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Diathermy
Kenny Low
Dec 2009
Urology registrar Thursday
teaching
Overview
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Electrical properties
Mechanism of electrosurgery
Cutting versus coagulation
Return pad
Capacitors
Ligasure/Argon beam coagulators
Electrical terms
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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
Mechanism of eletrosurgery
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Frequency of current flow
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Power point 50Hz (50 cycles/s)
Nerve and muscle stimulation – cease at 100kHz
Electrosurgery – frequency 200kHz + (300-3000kHz)
(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
Cutting versus coagulation
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Different waveforms create different tissue effects
Cutting current
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Coagulation current
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Intermittent waveform (“on” time reduced)
Less heat produced – coagulum rather than vaporisation
Higher voltages
Blends
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Constant waveform
Heat produced quickly – vaporisation of tissue
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
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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
Return pad
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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
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Problems
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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
Return pad
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Pad site burns
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Problems: burn = current X time / area
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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)
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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)
Dangers and Precautions
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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
Dangers and Precautions
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suboptimal effectiveness – do not increase power, check
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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
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the demand pacemaker
synchronous P wave pacemaker for heartblock
Minimal access surgery
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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)
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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
Ligasure/ABC
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Ligasure
Bipolar technology – feedback response,
reliable seal created for vessels up to 7mm
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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)
Ligasure/ABC
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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
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Less smoke
Non contact coagulation
Decreased blood loss, argon gas blows away blood
at bleeding site
Less tissue damage
Flexible eschar