1. Kenny Low Dec 2009 Urology registrar Thursday teaching
Diathermy
Kenny Low
Dec 2009
Urology registrar Thursday teaching

2. Overview Electrical properties Mechanism of electrosurgery
Cutting versus coagulation
Return pad
Capacitors
Ligasure/Argon beam coagulators

3. Electrical terms
Voltage: potential difference providing force to push current through resistance
Current: flow of electrons during a period of time
Resistance: obstacle to current flow
Circuit: pathway for current flow

4. Mechanism of eletrosurgery
Frequency of current flow
Power point 50Hz (50 cycles/s)
Nerve and muscle stimulation – cease at 100kHz
Electrosurgery – frequency 200kHz + ( kHz) (allows current flow without stimulation of nerve and muscles)
Circuit (monopolar) – generator, active electrode (diathermy pen), patient, return electrode (diathermy pad)
Bipolar – active and return electrode between two tines of forceps

5. Cutting versus coagulation
Different waveforms create different tissue effects
Cutting current
Constant waveform
Heat produced quickly – vaporisation of tissue
Coagulation current
Intermittent waveform (“on” time reduced)
Less heat produced – coagulum rather than vaporisation
Higher voltages
Blends
Modification of on/off time
Blend 1 50/50 (on/off)
Blend 2 40/60
Blend 3 25/75
Coagulation 6/94
Cutting/fulguration/dessication
Cutting – spark, producing maximal current density
Fulguration – sparking with coagulation waveform, char and coagulum over wide area
Dessication – contact with tissue. Current density reduced by doing this – cell drying

6. Return pad
Vital to safety: completes the circuit to allow current back to ground
Current will always seek ground through the most conductive object – may not be the return pad
Problems
RF current division (part of current returns to ground through an alternative circuit). Leads to alternate site burns (e.g. ECG electrodes)
Solution: isolated systems – circuit must be completed by the generator

7. Return pad Pad site burns Problems: burn = current X time / area
Pad site needs sufficient area and conductivity to safely remove current without producing excess heat
Only difference between active electrode and return electrode is relative size and conductivity
Solution: Return electrode monitoring (REM)
Actively monitor impedence at pad site, direct relationship between impedence and pad site contact area
Seen with the split return pads (two separate areas – impendence current/a second circuit flows through return pad)

8. Dangers and Precautions
aim of diathermy safety should be to prevent mains voltage from entering the patient circuit
care with use on pedunculated structures
flammable anaesthetic gases – sparks prohibited within 25 cm of gases
electrocution
alcohol preps
gas accumulation within the bladder
poor plate to patient contact – thermoelectric burn

9. Dangers and Precautions
suboptimal effectiveness – do not increase power, check
faulty foot switch connection
faulty active electrode
poor plate / patient contact
cable problem
internal failure of the machine
incorrect solution
diathermy burns with earthed machine – ECG dots
noise activation
care with placement of plate and place as close as possible to operative site
all parts of cable insulated
avoid saline – conducts current and therefore no cutting effect
other OT equipment
metallic parts of light cables, video cameras are earth free and therefore safe
pacemakers
usually show little or no response to diathermy however 2 types may give rise to problems
the demand pacemaker
synchronous P wave pacemaker for heartblock

10. Minimal access surgery
Direct coupling – e.g. touching diathermy to forceps in open surgery, accidentally energising secondary instrument out of view
Insulation failures: sparks through insulation, worse with high voltages (i.e. high coagulation settings)
Capacitor: can occur when a two conductors are separated by a non conductor (e.g. metal electrode tip, insulation, metal cannula)
Current through electrode tip and induce current in metal cannula via electrostatic field
Plastic systems reduce capacitance but the patients body can act as the second conductor

11. Ligasure/ABC Ligasure
Bipolar technology – feedback response, reliable seal created for vessels up to 7mm
Initial resistance measured
Pulsed energy with continuous feedback
Ceased when tissue response complete
Said to have less thermal spread than conventional bipolar and comparable to ultrasonic coagulation
Comparable seal to sutures or clips (mechanical ligation)

12. Ligasure/ABC ABC (argon beam coagulation)
Argon – noble gas, heavier than air, cheap, non combustable
Ionises with radiofrequency energy
Provides a stream of electrical current to the tissues
Advantages
Less smoke
Non contact coagulation
Decreased blood loss, argon gas blows away blood at bleeding site
Less tissue damage
Flexible eschar