Electrosurgery - diathermy Flashcards
What is diathermy?
High frequency AC current (e.g. 200kHz)
Why is low frequency current not used?
Low frequency current (<0.1MHz) stimulates nerves and muscles so is not used.
What frequency do domestic appliances use
50Hz
What determines the heat of diathermy?
The current
What are the 3 main components of diathermy?
- Active electrode (tip)
- Dispersive/return electrode (plate)
- Generator
What are the two types of diathermy?
Monopolar
Bipolar
Where route does the current follow in monopolar diathermy?
Current passes in a circuit from the generator to the active electrode (diathermy tip), through the patient, to the diathermy pad (the return electrode)
Where is the maximum heat in a monopolar diathermy circuit?
In the point of least cross sectional area (e.g. the tip)
What is altered to change diathermy to coagulation?
The voltage is increased
The interrupted frequency waveform produces less heat than a continuous sine wave (there are gaps between each wave, so it is 6% “on”, 94% “off”).
Which produces more heat - cut or coag?
Cut
What happens to cellular proteins on coag settings?
The reduced heat still denatures cellular proteins, which form a coagulum; this is a protein rich mixture that allows sealing of smaller blood vessels and control local bleeding
What kind of waveform is used on “cut” settings?
Lower voltage with a continuous wave from makes the “cut” diathermy setting constantly “on”.
What happens to cells and tissue when low voltage “cut” diathermy is applied?
A continuous sine wave produces intense heat that vapourises water, explodes cells, and produces minimal coagulum, with minimal haemostasis
What is the “blend” setting for diathermy?
“Blend” dampens down a portion of the cutting waveform, allowing for greater formation of a coagulum and therefore more control of local bleeding.
Where route does the current follow in bipolar diathermy?
The active and return electrodes are in the handpiece, therefore current only flows through the surgical site between electrodes, not through the patient
In what patients is bipolar diathermy favourable?
Patients with pacemakers (and presumeably with metal that can’t be removed)
Give four potential complications of diathermy use
- Accidental use - burns of undesired tissue/surgeon’s hand
- Fire
- Insulation failure (esp during laparoscopy)
- Pacemaker malfunction
How do modern pacemakers mitigate the risk of diathermy?
They can be turned off during surgery
What are the risks of diathermy with new pacemakers>
Diathermy can still make new pacemakers reset or fire, or can cause thermal damage to the heart, via the electrode lead
How may the risks of diathermy be best mitigated in patients with pacemakers?
- Place the plate as close to the site of surgery as possible
- Monitor the patient, have a defibrillator bedside
- Use alternatives, e.g. ultrasonic scalpel (harmonic).
