier to close the current circuit: and lower power settings are required.
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