electrical safety for anesthesiologists

1. Presenter: Dr. Sabin Bhandari
Moderator: Dr. Asish Ghimire

2. Electricity is actually made
up of extremely tiny particles
called electrons, that you
cannot see with the naked
eye unless you have been
drinking.
Dave Barry
In The Taming of the Screw: How to
Sidestep Several Million Homeowner's
Problems (1983), 12.

3. Bread has been made (indifferent) from potatoes;
And galvanism has set some corpses grinning,
But has not answer'd like the apparatus
Of the Humane Society's beginning,
By which men are unsuffocated gratis:
What wondrous new machines have late been spinning.
Lord George Gordon Byron

4. • Principles of Electricity
• Electrical Shock Hazards
• Grounding
• The line isolation monitor
• Ground fault circuit interrupter
• Electrosurgery
• Electromagnetic interference(EMI)
OUTLINE

5. Electricity is the flow of
electrons
PRINCIPLES OF ELECTRICITY

6. Conductor- Any substance that
permit flow of electrons
Insulator- Any substance that does
not allow the flow of electrons

7. DC- Electrons flow in one
direction
PRINCIPLES OF ELECTRICITY…
DIRECT AND ALTERNATING CURRENTS
Note: Current leaves the source and
returns to the source

8. AC- Electron flow switches
direction at regular interval.
120 times/sec
for 60 Hz current

9. Ohm's law:
V OR E = I × R
where,
E is electromotive force (in
volts),
I is current (in amperes),
R is resistance (in ohms).
PRINCIPLES OF ELECTRICITY…

10. Ohm’s law for fluid
Pressure = Flow * Resistance
Basis for the physiologic
equation
B.P. = CO * SVR
Where, B.P. is blood pressure
CO is cardiac output
SVR is systemic vascular
resistance

11. Electrical power is measured in
watts.
Wattage (W) is the product of
the voltage (E) and the current
(I), as defined by the formula:
P or W = E × I
P = (I × R) × I
P = I2 × R
Note: power can also be thought as a
measure of heat produced
PRINCIPLES OF ELECTRICITY…

12. The amount of electrical work done is
measured in watts multiplied by a unit of
time.
The watt-second (a joule, J) is a common
designation for electrical energy
expended in doing work.
The kilowatt-hour is used by electrical
utility companies to measure larger
quantities of electrical energy.
PRINCIPLES OF ELECTRICITY…
ELECTRICAL ENERGY

13. Impedance, Z, is defined as the sum of the forces that oppose
electron movement in an AC circuit.
Impedance consists of resistance (ohms) but also takes
capacitance and inductance into account.
When referring to AC circuits, Ohm's law is defined as:
E = I × Z
PRINCIPLES OF ELECTRICITY…
IMPEDANCE

14. Inductance is a property of AC
circuits in which an opposing EMF
can be electromagnetically
generated in the circuit
Whenever electrons flow in a wire,
a magnetic field is induced around
the wire.
PRINCIPLES OF ELECTRICITY…
INDUCTANCE

15. If the wire is coiled repeatedly around an iron
core, as in a transformer, the magnetic field
can be very strong thus impeding the flow of
current.
The impedance is directly proportional to the
frequency (f) times the inductance (IND):
Zα (f × IND)
The net result of inductance is to increase
impedence.

16. Capacitance is the measure of that
substance's ability to store charge.
A capacitor consists of any two
parallel conductors that are
separated by an insulator.
PRINCIPLES OF ELECTRICITY…
CAPACITANCE

17. In a DC circuit, there is only a momentary current flow, the
circuit is not completed and no further flow occurs
A capacitor in an AC circuit permits current flow even when
the circuit is not completed by a resistance.
The capacitor plates are alternately charged—first positive
and then negative with every reversal of the AC current
direction—resulting in an effective current flow, even though
the circuit is not completed.
PRINCIPLES OF ELECTRICITY…

18. The impedance is inversely proportional to the product of the
frequency (f) and the capacitance (CAP):
Zα1/(2×π× f × CAP)
For DC, f becomes 0 and impedence becomes infinitely large
For AC, the greater the AC frequency, the lower the
impedance

19. Impedance and capacitance are inversely related
As current increases in frequency, the net effect of both
capacitance and inductance increases
Total impedance however decreases as the product of the
frequency and the capacitance increases.
PRINCIPLES OF ELECTRICITY…

20. Inherent in all electrical equipment
Capacitance that was not designed into the
system but is incidental to the construction of
the equipment
An ordinary power cord consisting of two
insulated wires running next to each other will
generate significant capacitance simply by being
plugged to a circuit though not turned on.
PRINCIPLES OF ELECTRICITY…
STRAY CAPACITANCE/CAPACITIVE COUPLING-

21. • Principles of Electricity
• Electrical Shock Hazards
• Grounding
• The line isolation monitor
• Ground fault circuit interrupter
• Electrosurgery
• Electromagnetic interference(EMI)

22. If electrical system are not properly wired, persons can be
electrocuted
• DC – less dangerous
• AC – 3 times as dangerous as DC
ELECTRICAL SHOCK HAZARDS

23. Why electricity is particularly
dangerous in the operating
room ??
1. Operating rooms are full
of electrical equipment.
ELECTRICAL SHOCK HAZARDS

24. 2. Anaesthetized patients
are "helpless" and can't
move away from a
shock.

25. 3. Operating rooms are full of
fluids

26. 4. Electrical current is invisible

27. Electrical accidents or shocks occur
when a person becomes part of, or
completes, an electrical circuit.
To receive a shock,
1. one must contact the electrical
circuit at two points, i.e., a closed
loop must exist
2. and there must be a voltage source
that causes the current to flow
through an individual.

28. The power company attempts to maintain the line voltage
constant at 120 volts.
They use AC at a frequency of 60 Hz
Why are our homes and hospitals supplied with AC and
not DC ?

29. TRANSFORMERS

30. A transformer "transforms"
voltage to a higher voltage or a
lower voltage
If it transforms the input voltage
to a higher output voltage, it is
called a "step up" transformer.
If it transforms the input voltage
to a lower output voltage, it is
called a "step down" transformer.

31. • The input AC goes into
the primary coil (pink)
• This produces a
changing magnetic field
(blue arc with arrows)
• The changing magnetic
field induces a current
in the secondary coil
(green)
Electrical energy is thus transferred from the primary
coil to the secondary coil.

32. If DC is used, the transformer
would not work.
The magnetic field would be non
changing and thus would not
transfer energy across to the
secondary coil.
Thus a transformer works only
with AC

33. WHY ARE TRANSFORMERS SO IMPORTANT ?
The electricity has to travel far
distance before reaching
homes and hospitals.
When electricity travels in
wires, it loses energy. I
If this happens over huge
distances, there will be nothing
left when the wire reaches us.

34. Wires carrying a low voltage
have higher losses than wires
carrying an high voltage
To minimize losses, the
power company transmits
electricity at high voltages.

35. Generators produce a relatively
low voltage.
This low voltage is raised by a
step up transformer to an high
voltage, which is used to send
the electricity over a long
distance.
As the wires reach us, the high
voltage is reduced using a
series of step down
transformers.

36. Because higher frequencies cause
greater power loss through
transmission lines
And lower frequencies cause a
detectable flicker from light sources.
WHY USE A FREQUENCY OF 60 HZ

37. Electrical accidents or shocks occur
when a person becomes part of, or
completes, an electrical circuit.
To receive a shock,
1. one must contact the electrical
circuit at two points, i.e., a closed
loop must exist
2. and there must be a voltage source
that causes the current to flow
through an individual.

38. First, the electrical current can disrupt the normal
electrical function of cells.
Depending on its magnitude, the current can
• Contract muscles,
• Alter brain function,
• Paralyze respiration, or
• Disrupt normal heart function, leading to ventricular fibrillation
CONSEQUENCES OF PASSAGE OF CURRENT
THROUGH THE BODY

39. The second mechanism involves the dissipation of electrical
energy throughout the body's tissues.
An electrical current passing through any resistance raises
the temperature of that substance.
If enough thermal energy is released, the temperature will
rise sufficiently to produce a burn.

40. The severity of an electrical shock is
determined by:
1. The amount of current (no of
amperes), which in turn, will
depend upon voltage source and
skin resistance of the person
2. The duration of the current flow
Skin resistance varies from a few
thousands to 1 million ohms.

41. Electric shock
Macro shock Micro shock
Note: While both can be fatal, when we talk about macro shock versus micro shock, we
generally are referring to risk of ventricular fibrillation.

42. Ventricular fibrillation (VF) causing
current can reach the heart in two ways:
One route it can take is to go through
the skin and tissues to reach the heart.
The skin normally has a very high
resistance to current flow.
Therefore, for “enough” current to reach
the heart and cause ventricular
fibrillation (VF), the current given to the
skin has to be fairly large.

43. Macro shock refers to large amounts of current flowing
through a person, which can cause harm or death.
If applied directly to the heart, it will also cause VF.
remote from the heart.

44. The other way is to give current
straight to the heart without it
having to go through the skin and
tissues.
A shock may be given directly to
the heart by something that
conducts electricity very well, such
as an pace maker wire or a
conducting fluid filled tube such as
a central venous pressure (CVP)
catheter.

45. The shock current that goes straight to the heart bypasses the high
resistance skin path and follows a low resistance pathway straight
to the heart.
Because the resistance is low, only a small current is needed to
cause VF.
Such type of individuals who has an external conduit that is in
direct contact with the heart are known as ELECTRICALLY
SUSCEPTIBLE PATIENT.
Micro shock refers to very small amounts of current and applies
only to electrically susceptible patient

46. Macro shock: Large
current able to go
through skin and
tissues to heart
Micro shock: Small
current able to go
through direct
connection to heart
IN SUMMARY

47. A way of expressing the amount of current that is applied per
unit area of tissue.
Current density is the amount of current that is applied per
unit area of the tissue
The diffusion of current in the body tends to
be in all directions.
The greater the current or the smaller the area
to which it is applied, the higher the current density.
CURRENT DENSITY

48. In relation to the heart, a current of 100 mA (100,000 µA) is
generally required to produce ventricular fibrillation when
applied to the surface of the body.
Only 100 µA (0.1 mA) is required to produce ventricular
fibrillation when that minute current is applied directly to the
myocardium through an instrument having a very small contact
area, such as a pacing wire electrode
In this case, the current density is 1000 fold greater when
applied directly to the heart, thus only 1/1000 of the current is
required to cause VF.

49. Current Effect
1 mA (0.001 A) Threshold of perception
5 mA (0.005 A) Accepted as maximum harmless
current intensity
10–20 mA (0.01–0.02 A) “Let-go” current before sustained
muscle contraction
50 mA (0.05 A) Pain, possible fainting, mechanical
injury; heart and respiratory
functions continue
100–300 mA (0.1–0.3 A) Ventricular fibrillation will start, but
respiratory center remains intact
6000 mA (6 A) Sustained myocardial contraction,
followed by normal heart rhythm; temporary respiratory paralysis;
burns if current density is high
EFFECTS OF 60-HZ CURRENT ON AN
AVERAGE HUMAN FOR A 1-SECOND
CONTACT
MACRO SHOCK

51. The “let-go” current is defined as that current above which
sustained muscular contraction occurs and at which an
individual would be unable to let go of an energized wire

52. Current Effect
100 μA (0.1 mA) Ventricular fibrillation
10 μA (0.01 mA) Recommended maximum 60-Hz
leakage current
MICRO SHOCK

53. • Principles of Electricity
• Electrical Shock Hazards
• Grounding
• The line isolation monitor
• Ground fault circuit interrupter
• Electrosurgery
• Electromagnetic interference(EMI)

54. Grounding is a common return path for electric current.
Electrons do not go to ground, they take the path of ground
to return to the source.
CONCEPT OF GROUNDING

55. A typical power cord supplying to
the house or hospital consists of 2
conductors
One, designated as hot or live
carries the current to the
impedence
The other wire which is also
connected to mother earth using a
wire, is called neutral and it returns
the current to the source.
Hot wire
Power supply to a hospital
CONCEPT OF GROUNDING

56. The electrical supply system (electrical grid)
is mostly outside and vulnerable to the
lightning strikes.
This lightning can result in very high
currents that could travel through the wires
into the hospital, causing major destruction.
The dangerous current from the lightning
strike goes through the neutral wire (see
arrows) to the "wire from neutral to earth”
and from there to earth instead of going to
home or hospital and causing damage.
WHY DO THE ELECTRICAL ENGINEERS
CONNECT THE NEUTRAL WIRE TO MOTHER
EARTH?

57. Electrons do not go to ground, they take the path of
ground to return to the source.
Grounding is a common return path for electric current.

58. For an individual to receive an
electric shock, he or she must
contact the loop at two points.
Only one additional contact point is
necessary to complete the circuit
and thus receive an electrical shock.
This is an unfortunate and
inherently dangerous consequence
of grounded power systems.

59. In electrical terminology, grounding is applied to two separate
concepts.
The first is the grounding of electrical power,
The second is the grounding of electrical equipment

60. Power can be grounded or ungrounded and that power can
supply electrical devices that are themselves grounded or
ungrounded are not mutually exclusive
Whereas electrical power is grounded in the home, it is usually
ungrounded in the OR.
In the home, electrical equipment may be grounded or
ungrounded, but it should always be grounded in the OR.

61. Diagram of a house with older style wiring that
does not contain a ground wire
Diagram of a house with modern wiring in which
the third, or ground, wire has been added

62. In modern electrical wiring
systems, the third or
equipment ground wire is
used which does not
normally have current
flowing through it.
In the event of a short
circuit, an electrical device
with a three-prong plug (i.e.,
a ground wire connected to
its case) will conduct the
majority of the short-
circuited or “fault” current
through the ground wire and
away from the individual.

63. Thus, in a grounded power
system, it is possible to have
either grounded or
ungrounded equipment,
depending on when the
wiring was installed and
whether the electrical device
is equipped with a three-
prong plug containing a
ground wire or a two prong
plug without a ground wire.
GROUNDED EQUIPMENT SYSTEM

64. There is one instance in which it is acceptable for a piece of
equipment to have only a two-prong and not a three-prong plug.
This is permitted when the instrument has what is termed double
insulation.
These instruments have two layers of insulation and usually have a
plastic exterior.
Double insulation is found in many home power tools and is seen
in hospital equipment such as infusion pumps.
DOUBLE INSULATION

65. Double-insulated equipment is permissible in the OR with
isolated power systems.
If water or saline should get inside the unit, there could be a
hazard because the double insulation is bypassed.
This is even more serious if the OR has no isolated power or
GFCIs.

66. Neutral grounded power system protects from
lightning or electrical storm but predisposes to
electric shock.
Can a transformer be placed inside the hospital
where it will be safe from such lightning strikes
thus eliminating the need for grounding of wires
???.
Unadvisable because the step down
transformer works with very high voltages
which would present an hazard to those
working inside the building.
Solution: Another transformer inside
the hospital !!!
No problem of electrical storm or high
voltage hazard
No need for grounding, thus
increasing the safety margin.

67. HOW DOES IT INCREASE THE SAFETY ??
The step down transformer outside has
a wire from neutral to earth for safety
(blue arrow).
On the other hand, the second
transformer inside the hospital is safe
and do not need a 'wire to earth' for this
transformer. (wire "absence" shown by
green arrow) .
There is a gap ( green arrow)
between the coils due to which there
is no direct electrical connection
between the two sides.
This gap prevents unwanted currents
such as those due to shocks from
going from one side to the other.

68. In other words, this transformer "isolates" the circuit on one
side (blue area) from the circuit on the other side (green area).
Because of this, it is called "isolation transformer".

69. In the OR, the isolation
transformer converts the grounded
power on the primary side to an
ungrounded power system on the
secondary side of the transformer.
A 120-volt potential difference
exists between line 1 and line 2.
There is no direct connection from
the power on the secondary side to
ground.
The equipment ground wire,
however, is still present.

70. Faulty equipment plugged into an isolated power system
does not present a shock hazard

71. Till now we assumed that the isolated power system is
perfectly isolated from ground.
Perfect isolation is impossible to achieve.
All AC-operated power systems and electrical devices
manifest some degree of capacitance.

72. As previously discussed, electrical power cords, wires, and
electrical motors exhibit capacitive coupling to the ground
wire and metal conduits and “leak” small amounts of
current to ground
This does not usually amount to more than a few milli
amperes in an OR.
So an individual coming in contact with one side of the
isolated power system would receive only a very small
shock (1 to 2 mA).

74. Modern patient monitors electrically isolates all direct patient
connections from the power supply of the monitor by placing a
very high impedance between the patient and any device.
This limits the amount of internal leakage through the patient
connection to a very small value.
The standard currently is <10 µA.

75. One should never simultaneously touch an electrical device and a
saline-filled central catheter or external pacing wires.
Whenever one is handling a central catheter or pacing wires, it is
best to insulate oneself by wearing rubber gloves.
One should never let any external current source, such as a
nerve stimulator, come into contact with the catheter or wires.
WHAT CAN WE DO TO PREVENT
MICROSHOCKS…

76. • Principles of Electricity
• Electrical Shock Hazards
• Grounding
• The line isolation monitor
• Ground fault circuit interrupter
• Electrosurgery
• Electromagnetic interference(EMI)

77. A device that continuously monitors the
integrity of an isolated power system (IPS).
It is essential that a warning system be in
place to alert the personnel that the power is
no longer ungrounded.
The device has a meter that displays a
continuous indication of the integrity of the
system
THE LINE ISOLATION MONITOR

78. Determines the degree of
isolation between the two power
wires and the ground
continuously
Predicts the current flow that
would occur if a fault did occur
The LIM is actually measuring
the impedance to the ground of
each side of the IPS

79. The LIM is actually connected to both sides of the
isolated power output and once this preset limit is
exceeded, visual and audible alarms are triggered.
For example, if the LIM were set to alarm at 2 mA
Using Ohm’s law :
Z = E/I
Z = (120 volts)/(0.002 ampere)
Z = 60,000 ohms, the impedance for either side of
the IPS would be 60,000 ohms
If either side of the IPS had less than 60,000 ohms
impedance to the ground, or when the maximum
current that a short circuit could cause exceeds
2 mA, the LIM would trigger an alarm.

80. A LIM alarm indicates the
existence of a single problem
(SINGLE FAULT), a faulty
piece of equipment is
plugged into the IPS.
-i.e. ungrounded system
becoming grounded
-back to regular power
-no chance for shock

81. A second problem (TWO FAULTS) are
required for SHOCK to occur:
• A faulty piece of equipment
• Unsafe environment like electric
device + pool of normal saline

82. If faulty piece of equipment is plugged
into the isolated power system, the LIM
alarm will go off (single fault)
The system would be converted to the
equivalent of a grounded power system.
This faulty piece of equipment should
be removed and serviced as soon as
possible.
CASE SCENARIOS

83. This piece of equipment could still be used
safely if it were essential for the care of the
patient.
Continuing to use this faulty piece of
equipment would create the potential for a
serious electrical shock e.g. standing in a
pool of normal saline.

84. The second situation involves connecting many
perfectly normal pieces of equipment to the isolated
power system.
If the total leakage exceeds 2 mA, the LIM will
trigger an alarm.
The LIM alarm would sound because the 2-mA set
point was violated.
For this reason, the newer LIMs are set to alarm at 5
mA instead of 2 mA.
CASE SCENARIOS

85. If the gauge reads >5 mA, most likely there is a faulty piece
of equipment present in the OR.
The next step is to identify the faulty equipment, which is
done by unplugging each piece of equipment until the alarm
ceases.
If the faulty piece of equipment is not of a life-support
nature, it should be removed from the OR.
ALARM RINGS !!!!!

86. If it is a vital piece of life-support equipment, it can be safely
used.
No other electrical equipment should be connected during the
remainder of the case, or until the faulty piece of equipment
can be safely removed.

87. LIM does not protect against microshock since it detects 2
mA- 5 mA
LIM does not protect from microshock, it warns of a
potential problem
REMEMBER MICROSHOCK VS
MACRO SHOCK ????

88. • Principles of Electricity
• Electrical Shock Hazards
• Grounding
• The line isolation monitor
• Ground fault circuit interrupter
• Electrocautery
• Electromagnetic interference(EMI)

89. Circuit breakers/interrupters are also
called “trip switches”
These “high current stopping” devices
work together "as a team" with the “wire
from the equipment case to ground” and
“breaks” (stops) the current flow if the
current flow exceeds a set limit
Once the high current problem is solved,
the switch can easily be pushed into the
ON position and the current will flow
again
CIRCUIT INTERRUPTER

90. Under normal conditions without a
fault, a normal current is going to the
equipment through the circuit breaker
which, because the current is not
high, remains in the ON position
In case of fault, the shock current
goes to the equipment case and then
goes to the ground.
This pathway has a very low resistance
and therefore current can flow very
easily which leads to a very large
current passing through the circuit
breaker.
The high current makes the circuit
breaker to move into the OFF
position and stops further current
flow.

91. This system protects for only relatively large currents, such as
10 amperes
Unfortunately, currents that are much smaller than this , such
as 100 milliamperes (100 times smaller than 10 amperes) can
cause fatal ventricular fibrillation
The ground fault circuit interrupter (GFCI, or GFI) is
another device used to prevent individuals from receiving an
electrical shock in a grounded power system
GROUND FAULT CIRCUIT INTERRUPTER

92. Works as an “unequal current
stopper”
The GFCI monitors both sides of the
circuit for the equality of current flow
It continuously checks to see if the
amount of current that leaves to the
equipment equals the amount of
current that returns from the
equipment i.e. it compares the current
flowing in the live wire and the
neutral wire to see if they are equal.
If there is a difference (i.e. it is not
equal), it switches OFF and stops the
current flow
WORKING PRINCIPLE

93. Since the GFCI can detect very small current
differences (in the range of 5 mA), the GFCI
will open the circuit in a few milliseconds,
thereby interrupting the current flow before a
significant shock occurs
It may be installed as an individual power
outlet or may be a special circuit breaker to
which all the individual protected outlets are
connected at a single point.
The special GFCI circuit breaker is located in
the main fuse/circuit breaker box.

94. Used to prevent electrical shock in grounded power system.
GFCI outlets enhance electrical safety by serving as emergency
circuit breakers that shut off power when one of the two power
lines in the outlet is accidentally connected to ground.
Thus, the GFCI is a “first fault” detector

95. If the OR has a GFCI that tripped, then one should first attempt
to reset it by pushing the reset button because a surge may have
caused the GFCI to trip.
If it cannot be reset, then the equipment must be removed from
service and checked by the biomedical engineering staff
It is essential that when GFCIs are used in an OR, only one outlet
be protected by each GFCI.
They should never be “daisy-chained,” so that one GFCI protects
multiple outlets

96. The disadvantage of using a GFCI in the OR is that it interrupts
the power without warning.
A defective piece of equipment could no longer be used, which
might be a problem if it were of a life-support nature.
If the same faulty piece of equipment were plugged into an IPS,
the LIM would alarm but the equipment could still be used.

97. First, the grounded power provided by the utility company can be
converted to ungrounded power by means of an isolation
transformer.
The LIM will continuously monitor the status of this isolation
from ground and warn when grounding has been lost.
In addition, the shock that an individual could receive from a
faulty piece of equipment is limited to a few milliamperes.
MEASURES AGAINST HAZARDOUS
CURRENT FLOWS IN OR

98. Second, all equipment plugged into the isolated power system
has an equipment ground wire that is attached to the case of the
instrument.
The equipment ground wire serves three functions.
1. It provides a low-resistance path for fault currents to reduce
the risk of macroshock.
2. It dissipates leakage currents that are potentially harmful to
the electrically susceptible patient.
3. It provides information to the LIM on the status of the
ungrounded power system.

99. • Principles of Electricity
• Electrical Shock Hazards
• Grounding
• The line isolation monitor
• Ground fault circuit interrupter
• Electrosurgery
• Electromagnetic interference(EMI)

100. Often “electrocautery” is used to
describe electrosurgery
Electrocautery refers to direct
current whereas electrosurgery uses
alternating current
During electrocautery, current does
not enter the patient’s body. Only
the heated wire comes in contact
with tissue
In electrosurgery, the patient is
included in the circuit and current
enters the patient’s body.

101. HISTORY LESSON
The first electrosurgical unit was developed in 1926 by Dr.
Harvey Cushing (a neurosurgeon) and Dr. William Bovie, a
Harvard physicist
The name “Bovie” has been associated with electrosurgical units
ever since

102. Electro surgery is the application
of a high-frequency electric
current to biological tissue as a
means to cut, coagulate, desiccate,
or fulgurate tissue.
Electrosurgical devices are
frequently used during surgical
operations helping to prevent
blood loss in hospital operating
rooms or in out patient
procedures.
INTRODUCTION

103. SYSTEM COMPONENTS
1. Generator (electrosurgical unit)
2. Inactive dispersive electrode (grounding
pad)
3. Active electrode (“Bovie” pencil)

104. The electrosurgical generator is the source of the
electron flow and voltage.
An electrosurgical generator takes 60 cycle
current and increases the frequency to over
200,000 cycles per second.
Nerve and muscle stimulation cease at 100,000
cycles/second (100 kHz)
At this frequency electrosurgical energy can pass
through the patient with minimal neuromuscular
stimulation and no risk of electrocution
WORKING PRINCIPLE

105. ESU is a form of highly controlled localized tissue burn.
Uses the principle is of current density.
“When a current is applied over a small area, the current
density is high and heating may occur”
During electrosurgery, high currents enter the patient
through a small-area surface electrode at the tip of the
cutting tool which confers high resistance attributable to the
small area.
Heat generated is proportional to I2 × R.
The tip of the electrode is also designed to produce lower
current densities (low I2R) at points farther than a few
millimeters from the electrode tip
WORKING PRINCIPLE

106. TYPES OF ESU UNITS
Monopolar
Bipolar
(Some ESU units have both monopolar & bipolar capability)

107. MONO-POLAR (FLOW OF CURRENT)

108. In most modern ESUs, the ESU is isolated
from ground so that the only route for
current flow would be via the return
electrode
If it is grounded or in older ESUs the
current could return via alternate pathways
which includes the OR table, stirrups, staff
members, and other equipments e.g. ECG
electrodes.
Even with isolated ESUs, the decrease in
impedance due to marked capacitative
coupling allows the current to return to the
ESU by alternate pathways

109. MONOPOLAR MODES
Electrosurgical generators are able
to produce a variety of electrical
waveforms.
Cut
Coag
Blend- produces cutting effect
with hemostasis

110. CUT
When this mode is activated, the instrument
delivers a sustained high frequency AC
waveform
Current density at the implement is higher
with this mode than any other because the
average power is higher
Local heating causes tissue destruction which
is limited to the tip of the implement allowing
for effective cutting in the absence of
widespread thermal tissue damage

111. COAGULATION
When activated, the instrument delivers bursts of
high-frequency AC interrupted by periods of no
current flow so that the duty cycle (on time) is
reduced.
The percentage duration of current flow is set by
the manufacturer and is often in the region of
10% current 90% no current
Local tissue heating occurs and is more
widespread than that seen in a cutting mode
leading to extensive local tissue destruction

112. BLEND
A “blended current” is not a mixture of both
cutting and coagulation current but rather a
modification of the duty cycle.
When activated, the instrument delivers bursts of
high-frequency AC interrupted by periods of no
current flow
From Blend 1 to Blend 3 is a progressive reduction
of duty cycle i.e., the ratio of current : no current
decreases.
A lower duty cycle produces less heat.
Consequently, Blend 1 is able to vaporize tissue
with minimal hemostasis whereas Blend 3 is less
effective at cutting but has maximum hemostasis.

114. REM SYSTEM(RENEWABLE ENERGY
MANAGEMENT SYSTEMS)
Most ESU units on the market today have
REM technology
REM system continually monitors the heat
build-up under the grounding pad
If the system detects excess heat build-up it
will shut off the current flow to prevent
patient injury

115. BIPOLAR ELECTROSURGERY
• Generator (ESU unit)
• Active electrode (cautery pencil)
• Patient
• Electrode tip
• Generator

116. BIPOLAR ELECTROSURGERY
Bipolar electrosurgery uses 2-tined bipolar forceps
One tine of the forceps serves as the active electrode, and the
other tine serves as the return electrode
A grounding pad is not needed for bipolar-only cases
The electrical current is confined to the tissue
between the tines of the bipolar forceps

117. 1. Burn
1. Low frequency “stray” current
1. Explosion hazards
2. Electrosurgical smoke
SAFETY CONCERNS

118. Place dispersive pad over a well-vascularized muscle mass
Avoid placing grounding pad over bony prominences, hairy sites, scar
tissue, excess adipose tissue
Place grounding pad as close to the surgical site as possible
Grounding pad should be placed so that the entire surface of the pad is
in uniform contact with the pad site
Avoid any tenting or gaps where parts of the pad are not in contact with
the patient
SAFETY MEASURES

119. SAFETY MEASURES
Inspect machine for frayed or broken wires before use.
Active electrode wire should be free of kinks
Use lowest setting that is effective

120. SAFETY MEASURES
Recommended practice: keep ESU pencil in non-conductive
holder when not in use - this prevents accidental activation
Prep or irrigation solutions should not pool near the grounding
pad
Don’t allow ESU pedal to stand in pool of liquid

121. SAFETY MEASURES
No part of the patient should be touching any grounded metal
objects (IV pole, Mayo stand, metal surfaces of OR bed)
Electrical current always seeks the path of least resistance—
patient might have an alternate site burn where their body is in
contact with metal

122. • Principles of Electricity
• Electrical Shock Hazards
• Grounding
• The line isolation monitor
• Ground fault circuit interrupter
• Electrosurgery
• Electromagnetic interference(EMI)

123. Telephones, cordless telephones, walkie-talkies, and wireless
internet access devices emit electromagnetic interference (EMI)
EMI emitted by these devices may interfere with implanted
pacemakers or various types of monitoring devices and ventilators
in critical care areas
One case of a patient death has been reported when a ventilator
malfunctioned secondary to EMI
ELECTROMAGNETIC INTERFERENCE

124. Currently, the FDA guidelines are that the cellular telephones be
kept at least 6 inches from the pacemaker.
A patient with a pacemaker should not carry a cellular telephone
in the shirt pocket, which is adjacent to the pacemaker.

125. There appears to be little risk if hospital personnel
carry a cellular telephone and if they ensure that it is
kept at a reasonable distance from patients with a
pacemaker.
The Emergency Care Research Institute (ECRI)
reported in October 1999 -walkie-talkies were far
more likely to cause problems with medical devices.
The ECRI recommends
cellular telephones  1 meter from medical
devices,

126. Any questions ???

127. Miller’s Anesthesia, 7th edition
Clinical Anesthesia, 7th edition; Paul G. Barash
Clinical Anaesthesiology, 5th edition; Morgan
Physics, Pharmacology and Physiology for Anaesthetists; Key
concepts for the FRCA; 2nd edition; Matthew E. Cross, Emma V. E.
Plunkett
http://www.howequipmentworks.com/physics/electricity/elecsafety/electrica
lsafety.html#why
REFERENCES…