maxium® smart C Electrosurgery Unit with maxium® smart Beam
20
Revision 1
To prevent high current densities by leakage currents to other medical devices, note the following:
•
When simultaneously using electrosurgery and monitors on the same patient, use only such systems
where possible leakage currents are reduced to non-hazardous strength by constructive measures, e.g.
ECG monitors whose leads comprise protective resistors or HF reactors.
Do not use needle electrodes for monitoring – their low surface and resulting high current density are a
source of trouble.
Use the active electrode only at a distance of at least 15 cm from any ECG electrodes.
•
Non-electrical medical units such as infusion cannulae or trocars may also cause a high density of
leakage currents if they have an electrically conductive connection to the ground. Such a connection
can also be formed by electrolytes such as sodium chloride solution.
5.2
Risks from Current Concentration
In the schematic representation of the flow of the current through the patient given in section 4.2
“Monopolar application of HF current”, page 14, the current density (field line density) of the HF current
entering the patient from the active electrode seems to decrease very quickly from the contact point of the
active electrode, the HF current then flowing to the neutral electrode at low current density. In fact, the
human body is an anatomically complex structure whose electrical conductivity is not homogeneous but
heavily structured by anatomical features. As a result, locally the flow field may deviate strongly from the
schematic diagram in section 4.2 “Monopolar application of HF current”, page 14. There is a risk of burns
whenever due to the anatomical features of the operating field the currents either cannot dissipate or
condense again. Basically, according to the nature of the danger two types of current condensations are to
be distinguished here:
•
Current condensation in the area of the neutral electrode
•
Current condensation inside the body
Experience has shown that most incidents in connection with the use of electrosurgery result from this
issue.
5.2.1
Current condensation in the area of the neutral electrode
Areas with low electrical conductivity in relation to
the rest of the body and immediately under the
neutral electrode can extremely distort the flow field
by casting a “shadow” within the flow field.
The neutral electrode is then no longer able to
absorb the power evenly over its entire surface.
Areas of higher current density result, with a risk of
burns.
