What is HF surgery?
In high-frequency surgery, alternating current in combination with high frequency is guided through the body. Tissue is specifically damaged or cut. In contrast to a cut with a normal scalpel, the bleeding is also breastfed in HF surgery, since affected vessels can be closed equally.
Application techniques of HF surgery
Monopolar technology
Monopolar technology is the most frequently used technology. One of the poles (neutral electrode) of the high -frequency voltage source is connected to the patient via an area as large as possible. The surgical instrument is the other pole (active electrode). The electricity flows via the active electrode via the path of the lowest resistance to the neutral electrode. The power density is highest in the near future of the active electrode. The thermal effect is the most here. With the square of the distance, the electricity density also decreases. In order to prevent burns and keep the power density in the body low, the electrode should be as large as possible. Due to the large area of the neutral electrode, the skin below is not noticeably heated. To prevent burns, the correct positioning of the neutral electrode is decisive.
Bipolar technology
In the case of bipolar application technology, the current only flows through the part of the body in which the surgical process (cut or coagulation) takes place. Two isolated electrodes are led directly to the area to be operated on. The HF voltage lies between the electrodes. The circuit is closed over the fabric in between. The thermal effect takes place in the tissue between the two electrodes. In contrast to the monopolar technology, the path of the current flow is exactly evident here. In addition, only about 20 - 30 % of the performance of monopolar technology is required. The surrounding tissue also remains undamaged and the measuring devices on the patient are not disturbed. The bipolar application technology is used particularly in critical, precise applications. These include micro, neuro and ENT surgery.
What is the frequency range in HF surgery?
In a frequency range between 300 kHz and 2000 kHz, HF surgery is used. To prevent Faradaysation (disturbing muscle twitching), the frequency range must be over 300 kHz. However, Faraday irritation can also arise in a company frequency. Therefore, capacitors (under 2500 Pf) are built into the circuit with a low capacity. However, muscle twitches cannot be completely excluded. The upper limit of 2000 kHz was determined to avoid hurtful burns on the patient.
HF generators and how they work
HF generators have a maximum output of 400 W. In a transistorized surgical winner, the oscillator controls the power amplifier over a driver level with a frequency of approx. 700 kHz. In the case of superficial coagulation, the oscillator is scanned with approx. 20 kHz and in a ratio of 1: 5. Two separate controllers set the operating voltage of the driver level and the cutting performance. The power amplifier has several parallel powered performance transistors that work in switching operation. This enables good efficiency. The secondary circuit of the power amplifier transformer leads to the connection of the electrode (active or neutral) via filter capacitors. The neutral electrode can either be grounded directly or capacitive or operated electrically. Thanks to the patient protection circuit, the generator only works with a connected N.Eutral electrode. An acoustic alarm indicates an interruption of the supply line.
