What is Joules law of thermodynamics?
Heat = current squared x resistance of tissues x duration of current flow
What is current?
The rate of flow of electrons.
Coulomb per sec.
What is voltage?
The force/energy needed to move a unit of charge from one point to another
Joules per coulomb
What is resistance?
Ratio of potential difference to current.
Volt per ampere
What is power?
Rate at which work is done.
Joules per second.
What is frequency?
The number of cycles per second.
How may thermal effect be regulated?
Current.
Modulation level.
Surface area of electrode.
Condition of active electrode: charring and eschar increases resistance.
Tissue resistance: decreases as frequency of AC increases.
Why does electrosurgical instruments have a base operating frequency of >300 kHz?
Because low frequency currents can effect nerve and muscles cells e.g. AC from wall outlet has frequency of 50-60 Hz causing depolarisation of nerves and muscles resulting in paralysis (cardiac arrest, tetany).
Compare and contrast the mechanism of action of coagulation vs cutting:
Coagulation:
- Temp 60-70 degrees Celsius
- Action: slow boiling of intracellular fluid causing cell shrinkage and adjacent cells link up to form chains.
- Waveform: intermittent, allows cooling between pulses.
- Voltage: high 5000 V
Cutting:
- Temp 100 degrees Celsius
- Action: rapid boiling and vaporisation of intracellular fluid causing cell rupture.
- Waveform: continuous with no time for tissue to cool between pulses
- Voltage: low 1000 V
What is monopolar diathermy
Diathermy with a single active electrode.
List the main mechanisms or types of electrosurgical injury
- Direct couple or alternate pathway: activating generator near or while touching another metallic instrument and causing injury to adjacent organ.
- Base plate electrode burn
- Smoke: toxic substances and can also disperse infective viruses.
- Thermal spread: intentional injury to nearby tissues.
- Capacitive coupling: accidental ‘charging’ of a metallic sheathed/insulated instrument; later energy is discharged when contacts patient tissue causing injury.
- Fire
What is fulguration?
What temperature is typically achieved?
What waveform mode (cut or coag) and surgical mode (contact or non-contact) is required?
Fulguration/carbonisation is a type of superficial coagulation created by arcing modulated high voltage current to tissue that is rapidly desiccated and coagulated. Results in carbonisation.
200 degrees Celscius.
Waveform: coag
Surgical mode: non-contact
Order these tissues from least to most resistant:
- Gall bladder
- Lung, scar, adhesions
- Bowel, brain gray matter, adipose, spleen.
- Blood
- Mesentery, brain white matter, omentum
- Oral cavity, liver
- Prostate, muscle, eye, skin, kidney, pancreas
Most
4. Blood
7. Prostate, muscle, eye, skin, kidney, pancreas
6. Oral cavity, liver
1. Gall bladder
3. Bowel, brain gray matter, adipose, spleen.
5. Mesentery, brain white matter, omentum
2. Lung, scar, adhesions
Least
What are the advantages and disadvantages of advanced bipolar energy devices?
Advantages:
• Consistent vessel sealing
• Reduced thermal spread
• Reduced tissue sticking
Disadvantages:
• Both electrodes must be in contact with tissue
• Surgical plume
What are the advantages and disadvantages of ultrasonic devices?
Advantages:
• Cuts and coagulates simultaneously
• No current passes through patient’s body
Disadvantages: • Devices have poor grasping ability • Cannot coagulate without cutting • Generally poor coagulation of medium to large vessels • Technique dependent
What is the expected thermal spread of a 10 mm Ligasure device?
1.8 mm
What is the expected thermal spread of a harmonic scalpel?
up to 25 mm
What is the expected thermy spread of traditional bipolar?
2 to 22 mm
What factors affect thermal spread?
§ Type of electrode § Power setting § Cut vs Coag waveform § Desiccate vs fulgurate technique § Length of activation § Type of tissue § Tissue thickness § Moisture content: higher moisture content = better conductor
Why is bipolar safer than monopolar?
Current does not pass through the patient but rather only through local tissue from one electrode to the other.
Almost no change of alternate pathway burns.
Where should a monopolar return electrode NOT be placed?
- Over areas of vascular insufficiency
- Irregular body contour
- Bony prominences.
- Scar tissue
- Prosthetics
- Heavy hair: needs to be shaved.
Rate of major complication in laparoscopy
Less than 0.5%
