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Fig. 5.14. Burns under the neutral electrode the larger the neutral electrode, the smaller the current density.

Prescribed application arrangement? A prescribed application arrangement can restrict the possibilities of fixing the electrode. Neutral electrodes with integrated connection cable or clip-on connection lead?

A clip-on solution is usually less expensive, but in some indications (heart surgery, paediatric surgery) a clip should be avoided so as not to harm the patient through pressure necrosis

Fig. 5.14. Burns under the neutral electrode

5.2.4 Burns under the neutral electrode?

Unsuitable application points

The following application points or an application leading the current through these points should be avoided: 4 Bony structures:

They have a high electrical resistance. This could result in a higher power setting in the device. 4 Scar tissue:

This is also dry tissue with high resistance and therefore not suitable as an application point 4 Metal implants:

Metal implants in the body can be artificial hip joints, pacemakers or other conductive implants. Electric current has the physical property of seeking the way of least resistance, so it will prefer to flow across these particularly good conductors. There is then a risk that the current density and therefore energy density at the entrance or exit point is so high that internal burning is caused.

4 ECG electrodes, monitor leads, etc:

If a neutral electrode is placed on these similarly conductive materials, high-frequency current can overcome any existing insulation and couple into these conductors. Here again there is a risk that the current density and therefore energy density at the entrance or exit point is so high that internal burning is caused.

Considerations when choosing the neutral electrode

The following considerations should be included when selecting the individual neutral electrodes: 4 Gel or adhesive electrodes?

A gel electrode adapts to uneven parts of the skin and hair growth better than an adhesive electrode. Shaving is not usually necessary in top quality gel electrodes, thus avoiding the risk of micro-lesions. 4 Neutral electrode with small or large contact surface The task of the neutral electrode is to achieve the smallest current concentration possible, which means

Burns from high-frequency current under the neutral electrode: how do such burns occur, how can they be detected, and how can they be avoided?

A burn from high-frequency current is always generated when the current density is very large in a small point. The same electrosurgical effect is then caused at this point as at the »active« electrode, resulting in a tissue lesion in the form of a 3rd degree burn. In the case of intensive activation, the tissue continues to burn and the lesion spreads (O Fig. 5.14).

Possible causes for concentration of current under the neutral electrode

4 Contact surface is too small:

The neutral electrode has not been adhered completely or has worked partly loose during the operation. When reusable rubber neutral electrodes are being used, the contact surfaces can very quickly become inadequate or too small (tent formation, placed on body recesses or uneven areas of skin). 4 Good contact over a small area:

The neutral electrode is in contact across its complete surface, but parts of this contact surface have far better contact. This can happen if liquids flow under the neutral electrode, or when adhesive electrodes are applied with the fingertips and not pressed on with the full surface of the hand.

Today damage of this kind is caused only rarely because of the safety features integrated in high-frequency surgical devices. But in many cases, skin lesions are incorrectly said to be damage caused by high-frequency current (O Figs. 5.15 and 5.16):

These are changes to the skin consisting of reddening, blisters and flaky skin caused by the following factors:

4 Heat: e.g. warming mats, warming cushions, warm surroundings ... 4 Pressure, e.g. from the patient's own weight, poor positioning, the surgeon leaning on the patient .

Fig. 15. Skin lesions
Fig. 5.16. Skin lesions

Time: the entire time for the operation, also including the time for transporting and preparing the patient Chemicals, e.g. alcoholic cleaning and disinfectant, urine ...

Moisture, e.g. sweat, water, amniotic fluid ...

danger for the user, the patient and all staff working in the operating theatre.

User know-how. Most manufacturers of products for high-frequency surgery provide information on how the equipment functions and its correct use (e.g. courses, instructions, manuals, etc.). Every user (doctors, operating staff, medical technicians) should make himself familiar with the handling and possibilities of the HF surgery device being used; this is a mandatory requirement according to the Medical Product Owner Ordinance (MPBe-treibV) §§ 2.2, 2.4, 2.5 and § 5. In addition, offers for advanced training should be taken up in order to acquire basic knowledge about the procedures and techniques involved as well as operating the devices.

Power settings. High-frequency devices are often adjusted to very high power settings. These high power settings can then cause problems such as ECG artefacts or faults in the monitor. Apart from that, usually excessive amounts of tissue undergo necrosis with an unnecessary burden on the patient. The same effect can be produced at a lower power setting simply by the choice of electrode (change from knife electrode to needle electrode). The aim should always be to choose the lowest possible power setting to minimise the potential risks.

Choice of the right system. Which is the right system which will cause the least harm to the patient? The bipolar system has only a locally limited effect, but the high power setting required for some indications causes extensive damage to the tissue, which can be avoided when using the monopolar system with less power and a fine needle electrode.

Not all the above factors have to be present to cause such changes to the skin. Such skin lesions are not caused by the influence of high-frequency current.

It is important for the user to recognise which cause is involved in order to take the necessary measures.

5.3 Rules for safe use

5.3.1 General

According to the regulations of the Medical Product Law (MPG), high-frequency surgical devices are classified in class IIb. The classification is based on a risk analysis, and the risk potential posed by the use of high-frequency surgery is set on equal terms with the risks from radiotherapy equipment, lasers, anaesthetic equipment and respirators.

It is therefore vital for every user to know the rules for safe use of high-frequency surgery, to minimise the risk of

Choice of the right mode. Not every mode is ideally suited for every indication; the choice should depend on the indication. There is no point in choosing a fulguration or spray mode, i.e. non-contact coagulation, when working with the forceps coagulation system (contact coagulation). This can cause injuries to the surgeon from discharges through the gloves (7 see also: »Glove discharges«).

5.3.2 Use of high-frequency surgery in minimally invasive surgery

As far as minimally invasive surgery is concerned, the same rules naturally apply as for open use of HF surgery. But there are additional dangers involved because of the limited vision, the usually confined space available and the special instruments.

Insulation faults. Defect insulation of the active electrode can cause unwanted burns. Even only slightly damaged

Insulation faults

Risk of internal burning from high current density with damaged insulation

Fig. 5.17. Insulation faults

Risk of internal burning from high current density with damaged insulation instrument insulation (scratches, blisters, cracks ...) can puncture during an operation and cause serious injuries (O Fig. 5.17).

Direct coupling. Direct coupling refers to the contact of an active instrument with another conductive instrument, e.g. forceps, needle holder etc. Tissue contact by this instrument then inevitably causes unwanted damage (O Fig. 5.18).

Capacitive coupling. Two electrical conductors separated by insulation have the property of saving energy in an alternating current circuit. This kind of electrical element is called »capacitor«. A monopolar instrument (conductor), its insulation and a metal trocar (conductor) constitute this kind of energy accumulator. As long as the metal trocar has widespread contact with the abdominal wall, no energy can gather. But as soon as it becomes insulated from the patient by a plastic fixator (grip), this energy accumulator becomes charged and discharges its energy on contact with conductive structures (colon, mesenteri-um etc.), causing burns (O Fig. 5.19).

The following recommendations should be observed to reduce the risks for minimal invasive surgery. 4 Check the insulation of monopolar instruments thoroughly.

Replace instruments as soon as any signs of scratches, scores etc. can be seen or felt. Use disposable instruments.

4 Use low power settings.

The risk of injuring the patient decreases with lower power settings. 4 Avoid high-voltage modes as far as possible.

The high-voltage modes fulguration and spray should only be used specifically and deliberately, e.g. for fulguration of the liver bed during a cholecystectomy.

4 Only activate the instruments when in contact with the tissue.

This avoids charging any energy accumulators and unwanted »hot« contacts with other instruments. 4 Avoid bringing the active electrode into contact with or into the vicinity of other metal instruments. Alternative current paths via these instruments can be avoided in this way. 4 Use purely metal or purely plastic trocars. No capacity is generated.

5.3.3 Other information

Use of high-frequency surgery for pacemaker patients

The heart is a muscle which is not impaired in its functions or damaged by the flow of high-frequency current.

Fig. 5.17. Insulation faults

Direct coupling

Field of vision

Active electrode

Risk of burns from direct contact with a metal instrument

Fig. 5.18. Direct coupling

Capacitive coupling m

Plastic

Risk of burns from capacitive coupling to metal and a non-conductive plastic sleeve. Recommendation: use metal sleeves

Active electrode

Fig. 5.19. Capacitive coupling

However, if a pacemaker probe is implanted in the heart, a current can easily couple into this conductive probe. A burn can then be caused at the exit point in the heart muscle as a result of the high current density at the tip of the probe (small surface). The pacemaker is not hindered in its internal settings and functions, but the necrotised tissue in the heart cannot stimulate an emitted pulse.

The recommendations for using high-frequency surgery in pacemaker patients are as follows:

4 The safest solution is not to use electrosurgery at all, but this is not always practicable. 4 The current flow is limited locally in the bipolar system.

4 When using the monopolar system, avoid an obvious flow of current across the pacemaker, probe and heart muscle. 4 Use a low power setting.

4 Consult the recommendations issued by the pacemaker manufacturer.

Use with inflammable gases and substances

The use of high-frequency surgery generates sparks. But these sparks are also capable of igniting flammable and explosive gases and vapours. Care is required when opening hollow organs (e.g. colon, oesophagus) and in the presence of alcoholic disinfectants.

Glove discharges

The glove discharge is usually a painful effect. This refers to the destruction of the surgeon's glove by a high-energy spark during coagulation using forceps (contact coagulation (O Fig. 5.20).

There are several reasons for this discharge: On the one hand, if the power setting is too high, this can cause discharge through the glove. On the other hand, the quality of the glove always plays a role.

But the cause is normally to be found in using the wrong technique.

If the fulguration or spray mode has been selected on a high-powered high-frequency surgery device but the user then proceeds with contact coagulation using forceps, the tissue around the forceps dries out and forms a high electrical resistance. The high-frequency current then looks for an alternative path by using the lower resistance of the glove and closes the circuit across the surgeon who is in contact with the patient and thus with the neutral electrode. This effect is provoked all the more if the electrode handle was already activated before contact with the forceps or the forceps are already carbonised.

The remedy is to reduce the power, adjust the desiccation mode, not to use carbonised instruments and not to activate the electrode handle until the first contact with the forceps.

Wiring

A wound up cable gives a tidy impression, but also constitutes a risk. Winding the cable creates an electromagnetic coil - a transformer - which generates a magnetic field and another current circuit. If the wound cable is then fixed with a metal clip (towel clip) this reinforces the effect even further (O Fig. 5.21).

If the towel clip touches the patient, this can cause burns. The cable should therefore be laid out on the floor to its full length. If cables are routed parallel to each other, electrical energy can couple into the other cable and cause interference (e.g. artefacts in the ECG monitor).

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