2. • “ the cutting and coagulation of body tissue with high frequency ( i.e.
radiofrequency ) current ’’
• term “diathermy” is derived from the Greek words “Therma”,
meaning heat, and “Dia”, meaning through. Diathermy literally
means “Heating through”.
• 1908 German physician Karl Franz Nagelschmidt coined the term
diathermy, and performed the first extensive experiments on
patients.
3. • Depending on the amount of heat generated, diathermy can be used to
merely warm or to destroy tissue.
• In the first instance, it is particularly beneficial in relieving muscle soreness
and sprain.
• In the second, as an adjunct to surgery, diathermy is used to coagulate,
prevent excessive bleeding, and seal off traumatized tissues.
4. PRINCIPLE
• Principle = current density
• When a current is applied over small area , the current density is high
and heating occurs
• If same current applied over large area , then current density is low ,
no heating occurs
5. • Before injury, the dipole molecules of the body tissue are arranged
on the basis of polarity .
• When the tissue is damaged the dipoles distribution become
irregular and deviates from polarity based arrangement .
• Under the influence of an electric field , they rotate according to
the polarity of their charge in the direction of the field lines and get
rearranged and tends to acquire its previous stage of polarity.
6. SHORT WAVE
• In shortwave diathermy, the part to be treated is placed between two
condenser plates, and the highest temperature is concentrated in the
subcutaneous tissues. It is usually prescribed as treatment for deep
muscles and joints and is sometimes used to localize deep
inflammatory disease and sinusitis, kidney stones, and pelvic
infections.
• Shortwave Has Three Main Frequencies:
• 27.12 MHz, wavelength 11 M (most common used one).
• 13.56 MHz wavelength 22 M.
• 40.68 MHz 7.5 M.
7. Ultrasound
• employs high-frequency acoustic vibrations which, when propelled
through the tissues, are converted into heat.
• especially useful in the delivery of heat to selected musculatures and
structures because there is a difference in the sensitivity of various
fibers to the acoustic vibrations some are more absorptive and some
are more reflective. For example, in subcutaneous fat, relatively little
energy is converted into heat, but in muscle tissues there is a much
higher rate of conversion to heat.
• The therapeutic ultrasound apparatus generates a high-frequency
alternating current, which is then converted into acoustic vibrations.
• The apparatus is moved slowly across the surface of the part being
treated.
8. MICROWAVE
• Microwave diathermy uses radiation of very high frequency & short
wavelength similar to radar waves.
• All physiologic responses are due to its heating effect.
• Microwave diathermy is used in the management of superficial
tumours with conventional RT & CT.
9. ELECTROCAUTERY
• Surgical diathermy is usually better known as "electrosurgery". (It is also
referred to occasionally as "electrocautery“)
• Electrosurgery and surgical diathermy involve the use of high frequency
A.C. electrical current in surgery.
12. • High frequency currents (in the range of 1-3 MHz) can be used in
operating rooms for surgical purposes involving cutting and
coagulation.
• Surgical diathermy machines depend on the heating effect of
electric current.
• When high frequency current flows through the sharp edge of a
wire loop or band loop or the point of a needle into the tissue ,
there is a high concentration of current at this point.
• The tissue is heated to such an extent that the cells which are
immediately under the electrode, are torn apart by the boiling of
the cell fluid.
• The indifferent electrode establishes a large area contact with the
patient and the RF current is therefore, dispersed so that very
little heat is developed at this electrode.
• This type of tissue separation forms the basis of electro-surgical
cutting.
13. • Types of Electro surgery techniques
• Cutting (Electrotomy)
• Coagulation
• Fulguration
• Desiccation
• Haemostasis
14. Cutting
• A combination of fine wire electrodes, high RF voltage and
high cutting speeds are necessary for confinement of tissue
destruction in electro-surgery.
• These parameters are of great value in microsurgery since
localization of electrosurgical effects would be accompanied
by coagulation and hemostasis.
• Evolving steam bubbles in the tissues at the surgical tip
continuously rupture the tissue and are responsible for the
cutting mechanism
15. Coagulation
• Electro-surgical coagulation of tissue is caused by the high
frequency current flowing through the tissue and heating it
locally so that it coagulates from inside.
• The coagulation process is accompanied by a grayish-white
discoloration of the tissue at the edge of the electrode.
• In contrast to a thermocauter, better coagulation can be
achieved by high frequency currents because it does not
cause superficial burning
16.
17. Fulguration
• The term 'fulguration' refers to superficial tissue destruction
without affecting deep-seated tissues.
• This is undertaken by passing sparks from a needle or a ball
electrode of small diameter to the tissue.
• When the electrode is held near the tissue without touching
it, an electric arc is produced, whose heat dries out the tissue.
• Fulguration permits fistulas and residual cysts to be
cauterized and minor haemorrhages to be stopped.
18. Dessication
• In desiccation, needle-point electrodes are stuck into the
tissue and then kept steady.
• Depending upon the intensity and duration of the current, a
high local increase in heat will be obtained.
• The tissue changes due to drying and limited coagulation.
20. HAEMOSTASIS
• The concurrent use of continuous radio-frequency current for cutting
and a burst wave radiofrequency for coagulation is called
Haemostasis mode.
• The cutting current usually results in bleeding at the site of incision,
whereas the surgeon would require bloodless cutting.
21. • Requires ahigh temperature arc, exceeding1000°Cat the operative site.
• The cross-section of the arc is extremely small, less than 1 mm diameter,
leading to a high current density in the arc.
• Heating effect α (current density) 2
• Other factors affecting the rise in temperature are
– the composition of the tissues and
– the magnitude of cooling provided by the local blood flow or any other heat
transport system.
22. Electro-surgery techniques
The electric current can flow only if the electric circuit is closed.
In terms of current flow, there are two types of electro-surgical techniques:
the mono-polar and the bi-polar technique.
Mono-polar technique:
In the mono-polar technique the current flows from the active electrode
through the patient to the neutral electrode (patient plate) from which it
returns to the generator.
The cutting or coagulating effect depends on the contact area between the
mono-polar active electrode and the tissue, which is very small compared
with the contact area between the patient plate and patient's skin.
Bi-polar technique:
Here two electrodes are used. The current flows through the tissue between
the tips of the two electrodes and returns to the generator without passage
through the patient.
The bipolar surgery is not only safer than mono-polar but is also more precise
since the current only flows locally at the specific site where it is actually
required for heat generation. In addition, the risk of inadvertent burning of
the patient at the patient plate is very low.
Therefore, the bi-polar technique is becoming a method of choice wherever
possible.
23. • A surgical diathermy machine consists of a high frequency power
oscillator.
• The earlier machines consisted of spark-gap oscillators whereas the
current practice is to use thermionic valves or solid-state oscillators.
• A majority of the earlier units have access to both these power sources,
viz. an RF generator and a spark-gap generator.
• The RF generator provides an undamped high frequency current
(typically 1.75 MHz) which is suitable for making clean cuttings.
• The spark-gap generator produces damped high frequency current which
is specifically suitable for the coagulation of all kinds of tissues.
• By blending the currents of the tube and spark-gap generator, the degree
of coagulation of wound edges may be chosen according to the
requirements.
24. Technical
developments• Nowadays, vacuum tube & spark gap units replaced by solid
state generators
• Disposable, self-adhering dispersive electrode (ground pads)
are used instead of large plate electrode
• More safety features are included in the design like
– Dispersive electrode cable continuity
– Patient circuit continuity
– Path current monitors
• Frequency of operation of solid state diathermy machines is
250 kHz-1 MHz
• They deliver 400 W in 500 Ω load at 2000V in the cutting
mode and 150 W in coagulation mode
• In coagulation, the burst duration is 10-15 s and repetition
frequency of the burst is 15kHz.
26. Heart of the system is the logic board and the control
panel which produces the timing signals for all modes of
operations.
An astable multi-vibrator generates 500 kHz square pulses
The output from this oscillator is divided into a number of frequencies which are
used as timing signals.
250 kHz- drives output stages on the power output board
15 kHz - produces repetition rate for 3 cycles of the 250 kHz to make up
coagulating output (pulse width 12 µs)
250 kHz signal is used for cutting and it controls a push pull parallel power transistor
output stage.
Output of this high power push pull amplifier is applied to a transformer which
provides voltage step-up and isolation.
Tomeet the high power requirements, 20 transistors are used in a parallel darlington
circuit
Power output amplifier circuitry varies in different machines. Modern machines
use BJT(BIPOLAR JUNCTION TRANSISTOR ) and MOSFET(METAL OXIDE SEMI
CONDUCTOR FIELD EFFECT TRANSISTOR )
27. Each mode of operation is identified easily with
an audio tone generator
1kHz – coagulation; 500Hz – cutting; 250Hz-hemostasis
Isolator switch provides isolated switching control between active hand
switch and the rest of the machine.
A high frequency transformer coupled power oscillator is used in which isolated
output winding produces a DC voltage. The load put on the DC output by the
hand switch is reflected back to the oscillator, accomplishing isolated switching.
There is a provision to interrupt the power output if so desired.
Logic circuits also receive external control signals and operate the isolating
relays, give visual indications and determine the alarm conditions. They receive
information from the foot-switch, finger switch and alarm sensing points.
A thermostat is mounted on the power amplifier heat sink. In case of over
temperature, it becomes open-circuited, signaling an alarm and interrupting
the output.
28. a) In the earthed output system, the indifferent electrode is connected conductively to
protective earth (Fig. a).
(b) The earth referenced system uses a capacitor to connect the indifferent electrode to
earth Fig. b). This permits RF currents to flow to earth through the diathermy machine. It
effectively blocks the passage of low frequency currents (50 Hz )
(c) In the isolated system, the return electrode is floating, i.e., there is no intentional
connection to earth (Fig. c). The RF leakage current is due to stray capacitance within the
machine
29. • With a conventional electro-surgical unit, there is a
considerable fluctuation of the output voltage throughout the 3-s period of the cut.
This is linked to the following factors:
Size and Shape of the Cutting Electrode: The conditions are different for the generator
if, cutting is performed with electrode of large surface area or with a fine needle.
Type and Speed of Cut: The cutting quality is determined by the speed with which the
electrode is moved (quick or slow) and by the type of cut (superficial or deep)
Different Tissue Properties: Tissue has a strong influence on the quality of the cut. For
example, in tissues with a high resistance such as fat, the output voltage is increased
whereas in tissues with a low electric resistance, such as nerves and blood vessels, the
output voltage may drop significantly.
30. Introduction-Microprocessor based
• When the maximum output voltage becomes above 600°C severe carbonization occurs.
• When the minimum value of the output voltage goes below 200°C cutting action
is not achieved.
• To overcome this problem, microprocessor- controlled automated systems have been
developed so that the output voltage or the spark intensity remain constant.
• Here, the variables current, tissue resistance, voltage and spark intensity are registered by
means of an inbuilt sensor system and then processed as defined output signals.
• The automatic control operates on two different criteria:
- Voltage control: whereby the selected voltage is controlled and held constant.
- Spark control: by which the selected spark intensity is held constant.
• The design of the control system ensures that the cutting quality is independent of size and
shape of the electrode, the type and speed of the cut and the varying tissue properties.
31. Microprocessor based surgical diathermy
coagulation modes: Soft coagulation (a): no electric arcs are produced between the coagulation electrode and
the tissue during the entire coagulation process to prevent the tissue from becoming carbonized. Soft
coagulation - coagulation electrodes in direct contact with the tissue to be coagulated.
• Forced Coagulation (b): electric arcs are generated between the coagulation electrode and the tissue in
order to obtain deeper coagulation than could be achieved with soft coagulation, when using thinner or
smaller electrodes.
• Spray Coagulation (c): electric arcs are deliberately produced between the spray electrode and tissue, so
that direct contact between electrode and tissue is unnecessary. Spray coagulation is used both for surface
coagulation and haemostasis of vessels not directly accessible to coagulation electrodes, such as those
hidden in bone fissures.
32. Electrodes used
• The bi-polar technique is used in most of the
applications involving surgical diathermy.
• The high potential terminal of the diathermy
is connected to the cutting electrode which is
mounted in an insulated handle.
• The cutting electrodes are available in a
variety of shapes, the choice depending upon
the nature of application.
• Lancet electrodes are normally used for cutting applications
• Needle electrodes are preferred for epilation and desiccation.
• Loop electrodes are employed for exsecting (or opening up) channels and extirpating
growths, etc.
• The active electrodes for coagulation purposes are of ball type or plate type.
• In electro-surgery, the surgeon is able to switch
the high frequency current on and off himself.
• This can be done with a finger-tip switch in the
electrode handle or a foot switch.
33. Electrodes
• The low potential terminal of the radio frequency output leads is connected to the
indifferent or dispersive electrode which is a lead plate (15 x 20 cm) wrapped in a cloth
bag, soaked in saline solution and strapped onto the patient's thigh.
• An alternative arrangement is to use a flexible non-crumpling stainless steel sheet
plate without any covering.
• Good contact is established with the film of perspiration rising between the plate and
the patient's body. Quite often, a liberal amount of conductive paste like ECG paste is
applied to the plate. This gives excellent electrical contact and removes the need to
keep a wet gauze pad.
• However, problems may arise if the paste is not cleaned from the plate after use as it
may form a hard insulating layer.
34. • An alternative approach is to use capacitively coupled plates in which no direct
contact is made between the metal of the indifferent electrode and the
patient's skin.
• The electrode comprises a large sheet of thin metal sandwiched between two
sheets of neoprene, which formed a capacitor with the patient's body.
• This capacitor allows an easy path for the passage of the high frequency
diathermy currents. But there is a problem of introducing burn hazard when
alternative current paths when other equipment with grounded patient
connection is used.
• The common reason for faulty performance of an electro-surgical unit is
improper
• placement of the indifferent electrode.
• This electrode must be placed in firm contact with a fleshy portion of the patient
and as near as possible to the operating site.
• Poor contact or excessive distance from the operating site causes a loss of energy
available for the actual surgical procedure.
35. • RISKS ASSOCIATED WITH DIATHERMY Diathermy should be avoided in
following cases:
• implanted metal devices
• peripheral vascular disease
• tissue with restricted blood supply (ischemia)
• cancer
• bleeding disorders , wound dressings
• severe heart, liver, or kidney conditions
• pregnancy
36. PACEMAKER
• Responses to ELECTROCAUTERY
oInhibtion of pacing
oAsynchronous pacing
oMyocardial burns
oVentricular fibrillation
37. ICD
• Responses to electrocautery
oInhibition of pacing
oAsynchronous pacing
oInappropiate tachytherapy
oInhibition tachytherapy
38. • PRECAUTIONS
• Bipolar cautery
• If unipolar cautery , active cautery tip close to the site of operation and
indifferent plate as far as away from pacemaker
• Electrocautery should not be used within 15 cms from pacemaker
• Short bursts with long pauses are preferred – 1 second burst with 10 second
pause
• Pacemaker programmed to asynchronous mode
• If defibrillation is required , paddles must be placed as far as possible from
pacemaker generator
• In elective cardioversion , lowest voltage necessary should be utilized
