maxium® smart C Electrosurgery Unit with maxium® smart Beam
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Revision 1
5.1.1
Patient shunts
The spatial separation of operation field and neutral
electrode causes a very extensive flow field to be
formed. Here the currents do not necessarily all have
to flow within the body. They may exit the body and
re-enter it in another place before reaching the
neutral electrode. Depending on where the neutral
electrode is applied, such transitions may occur from
the body to a conductive surface (operating table),
from limbs to trunk or from one limb to another.
If any contact point where the current leaves or
enters the body is very small or poorly conductive
(e.g., small finger on the thigh or on the operating
table), then the current passing over may cause burns
there.
The decisive factor for burns by HF current is the current density (current per area).
The risk of burns is particularly high where high-power monopolar cutting and contact coagulation currents
are used, while it is very low in purely bipolar application.
5.1.2
High-frequency leakage currents
Wherever a circuit conducts high AC voltage against
the ground, power may “leak”, which is why this type
of currents is also commonly known as leakage
currents.
For an electrosurgery unit, that means that a small
portion of the power fed into the patient by the
active electrode will not flow back to the neutral
electrode but rather be dissipated to the ground,
whence it finds its way back to the generator via the
mains cable or the bonding connection.
These currents are usually distributed over a large
area; their current density is low and their physio-
logical effect insignificant (unlike the interference
effect on other electromedical units).
This changes when such leakage currents are absorbed by the patient in concentrated form via a conduc-
tive connection to the ground. If the area for transition from the patient to this ground connection is small
enough, then burns may result. Such a transition may also be formed between the patient and the user or a
member of his team which is also grounded.
