intermiate equipments(1).ppt

Contents
Introduction
Principle of ESU
Application
Types of ESU
Techniques of ESU
Operation
Safety
Maintenance & Performance checkup
Troubleshooting
2

Introduction & History
Electrosurgery is a simple, well
proven, method of making
surgical incisions, control
bleeding and destroying
unwanted tissue cells by the use
of a high frequency
"electrosurgical current".

History
• 1875 – Electric current was passed through wire loop until
they were red hot and heat was transferred to tissue by
contact with the red hot wire
• The ESU developed by Cushing and Bovie was a spark-gap
unit that consisted of two small metal conducting pieces
separated by an air gap. It worked like the familiar
automobile spark plug. When voltage rises enough to jump
across the air gap, the air becomes ionized and functions as a
conductor.

History
• 1924 – Ground reference generator by Dr. Harvey
Cushing and Bovie
• 1970 – solid state generator
• 1980 – Argon Electrosurgery

History
• Founder - Dr. Harvey Cushion and
William Bovie.
6

Principle of Electro
surgery in OR
The electrosurgical generator is the
source of the electron flow and
voltage.
The circuit is composed of the generator,
active electrode, patient and patient
return electrode.
The patient’s tissue provides the
impedance, producing heat as the
electrons overcome the impedance
7

Frequency
spectrum
Because nerve and muscle stimulation cease
at 100,000cycles/second(100kHz) ,
electro surgery can be performed
safely at radio frequencies above
100kHz.
An ESU generator takes 50Hz current and
increase the frequency to over
20,000kHz. At this frequency ESU
energy can pass through the patient with
minimal neuromuscular stimulation and
no risk of electrocution
8

Why HF current not giving shock?

 Effects of high current to the human body
 The large abnormal electric current (ion currents) cause nerves to fire,
which causes muscles to tense up, and this can include the heart muscle
and the diaphragm
 Suddenly-tensed muscles can throw the body across a room hard enough
to break bones or cause concussions.
 Also, electric currents directed through your heart can trigger fibrillation,
which is a type of fast, quivering heartbeat which does not pump blood.
Once fibrillation is triggered, it might not stop by itself.
 And finally, large electric currents can cause heating which cooks tissue.

Effect of HF current
A DC current flows constantly and uniformly throughout the cross-section of
a uniform wire.
An AC current of any frequency is forced away from the wire's center,
toward its outer surface. This is because the acceleration of an electric
charge in an alternating current produces waves of electromagnetic
radiation that cancel the propagation of electricity toward the center of
materials with high conductivity. This phenomenon is called skin effect.
Since the current tends to flow in the periphery of conductors, the effective
cross-section of the conductor is reduced. This increases the effective AC
resistance of the conductor and results higher energy loss due to ohmic
heating (also called I2R loss).

Effect of HF current to the body
very high frequencies (like above 20khz), the current will show
tendency to flow the skin surface . It will not show the
tendency to flow deep
The High frequency , the nerves muscles will not contract,
instead they sit still and quiver. This doesn't fire nerves, so the
pain and muscle contractions,
Since its flowing on small area of surface the heat energy will
produce high than normal current flow

Principle
• Active Electrode – High Current
Concentration
• Dispersive Electrode – Low
Current and Heat dissipates
• Current concentration or density
depends on the size of the area
through which the current flows.

Confusion……??
• Electro Cautery Unit
• Electro Surgical Unit

Electrocautery
 Electro cautery refers to direct current (electrons
flowing in one direction) whereas electro surgery
uses alternating current.
 During electro cautery, current does not enter the
patient’s body. Only the heated wire comes in
contact with tissue. In electro surgery, the patient is
included in the circuit and current enters the
patient’s body.
 A high amount of current is passed through the
electrode and burning or coagulate the tissue.
 Electrode for Electro cautery is Scalpel / Wire
 Electrocautery is used in surgery to burn unwanted
or harmful tissue. Also used to stop hemorrhage.

Electro Surgical Unit
 A high frequency Current flows through
active electrode ( AC source)
 Cell ruptured- fumes or evaporates
 Return path through Dispersive Electrode
 Patient is included in circuit
16

Effect of RF current on
Cell
• When a high frequency current is applied to
the tissues, the tissue gets torn apart and
gets the following effects
• Thermal Effect
• Electrolytic Effect and
• Faradic Effect

ELECTROSURGICAL TISSUE EFFECT
1. Electro surgical cutting
Electrosurgical cutting divides tissue with
electric sparks that focus intense heat at
the surgical site.
By sparking to tissue, the surgeon produces
maximum current concentration.
This will produce greatest amount of heat
over a very short period of time, which
results in vaporization of tissue.

Electrosurgery-Cutting
• The RF current applied to
the tip of Electrode
• The cutting waveform has
100% Duty Cycle

2.Fulguration (Blend)
Electrosurgical fulguration (sparking with
coagulation)coagulates and chars the
tissue over a wide area.
Since the duty cycle is only about 6%, less
heat is produced and the result is the
creation of a coagulation rather than
cellular vaporization.
In order to overcome the high impedance of
air, the coagulation waveform has
significantly higher voltage than the
cutting current.

Blend Waveform
• It is a combining characteristics of cutting and coagulation
waveform that results in cutting with moderate hemostasis.
21

Desiccation(Coagulation)
Electrosurgical desiccation occurs when the
electrode is in direct contact with the tissue.
Desiccation is achieved most efficiently with the
“cutting” current.
By touching the tissue with the electrode, the
current concentration is reduced. Less heat is
generated and no cutting action occurs.
The cells dry out and form a coagulum rather than
vaporize and explode
 Coagulation By Needle Electrode or Ball
Electrode can be achieved

Desiccation (Coagulation)
In this mode ,needle or ball electrode is
kept steady inside the tissue.
When RF current flows through the
tissue cell, it becomes hot and water
evaporates slowly so cell plasma gets
coagulated.

Many surgeons routinely “cut” with the coagulation current. Likewise,
can coagulate with the cutting current by holding the electrode in
direct contact with tissue.
It may be necessary to adjust power settings and electrode size to
achieve the desired surgical effect. The benefit of coagulating with
the cutting current is that you will be using far less voltage.
Likewise, cutting with the cut current will also accomplish the task with
less voltage. This is an important consideration during minimally
invasive procedures.

Variable impacting Tissue effect
• Waveform
• Power Setting
• Size of Electrode
• Time
• Manipulation of Electrode
• Type of Tissue
• Eschar

Variable impacting
Tissue effect
Waveform:
ESU generators are able to produce a
variety of electrical waveforms.
As waveform changes, so will the
corresponding tissue effect like cutting,
coagulation, and blend.
26

Variable impacting Tissue effect
 Size of the electrode: The smaller the electrode, the higher the current
concentration. Consequently, the same tissue effect can be achieved with a
smaller electrode, even though the power setting is reduced.
 Time: At any given setting, the longer the generator is activated, the more
heat is produced. And the greater the heat, the farther it will travel to
adjacent tissue (thermal spread).
 Manipulation of the electrode: This can determine whether vaporization
or coagulation occurs. This is a function of current density and the
resultant heat produced while sparking to tissue versus holding the
electrode in direct contact with tissue.
 Type of Tissue: Tissues vary widely in resistance.
 Eschar: Eschar is relatively high in resistance to current. Keeping
electrodes clean and free of eschar will enhance performance by
maintaining lower resistance within the surgical circuit.

Application
• Widely used in Operation Room to perform surgical
operation on patient.
• Most suitable for delicate Neurosurgery, Plastic Surgery
and Ophthalmic Surgery.

Application
To remove small lesions, moles, fungus, bacteria, hair
follicles.
Ophthalmic, Neurology, ENT ( To stop Nose Bleeding),
Gynecology, Dermatology
Laparoscopy and Trans Urethral resection of Prostate
(TURP)
Organs - Liver, Spleen, Thyroid, Lungs and Heart Surgery

Operating Frequency
 The frequency of operation of solid state surgical diathermy
machine is 300KHz – 3MHz
 {Ex- Load of 500Ώ, output 400W i.e about 2000 Volt in
cutting mode and 150 W in Coagulation mode.}

TYPES OF ESU
1. SPARK GAP GENERATORS
2. SOLID STATE GENERATORS
3. GROUNDED ELECTROSURGICAL
SYSTEMS
4. ISOLATED ELECTROSURGICAL
SYSTEM
5. DEACTIVATED ISOLATED

Types of ESU
Spark Gap Generator
 Transistor circuits
 Vacuum Tubes
 Less safety for handling
Solid State Generator
 Transistor Based Amplifier
 Oscillator Circuit
 Modified waveform- Blend
Waveform
 High safety
32

TYPE OF ESU
Types
of ESU
Spark Gap
generator
Solid State
Generator
Grounded
ESU
Isolated
System
De
activated
isolated
system
Argon
enhanced
esu

Spark gap generator
Spark Gap Generator
• Transistor circuits
• Vacuum Tubes
• Less safety for handling

Solid state generator
Solid State Generator
• Transistor Based Amplifier
• Oscillator Circuit
• Modified waveform- Blend Waveform
• High safety

Grounded ESU system
• Electrosurgical technology has changed dramatically since its
introduction in the 1920s.
• Generators operate by taking alternating current and increasing its
frequency from 50 / 60Hz to over 20oKhz
• Originally, generators used grounded current from a wall outlet. It
was assumed that, once the current entered the patient’s body, it
would return to ground through the patient return electrode.
Disadvantages- Grounded ESU system
But electricity will always seek the path of least resistance. When there
are many conductive objects touching the patient and leading to
ground, the current will select as its pathway to ground the most
conductive object—which may not be the patient return electrode.
Current concentration at this point may lead to an alternate site
burn.
36

Grounded ESU system
In Grounded ESU system , the current may split (or
divide) and follow more than one path to ground.
The circuit to ground is completed whether it travels the
intended electrosurgical circuit to the patient return
electrode or to an alternate ground referenced site.
Patients are thereby exposed to the risk of alternate site
burns because
1)current follows the easiest, most conductive path;
2) any grounded object, not just the generator, can
complete the circuit;
3) the surgical environment offers many alternative
routes to ground;
4) if the resistance of the alternate path is low enough and
the current flowing to ground in that path is
sufficiently concentrated, an unintended burn may be
produced at the alternate grounding site.
37

Isolated ESU
 In 1968, electrosurgery was revolutionized by isolated
generator technology.
 The isolated generator isolates the therapeutic current from
ground by referencing it within the generator circuitry.
 In other words, in an isolated electrosurgical system, the
circuit is completed not by the ground but by the generator.
 Even though grounded objects remain in the operating room,
electrosurgical current from isolated generators will not
recognize grounded objects as pathways to complete the
circuit.
 Isolated electrosurgical energy recognizes the patient return
electrode as the preferred pathway back to the generator.
 By removing ground as a reference for the current, the
isolated generator eliminates many of the hazards inherent in
grounded systems, most importantly current division and
alternate site burns.
38

isolated ESU system
 Disadvantages – Isolated system
 If the circuit to the patient return electrode is broken, an
isolated generator will deactivate the system because the
current cannot return to its source.
 Generators with isolated circuits mitigate the hazard of
alternate site burns but do not protect the patient from
return electrode burns, such as the one shown at right.
 Historically, patient return electrode burns have accounted
for 70% of the injuries reported during the use of electro
surgery.
 Patient return electrodes are not “inactive” or “passive”.
The only difference between the “active” electrode and
the patient return electrode is their size and relative
conductivity.
 The quality of the conductivity and contact area at the
pad/patient interface must be maintained to prevent a
return electrode site injury.
39

Recent Technology
Tissue Response Technology
It uses a computer-controlled tissue feedback system that senses
tissue impedance (resistance) and automatically adjusts the
current and output voltage to maintain a consistent surgical
effect.
Advantage - Reduces the need to adjust power settings for
different types of tissue.
It also gives improved performance at lower power settings and
voltages, which helps to reduce the risk of patient injury.

Argon Enhanced Technology
 Argon enhanced electro surgery
incorporates a stream of argon gas to
improve surgical effectiveness of
electrosurgical current
 Argon Gas is highly conductive and It
produces a beam like manner and creates
a bridge between electrode and tissue
without any resistance
 Argon Gas Properties :
Inert Gas
Non combustible
Easily ionizes
Displays the blood to visualize surgical site
Less smoke

Modes of Electrosurgery
Monopolar Surgery
Bipolar Surgery

Monopolar Surgery
 RF current flows through ESU and
Active Electrode
 Returns to ESU through Return
Electrode.
 Used for cut and coagulation.
43

Bipolar Electrosurgery
Output current flows via BIPOLAR electrode in one terminal
Returns the current through another terminal
It is much safer than Monopolar surgery
Used for cut and coagulation too.
44

Advantages of Bipolar
• It is much safer than Monopolar
• RF current flows only through well defined area, while in
Monopolar current flows back through large section of patient
body
• Risk of patient touch is low
• Less Interference for other instruments
• No ‘patient plate’ or ‘Return electrode’ is required

Electrode
• There are two types of Electrodes used in Electrosurgery
1. Active Electrode
2. Dispersive Electrode.(patient return electrode)

Active electrode
• There are two types of Active Electrode
Cutting Electrode
Coagulation Electrode

Cutting Electrode
 Cutting Electrode – They are available in different
shapes (Angulated, Needle or wire loop shape)
Wire Loop Electrode Angulated Electrode
48

Coagulation Electrode
These are available in the blunt shape, ball shape
or Bipolar type. The density area of this
electrode is bit larger than cutting electrode.
Bipolar Electrode Ball Type Electrode
49

Dispersive Electrode(patient Return
electrode)
• It is also called as ‘Indifferent Electrode’ or
‘Patient Return Electrode’
• The function of the patient return electrode is to remove current
from the patient safely.
• A return electrode burn occurs when the heat produced, over time,
is not safely dissipated by the size or conductivity of the patient
return electrode.
• BURN = CURRENT x TIME
AREA
50

Dispersive / Passive Electrode
 Lead (Metal) plate wrapped in wet cloth bag.
 Disposable Type Electrode.
 Area should be larger than active electrode about more than 100cm²
Single Contact Surface Double Contact Surface.
51

Placement and area of affect
The patient becomes the part of
electronic circuit
As the current seeks for shortest and
less resistive path to ground, user
should be aware that position of patient
return electrode should be as shorter as
possible.
52

Placement and area of affect
 If a return electrode is placed far from the
operating task, the current has to travel a
long distance, resulting increase in the
power setting.
 Accidentally, if any part of the patient body
touches to ground, a burn effect will occur at
that site.
 Ideally the arms or muscular abdomen can
be a suitable site for placement of patient
return electrode.
53

Ideal patient return electrode
The ideal patient return electrode safely
collects current delivered to the patient
during electrosurgery and carries that
current away.
To eliminate the risk of current
concentration, the pad should present a
large low impedance contact area to the
patient.
Placement should be on conductive tissue
that is close to the operative site.
54

Patient return electrode
monitoring REM
REM™ contact quality monitoring was developed to
protect patients from burns due to inadequate contact
of the return electrode. Pad site burns are caused by
decreased contact area at the return electrode site
The system is designed to deactivate the generator
before an injury can occur, if it detects a dangerously
high level of impedance at the patient/pad interface.

ADAPTIVE TECHNOLOGIES
1.Instant Response Technology
COMPUTER CONTROLLED OUT PUT IS AUTOMATICALLY ADJUSTED
 Measures tissue impedance/resistance at the electrode contact site
 Provides instant response to changes in any tissue impedance
 Produces consistent tissue effect as demonstrated by a high power
efficiency rating (PER)of approximately 98 out of 100
 Controls maximum out put voltages
Reduces capacitive coupling and video interference
Minimizes sparking
* Power Efficiency Rating (PER) is a measure of the ability of an
electrosurgical generator to accurately deliver the selected power into
a wide range of tissue types.

ADAPTIVE TECHNOLOGIES
Vessel sealing technology
 Vessel sealing technology™ is an electrosurgical technology
that combines pressure
and energy to create a seal.
 Reliable, consistent permanent vessel wall fusion
 Minimal thermal spread
 Reduced sticking and charring
 Seal strength higher than other energy-based techniques
 Seal strengths comparable to existing mechanical based
techniques

RF Ablation system
The electrode’s internal circulation of water
cools the tissue adjacent to the exposed
electrode, maintaining low impedance
during the treatment cycle.
Low impedance permits maximum energy
deposition for a larger ablation volume
58

ELECTROSURGERY SAFETY
CONSIDERATION
When electrosurgery is used in the context of
minimally invasive surgery, it raises a new
set of safety concerns. Some of these are:
• Insulation failure,
• Direct coupling of current,
• Capacitively coupled current.

Electrosurgery safety consideration
 Insulation failure
 Many surgeons routinely use the coagulation waveform. This
waveform is comparatively high in voltage. This voltage or
“push” can spark through compromised insulation. Also, high
voltage can “blow holes” in weak insulation.
 Breaks in insulation can create an alternate route for the
current to flow. If this current is concentrated, it can cause
significant injury.

Direct Coupling
Direct coupling occurs when the user accidentally activates the
generator while the active electrode is near another metal
instrument.
The secondary instrument will become energized. This energy
will seek a pathway to complete the circuit to the patient return
electrode.
There is potential for significant patient injury

Capacitor coupling
a)Metal cannula system:
During Surgical procedures, an “inadvertent capacitor” may be
created by the surgical instruments. The conductive active
electrode is surrounded by nonconductive insulation. This, in
turn, is surrounded by a conductive metal cannula.
A capacitor creates an electrostatic field between the two
conductors and, as a result, a current in one conductor can,
through the electrostatic field, induce a current in the second
conductor.

Capacitor coupling
b) Plastic cannula system
Capacitance cannot be entirely
eliminated with an all plastic
cannula. The patient’s
conductive tissue completes the
definition of a capacitor.
Capacitance is reduced, but is
not eliminated
63

SURGICAL SMOKE EVACUATION
SYSTEM
SURGICAL SMOKE IS CREATED WHEN TISSUE GET
HEATED UPAND FLUID GETS VAPORISED BY THE
THERMALACTION OF ESU SOURCE
Viral DNA, Carcinogens, bacteria and irritants are known to be
present in ESU smoke
National Institute of occupational safety and health NIOSH and the
centre for disease contrio(CDC)also studied and conclude that
“ the smoke plume can contain the toxic gases such as benzene,
hydrogen cynaide and formaldehyde,bioaerosols, dead and live
cellular material( including blood fragments and viruses “
This smoke to be removed with smoke evacuation unit

Power Settings
 The power settings for various procedures varies from one user to
another, as different surgical techniques are used with different
electrodes
 Monopolar
Low Power
Oral surgery
Dermatology
Polypectomy
Plastic surgery
Neurosurgery
Vasectomies
Hand surgery

Power Settings
 Medium Power
Orthopedic surgery
Normal thoracic
 General surgery
Head/neck/ENT surgery
Vascular surgery
Transurethral resections (using fine loops)
 High Power
Transurethral resections (using ball ends and thicker loops)
Thoracotomies for heavy coagulation

Power Settings
Bipolar
MICRO-BIPOLAR (up to 15 watts output)
Low Power
Eye surgery
Fine neurosurgery
Medium Power
Neurosurgery
Fine plastic surgery
High Power
Hand surgery
Plastic surgery

Power Settings
• MACRO-BIPOLAR (up to 50 watts output)
• Low Power
Hand surgery
Plastic surgery
• Medium Power
General surgery
• High Power
Orthopedic surgery

Front Panel
• On/Off Switch – To switch ON
and Off the ESU.
• Coag Dial – Clock wise rotation
of dial to increase the output
gradually
70

Front Panel
• CUT Dial – To increase the current
density to cut a tissue.
• Pure / Blend Selector – Switch or key
to select the type of cutting current,
either PURE for minimum hemostasis
or BLEND for average hemostasis
while cutting.
71

Indicator
 COAG Mode – Indicator illuminates blue
when activating the output.
 CUT Mode – Indicator illuminates yellow
when CUTTING (Pure or Blend) is selected.
 Patient Return Electrode fault Indicator- for
poor patient contact alarm
72

Front Panel
• Monopolar Receptacle – It will accept
three pin hand switch forcep. Only
hand switch mechanism will work.
• Monopolar Receptacle – Standard
receptacle for accessories. It will
activate only if footswitch is connected.
73

Front Panel
Patient Return Electrode Receptacle –
The two pin connector to attach patient
return electrode in Monopolar procedure
Bipolar Receptacle – It accepts three pin
receptacle for bipolar electrode. This will
activate with and without footswitch.
74

Rear Panel
• Foot Switch Receptacle – It accepts
monopolar footswitch connector.
• Audio volume Control – The tone volume
can be adjusted for Cut, Coag and Bipolar
mode.
• Equipotential Lug – It may be connected
to earth ground with a cable.
75

Operation
Visual Inspection
Check continuity and condition of power cable, plugs and
Accessories cable.
Check for any crack, insulation break , frayed cable
Generator tone should be at an audible level
Check instrument for proper functioning before operation.

Functional Test
 Attach footswitch to rear panel or to the ESU receptacle end.
 Attach Power Cord to AC plug.
 Put ‘ON’ the main switch of ESU.
 Wait for self test to pass.
 Connect Monopolar / Bipolar Electrode and cable to respective
connector.
 Switch ‘ON’ the High Frequency by means of pressing footswitch
or handle switch.
 Increase the ‘Energy Level’ and look for audible sound and visual
light indicator.
 Confirm all the time lowest power setting and confirm with
surgeon.

Keep in mind……..
 Always prefer lowest power setting and confirm
with surgeon.
 Do attend for checking audible and visual signal.
 Patient Return Electrode is not required for
Bipolar mode.
 Sparking at active electrode is a common
occurrence.
 There is no guarantee for where the current flows
or where other tissue being affected.

Power Supply
The power supply generates the supply of
+5VDC, -5VDC, +15VDC, -15VDC, +24VDC,
which is supplied to all units. It is basically like a
low voltage power supply. The 5VDC are used for
the front panel control and Display. It also
monitors the generated voltage for diagnostic
purpose to measure the current drawn from power
supply.

Power Supply
• RF output Board – It has a power amplifier
assembly, which comprises with Bipolar,
Monopolar, CUT/ COAG and BLEND waveform.
• The output circuit is fully isolated. It generates the
out put as per front panel instruction given to Main
Board and Logic Control Board.

Power Supply
• It generates the Switch mode pulse pattern
generator, Drive circuit for output switching
power MOSFETS and High Frequency filtering
components.
• In enhanced type generator, the output power is
managed and controlled according to patient’s
tissue impedance

• Memory Board – The function of this board is to
accept operating mode control signal from front
panel, rear panel and foot switch.
• It checks and identifies that which connector is in
use and monitors its continuity.
• Interfaced Front Panel switch signals decode and
passes information to Display.

Memory Board
• It has a microprocessor, used together with
EPROM as program memory and RAM.
• The analog to digital conversion of signal to
convert the commands received from front panel
and fed to logic board.
• It also generates the audible command whenever
any fault occurs during self-test and operation. It
detects all front panel operation and acts as per
instruction

Logic Board / Relay Board – The board is mainly
interfaced with Main Board or sometimes all
functions of Main Board are incorporated.
It is a liaison between front panel and output
required. All signals are inter-related to this board.
It gives the power output command to RF or Power
output board and monitors the output. It has relay
board too, which activates according to finger
switch or foot switch control.

• Front Panel – It consists of membrane keyboard,
Power switch, Patient Return Electrode,
Monopolar, Bipolar connector.
• Front panel also interfaces with Display Board and
Power Supply Board. The Power Supply Switch
supplies the AC mains current to the
Electrosurgical Unit.

• Display Board – It is located in the Front Panel
Assembly. It contains RF indicator lamp, Seven segment LED,
Monopolar / Bipolar mode of surgery.
• The RF indicator lamps are used for visual indication of
presence of RF power during activation. The improper
attachment of Patient Return Electrode is visually indicated by
Patient Return LED.
• It also contains LED driver circuit and Seven Segment
Display, which indicates the Bipolar, Monopolar, Cut,
Coagulation power settings.

• Audio Tone Generator – It
receives the command from Main
board, which activates the Audio
oscillator circuit.
• Audio circuitry gets ON at time of
activation of high frequency, any
malfunction or Fault of ESU,
improper or loose attachment of
patient Return Electrode and
Power up.

Isolation Board
The patient interface board is interfaced with the Main Board. It has
several different functions, which is concerned with patient
connected parts and provides the patient isolation voltage.
 It monitors the patient plate continuity, plate voltage, BIPOLAR
forceps switch, CUT / BLEND, and COAG finger switches and
patient earth monitor.
 It monitors the high frequency leakage current. This board passes
the Active electrode signals to main board and continuously monitors
the patient plate continuity. If any break occurs in plate lead or not
plugged IN, the related signal activates and passes to main board to
generate audible signal.

Safety
General Safety
High Frequency (Sometimes referred to as radio frequency or HF)
surgery can result in serious injuries to patient if carelessly or
incorrectly applied. HF surgical instrument should be used on
patient exclusively by personnel familiar with feature and operation
of the equipment.
In order to prevent accidental injuries due to fault, failure to
equipment or its accessories, the equipment and its accessories
should be regularly checked for proper and safe operation.
Electrodes and cables are to fasten carefully.

Safety
Hazardous electrical out put
 Electrosurgical unit is recommended to use only by qualified
medical personnel. To avoid burns, do not touch active
electrodes.
 Do not operate in explosive atmosphere
 To avoid explosion, do not operate unit in an explosive
atmosphere.
 Prevent Electrosurgery use in the presence of flammable gases,
flammable liquids, or flammable objects

Electrical Safety
 Electrosurgical units may cause interference with improperly shielded
medical equipment.
 Use proper power cord.
Use only a power cord in a good condition with properly grounded
receptacle.
 Use the proper fuses
To avoid fire hazard, use only fuses of correct type, voltage rating and
current rating as specified. Remove the power cord during replacement
of fuse.
 Do not touch the active electrode to grounded metal parts or to the
patient plate for function proving.
 The cables to HF-electrodes should be as short as possible and must be
arranged without loops so that they touch neither the patient nor other
cables. Only cables recommended by the manufacturer should be used.
 Foot switches used in explosion hazard areas must be explosion proof.

Patient Safety
Ensure that there is no air gap between patient’s body and
patient return electrode.
Ensure that no small-surface area contact is made between the
patient and any of the metal parts of the treatment chair, table,
saline water stand, which conduct ground potential. Heat may
be generated at such points leading to undesired burns.
The patient plate shall be reliable in good contact with the
patient‘s skin for the whole operation;
If patient plate is fastened at limbs, Be careful that it doesn’t
affect the supply of blood.

Patient Safety
The return path of the HF-current shall be as short as possible
and in longitudinal or diagonal direction of the body. It should
not go transversely through the body, especially at the thorax.
The patient with pacemaker should be treated and consulted
through cardiology department as the high frequency may affect
or damage to the pacemaker. Outpatient with pacemakers
should not be treated using a HF generator.
Avoids skin to skin contact, such as fingers touching the patient's
leg, when ESU is activated.

Patient return Electrode
safety precautions
Discard the disposable packages that have expired.
Use ‘Patient Return Electrode’ according to the manufacturer’s
documented instruction.
Inspect patient return electrode before each use for wire breakage or
fraying.
Select appropriate size patient return electrode for patient (i.e,
neonate/infant, pediatric, adult).
Do not cut patient return electrode to accommodate patient size.
Shave, clean and dry at application site as needed.

Patient return Electrode safety
precautions
 Place patient return electrode on positioned patient on a clean,
dry skin, convex area in close proximity to operative site.
 Avoid bony scar tissue, skin over an implanted metal
prosthesis, hairy surfaces, pressure points, tissue, and areas
where fluid may pool.
 Apply finger pressure to adhesive border of the electrode and
massages entire pad area to ensure adequate contact with the
patient's skin.

Patient return Electrode safety precautions
 Follows manufacturers' guidelines for alarm system, check prior to use.
 Check patient return electrode connections to confirm that they are clean,
intact, and can make effective contact.
 Remove patient return electrode gently to protect skin.

Active Electrode safety precautions
Avoid coiling, bundling, or clamping of active and patient return
electrodes.
Avoid wrapping the active electrode cord around a metal
instrument.
Remove all metal patient jewelry to prevent current diversion and
to avoid contact with other metals.
Place active electrodes in a non-conductive holster designed to hold
electrosurgical pencils and similar accessories, when they are not in
use.

Active Electrode safety precautions
Activate electrode mode and function.
Keep active electrode free from debris
Record placement of patient return electrode,
identification number of unit, and settings
used.
Inspect insulation on reusable and disposable
electrodes before and after use

Preventative Maintenance
 Chassis / Housing - Check Exterior of unit for cleanliness and general physical
condition. Be sure that plastic housings are intact, that all hardware is present and
fitting are firm and tight, and that there are no signs of spilled liquids.
 Mount / Fasteners - If the device is mounted on a stand or cart, examine the condition
of the mount. If it is attached to a wall or rests on a shelf, check the security of this
attachment.
 AC Plug / Receptacles – Check AC power plug for damage. Attempt to wiggle the
blades to check that they are secure. Shake the plug for loose screws. If any damage is
suspected, open the plug and inspect it. Check the fuse and fitting position.
 Line Cord - Inspect the cord for damage & excessive bending. If damaged, replace the
entire cord. Verify the minimum power cord length before cutting the defective
position.
 Strain Relief - Examine the strain relief at both ends of the line cord. Be sure that they
hold the cord securely.
 Circuit Breaker / Fuse - If the device has an external circuit breaker, check that it
operates freely. If the device is protected by an external fuse, check its value and type
against that marked on the chassis and ensure that a spare is provided.

Preventative Maintenance
 Connectors – Examine all cables of the ESU for proper fittings and firm contact of
connectors.
 Probes - Confirm that probes for their physical condition. For disposable probes check expiry
date.
 Controls / Switches - Examine all controls and switches for physical condition, secure
mounting, and correct motion. Look for loose connections. Check for proper alignment, as
well as positive stopping. Confirm the functioning of each switch and controls proper
functioning.
 Indicators / Displays - Confirm the operation of all indicators on the unit that all segments of
a digital display function and functioning of Alarms.
 Audible Signal - Operate the device to activate any audible signals.
 Labeling - Check for necessary labels, and instruction cards are present.
 Dispersive Electrode cable continuity – Check the patient return electrode continuity and any
alarm functioning on removal.
 Accessories (Footswitch) – To check the physical integrity, connection and proper operation
of all accessories related to ESU

Safety Test Procedure
 Switch on the safety analyzer and connect the Test lead between
ENCL and EARTH
 Press set up in the main menu.
 Press ‘CAL’ in the system set up.
 Press “Calibrate Test Lead Enclosure/Ground.
 The test results are displayed once the Calibration is complete.
 Connect the Main Plug of the Electrosurgical Unit (ESU) to the Safety
Analyzer Terminal on the front panel.
104

Safety Test Procedure
 Connect the calibrated Test lead between ENCL on the Safety
Analyser Terminal to the Chassis or the ground terminal of the
Electrosurgical Unit (ESU).
 Ensure that the main switch on the Electrosurgical Unit (ESU) is
switched ‘ON’.
 In the main menu, press Equipment Code and enter the Asset
number of the ESU.
 Press Equipment Classification and select classification.
 Press Start in the main menu to start the test.
 Once the Electrical Safety Test is over, print the test result.

Quantitative Test
 Connect the Electrosurgical Unit to the Electrosurgical Analyzer and
verify output power generated by ESU. Procedure to check Output
 Power up the Electrosurgical Analyzer and wait for self test to pass.
 Attach the Monopolar Electrode and patient return electrode to the
ESU.
 Connect and hold Active electrode with crocodile pin to the
Electrosurgical analyzer jack, similarly connect the patient return
electrode.
 Put ‘ON’ the ESU analyzer and wait for self test to pass.
 Once the Main display appears select the particular load (e.g. 500 )
 Put ‘ON’ the ESU and wait to complete the self-test.

Quantitative Test
Select CUT mode and minimum power out put energy on
Monopolar by pressing UP and DOWN arrow key.
Press the Hand switch or foot switch to get the output.
Note the audible sound and measured power output.
Selected Output on ESU and Displayed output on ESU
analyzer should be same or with in range of tolerance.
Select the different power and note down the readings. (If
it differs refer service manual for calibration)
Similarly check for COAG mode.
Check for Bipolar mode.

Troubleshooting
• Servicing Techniques
• Service Manual
• Guess or Judge
• Step by step procedure to
troubleshoot.

Troubleshooting
USER CHECKLIST
 Check the Electrosurgical Unit (ESU) for physical damage.
 Verify all accessories cords are connected properly.
 Check the condition of power cord, it should not be frayed,
damaged, crack or exposed of any wire otherwise replace the
same immediately.
 Check the fuse of ESU. It should be firmly fitted inside the fuse
socket. Also check for any corrosion and damages if so replace the
same rating of fuse as mentioned in manual and on ESU.

Troubleshooting
Disconnect the power cord and check for Footswitch receptacle
damage or obstruction. If found replace the rear panel or rear panel
connector.
Check for the firm contact of Bipolar Instrument receptacle on front
panel for obstruction and damage. If found replace the front panel or
front panel connector.
Check for the firm contact of Monopolar instrument receptacle on
front panel for any obstruction and damage. If found replace the
front panel or front panel connector.
Check the patient return electrode receptacle for any broken pins
and obstruction. If found replace the front panel or front panel
connector

Recommendation to avoid esu
patient complication
 Inspect insulation carefully
 Use lowest possible power setting
 Use a low voltage waveform(cut)
 Do not activate in open circuit
 Do not activate when direct contact with another instrument
 Use bipolar surgery when appropriate
 Select an all metal cannula system as the safest choice. Do not
use hybrid cannula system that mixes metal and plastic

Tools and equipments for
maintenance and calibration
• BME/T tools box
• ESUA
• ESA
• Oscilloscope(optional)

Practical activity
• Read user and service manuals of given device
• List parts of machine by observation of the device
and explain the purpose of each
• Draw schematic diagram of device( electrical)
• Measure the functionality of each components
• Check the overall functionality of the device by
doing performance test
• Fill the sheets of PM

Learning Goal(Mission)
1. To understand Defibrillator design and
working principle
2. Being able to perform maintenance and
Troubleshooting

Contents
1. Introduction
2. application
3. Working principle and type
4. Troubleshooting and Routine
Maintenance

Definition
• Defibrillator is a device which delivers a
therapeutic dose of electrical energy to the
heart
• Defibrillation is a process in which an
electronic device sends an electric shock to the
heart to stop an extremely rapid, irregular
heart beat, and restore the normal heart
rhythm.
• It can be external (placed on the chest)
or internal (surgically placed in the chest).

Function/application
 Ventricular fibrillation is a cardiac condition where individual
heart muscles Contract in a random, uncoordinated way the heart
seems to shiver, and blood circulation stops. The application of an
electric shock to restore normal Heart function is the only way to
effectively treat a ventricular fibrillation and prevent death.

Defibrillation Waveform type of defibrillstor
Current delivered
in one direction
Current delivered
in two directions
Monophasic Biphasic

Cardiac Dose
• Defibrillation requires
adequate current –
Transcardiac current to
flow across the heart
• As Transcardiac current
flows, it delivers energy
to the heart
Transcardiac
current

Cardiac Dose
Transcardiac current
• As little as 5% of defibrilla
tor’s current crosses the he
art !
• The rest is “shunted”
– Does not deliver energy
to the heart
Defibrillator current
Shunt current

Cardiac Dose
• Shunting is patient-dependent
– Reflected in reduced patient
impedance ()
• Defibrillator must adjust
– Small change in shunting,
BIG change in transcardiac
current
– Low  requires more
defibrillator current
15 A
1.5 A
transcardiac
current
6.75 A
6.75 A
15 A
7.13 A
7.13 A
0.75 A
transcardiac
current

Water Tank Analogy
• A basic understanding of
electricity is often helpful in
understanding the differences
between biphasic waveforms.
Components of electricity are
often described in terms of
water: voltage is analogous to
pressure - such as that created
in a tank of water; current is
analogous to flow

200 µF
More energy
and/or voltage
100 µF
Less energy
and/or voltage
The physics behind how a defibrillator work
ENERGY
( VOLTS )
>
• The Capacitor of defibrillator store a large amount of energy in the
form of electrical charge then over a short period of time, the
capacitor
Releases the stored energy.

Energy, Voltage, and Current
Voltage, Current, and Impedance
• V x I = Watts (or Power; P)
• P x t (or Wattseconds) = Energy
• Current is determined by initial voltage and patient
impedance
• V = IR; I = V/R
Ohm’s Law

• Energy and current are NOT the same
• Peak current best predictor of defibrillation success
• Energy is best predictor of myocardial dysfunction
360 Joules 360 Joules
(10 ma over 6 min)
(20 amps over 10ms)
Energy vs. Current

50
40
30
20
10
0
-10
-20
0 5 10 15 20 25 30 35 40 45
50, 200 J
75, 210 J
125, 220 J
Time (msec)
Current (A)
• High peak current/voltage
leads to dysfunction
• Tail end of high impedance
waveform is associated
with refibrillation risk
Monophasic Waveform
Higher Peak current,
Increase Cardiac
muscle damage rate

50
40
30
20
10
0
-10
-20
0 5 10 15 20 25 30 35 40 45
• Designed to deliver selected
energy by changing duration
• Lower peak current, but
duration
lengthens with increased
impedance
• Refibrillation risk increases
when duration >20msec
Time (msec)
Current (A)
50, 200 J
75, 210 J
125, 220 J
Monophasic Waveform

Bi-phasic
technology
-30
-20
-10
0
10
20
30
40
50
-5 0 5 10 15 20 25
Time (msec)
Current
(A)

What makes a Good Biphasic ?
• Cardiac Dose
– Transcardiac current
• Waveform Shape
– Duration
– Phase ratio
– Tilt
Time
Voltage
Time
Voltage
Time
Voltage

Cleaning
• The defibrillator may be surface-cl
eaned by using a soft cloth dampe
ned with
• Either a commercial, nonabrasive
cleaner solutions.
• Quatemary Ammonium
• Alcohol-70% Isopropyl
• 10%Chlorine bleach solution
• PDI sani-Systerm
• For cables, sensors, cuffs, and pro
bes, follow cleaning instructions in
the directions for use shipped with
those components.

Safety and Function checks
1. Inspect the exterior of the defibrillator for
damage.
2. Inspect labels for legibility. If the labels are
to legible, contact Manufacturer
3. If the defibrillator has been visibly damaged o
r subjected to mechanical shock (for example,
if dropped), Perform the performance tests as
described in Performance Verification section.
If the defibrillator fails these performance test
s, refer to Troubleshooting section.
4. Perform the electrical safety tests detailed in
Performance Verification section. If the defibr
illator fails these electrical safety tests, do not
attempt to repair. Contact manufacturer
5. Inspect the fuses for proper value and raing.
Qty2,6.3,250 volts for AC mains

Picture Safety and function tests

Checks Battery
1. If the defibrillator has not been used for a long period
of time, more than 6 months, the battery will need ch
arging.
2. Note: Storing the defibrillator for a long period with
out charging the
3. battery may degrade the battery capacity. The batter
y may
4. require a full charge/discharge cycale to restore nom
al capacity.
5. CAUTION: if the defibrillator is to be stored for a pe
riod of 2 months
6. Longer, it is recommended to notify service personal t
o re move the battery prior to storage.
7. CAUTION: if the battery shows any signs of damage,
leakage,of cracking, it must be replaced immediately.

Performance
• Manual Self-Test
• Connect the defibrillator to an
AC power soursce.
• Rotate the Mode select knob t
o monitor mode to turn on the
defibrillator
• Press Setup soft key.
• Rotate Multi function knob an
d select Manual self test menu
.
• Manual self-Test is started as
Figure this below

1) Checking external paddles
2) Energy discharge test
3) Checking 360J energy charge and disarm
4) Battery test
5) HV Capacitor test
6) Recorder Test
7) Date and time check.
8) ECG and Sync test
Parts and Performance

Performances verification
Required Equipment

Firmware Download
① Connect the defibrillator/monitor to AC power source.
② Connect SD memory card containing the software to SD card port on the
the right panel of the defibrillator/monitor.
③ Rotate Mode select knob to monitor to turn on the defibrillator/monitor.
④ Press Setup soft key then select Service menu using Multi function knob.
⑤ Enter the pass code.
⑥ The defibrillator/monitor will display the Software update screen.
⑦ Choose Software update menu and then select Main software or Analog
software menu or Display software menu or Voice prompt menu.

Categories Problem Check Point
Power
 No battery charge
 No turn on
 Battery/ SMPS/ Charger board
Display  Display malfunction  Main board / CPU / LCD
Controls  Controls malfunction  Front board / Main board
ECG  ECG malfunction  ECG board / Main board / HV board
NIBP  NIBP malfunction  NIBP module / Main board
SpO2  SpO2 malfunction  SpO2 module / Main board
Temperature  No display  Temperature board / Main board / CPU
Respiration  No display  ECG board / Main board / CPU
IBP  No display  IBP module / Main board / CPU
Defibrillation
& Pacing
 Pacing malfunction
 Defibrillation Failure
 HV board/ Main board / CPU
Troubleshooting

Tools and equipments for
maintenance and calibration
• BME/T tools box
• DA
• ESA
• Oscilloscope(optional)

The Anesthesia Machine: Introduction

Objectives
• Know the definition of an Anesthesia Machine
• Know the different parts of an Anesthesia
Machine and their use.
• Set up and use of anesthetic machine
• System check out
• Common Problems and repairs

What is an Anesthetic Machine?
• A medical equipment used to administer anesthesia to patients.
• monitors patient and allow the anesthetist/anesthesiologist (user) to
make necessary adjustment in order to keep patients under stable state of
anesthesia.
• gives the patient a mixture of anesthetic gases and oxygen.
• Has incorporated devices that monitors vital signs (HR,BP, Temp, SPO2…)
• Has alarm systems to allow failsafe operations.
• Has a protection system that prevents the surgeons, anesthetists… to
inhale anesthetic gases.(scavenging system)

What is Anesthetic Gas?
 Gas used to temporarily keep the patient in total unconsciousness.
(General anesthesia)
 2 types of anesthetic gases are common:
1. Ether Halogenated (most common):e.g. ISOFLURANE,SEVOFLURANE
2. Non-Ether Halogenated hydrocarbons: e.g. HALOTHANE, CHOLOROFORM
 Non-Ether Halogenated hydrocarbons are no longer used in
developed countries because they are toxic, but are very common
in Third World. E.g. HALOTHANE is very common in Rwanda.
 Other types of anesthetic gases: XENON (costly)
 The Anesthetic gases are stored in liquid state at room
temperature but are very volatile.
 A vaporizer is used to administer the anesthetic gases to patients

vaporizer
bellow
Corrugated
tube
Soda lime
Flow
meter
ventilator
APL valve
Scavenging
system

 APL (Adjustable Pressure Limiting) valve: Pressure limiting
valve which releases gas over an adjustable range of pressures
on purpose to control system pressure and thus
intrapulmonary pressure, or to release excess anesthetic gases
and vapors.
 Scavenging System: An assembly of specific components that
collect excessive exhaled gases and exhausts them out of the
operating room to minimize pollution.
 Soda lime: A mixture of sodium and calcium hydroxides that
absorbs liquids and gases, especially CO2 from breathing
gases.
 Vaporizer: Used to produce an accurate amount of gas from a
volatile liquid anesthetic gas. It has a dial or knob to know and
to regulate the percentage of anesthetic gases given to the
patient.

The Anesthesia Machine
High Intermediate Low Pressure Circuit

High Pressure System
• Gas from the high pressure cylinders or from a
compressor and an O2 plant is supply via the
back of the anesthesia machine (2200 psig for
O2)
• The high pressure side consists of:
– Hanger Yolk (reserve gas cylinder holder)
– Check valve (prevent reverse flow of gas)
– Cylinder Pressure Indicator (Gauge)
– Pressure Reducing Device (Regulator)
• Cylinders are not used if there is wall-mounted
gas supply.

Pressure Reducing Device
• Reduces the high and variable pressures found in a cylinder to
a lower and more constant pressure found in the anesthesia
machine (45 psig)
• Reducing devices are preset so that the machine uses only gas
from the pipeline (wall gas), when the pipeline inlet pressure
is 50 psig.
This prevents gas use from the cylinder even if the cylinder is
left open (i.e. saves the cylinder for backup if the wall gas
pipeline fails)

Intermediate Pressure System
 Gets gas from the cylinder regulator or the
hospital pipeline at pressures of 40-55 psig
 Consists of:
 Pipeline inlet connections
 Pressure gauges
 Pipes
 Gas power outlet
 Master switch
 Oxygen pressure failure
devices
 Oxygen flush
 Additional reducing
devices
 Flow control valves

Pipeline Inlet Connectors
 Mandatory N2O and O2,
usually have air and suction
too
 Inlets are non-interchangeable
due to specific threading as
per the Diameter Index Safety
System (DISS)
 Each inlet must contain a
check valve to prevent reverse
flow (similar to the cylinder
yolk)

Oxygen Pressure Monitors
• An anesthesia machine is designed such that it sounds an
alarm whenever the oxygen supply pressure falls below
normal range. (O2 concentration should not be below 19%)

Oxygen Pressure Failure Devices
• A Fail-Safe valve is found in each gas line supplying
the flow meters. This valve shuts off or
proportionately decreases the supply pressure of all
other gasses with the decrease in O2 supply
pressure.
• 2 kinds of fail-safe valves exist:
– Pressure sensor shut-off valve (e.g. Ohmeda)
– Oxygen failure protection device (e.g. Drager)

Pressure Sensor Shut-Off Valve
• Oxygen supply pressure opens the valve as long as it is
above a pre-set minimum value (e.g.. 20 psig).
• If the oxygen supply pressure falls below the threshold
value the valve closes and the gas in that limb (e.g..
N2O), does not advance to its flow-control valve.

Oxygen Failure Protection Device
(OFPD)
• Based on a proportioning principle rather than a shut-
off principle
• The pressure of all gases controlled by the OFPD will
decrease proportionately with the oxygen pressure

Oxygen Flush Valve
• Receives O2 from pipeline inlet or cylinder reducing device and
directs high, unmetered flow directly to the common gas outlet
(downstream of the vaporizer)
• Machine standard requires that the flow be between 35 and 75
L/min
• The ability to provide jet ventilation
• Hazards
– May cause barotrauma

Second-Stage Reducing Device
• Located just upstream of the flow control
valves
• Receives gas from the pipeline inlet or the
cylinder reducing device and reduces it further
to 26 psig for N2O and 14 psig for O2
• Purpose is to eliminate fluctuations in
pressure supplied to the flow indicators
caused by fluctuations in pipeline pressure

Low Pressure System
• It goes from the flow control valves to the gas outlet and
consists of:
– Flow meters
– Vaporizer mounting device
– Check valve
– Common gas outlet

Flowmeter assembly
• When the flow control valve is
opened the gas enters at the
bottom and flows up the tube
elevating the indicator
• The indicator floats freely at a
point where the downward
force on it (gravity) equals the
upward force caused by gas
molecules hitting the bottom
of the float

Arrangement of the Flow-Indicator
Tubes
• In the presence of a flowmeter leak (either at the “O” ring or the glass of the
flow tube) a hypoxic mixture is less likely to occur if the O2 flowmeter is
downstream of all other flowmeters
• In A and B a hypoxic mixture can result because a substantial portion of oxygen
flow passes through the leak, and all nitrous oxide is directed to the common
gas outlet
* Note that a leak in the oxygen flowmeter tube can cause a hypoxic mixture, even when
oxygen is located in the downstream position

Proportioning Systems
– Mechanical integration
of the N2O and O2
flow-control valves
– Automatically
intercedes to maintain a
minimum 25%
concentration of oxygen
with a maximum
N2O:O2 ratio of 3:1

Limitations of Proportioning
Systems
• Machines equipped with proportioning systems can
still deliver a hypoxic mixture under the following
conditions:
– Wrong supply gas
– Defective pneumatics or mechanics
– Leak downstream (e.g.. Broken oxygen flow tube)
– Inert gas administration: Proportioning systems generally
link only N2O and O2

Vaporizers
• A vaporizer is an device designed to change a liquid
anesthetic agent into its vapor and add a controlled
amount of this vapor to the fresh gas flow

Classification of Vaporizers
Methods of regulating output concentration
Concentration calibrated (e.g. variable bypass)
Measured flow
Method of vaporization
Flow-over
Bubble through
Injection
Temperature compensation
Thermocompensation
Supplied heat

Generic Bypass Vaporizer
• Flow from the flowmeters
enters the inlet of the
vaporizer
• The function of the
concentration control valve is
to regulate the amount of
flow through the bypass and
vaporizing chambers
Splitting Ratio = flow though vaporizing
chamber/flow through bypass
chamber

Factors That Influence Vaporizer
Output
• Flow Rate: The output of the vaporizer is generally
less than the dial setting at very low (< 200 ml/min) or
very high (> 15 L/min) flows
• Temperature: Automatic temperature compensating
mechanisms in bypass chambers maintain a constant
vaporizer output with varying temperatures
• Back Pressure: Intermittent back pressure (e.g.
positive pressure ventilation causes a higher vaporizer
output than the dial setting)

Factors That Influence Vaporizer
Output
• Atmospheric Pressure: Changes in atmospheric
pressure affect variable bypass vaporizer output as
measured by volume % concentration, but not (or
very little) as measured by partial pressure (lowering
atmospheric pressure increases volume %
concentration and vice versa)
• Carrier Gas: Vaporizers are calibrated for 100%
oxygen. Carrier gases other than this result in
decreased vaporizer output.

The Circuit: Circle System
• Arrangement is variable, but to prevent re-
breathing of CO2, the following rules must be
followed:
– Unidirectional valves between the patient
and the reservoir bag
– Fresh-gas-flow cannot enter the circuit
between the expiratory valve and the patient.
– Adjustable pressure-limiting valve (APL)
cannot be located between the patient and
the inspiratory valve

Circle System
 Advantages:
 Relative stability of inspired concentration
 Conservation of respiratory moisture and heat
 Prevention of operating room pollution
 PaCO2 depends only on ventilation, not fresh gas
flow
 Low fresh gas flows can be used
 Disadvantages:
 Complex design = potential for malfunction
 High resistance (multiple one-way valves) = higher
work of breathing

The Adjustable Pressure Limiting
(APL) Valve
• User adjustable valve that releases gases to the
scavenging system and is intended to provide
control of the pressure in the breathing system
• Bag-mask Ventilation: Valve is usually left
partially open. During inspiration the bag is
squeezed pushing gas into the inspiratory limb until
the pressure relief is reached, opening the APL
valve.
• Mechanical Ventilation: The APL valve is excluded
from the circuit when the selector switch is changed
from manual to automatic ventilation

APL valve
• Protects the breathing circuit or ventilator from
excessive positive or negative pressure.

Checking Anesthesia Machines
Categories of checks:
• Emergency ventilation equipment
• Gas supply/High pressure system
• Low-Pressure system
• APL valve and Scavenging system
• Breathing system
• Manual and automatic ventilation system
• Monitors
• Final configurations

High Pressure Leak test.
1.Machine OFF
2.Connect cylinders, turn each ON then OFF
3.Cylinder pressure should not drop
4.If there is a leak disconnect the Ventilator and
the Aux oxygen.
5.If still a leak plug Fresh Gas Outlet

187
Low Pressure Leak Test.
1. Machine OFF
2. Vaporisers OFF
3. Flowmeters OPEN
4. Use bulb to create negative pressure, bulb should not
inflate.
5. Open Vaporiser one at a time.

Breathing system leak test.
1. Connect patient circuit and connect test lung.
2. Close APL valve.
3. Vent/bag switch to Bag. (Maybe called Vent/Manual
Spont)
4. Close Flowmeters, Oxygen to minimum.
5. Depress Oxygen Flush to inflate bag to pressure of
30cmH20.
6. Pressure should hold for at least 5 seconds
188

Ventilator bellow leak test.
1. Set the Bag/Vent switch to Ventilator
2. Vent/bag switch to Ventilator. (Maybe called
Vent/Manual Spont)
3. Push the flush to fill bellows
4. Observe bellows do not fall (leak test)
5. Set the oxygen flow to 5 L – check that the end
expiratory pressure does not exceed 3cm H2O on the
airway pressure gauge
189

191
Ventilator Functional Check
1. Reduce oxygen flow to minimum
2. Set the controls as per hospital regimes e.g.
3. Ventilator mode, Volume Control
4. Ventilator Tidal volume – 400mls
Rate - 12
I:E ratio 1:2
P limit 40 cmH2O
PEEP OFF
Ensure:
The bellows inflate and deflate during mechanical
ventilation
The ventilator displays the correct data
Tidal volume is 400mls (+ or – 10% ) after 6-8
breaths

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