Viva Practice for the FRCS(Urol) and Postgraduate Urology Examinations, 2nd ed.

Diathermy

Q. What is shown in Figure 14.1?

Figure 14.1

A. Figure 14.1 is an image of a diathermy machine.

Q. What is diathermy?

A. The passage of high-frequency alternating current, in the range 400 KHz-10 MHz, through body tissue. Where the current is concentrated, heat up to 1000°C is produced, to allow cutting or coagulation of tissue [2].

Nerves and muscles are not stimulated with such a high-frequency alternating current (400 KHz-10 MHz) as there is no time for the cell membranes of nerve and muscle to become depolarised (they are stimulated at lower frequencies only).

Q. What sort of diathermy do you use in theatres, and how does it work?

A. The main types of diathermy used in an operating theatre are monopolar and bipolar.

Monopolar diathermy involves the delivery of high-frequency current from a diathermy generator, to the active electrode (diathermy forceps or standard resectoscope loop or ball). High current density at the active electrode, which has a small surface area, results in heat at the point of contact with tissue. Current density then spreads from this point, throughout the body, returning to the diathermy generator via the patient electrode plate (Earth Plate), which is the diathermy pad placed on the patient. Low current density at this electrode plate, due to its large surface area (70-150 cm²), results in no heat formation. Importantly, the patient electrode plate should be a well-vascularised area away from any prosthesis and the underlying skin should be free of scarring or hair to allow good contact of the plate with the patient.

With bipolar diathermy, current passes down one limb of forceps (active electrode) and back to the diathermy generator via the other limb (patient electrode plate). The advantages are that there is no need for a plate to be placed on the patient. The disadvantages are that there is no cutting facility, the forceps need to be kept apart and there is less power.

Q. What is the difference between cutting and coagulation?

A. The differences are listed in Table 14.2 and Figure 14.2.

Table 14.2 Differences between cutting and coagulation

Note: Blend only works in cutting mode - pulsed output (50% on and 50% off).

Q. What are the potential complications and precautions with diathermy?

A. The complications and precautions are as follows:

Burns

Due to misapplication of the patient electrode plate

Metal prosthesis or implants should not be touched directly with the active electrode or the patient electrode plate

Use of inflammable preparatory solution may result in superficial burns on skin or in cavities

Figure 14.2 Cutting and coagulation waveforms.

Explosions

In obstructed hollow viscera

If inflammable volatile anaesthetic agents are used (ether)

High-voltage electrocution

To the patient or the surgeon because of faulty cables

Obturator kick

End artery necrosis

Especially with monopolar diathermy, during penile surgery

Pacemakers

Diathermy needs to be used with caution in patients with pacemakers (see following discussion)

Q. How are diathermy burns avoided?

A. Inflammable liquids (e.g. containing alcohol) should be avoided. The patient electrode plate should be of at least 70 cm² in size, and placed appropriately (see previous discussion). The patient should not be in contact with any other metal objects (e.g. drip stands). Additionally, touching other instruments with the diathermy probe (either inadvertently or purposefully) should be avoided (direct coupling).

Q. You are in the middle of a transurethral resection of the prostate (TURP), when the diathermy stops working. How do you resolve the situation to complete the procedure?

A. I perform a series of checks, as follows:

1. Make sure that the machine has not been switched off inadvertently

2. Check that the diathermy cable is still connected to the diathermy machine

3. Ensure that the diathermy cable has not broken

4. Make sure that the diathermy cable is properly connected to the working element of the resectoscope

5. Ensure that the loop is not broken

6. Check that the irrigating fluid is still glycine (1.5%)

7. Make sure that the patient electrode plate is appropriately attached to the patient and that the return cable to the diathermy machine is still connected

Q. You are contacted by your junior colleague regarding a 78-year-old patient who is due to have a TURP in 2 weeks time. The doctor suspects the patient has a pacemaker and wishes to seek advice. What are the potential risks?

A. The main risks with pacemakers and implantable cardioverter defibrillators (ICDs) are pacemaker inhibition, phantom reprogramming and ventricular fibrillation.

Pacemaker inhibition: the high frequency of the diathermy current may simulate cardiac electrical activity, thus inhibiting the pacemaker. If the patient is pacemaker-dependent, the heart may stop beating.

Phantom reprogramming: the high frequency of the diathermy current may simulate the radiofrequency impulse by which pacemakers are reprogrammed. As a result the pacemaker may start to work in an entirely different mode.

Q. What precautions should be taken before, during and after the operation?

A. All information of the pacemaker/ICD should be available, including type of device (pacemaker/ICD), serial numbers, date of implantation, hospital implanting the device, indication and date/result of last check. Patients should have a card displaying this information. The cardiac clinic should be contacted to determine the precise indication for the device, and to determine whether the device is due for replacement.

Generally, diathermy should be avoided in the first instance in such patients, and an alternative treatment strategy should be considered. If the surgical procedure is deemed unavoidable, then the following points should be considered.

Prior to the surgery, carefully consult the cardiologist, pacemaker clinic and cardiac technician in elective cases (see previous discussion). Most devices will not need to be adjusted pre-operatively; however advice should still be sought as the consequences may otherwise be life threatening. ICDs are generally set to ‘monitor only’ to prevent inadvertent activation, and should of course be switched back after the operation. Consider if procedure can be performed with bipolar diathermy (e.g. TURP).

During the procedure, the patient plate electrode should be sited so that the current path does not go right through the pacemaker. Furthermore, ensure it is properly applied. Avoid inappropriate grounding through ECG leads. The diathermy machine should be well away from the pacemaker (>15 cm). The patient’s heart rate should be continuously monitored; a defibrillator should be immediately available, as well as an external pacemaker. Surgically, short bursts of diathermy should be used and the operative time should be as short as possible. Antibiotic prophylaxis should be given and fluid overload should be avoided in these cases.

Clinical magnets may be secured over ICDs to prevent inadvertent shocks and to allow pacemakers to function at a fixed rate. However, they are very rarely used in current practice, because of the risk of phantom reprogramming.

In emergency situations pre-operative checks may not be possible. The device should however be checked post-operatively as soon as practicable [3].