Diathermy and its safe useDiathermy and its safe use

DiathermyDiathermy

Diathermy is frequently used to coagulate a Diathermy is frequently used to coagulate a bleeding vessel or to cut tissues.bleeding vessel or to cut tissues.

Unipolar diathermy is commonly used.Unipolar diathermy is commonly used. ComponentsComponents

– 1. Diathermy active electrode.1. Diathermy active electrode.– 2. Patient's plate.2. Patient's plate.– 3. Diathermy case (where the frequency of the current 3. Diathermy case (where the frequency of the current

used can be adjusted.)used can be adjusted.) An isolating capacitor is situated between the patient's An isolating capacitor is situated between the patient's plate and earth.plate and earth.

Mechanism of actionMechanism of action

• Heat is generated when a current passes through Heat is generated when a current passes through a resistor. a resistor.

• The amount of heat generated (H) is proportional The amount of heat generated (H) is proportional to the square of current (Ito the square of current (I22) divided by the area (A) ) divided by the area (A) (H=I(H=I22/A)./A).

• A large amount of heat is produced at the_tip of A large amount of heat is produced at the_tip of the diathermy forceps because of its small size the diathermy forceps because of its small size (high current density). (high current density).

• Whereas at the site of the patient's plate, because Whereas at the site of the patient's plate, because of its large surface area, no heat or burning is of its large surface area, no heat or burning is produced (low current density).produced (low current density).

Mechanism of actionMechanism of action

A high frequency current 500 000 -1 000 A high frequency current 500 000 -1 000 000 Hz is used. 000 Hz is used.

This high frequency current behaves This high frequency current behaves differently from the standard 50 Hz current. differently from the standard 50 Hz current. It passes directly across the preccordium It passes directly across the preccordium without causing ventricular fibrillation. without causing ventricular fibrillation.

High frequency currents have a low tissue High frequency currents have a low tissue penetration without exciting the contractile penetration without exciting the contractile cells.cells.

Mechanism of actionMechanism of action

The isolating capacitor has The isolating capacitor has low impedancelow impedance to a high frequency current, i.e. diathermy to a high frequency current, i.e. diathermy current. current.

The capacitor has a The capacitor has a high impedancehigh impedance to 50 to 50 Hz current Hz current

Thus protecting the patient against electrical Thus protecting the patient against electrical shock.shock.

Mechanism of actionMechanism of action

Earth-tree circuit diathermy can be used.Earth-tree circuit diathermy can be used. The patient, the tip of the diathermy forceps The patient, the tip of the diathermy forceps

and the patient plate are not connected to and the patient plate are not connected to earth. This reduces the risk of burns to the earth. This reduces the risk of burns to the patient.patient.

This type of circuit is known as a This type of circuit is known as a floating floating patient circuitpatient circuit

Mechanism of actionMechanism of action

Bipolar diathermy does not require a patient Bipolar diathermy does not require a patient plate. plate.

The current flows through one side of the The current flows through one side of the forceps, through the patient and then back forceps, through the patient and then back through the other side of the forceps. through the other side of the forceps.

Usually low power can be achieved from a Usually low power can be achieved from a bipolar diathermy. bipolar diathermy.

Bipolar diathermy is frequently used during Bipolar diathermy is frequently used during neurosurgery or ophthalmic surgery.neurosurgery or ophthalmic surgery.

Problems in practice and safety Problems in practice and safety featuresfeatures

If the area of contact between the plate and If the area of contact between the plate and patient is reduced, the patient is at risk of being patient is reduced, the patient is at risk of being burned at the site of the plate. burned at the site of the plate.

If the plate is completely detached, current might If the plate is completely detached, current might flow through any point of contact between patient flow through any point of contact between patient and earth, for example earthed ECG electrodes or and earth, for example earthed ECG electrodes or temperature probes.temperature probes.Modern diathermy machines do not function with Modern diathermy machines do not function with any of the above.any of the above.

Problems in practice and safety Problems in practice and safety featuresfeatures

If the area of contact between the plate and If the area of contact between the plate and patient is reduced, the patient is at risk of being patient is reduced, the patient is at risk of being burned at the site of the plate.burned at the site of the plate.

If the plate is completely detached, current might If the plate is completely detached, current might flow through any point of contact between patient flow through any point of contact between patient and earth, for example earthed ECG electrodes or and earth, for example earthed ECG electrodes or temperature probes.temperature probes.

Modern diathermy machines do not function with Modern diathermy machines do not function with any of the above.any of the above.

Problems in practice and safety Problems in practice and safety featuresfeatures

Electrical interference with other electrical monitoring Electrical interference with other electrical monitoring devices.devices.

The use of electrical filters can solve this problem.The use of electrical filters can solve this problem. Interference with the function of cardiac pacemakers.Interference with the function of cardiac pacemakers. Damage to the electrical circuitsDamage to the electrical circuits or or changes changes in in the the

programming can occur.programming can occur. This is more of a hazard with cutting diathermy than with This is more of a hazard with cutting diathermy than with

coagulation diathermy.coagulation diathermy. Modern pacemakers are protected against diathermy.Modern pacemakers are protected against diathermy.

Pacemaker interferencePacemaker interference

Electromagnetic interferenceElectromagnetic interference (EMI) (EMI)– 0 and 100 and 1099 Hz (e.g. AC power supplies and electrocautery) Hz (e.g. AC power supplies and electrocautery)– microwaves with frequencies between 10microwaves with frequencies between 1099 and 10 and 101111 Hz (including Hz (including

ultra high frequency radio waves and radar)ultra high frequency radio waves and radar)

can cause device interference.can cause device interference. X-rays, gamma rays and infrared and ultraviolet light do not X-rays, gamma rays and infrared and ultraviolet light do not

cause interference. cause interference. EMI may enter the pacemaker or defibrillator byEMI may enter the pacemaker or defibrillator by

– direct contact between the patient and the source,direct contact between the patient and the source,– exposure to an electromagnetic fieldexposure to an electromagnetic field

Device leads act as antennae. Device leads act as antennae.

Pacemaker interferencePacemaker interference

Devices are generally protected byDevices are generally protected by– circuit shielding using titanium casing circuit shielding using titanium casing – noise protection algorithms that filter out unwanted signals. noise protection algorithms that filter out unwanted signals.

Possible responses to external interference include Possible responses to external interference include – inappropriate inhibition or triggering of a paced outputinappropriate inhibition or triggering of a paced output– asynchronous pacingasynchronous pacing– reprogramming (usually into a backup mode)reprogramming (usually into a backup mode)– damage to device circuitry and triggering a defibrillator discharge. damage to device circuitry and triggering a defibrillator discharge.

Asynchronous pacing and mode resetting are the most Asynchronous pacing and mode resetting are the most common outcomes of EMI and should be considered if common outcomes of EMI and should be considered if pacing modes appear to change suddenly or intermittently pacing modes appear to change suddenly or intermittently on ECG monitorson ECG monitors

Pacemaker interferencePacemaker interference

In some devices EMI may also cause a In some devices EMI may also cause a pacing mode change. pacing mode change.

This is usually the ‘backup’ or ‘reset’ mode This is usually the ‘backup’ or ‘reset’ mode (often the same mode as the ‘battery (often the same mode as the ‘battery depletion’ mode). depletion’ mode).

Assessed using telemetric interrogation. Assessed using telemetric interrogation. The backup or reset mode is usually VVI or The backup or reset mode is usually VVI or

VOO.VOO.

Pacemaker interferencePacemaker interference

The EMI generated by electrocautery that may affect the The EMI generated by electrocautery that may affect the device is related to the distance and orientation of the device is related to the distance and orientation of the current to the patient’s device and leads.current to the patient’s device and leads.

Radio frequency signals may be interpreted as cardiac Radio frequency signals may be interpreted as cardiac impulses, leading to inappropriate inhibition.impulses, leading to inappropriate inhibition.

Prolonged application of cautery can repeatedly trigger the Prolonged application of cautery can repeatedly trigger the NSP, resulting in asynchronous pacing, with function NSP, resulting in asynchronous pacing, with function returning to normal when electrocautery is stopped. returning to normal when electrocautery is stopped.

If electrocautery interference results in mode resetting, for If electrocautery interference results in mode resetting, for example from DDD to VVI or VOO, AV synchrony will be example from DDD to VVI or VOO, AV synchrony will be lost and may result in haemodynamic embarrassment. lost and may result in haemodynamic embarrassment. Such resetting will persist even after electrocautery is Such resetting will persist even after electrocautery is stopped.stopped.

Pacemaker interferencePacemaker interference

Implanted defibrillators may interpret Implanted defibrillators may interpret electrocautery interference as ventricular electrocautery interference as ventricular fibrillation, resulting in an inappropriate shock. fibrillation, resulting in an inappropriate shock.

pacemaker circuitry damage resulting in output pacemaker circuitry damage resulting in output failure, failure,

activation of maximum rate response pacingactivation of maximum rate response pacing pacing lead overheating and myocardial damagepacing lead overheating and myocardial damage transient threshold alteration.transient threshold alteration.