Principles of electro- and laser surgery

The use of electrosurgery in hysteroscopy dates back to the 1970s, when tubal cauterization was used for sterilization. In hysteroscopy, high-frequency electrosurgery provides hemostasis and tissue dissection simultaneously. The first report of electrocoagulation in hysteroscopy appeared in 1976, when Neuwirth and Amin used a modified urologic resectoscope to remove a submucous myomatous node.

The main difference between electrosurgery and electrocautery and endothermy is the passage of high-frequency current through the patient's body. The latter two methods are based on the contact transfer of thermal energy to tissue from any heated conductor or thermal unit; there is no directed movement of electrons through tissue, as in electrosurgery.

Mechanism of electrosurgical action on tissues

The passage of high-frequency current through tissue results in the release of thermal energy.

Heat is released in the section of the electric circuit that has the smallest diameter and, therefore, the highest current density. The same law applies as when you turn on a light bulb. The thin tungsten filament heats up and releases light energy. In electrosurgery, this occurs in the section of the circuit that has a smaller diameter and greater resistance, i.e., where the surgeon's electrode touches the tissue. Heat is not released in the patient's plate area, since its large area causes dispersion and low energy density.

The smaller the electrode diameter, the faster it heats the tissues adjacent to the electrode due to their smaller volume. Therefore, cutting is most effective and least traumatic when using needle electrodes.

There are two main types of electrosurgical effects on tissue: cutting and coagulation.

Various forms of electric current are used for cutting and coagulation. In the cutting mode, continuous alternating current with low voltage is supplied. The details of the cutting mechanism are not completely clear. Probably, under the influence of the current, there is a continuous movement of ions inside the cell, which leads to a sharp increase in temperature and evaporation of intracellular fluid. An explosion occurs, the cell volume instantly increases, the membrane bursts, and the tissues are destroyed. We perceive this process as cutting. The released gases dissipate heat, which prevents overheating of deeper tissue layers. Therefore, the tissues are dissected with a small lateral temperature transfer and a minimal necrosis zone. The scab of the wound surface is negligible. Due to superficial coagulation, the hemostatic effect in this mode is insignificant.

A completely different form of electric current is used in the coagulation mode. This is a pulsed alternating current with high voltage. A surge of electrical activity is observed, followed by a gradual attenuation of the sinusoidal wave. The electrosurgical generator (ESG) supplies voltage only for 6% of the time. In the interval, the device does not produce energy, the tissues cool down. The tissues are not heated as quickly as during cutting. A short surge of high voltage leads to devascularization of the tissue, but not to evaporation, as in the case of cutting. During the pause, the cells are dried out. By the time of the next electrical peak, the dry cells have increased resistance, leading to greater heat dissipation and further deeper drying of the tissue. This ensures minimal dissection with maximum penetration of energy into the depth of the tissue, denaturation of protein and formation of blood clots in the vessels. Thus, the ESG implements coagulation and hemostasis. As the tissue dries, its resistance increases until the flow practically stops. This effect is achieved by direct contact of the electrode with the tissue. The affected area is small in area, but significant in depth.

To achieve simultaneous cutting and coagulation, a mixed mode is used. Mixed flows are formed at a voltage greater than in the cutting mode, but less than in the coagulation mode. The mixed mode ensures drying of adjacent tissues (coagulation) with simultaneous cutting. Modern ECGs have several mixed modes with different ratios of both effects.

The only variable that determines the division of the function of different waves (one wave cuts, and the other coagulates the tissue) is the amount of heat produced. Large heat released quickly produces cutting, i.e., evaporation of tissue. Small heat released slowly produces coagulation, i.e., drying.

Bipolar systems operate only in coagulation mode. The tissue between the electrodes is dehydrated as the temperature increases. They use constant low voltage.