electrosurgery

Question 1

What happens to tissues when a current passes through?

Answer 1

• when a current passes through tissues a heating effect occurs
• amount of heat depends on resistance of tissue and density of current
  
  • the more current the higher the tissue heating effect
• An individual cell is irreversibly damaged when heated to above 45^oC (denaturation)
• Coagulation of the proteins occurs ~70^oC (visualised as blanching of tissues) - adequate for coagulation!!
• ~100⁰C intracellular water boils- tissues bubble + steam escapes s individual cells vapourise (remaining proteins become sticky-> walls of blood vessed firmly approximated
• When temp rises further residual tissue carbonised-> charred

Question 2

How to modify the current to produce different clinical effects?

Answer 2

• by either changing the waveform of the current or by changing the shape and hence current density of electrode used
• Cutting effect: narrow band of high density current focused on tissue will completely vapourise it
  
  • fine pointed electrode held just above tissue
  • cutting diathermy needle
  • cutting current: simple continuous sinusoidal waveform. Current flows continuously aka unmodulated current
  • ie high current low voltage continuous waveform
• Coagulation effect: current is delivered through a broad electrode in firm contact with tissue. Heat is rapidly dissipated through wide area of tissue limiting peak tissue temperature.
  
  • coagulation current : sinusoidal waveform is non continuous aka modulated current
  • as total energy remains the same interrupting current increases the voltage
  • pulses of current alternate with periods of no-flow which provides a heating effect and coagulation of blood vesssels.
  • higher voltages- deeper heating and greater coagulation effect. Also the greater the haemostatic effecr the more associated collateral damage, more smoker and more necrosis

Question 3

What is monopolar diathermy?

Answer 3

• A small sized active electrode produces heat at operating site.
• Electricity is returned to generator by passing through patient and being dispersed by a much larger return electrode placed on patients skin (thigh in gynae as return electrode should be as close to primary electrode as possible)

Question 4

What is bipolar diathermy?

Answer 4

• the primary and return electrode are the two blades of the forceps which are electrically insulated from each other
• Current passes through the two electrodes localised heating of tissue held between device blades
• no return electrode plate required, less risk of burns at sites distant from electrode
• as this method needs intimate contact between electrodes and tissues clinical effect = coagulation
• electrodes are fairly large, time required to heat is significant -> patience. If turn up power, will increase local heat and char tissue (rather than dissication- blanching and bubbling), increases impedece, preventing further penetration of heating effect
• ie good dissication white and unsatisfactory one looks black

Question 5

compare house current and surgical current

Answer 5

• House current
  
  • Low frequency 50Hz (50 oscillations/sec)
  • produces profound muscle stimulation and cardiac arrest. As current stimulates nerves causing depolarisation of NMJ. Continuous current prevents repolarisation therefore paralysis and cradiac arrect
  • Alternating current
• Surgical current
  
  • High frequency: 200kHz- 3.3MHz (1,000,000 times higher than household current)
  • neuromuscluar stimulation is lost above 100Hz and current can pass through tissue without producing such effects (as cannot pass through NMJ)
  • Alternating current at various voltages (200-10,000V)

Question 6

What are the risks of electrosurgical energy?

Answer 6

1. Monopolar electrode has 3 sites of potential damge
   
   1. active electrode
      
      • if activated at other than intended site will cause tissue damage (store in insulated holder not on pts abdomen, always have in site in abdo)
   2. current diversion
      
      • electrical energy always finds path of least resistance to earth
      • old machines had leakage of energy via electrodes, down metal drip pole etc -> burn of skin. New machines generators are isolated and all energy leacing is measured and all must return or alarm
   3. return electrode
      
      • if poorly applied/partially detached return electrode -> heating and burns
        
        • split plate technology improves/ resolves this:return electrode divided into two halves and these halves are separately connected to generator. interrogation current sent across the two halves to measure impedance. if plate partially detraches impedance increases and alarm sounds
      • if pt has unilateral artifical hip, place return electrode on opposite thigh. If bilateral artificial hips then return electrode on patients back.
      • avoid placing return electrode over scar or bong prominence
      • if has cardiac pacemaker, avoid monopolar diathermy
2. additional problems with use of electricity in laparoscopy
   
   1. capacitative coupling coupling
      
      • effect of introducing electricity via cannula
      • when two conductors are separated by insulator- capacitor is created: innulated active electrode within a metal cannula forms capacitor, which can produce a ‘capacitively coupled’ electrical current that is transferred from active electrode through intact insulation to metal cannula. Should the cannula come into contact with tissue, current is discharged-> damage tissue.
        
        • energy is not necessarily dangerous if allowed to dissipate through a low power density pathway (cannula out through abdo wall tissues)
        • problem if coupled energy is stored and not allowed to dissipate which occurs when a metal cannula is in a plastic thread mechanism.
          
          • Avoid mixedplastic/metal cannulae. use only metal or only plastic.
   2. insulation failure
      
      • if failure of insulation of shaft of active electrode can cause damage to bowel. may go unrecognised as often out of visual field
   3. direct coupling
      
      • direct coupling between active electrode and another conducting instrument- unwanted and unnoticed path, outside of laparoscopic view
        
        • sparking and arcing. may only appear as non working diathermy