Principles of Electrosurgery

Section: Endoscopy Curriculum: Curriculum, page 38

Diathermy

• High frequency (AC) current (200kHz)
  • NB low frequency <0.1MHz (NB domestic appliance current = 50Hz) stimulates nerves & muscles, so not used;
  • Heat depends on current
• Components:
  • Active electrode (tip)
  • Dispersive/return electrode (plate)
  • Generator to convert low to high frequency current

Monopolar

• Current passes in a circuit from the generator → active electrode = diathermy tip  → through the patient → to the diathermy pad = return electrode
  • Max heat at point of least cross-sectional area (eg tip)
• ground referenced; isolated
• coagulation = pulsed waveform, higher voltage
  • interrupted frequency waveform → produces less heat than a continuous sine wave
  • but enough heat to denature cellular protein → forms a coagulum = a protein-rich mixture that allows sealing of smaller blood vessels and control of local bleeding
• cutting = continuous wave form, lower voltage
  • continuous sine wave → produces intense heat
  • vaporizing water, exploding the cells = minimal coagulum production & so minimal hemostasis
  • most effective if held slightly away from tissue to create a spark
• blend: dampens down a portion of the cutting waveform, allowing for greater formation of a coagulum and therefore more control of local bleeding

Bipolar                  

• The active and return electrodes are in the hand piece, therefore current only flows through the surgical site between the electrodes; not through the patient
• Advantage in pts with pacemakers
• LigaSure – can deal with vessels up to 7mm, thermal spread less than traditional bipolar & thought to be comparable to ultrasonic shears

Complications:

o Fire § Especially with use of alcohol-based preps § Avoid pooling of prep o Insulation failure § May provide alternative exit path for current § If current density high enough then burning will occur o Inadvertent activation § Unintentional burns to patient of staff § Ensure sound is on and audible o Capacitive Coupling § When activated within laparoscopic ports § Electrostatic field generated and surrounding visceral burn § Only in metal ports, 5mm>10mm o Direct Coupling § Contact with other conductive instruments with damage to viscera in contact with other instrument § Metal, uninsulated only o Permanent Pacemaker function § Causes temporary inhibition, reset or thermal injury from elctrodes use Bipolar as doesn’t effect PPM o Return Plate burns § Poor contact between patient and return electrode § Prevention • Trim hair to improve contact • Apply to dry skin • Plate with large surface area • Don’t fold plate • As close to the operative site as possible and practicable • Large, well vascularized muscle mass • Avoid scars and boney prominences • Don’t apply over prostheses o Surgical Smoke § May contain noxious chemicals § Theoretical risk to staff with inhalation § Recommended use of suction devices where possible

• pacemakers:
  • modern pacemakers pause during diathermy (old ones fired → fibrillation)
  • but may still make the pacemaker fire or reset or cause thermal damage to the heart, via the electrode lead
  • Mx
    • plate as close to site of surgery as possible;
    • monitor patient, have a defibrillator
    • alternative: use ultrasonic scalpel (‘harmonic’)

Argon beam coagulation therapy

• uses a coaxial flow of argon gas to conduct monopolar current to the target tissue
  • the gas allows more accurate placement of the current flow
• can operate only in two modes: pinpoint coagulation or spray coagulation
• does not cut, even the most delicate tissue
• advantages
  • allows use of coagulation without contact of the electrode – therefore no buildup of eschar (eschar resistant to current)
  • ↓ smoke & odor
  • ↓ tissue damage, as the current is more accurately targeted
  • improves coagulation and ↓bleeding
• applications: eg liver surgery and endoscopy

Ultrasonic scalpels

• electrical current is converted to ultrasonic vibrations (at a frequency up to 55,500 cycles per sec) → produce cellular friction and denature proteins → form a coagulum, sealing blood vessels
• the coagulation occurs at a much lower temp (eg 50-100 oC), cf conventional diathermy (150-400 oC) → less lateral tissue damage, little eschar, less smoke
• disadvantage: cost
• no current passed through patient, therefore also safe for pacemakers