Electrosurgery Flashcards
What is Joule’s law of thermodynamics?
Heat = current (I) squared x tissue resistance x time
Define electrosurgery.
The cutting or coagulation of tissues using electrical current.
What is current?
The flow of electrons, i.e. the rate of flow of charge. (I) Measured in amps.
Current (I) = Volatage (V) / Resistance (R)
What is voltage?
The potential difference, i.e. the energy required to create the flow of electrons. (V) Measured in volts.
What is power?
The rate at which work is done. Power = V x I measured in watts.
What is resistance/impedence?
The ratio of potential difference to current. (R) Measured in Ohms.
What is Ohms law?
V = I x R
What happens to tissue at different temperatures?
45
70
90
100
200
45 - permanent tissue damage / denaturation
70 - coagulation
90 - desiccation / blanching
100 - vaporisation
200 - carbonisation
What is the difference between DC and AC? Which is used in electrosurgery?
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.
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?
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.
What affects the thermal effect of electrosurgery?
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
Name some tissues in order of increasing resistance.
Blood muscles / heart /kidneys liver / spleen Brain Lungs Fat
What is modulation and why is it important?
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.
What happens at the cellular level with cutting?
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.
What is fulguration?
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.
Compare cutting and coagulation current.
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
What is the difference between monopolar and bipolar?
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)
Are diathermy machines earthed? Why?
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.
Why does the base plate have to be large?
Joules law :
heat = I x T / surface area
Therefore the larger the surface area, the lower the heat effect and risk of burns.
Describe the important steps and safety features to avoid alternate pathway burns when using diathermy?
- 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
What happens at a cellular level with coagulation?
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.
What is blend diathermy?
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))
How is power affected in different mediums?
40w in air
= 80w in CO2 (laparoscopy)
= 100w in 1.5% glycine (hysteroscopy)
What are the safety issues in electrosurgery, and how can they be prevented?
- 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
- Alternative pathway burns
- correct application of baseplates
- return electrode monitoring
- Diathermy machine NOT earthed
- Direct coupling
- Activate away from other metal instruments
- Never allow assistant to activate bipolar/monopolar pedals
- capacitve coupling
- Avoid using ports which are mixed metal and plastic cannula
- do not activate instrument inside of port
- Plume
- Choice of instrument (e.g. harmonic)
- Short duration of activation
- Using suction devices
What are the benefits and problems with ultrasonic devices (e.g. harmonic scalpel)?
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
What is the risk of thermal spread with different elctrosurgical devices?
- Traditional bipolar 2-22mm
- Ligasure - 1.8mm (10mm device), 4.5mm (5mm device)
- Ensure - 1.1mm
- Harmonic - 0-3mm
What are the features for ‘cutting’
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
What are the features for ‘coag’
- 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
What is the Faraday effect?
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
Risk of burns: 3 points of potential damage
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
Extra issues with laparoscopy for burns:
- Impact of laparosopic field of view
- Effect of electricity through cannula (capacitive coupling, insulation failure)
What is capacitive coupling?
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.
Direct coupling?
Direct contact between active electrode and another conductor
Leads to unwanted/sometimes unnoticed current pathway
E.g. camera shaft, clips and staples, lap instruments
Insulation failure?
E.g. microinsufficiencies/imperfections, wear and tear
Can cause out of view burns
Biological contaminants?
Steam
Carbonated tissue
Blood
Possible bacteria/viruses
Chemical contaminants?
Plume
Formaldehyde
Hydrocarbons
Potential safety problems? (summary)
- Direct Coupling
- Capactitive coupling
- Insulation failure
- Hazards of surgical smoke
- Inadvertent injury with primary electrode (especially monopolar)
- Burns at site of return electrode
- Fire
Potential safety problems? (solutions)
- Use lowest possible power setting
- Use bipolar where possible
- Use low voltage waveforms
- Do not activate in open circuit
- Only activate electrode when entire arcs that could transmit current is in vie
- Brief intermittent activation>prolonged activation
- Insulation failure: use well insulated electrodes and check integrity before use
- Capacitive coupling: Use all metal cannulas (no hybrids)
- Direct coupling: take care when activating primary electrode close to other conductors
- Surgical smoke: suck away carefully
- Hold monopolar hook in insulated sheath when not in use
- Use isolated elecrical generator
- Use disposable split return plates and ensure good contact and appropriate site
14, No monopolar if pacemaker
Issue:
Capacitative coupling
Solution:
Use all-metal or all plastic cannulae
