Download Diathermy

Principles of Electrosurgery



ElectrosurgeryDiathermy is the use of high density radio frequency
electric current to produce heat
Electrocautery refers to direct current (electrons flowing in one direction)
whereas electrosurgery uses alternating current.
During electrocautery, current does not enter the patient’s body. Only
the heated wire comes in contact with tissue. In electrosurgery, the
patient is included in the circuit and current enters the patient’s body.
Electrosurgery












Used to either cut or destroy tissue or to produce coagulation
Mains electricity is 50-60 Hz but this produces intense muscle and
nerve activation
Nerve and muscle stimulation cease at 100,000 cycles/second (100
kHz)
Electrical frequency used by diathermy is in the range of 300 kHz to 3
MHz (radio frequencies)
Circuit consists of
1. electrosurgical generator - source of the electron flow and voltage.
2. active electrode
3. patient
4. patient return electrode (indifferent electrode).
Pathways to ground are numerous but may include the OR table,
stirrups, staff members, and equipment.
With newer isolated electrosurgical systems - electrosurgical current
from isolated generators will not recognize grounded objects as
pathways to complete the circuit. Isolated electrosurgical energy
recognizes the patient return electrode as the preferred pathway back
to the generator.
Machines do this by measuring impendence at the indifference
electrode.
The patient’s tissue provides the impedance, producing heat as the
electrons overcome the impedance.
The only difference between the “active” electrode and the patient
return electrode is their size and relative conductivity.
To minimise risk:
1. ensure large pad placed over tissues of low impendence as close
as possible (well vascularised muscle mass)
2. good contact
3. use lowest currents
The function of the patient return electrode is to remove current from
the patient safely. A return electrode burn occurs when the heat
produced, over time, is not safely dissipated by the size or conductivity
of the patient return electrode.
Monopolar diathermy





Electrical plate is placed on patient and acts as indifferent electrode
Current passes between instrument and indifferent electrode
As surface area of instrument is an order of magnitude less than that of
the plate - The only difference between the “active” electrode and the
patient return electrode is their size and relative conductivity.
Localised heating is produced at tip of instrument
Minimal heating effect produced at indifferent electrode
Bipolar diathermy


Two electrodes are combined in the instrument (e.g. forceps)
Current passes between tips and not through patient
Effects of diathermy





The only variable that determines whether one waveform vaporizes
tissue and another produces a coagulum is the rate at which heat is
produced. High heat produced rapidly causes vaporization. Low heat
produced more slowly creates a coagulum.
Heating effect depends on:
1. the current intensity
2. wave-form used
3. size of electrode - The smaller the electrode, the higher the current
concentration
4. duration activated
5. tissue – eschar have more resistance to current
6. distance from tissue – sparking vs direct contact
 sparking gives more cutting
Coagulation
1. Produced by interrupted pulses of current (50-100 per
second) – less heat
2. Square wave-form
3. Uses higher voltages thus more thermal spread
Cutting
1. Produced by continuous current – produces heat rapidly
2. Sinus wave-form
3. Uses lower voltages – less thermal spread
Blend
1. A “blended current” is not a mixture of both cutting and
coagulation current but rather a modification of the duty
cycle. As you go from Blend 1 to Blend 3 the duty cycle is
progressively reduced. A lower duty cycle produces less
heat. Consequently, Blend 1 is able to vaporize tissue with
minimal hemostasis whereas Blend 3 is less effective at
cutting but has maximum hemostasis.
Risk and complications





Can interfere with pacemaker function
Arcing can occur
1. direct coupling - with metal instruments and implants
2. insulation failure
3. capacitance coupling – occurs when 2 conductors separated by a
insulator discharges current into surrounding tissues. (endoscopic
diathermy)
Superficial burns if use spirit based skin preparation
Diathermy burns under indifferent electrode
Channeling effects if used on viscus with narrow pedicle (e.g. penis or
testis)
Lower Risks by:
* Inspect insulation carefully
* Use lowest possible power setting
* Use a low voltage waveform (cut)
* Use brief intermittent activation vs. prolonged activation
* Do not activate in open circuit
* Do not activate in close proximity or direct contact with another instrument
* Use bipolar electrosurgery when appropriate
* Select an all metal cannula system as the safest choice. Do not use hybrid
cannula systems that mix metal with plastic.
* Utilize available technology, such as a tissue response generator to reduce
capacitive coupling or an active electrode monitoring system, to eliminate concerns
about insulation failure and capacitive coupling.
* should not be used in the presence of flammable agents (i.e., alcohol and/or
tincturebased agents)”
*avoid oxygen rish environments
* The active electrode(s) should be placed in a clean, dry, well-insulated safety
holster, when not in use.
* Cords not be wrapped around metal instruments
Surgical smoke
Surgical smoke is created when tissue is heated and cellular fluid is vaporized by
the thermal action of an energy source.
smoke from electrosurgery is similar in content to that produced by a surgical laser.
Viral DNA, bacteria, carcinogens, and irritants are known to be present in
electrosurgical smoke.
Universal precautions indicate a smoke evacuation system should be used.
NIOSH (the National Institute of Occupational Safety and Health) and the CDC
(Center for Disease Control) have also studied electrosurgical smoke at length.
They state:
“Research studies have confirmed that this smoke plume can contain toxic gases
and vapors such as benzene, hydrogen cyanide, and formaldehyde, bioaerosols,
dead and live cellular material (including blood fragments), and viruses.”
Bibliography
Aigner N, Fialko C, Fritz A, Winks O, Zoch G. Complications in the use of
diathermy. Burns 1997; 23: 256-264.
http://www.valleylab.com/