In HF surgery, the desired thermal effect is produced by the flow of the current in the tissue itself (endogenous tissue heating). This has a range of different tissue effects in the patient’s tissue. In cautery, the tissue is heated from the outside (exogenously); it is only used for superficial haemostasis. Cutting tissue as in high-frequency technology is not possible with a cauter.

HF surgery enables stress-free cutting combined with simultaneous haemostasis of the tissue. It is an effective instrument for open surgical procedures as well as minimally invasive applications. Cutting and coagulation with high-frequency current is the gold standard in state-of-the-art surgery.

In HF surgery, an instrument passes a high-frequency alternating current through the tissue between two electrodes. By activating the HF instrument, the high-frequency alternating current generates heat in the tissue for the desired surgical tissue effects.

Electrosurgical cutting and electrosurgical coagulation.

Cutting: Vaporisation of intra- and extracellular fluid and destruction of cell membranes, resulting in a surgical incision.
Coagulation: Vaporisation of intra- and extracellular fluid without the destruction of cell structures. This leads to tissue shrinkage, seals the vessels and stops the bleeding, i.e. haemostasis. Coagulation normally uses voltages below 200 V while higher voltages are used for cutting.

In electrosurgery, alternating currents with a frequency of over 200,000 Hz (200 kHz) are used. This frequency range does not result in neuromuscular irritation.

The generator transforms low-frequency mains current into high-frequency alternating current (AC). The generator provides surgeons with the type of current required by HF instruments to achieve the desired tissue effect.

The yellow switch on the handle and the foot pedal activates the cutting current, whereas the blue switch activates the coagulating current. This colour code is an international standard.

In monopolar HF surgery, current flows from the active electrode through the tissue to the neutral electrode. In bipolar HF surgery, two active (and usually equal) electrodes are integrated into the instrument. Current only flows in the specific tissue region grasped between the two electrodes. A neutral electrode is therefore not required.

Key factors to achieve the desired tissue effects include:

• Tissue impedance
• Electrode geometry (current density)
• Amount of energy introduced
• Application duration
• Type of current applied

• Homogeneous surface coagulation with limited penetration depth
• Contactless procedure results in no tissue sticking to the electrode
• Low smoke production, i.e. better view of the operating field

Bipolar vessel sealing can be used to seal vessels up to 7 mm. The sealing cycle is controlled by the generator and sealing mode. An autostop signal automatically ends the process. Using this vessel sealing technology reduces the need for clips and ligatures.

Neutral electrodes are designed to close the current circuit between the patient and the HF generator. Neutral electrodes are only required in monopolar technique.

Neutral electrodes are attached to the patient's skin over a large area and without wrinkles. Where possible, depending on the location of the surgical site, place the neutral electrode on the nearest upper thigh or upper arm. Always make sure to keep a minimum distance of 20 cm between electrode and surgical site. The path of the current must not pass through the heart!

To minimise current density and, thus, local heating. This prevents any risk of thermal lesions on the surface of the skin.