3 Description
BOWA-IFU-11779-ARC400-V2.1.0-S0-EN Operating Manual ARC 400 29
3.6. The basis of modern HF surgery
Depending on its nature, value and frequency, the action of electrical
current on tissue may be described as electrolytic (destructive), faradic
(stimulating muscles and nerves) or thermal. HF surgery is based on
alternating currents with a frequency of at least 200 kHz, with the thermal
effect dominating. Its effect is primarily dependent on the time for which the
tissue is exposed to the current, the current density and the specific
resistance of the tissue, which on the whole falls with increasing water
content or increasing blood circulation. In practice, it is also necessary to
consider that portion of current which flows past the target tissue and can
heat up and damage other regions (such as during irrigation, seen more
with monopolar techniques than with bipolar ones).
Monopolar Method
Monopolar HF surgery deploys a closed current circuit in which current
flows from the active electrode of the instrument through the patient to a
neutral electrode with a large surface area and then back to the generator.
The contact area between the tip of the monopolar instrument and the
tissue is small so that the highest current density of the current circuit is
seen here, and brings about the desired thermal action.
Localized heat build-up is reduced to a minimum through the large surface
area and the special design of the neutral electrode.
Bipolar Method
With bipolar HF surgery two active electrodes are integrated into the
instrument and current flow is restricted to the tissue between the two
electrodes rather than the entire body of the patient.
No neutral electrode is therefore required.
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