Diathermy

1. 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 + (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

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