GIMA SpA
DIATERMO MB250 – DIATERMO MB400
MA303IGBa-19-03-2007 Manuale
d’Istruzioni / Instruction’s Manual
32
The high frequency used by electrosurgical needle, don’t allow to the electromagnetic field to penetrate deeply in the matter
and so the current crosses the conductor mostly in the external surface, reduces in a exponential way and becames negligible in
the center of the conductor section. This effect, called ‘skin-effect’cause a reduction of the useful section for the current
passage, an increase of the electrical resistance and becomes an important problem in the neutral electrode. Infact in this
electrode the current density is very high (KA/m
2
) on the edge, where the excessive increase of temperature by Joule effect
causes burns for the patient.
So it isn’t accidental that the burns for the patient, during the electrosurgical interventations, have the shape of the edge neutral
electrode. To reduce the burns risk have to dose opportunally the supply power (I
2
·
t) and to follow the rules for the application
of the neutral electrode on the patient (see cap. SAFETY).
2) Faradic Effect
The pulsed current causes the neuro-muscular stimulation, originated by stimulation of physiologic process of ionic exchange,
responsible of the transmission of stimulus that cause muscular spasms and cardiac symptoms of extrasystole and ventricular
fibrillation.
The effect of these stimulus is known like faradic effect and it is expressed by:
R= I /
√
F
The physiologic system of stimulus transmission follows a limit curve in which the pulsed currents or by low frequency
produce an impulse of stimulation. By alternating current in high frequency (higher than 200 kHz), used in the electrosurgical
needle, don’t have neuro-muscular reactions (the change of polarity is so fast that the patient doesn’t have consequences at a
level of the neuro-muscular reactions), and there isn’t an electrolytic damage of the organism. For this reason all the
equipments generator of the high frequency for surgical use (electrosurgical needle) work on base frequencies higher than
300kHz so that they don’t produce electric stimulation.
3) Electrolytic Effect
The use of high frequency currents reduces the electrolytic effect (ionic division) in the tissues, caused by the shortest period of
unidirectional conduction of the current.
