Electrosurgery

Goals:

• Limited thermal damage to target tissue only
• Adequate haemostasis
• Tissue cutting/vaporisation/transection

Theory:

• Current = flow of electrons per time (amperes)
• Voltage = force pushing current through the resistance (volts)
• Impedance/resistance = obstacle to the flow of current, measured in ohms
  • Impedance and resistance are essentially the same - impedance is for AC circuits, while resistance is for DC circuits. I suspect any difference between them is beyond the scope of what surgeons need to know.
• Technically, we almost always use electrosurgery (AC) as opposed to electrocautery (DC). In AC circuits, the patient is included in the circuit.

Tissue manipulation:

• Cut = continuous waveform which produces heat rapidly and vaporises tissue
  • Hold electrode slightly away from tissue to focus heat
• Blend 1-3: progressive decrease in the 'duty cycle' length, causing a gradual change from cut to coag. Blend 1 is close to 'cut', while blend 3 is close to 'coag'.
• Coag = higher voltage, shorter bursts. Produces a coagulum instead of vaporising.
• The only variable which determines whether one waveform vaporises tissue and another produces a coagulum, is the rate at which heat is produced.
• Dessication occurs when the instrument is held directly against a vessel - lower temp, dries and denatures and forms thrombus. Note that this is normally achieved using a forceps.
• Fulguration - superficial coagulation over a wide area - achieved by applying energy without making tissue contact
• Electrovaporisation
  • E.g. Prostate ablation

Monopolar:

• Alternating current utilising a completed circuit from the instrument, through the patient, to the return electrode, to the machine, and back to the instrument
• Impedance causes heating. Impedance increases with resistance (impedance is technically resistance plus reactance in AC circuits - I am using impedance in this topic)
  • Impedance can be increased by removing fluid, compressing arteries or putting tissue under tension.
    • Fluid conducts, and so reduces impedance, and since heat produced is proportional to impedance - fluid prevents heating
  • Increasing the length of time also obviously increases thermal change
  • Hence the mnemonic of how to increase thermal change at a point:
    • A - first decrease the AREA of contact
      • Pad is high area, low impedance, low current = low heating
      • Electrode is low area, high impedance, high current = intense heating
    • R - second increase tissue RESISTANCE/IMPEDANCE
    • T - third increase TIME
    • Current/wattage can also be increased, but this should come last - it increases the risk of unwanted thermal change
• Risk of electrocution is low when AC < 100khZ is used. Monopolar is higher frequency (300-3800kHz)
• Selecting wattage
  • Should be as low as possible to accomplish the task
  • 20W is low - forces you to use the ART acronym
  • Be aware that carbonisation occurs at 200-400 degrees - this should be avoided where possible - hallmark of non-refined technique

Bipolar (allows the application of both electrodes on the target tissue):

• Tissue sealing and haemostasis is achieved by compression of tissue and local delivery of RF energy, resulting in thermal change
• Compression is important - prevents continued flow of blood, which can act as a heat-sink. Don't compress too much, or the tissue will be bypassed.
• Safer on pedicled structures
• Minimal tissue damage
• No possibility of return electrode burns/alternate site burns/capacitive coupling/insulation failure
• Can get stuck to coagulated tissue - one option is to reactivate underwater, which can create steam and often dislodge, rather than just pulling off

Ligasure

• Maryland - available 23, 37 and 44cm
• Blunt tip - 23, 37, 44cm
• Curved small jaw open sealer/divider (I think this is the open one for thyroids)

Argon beam coagulation:

• Spray ionised argon onto surface and it causes coagulation and fulgaration as it is sprayed onto surface
• Blows away blood and fluid as it applies to surface
• Thinner, more flexible eschar
• Good in radiation proctitis bleeding for example
• Be aware - instillation of gas into a closed cavity can increase pressure - should leave a port open
• Risk of gas instillation into open vein - air embolism

Hazards:

• Hazards to patient
  • Hazards with careless use
    • Narrow pedicles can create higher current densities = ischaemia
      • Avoid by using bipolar instead of monopolar
    • Ignition - alcohol, anaesthetic gases, manitol, bowel prep
    • Inadvertent activation
    • Activation of PPM
      • Use magnet
      • Avoid monopolar
    • Internal defibrillators should be deactivated prior to OT and reactivated after
    • Direct coupling
      • Don't activate close to other laparoscopic instruments
      • Be very careful around staple lines or other small bits of metal
      • Be aware of arcing - may represent subtle failure of insulation
  • Hazards with careful use
    • Return plate burns
      • Surface area reduced - excessive hair, adipose tissue, bony prominences, fluid invasion, adhesive failure, scar tissure
      • For best results, choose a well-vascularised muscle mass, close to operative site
    • Neuromuscular stimulation
    • Insulation failure
    • Capacitive coupling
• Hazards to operative staff
  • Noxious gases
  • Burns

If not working

• Check all connections
• Patient/plate contact
• Generator settings
• Replace probe
• Replace machine