Electrosurgery

Question 1

What is Joule’s law of thermodynamics?

Answer 1

Heat = current (I) squared x tissue resistance x time

Question 2

Define electrosurgery.

Answer 2

The cutting or coagulation of tissues using electrical current.

Question 3

What is current?

Answer 3

The flow of electrons, i.e. the rate of flow of charge. (I) Measured in amps.

Current (I) = Volatage (V) / Resistance (R)

Question 4

What is voltage?

Answer 4

The potential difference, i.e. the energy required to create the flow of electrons. (V) Measured in volts.

Question 5

What is power?

Answer 5

The rate at which work is done. Power = V x I measured in watts.

Question 6

What is resistance/impedence?

Answer 6

The ratio of potential difference to current. (R) Measured in Ohms.

Question 7

What is Ohms law?

Answer 7

V = I x R

Question 8

What happens to tissue at different temperatures?

45

70

90

100

200

Answer 8

45 - permanent tissue damage / denaturation

70 - coagulation

90 - desiccation / blanching

100 - vaporisation

200 - carbonisation

Question 9

What is the difference between DC and AC? Which is used in electrosurgery?

Answer 9

DC - current always flows in the same direction. (e.g. in a simple battery) AC - current alternates between flowing in a forward (positive) directions and then backwards (negative) direction. AC current is used in electrosurgery, and in all power outlets.

Question 10

How does the current used from wall outlets differ from electrosurgery, and why is contact with electricity from a wall outlet dangerous when electrosurgery is not?

Answer 10

Both are AC. The frequency of a power outlet is 50-60Hz. Frequencies below 200Hz are capable of causing muscle/nerve depolarisation and hence causing life threatening arhythmias and tetanic muscle contractions. Electrosurgery works at frequencies >300kHz, so tissues are insensitive to the stimulus as the frequency is too fast for tissues to depolarise and depolarise in the formation of action potentials.

Question 11

What affects the thermal effect of electrosurgery?

Answer 11

1) The power setting (i.e. current)
2) The time it is activated for
3) The resistance of tissues
4) The surface area/shape of the electrosurgical instrument
5) The condition of the instrument (e.g. how much char is on it)
6) The modulation

Question 12

Name some tissues in order of increasing resistance.

Answer 12

Blood muscles / heart /kidneys liver / spleen Brain Lungs Fat

Question 13

What is modulation and why is it important?

Answer 13

It is the electrical waveform, or pattern by which an electrosurgery instrument cycles from positive to negative polarity, and the “off” time in between active cycles. It alters the heating effect on tissues.

Question 14

What happens at the cellular level with cutting?

Answer 14

Rapid increase in tissue temperate causes intracellular fluid to boil and the cell membrane bursts.

The rapid rise in cell temperature causes surrounding tissues to vaporise (leidenfrost effect), causing the cutting effect to precede direct contact of the electrode with the tissues.

Question 15

What is fulguration?

Answer 15

A technique of spray coagulation. It requires high voltage (>5000v) and the electrode to be held slightly away from tissues, causing the current to arc to the tissue, applying high density high voltage to a small area.

Question 16

Compare cutting and coagulation current.

Answer 16

Cutting:

• Modulation - 100% active, with no cooling time
• Lower voltage (1000v) and therefore less likely to arc if activated away from tissue
• Causes vaporisation effect
• Most effective when held slightly away from tissue to cause it to spark and deliver high density but short duration of current

Coagulation:

• Modulation - alternates betweens active and inactive cycles to allow tissue heating and cooling (typically 6% on, 94% off)
• Uses a higher voltage (5000v) and has higher risk of arcing if activated away from tissues
• Causes welding effect due to slower heating of tissues
• Risks: wider thermal spread, higher risk of arcing, sparking and alternative pathway burns

Question 17

What is the difference between monopolar and bipolar?

Answer 17

monopolar

• Uses one active electrode
• Current passes through the body to a base plate
• Has a wider thermal effect
• Increased risk of alternate pathways burns
• Base plate much bigger than electrode so there isn’t the same burn effect

Bipolar

• Electric current runs between 2 electrodes
• Current passes through short course
• Requires lower power
• Reduced thermal spread
• Minimal / no risk of alternative pathway burns
• Coag only
• Can be used safely if patient has inserted electrical device (e.g. pacemakers)

Question 18

Are diathermy machines earthed? Why?

Answer 18

No.

If they were earthed it could cause a short circuit to form from the activated electrode through the patients tissues in contact with the bed, and in turn the floor. Causing burns to the patients body in contact witht he bed.

Question 19

Why does the base plate have to be large?

Answer 19

Joules law :

heat = I x T / surface area

Therefore the larger the surface area, the lower the heat effect and risk of burns.

Question 20

Describe the important steps and safety features to avoid alternate pathway burns when using diathermy?

Answer 20

• Base plate needs return electrode monitoring
• Diathermy machine must NOT be earthed
• Base plate applied appropriately with full surface area contact with the skin
  
  • over well vascularised muscle mass
  • Not over bony prominences or scars or electrical devices/prostheses
  • Ensure area relatively hair free, dry, and not contaminated
  • As close to operating field as possible
• Consider using bipolar rather than monopolar - much lower risk of alternate pathway burns

Question 21

What happens at a cellular level with coagulation?

Answer 21

Intracellular fluid heats more slowly than with cutting current. As the intracellular fluid heats the cell membranes fuse together to form coagulum.

This is called ‘welding effect’.

Vessels seal by the blood boiling and retreating up the vessel, and the lumen is fused closed by clotting and welding effect.

Question 22

What is blend diathermy?

Answer 22

The modulation is altered to provide alternation between on/off cycles that can be between the typical cutting and coagulative currents (i.e. 50%/50% rather than 100 on (cutting), or 6% on 94% off (coag))

Question 23

How is power affected in different mediums?

Answer 23

40w in air

= 80w in CO2 (laparoscopy)

= 100w in 1.5% glycine (hysteroscopy)

Question 24

What are the safety issues in electrosurgery, and how can they be prevented?

Answer 24

1. Thermal spread
   
   • Lowest acceptable power setting
   • activate away from sensitive tissues (e,g, bowel) and only when in contact with desired tissue/instrument
   • Choice of instrument (e.g. bipolar over monopolar, harmonic)
   • Short duration of activation
2. Alternative pathway burns
   
   1. correct application of baseplates
   2. return electrode monitoring
   3. Diathermy machine NOT earthed
3. Direct coupling
   
   • Activate away from other metal instruments
   • Never allow assistant to activate bipolar/monopolar pedals
4. capacitve coupling
   
   • Avoid using ports which are mixed metal and plastic cannula
   • do not activate instrument inside of port
5. Plume
   
   • Choice of instrument (e.g. harmonic)
   • Short duration of activation
   • Using suction devices

Question 25

What are the benefits and problems with ultrasonic devices (e.g. harmonic scalpel)?

Answer 25

Benefits: * Less thermal spread (\<3mm, though studies of continuous activation with advanced sealing button showed up to 25mm) * No plume * No use of electric current - therefore no risk of alterate pathway burns/direct or capactive coupling, and no risk to ICDs/pacemakers etc. * Can cut and coagulate simultaneously * Good for dissection as well as cut/coag so makes a versatile instrument Problems: * User dependent * Expensive * Can't coagulate without cutting * May not be as effective for sealing large vessels \>7mm

Question 26

What is the risk of thermal spread with different elctrosurgical devices?

Answer 26

* Traditional bipolar 2-22mm * Ligasure - 1.8mm (10mm device), 4.5mm (5mm device) * Ensure - 1.1mm * Harmonic - 0-3mm

Question 27

What are the features for 'cutting'

Answer 27

Current: Narrow band of high density current Vaporises cells - by rapidly raising temperature of cells Clean incision, minimal haemostasis Small voltage Current flows continuously Low peak votage Unmodulated

Question 28

What are the features for 'coag'

Answer 28

- Broad band of current - High peak voltage - Limits peak tissue temperature: denatures proteins, forms coagulation, increased thermal spread - Modulated: sinus waveform is non-continuous - Pulses of current flow alternate with no flow - total energy the same- interrupted current, higher voltage

Question 29

What is the Faraday effect?

Answer 29

**Muscle and nerve fibres can be stimulated by electricity.** E.g. if electricity used in houses is conducted to human = neuromuscular action potentials causing tetanic muscle contraction and cardiac arythmias This is because the frequency of electricty is low (Approx 50-60Hz) Electrosurgical currents activate at a much higher frequency (\>300 kHz) -\> nerves/muscles are unable to depolarise and repolarise at this frequency, thus current can pass through tissues without the faraday effect

Question 30

Risk of burns: 3 points of potential damage

Answer 30

Active electrode * In advertent activation * Reduce: Store in insulated sheath Current division * Finds path of least resistance to earth * Reduce: use isolated electrosurgical generator Return electrode * If not properly connected to skin * Reduce: split plate return electrode

Question 31

Extra issues with laparoscopy for burns:

Answer 31

- Impact of laparosopic field of view - Effect of electricity through cannula (capacitive coupling, insulation failure)

Question 32

What is capacitive coupling?

Answer 32

Occurs when 2 conductors are separated by an insulator. e.g. when an electrode is activated within metal cannula that is insulated with plastic surround. Allows charge to build up in metal cannula and rather than being dissipated to surrounding tissue/skin (in whole metal cannula) the current will jump to tissues resulting in a burn. **Capacitance**: the property of an electrical current to pass from one conductor to another even whilst separated by an insulator.

Question 33

Direct coupling?

Answer 33

Direct contact between active electrode and another conductor Leads to unwanted/sometimes unnoticed current pathway E.g. camera shaft, clips and staples, lap instruments

Question 34

Insulation failure?

Answer 34

E.g. microinsufficiencies/imperfections, wear and tear Can cause out of view burns

Question 35

Biological contaminants?

Answer 35

Steam Carbonated tissue Blood Possible bacteria/viruses

Question 36

Chemical contaminants?

Answer 36

Plume Formaldehyde Hydrocarbons

Question 37

Potential safety problems? (summary)

Answer 37

- Direct Coupling - Capactitive coupling - Insulation failure - Hazards of surgical smoke - Inadvertent injury with primary electrode (especially monopolar) - Burns at site of return electrode - Fire

Question 38

Potential safety problems? (solutions)

Answer 38

1. Use lowest possible power setting 2. Use bipolar where possible 3. Use low voltage waveforms 4. Do not activate in open circuit 5. Only activate electrode when entire arcs that could transmit current is in vie 6. Brief intermittent activation\>prolonged activation 7. Insulation failure: use well insulated electrodes and check integrity before use 8. Capacitive coupling: Use all metal cannulas (no hybrids) 9. Direct coupling: take care when activating primary electrode close to other conductors 10. Surgical smoke: suck away carefully 11. Hold monopolar hook in insulated sheath when not in use 12. Use isolated elecrical generator 13. Use disposable split return plates and ensure good contact and appropriate site 14, No monopolar if pacemaker

Question 39

Issue: Capacitative coupling

Answer 39

Solution: Use all-metal or all plastic cannulae