maxium® smart C Electrosurgery Unit with maxium® smart Beam
14
Revision 1
4.2
Monopolar application of HF current
In monopolar application, the HF current is
introduced into the operation field via an electrode
on an electrode handle or other instrument. This so-
called
active electrode
has a small surface. Thus at
the transition point from the electrode to the patient,
current density is high, resulting in the electrosurgical
effect desired by the user. From this contact point,
the current spreads radially. Its current density
decreases rapidly with increasing distance from the
contact point. This requires the anatomy of the
contact point to allow formation of a radial current
density distribution, also known as flow field.
For closing the circuit, the current delivered to the patient is collected again via an electrode applied to the
patient’s skin. This electrode has a large surface, so that the current density remains low and without
physiological effect. It is called the
neutral electrode
(NE).
Between the active electrode and the neutral electrode, the current flowing through the patient forms a
flow field, whose current density will at some distance from the contact point usually be so low that it
exerts no adverse effect. However, a living organism does not constitute a homogeneous mass: Bones and
cavities form insulating barriers, and the various tissue types exhibit differing electrical conductivities.
Unintended concentrations of the current density may result. This is why the anatomical features of the
operation field and its surroundings must be taken into account. Moreover, the current flowing through the
patient produces a voltage drop which may cause of a whole host of unwanted side-effects. For further
information, please refer to section 5 “Risk Minimization and Safety Measures”, page 17.
The HF generator for monopolar applications is activated optionally via foot switch or finger switch on the
surgical electrode handle.
4.2.1
Monopolar cutting
The high energy density on the surface of the active electrode leads to formation of a vapor layer between
electrode and tissue, in which the physical processes take place which lead to dissection of the tissue. With
specially designed electrodes, monopolar cutting, also known as electrotomy, allows shaping cuts which
cannot be achieved with knives. In addition to the cutting currents, there are also such as effect coagulation
simultaneously with the cutting and thus immediate hemostasis. The color yellow is used by convention for
the identification of the currents for cutting.
4.2.2
Monopolar coagulation
Basically, two types of coagulation are to be distinguished. If the HF current enters the tissue from the
active electrode, heating it, this is called
contact coagulation
. The intended use is to stop major
hemorrhages and denature tissue volumes.
Typical examples include hemostasis of bleeding from transected vessels by application of electricity
directly to a hemostat. Denaturation of larger tissue surfaces is also known as
ablation
, of major tissue
volumes as
desiccation
.
