Electrosurgery Flashcards
Define current
Current: The rate of flow of electrons through a conductor (coulomb per second) - Amps
Define Resistance
Resistance: Opposing of the flow of current (volts per amp) - Ohms
Define Voltage
Voltage: Force required to move a unit of charge from one point to another i.e 1 amp flow through 1 Ohm of resistance (Joules per coulomb) - Volts
Define Power
Power: Energy(heat) produced per second i.e. the rate at which work is done. Current x voltage (Joules per second) - Watts
Define Frequency
Frequency - cycles of current per second - Hertz
What is Joules Law of Thermodynamics
Heat = Current (squared) x resistance x time
What factors regulate the thermal effect on tissues? (6)
(Think about Joules Law of thermodynamics: Heat = current (squared) x resistance x time
Current:
- Current and Output Power (feedback on generator)
- Modulation (the way AC is varied)
- The shape of the electrode (e.g. surface area)
Resistance
- Condition of the active electrode (charring)
- Tissue properties
Time
6. Cutting speed and duration of action
Order tissues from most resistance to least resistance
Fat Lungs Brain Liver/Spleen Muscle/kidney Blood
Explain Dessication in terms of:
Dessication:
Surgical effect: Cell wall and cytoplasm rupture, haemostasis of small vessels <1mm
Current waveform: Intermittent (Coag) or continuous (cut)
Contact with tissue: Yes
Characteristics: Similar to bipolar, significant lateral thermal spread.
Basically coagulating or cutting with monopolar coag.
Explain Vaporisation in terms of Surgical Effect Current Waveform Contact with Tissue Characteristics
Vaporisation
Surgical Effect: Tissue destruction and cutting
Current waveform: Continuous
Contact with Tissue: No
Characteristics: Low voltage sparks, moderate smoke
Basically cutting with monopolar cut
Explain fulgurisation in terms of: Surgical Effect Current Waveform Contact with Tissue Characteristics
Fulgurisation
Surgical effect: Tissue destruction and small vessel haemostasis <1mm
Current waveform: Intermittent
Contact: No
Characteristics: High voltage sparks, smoke and charring
Basically Coagulating like crazy from away from the tissues.
Explain Coaptation in terms of Surgical Effect Current Waveform Contact with Tissue Characteristics
Coaptation
Surgical effect: Denaturation and renaturation of proteins, sealing small vessels <2mm
Current waveform: Continuous or intermittent
Contact: Yes with compression of vessel wall.
Characteristics: Similar to bipolar, significant lateral spread.
Basically sealing the vessels with pressure as well, but using the monopolar.
What are the differences between coagulation and cut current?
Cut = unmodulated
- high current
- 100% duty cycle, continuous
- Low voltage (so less likely to arc, and therefore safer)
- Rapid temperature increase, boiling of intracellular fluid and rupturing of membranes
Coagulation = modulated
- Low current
- low duty cycle (non-continuous)
- High voltage
- The ‘off’ time in duty cycle allows tissues to cool, so they can’t vaporise. Instead they undergo denaturation and then renaturation so they weld (link up to form chains) and form a coagulum.
What are the advantages of Monopolar diathermy
Advantages of monopolar
- Largest range of functions: Dessication, fulguration, vapourisation, coaptation
- Readily available
- Inexpensive
- Versatile
- Range of variables
What are the disadvantages of monopolar diathermy
Disadvantages of monopolar
The current goes throught the patient’s body
Risk of capacitive coupling/current leakage
Lateral spread/thermal injury
Smoke plume
Poor vessel sealing
What are the advantages of bipolar diathermy (conventional)?
Advantages of bipolar No current through the patient Inexpensive Readily available Good vessel sealing <5mm Dessication, coaptation
What are the disadvantages of bipolar diathermy (conventional)?
Disadvantage of bipolar
Limited dissection capability
Risk of lateral thermal spread
Need for additional technology for transection
No audio feedback - more lateral spread and sticking
What is advanced bipolar and what are the advantages and disadvantages?
Advanced bipolar is impedance controlled bipolar diathermy - measuring tissue impedence at the electrode contact site, and altering the current accordingly to maintain a continuous effect, while controlling output voltage and minimise sparking.
Advantages Audio signal/cut off No current through patient Good vessel sealing Dessication, coaptation Decreased instrument traffic Usually has transection method Lowest possible power maintained for the desired tissue effect
Disadvantages
Relatively expensive
Limited dissection capacity
Risk of lateral thermal injury
What is ultrasonic technology and what are the advantages and disadvantages
Ultrasonic technology uses high frequency mechanical vibration - continuous oscillation of the active shaft and jaw (>55,000/sec), converting electrical energy into mechanical energy –> resulting in thermal energy
- This process disrupts hydrogen bonds, and produces heat which leads to denaturation of the protein and eventually separation of tissue.
Dessication and coaptation occur at lower frequencies, and cutting at higher frequencies
Advantages
- Versatile: coag and cut in the same instrument
- Decreased instrument traffic
- Minimal thermal spread
- Precise
- No smoke
- No current through patient
- Good vessel sealing
Disadvantages
- Inability to seal larger vessels
- Hot instrument - thermal injury to unintended organs
- Expensive
- User dependent (can be slower to effect haemostasis)
- No tissue feedback
How common are electrosurgical injuries?
0.1-0.5% laparoscopies
1.3% bowel injury–> 50% are due to electrosurgery
70% not recognised at the time, and 25% mortality.
What are the types of electrosurgical injuries?
Within the surgical field of view
- Direct iatrogenic injury (accidently activate the charge)
- Thermal spread causing injury to adjacent structures
(traditional bipolar up to 22mm). May be delay in onset of symptoms
Outside the surgical field of view
Stray current injuries
- Capacitive coupling - 2 conductors with a insulator in between that share charge. In laparoscopy if using metal cannula with plastic insulator around it, sitting in abdominal wall preventing charge from dissipating. If cannula comes in contact with tissue it will cause injury
- Insulation failure - breaks in the insulation (1-2% of new instrument) leading to leakage of the charge onto nearby tissue
- Direct coupling - electrode is in contact with another metal instrument, so current follows path of least resistance through the instrument to whatever it is touching.
- Alternate pathway burns - burns at site of metalware, or at electrode if inadequately placed base plate.
Smoke injury - toxins from retained smoke.
