Electrosurgery - diathermy

Question 1

What is diathermy?

Answer 1

High frequency AC current (e.g. 200kHz)

Question 2

Why is low frequency current not used?

Answer 2

Low frequency current (<0.1MHz) stimulates nerves and muscles so is not used.

Question 3

What frequency do domestic appliances use

Answer 3

50Hz

Question 4

What determines the heat of diathermy?

Answer 4

The current

Question 5

What are the 3 main components of diathermy?

Answer 5

1. Active electrode (tip)
2. Dispersive/return electrode (plate)
3. Generator

Question 6

What are the two types of diathermy?

Answer 6

Monopolar

Bipolar

Question 7

Where route does the current follow in monopolar diathermy?

Answer 7

Current passes in a circuit from the generator to the active electrode (diathermy tip), through the patient, to the diathermy pad (the return electrode)

Question 8

Where is the maximum heat in a monopolar diathermy circuit?

Answer 8

In the point of least cross sectional area (e.g. the tip)

Question 9

What is altered to change diathermy to coagulation?

Answer 9

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”).

Question 10

Which produces more heat - cut or coag?

Answer 10

Cut

Question 11

What happens to cellular proteins on coag settings?

Answer 11

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

Question 12

What kind of waveform is used on “cut” settings?

Answer 12

Lower voltage with a continuous wave from makes the “cut” diathermy setting constantly “on”.

Question 13

What happens to cells and tissue when low voltage “cut” diathermy is applied?

Answer 13

A continuous sine wave produces intense heat that vapourises water, explodes cells, and produces minimal coagulum, with minimal haemostasis

Question 14

What is the “blend” setting for diathermy?

Answer 14

“Blend” dampens down a portion of the cutting waveform, allowing for greater formation of a coagulum and therefore more control of local bleeding.

Question 15

Where route does the current follow in bipolar diathermy?

Answer 15

The active and return electrodes are in the handpiece, therefore current only flows through the surgical site between electrodes, not through the patient

Question 16

In what patients is bipolar diathermy favourable?

Answer 16

Patients with pacemakers (and presumeably with metal that can’t be removed)

Question 17

Give four potential complications of diathermy use

Answer 17

1. Accidental use - burns of undesired tissue/surgeon’s hand
2. Fire
3. Insulation failure (esp during laparoscopy)
4. Pacemaker malfunction

Question 18

How do modern pacemakers mitigate the risk of diathermy?

Answer 18

They can be turned off during surgery

Question 19

What are the risks of diathermy with new pacemakers>

Answer 19

Diathermy can still make new pacemakers reset or fire, or can cause thermal damage to the heart, via the electrode lead

Question 20

How may the risks of diathermy be best mitigated in patients with pacemakers?

Answer 20

1. Place the plate as close to the site of surgery as possible
2. Monitor the patient, have a defibrillator bedside
3. Use alternatives, e.g. ultrasonic scalpel (harmonic).