1. Electrical Safety
Cedric Dupont-Eisner M.D.

2. Electrical Safety
Steven L. Shafer, M.D. Professor of Anesthesia Stanford University Adjunct Professor of Biopharmaceutical Sciences University of California at San Francisco

3. Introductory Physics for Anesthesiologists
T. Turkstra, M. Eng, P. Eng, MD, FRCPC
April

4. Electrical Safety
Electrical safety in the OR is often regarded as being of historical interest only
Reality is that the OR environment is becoming more electrically complex by the year
More complications arise with the networking of electronic equipment which may not conform to the rigid safety standards of conventional medical equipment
device related injuries in USA every year
Electrocution 5th leading cause of accidental death in US

5. Why are patients at risk?
Placed on a metal table.
Wet
Surrounded by electrical devices.
Connected to multiple electrical devices, typically by low resistance pads
Can’t move away from current

6. Principles

11. Basics of Power Distribution
Service Entrance
Hot
120 volts
Neutral
Examine power distribution in room

12. Definitions
Materials that will not transfer electrons under normal circumstances are termed insulators
An excess of charge may be carried by some materials as a result of friction (static electricity)
This may later be discharged by contact with a conductor, or if the potential is sufficiently high by jumping a gap as a spark.

14. Principles Electricity is the flow of electrons Capacitance
Direct Current-electrons flow in 1 direction
Alternating Current-electrons switch directions at regular intervals
Capacitance
The ability of a capacitor to store a charge.
CAPAcitor - (two parallel conductors separated by an insulator-like a battery)

15. Definitions
When electrons move from one atom to another in a consistent direction, current is said to flow
The applied force to do this is described as potential difference, and energy is used up by the process (volts)
This energy can both fulfill its function or injure our patients if care is not taken
Materials that permit easy transfer of their electrons from one atom to another are termed conductors
Those that do so reluctantly are termed resistors

16. Ohm’s Law V=I R Voltage (V) =Current (I)  Resistance (R)
Variac example

17. What is 120 Volts? 120 volts is the root mean square voltage
Actual peak voltage is about 150 volts

18. Capacitative Linkage
If a material carries a negative charge, other nearby electrons will tend to move away
If the potential at that point varies from positive to negative, such as happens with all alternating current sources (most obviously with mains electricity) then the surrounding electrons will be attracted and repelled alternately
In other words, an alternating current can be induced in a material without an electrical source being directly connected to it. This is termed capacitative linkage.

19. Inductive Linkage Moving electrons generate a magnetic field
A moving magnetic field causes movement of electrons
AC current source will produces a moving magnetic field and therefore induces secondary current in any nearby wires without the need for direct contact
Inductive linkage is intentionally utilized in some devices e.g. transformers

20. Inductive Linkage
When two transformers are placed in series in a power supply it allows the power source for a medical device to be separated from any other parts of the circuitry
Consequent reduction in the risk of direct transmission of mains energy to the patient
This is known as a floating circuit—indicated by the surrounding box in the symbols and the letter F in the description of equipment

21. Safety Standards
As monitoring devices proliferated in OR’s, awareness of leakage currents grew
Because of capacitative and inductive linkage within medical devices, there will virtually always be some tiny current floating down wires to patients
Moderate currents are not a big issue, and the maximum permitted level is below that which can be sensed, or cause harm

22. Pickle Physics
Pickle is nearly saturated with Na Cl as part of pickling process
Na Cl provides conducting path
Na+ is reduced by electric current to Na0
When the Na0 is oxidized to Na+ by oxygen, a reaction giving off light at the frequency of Na.
Same color as Na lights on highways

23. Principles Electrical Shock
Body contact with 2 conductive materials may complete OR become part of a loop and cause a shock

24. Electrical Shock
If electrical systems are not properly wired, persons can be subjected to electric shock.
Resulting in injury or death

25. Electrical Shock
People become injured and death occurs when voltage pushes electrons through the human body, particularly through the heart.

26. Electrical Shock
Damage from electrical current is due to disruption of normal electrical function of cells or dissipation of electrical energy into human bodies (increased temp->burn).
Electrical function of cells – skeletal muscle contraction or v fib

27. Electrical Shock
Macroshock-large amount of current flow that can cause harm or death

28. The Effects of Current On The Human Body - (Source -Hand)
Around 1mA
Mild Tingling
1-5 mA
Painful
>15 mA
Tonic Muscle Contraction - unable to release grip, risk of asphyxia
75-100mA
Risk of VF
>5000mA
Tonic Ventricular Contraction, cardiac standstill and death

29. Application: Electrical Shock
What levels of current (mA) is dangerous?
<1 mA = imperceptable to touch
10 mA skeletal muscle shock (you can let go)
V Fib can be induced by:
100 mA of macroshock
100 μA (microamperes)of microshock current

30. Electrical Shock
Microshock-small amounts of current flow. Dangerous only to electrically susceptible patients via artificial conductive pathways to the heart.
(patients with external devices capable of conducting a charge-pacing wires, saline filled cvp catheters)

31. Application: Electrical Shock
DC-is less dangerous
AC-is more dangerous
3x DC is needed for VFib
High frequency current have low tissue penetration and does not excite contractile cells
Low frequency current penetrates more
The larger the area exposed to current the better (think about huge Bovie pad and small bovie tip)

32. Microshock
Of the current passing through a human hand, less than 0.1% passes through the heart
Therefore any cardiac effects result from tiny currents
The implication is that if you passed a current directly through the heart, much smaller currents can cause injury
5 seconds of sustained 50 A AC current produces sustained VF
This phenomenon is known as microshock.

33. Microshock
Anaesthetist can be earthing point for patient, and source for microshock -
IF you touch a faulty apparatus and SG catheter at the same time, small leakage current from poorly grounded device can be sufficient to cause VF, even though you don’t feel a thing…

34. Principles
Stray Capacitance/Capacitive Coupling, the cause of “leakage”
inherent in all electrical equipment.
Not designed into the system, but incidental to the equipment construction

35. Application: Electrical Shock
THE MAX LEAKAGE ALLOWED IN OR EQUIPMENT IS 10 μA (microamperes)

36. Grounding Electrical Power Grounding can exist in two forms GROUNDED
UNGROUNDED
Easy?

37. Grounding Think about your house:
2 prong outlets = no ground
3 prong outlets = grounded
Modern homes have a ground to reduce amount of shock

38. Protecting the Operator
Adequate grounding of casing
Don’t let operator touch casing
Non-conductive casing
Don’t assume all equipment is always in good shape - regular checks
Extension cables are frowned upon - frayed from over use, on floor, exposed to saline etc…….

39. Basic Toaster ______________________________ / \
______________________________
/ \
Hot _______________________/_____________/\/\/\/\/\/\/\ \
| | |
Neutral ______________________|______________/\/\/\/\/\/\/\| |
| (filament) |
Ground ______________________| |
| T o a s t e r |
|__________________________________|
(Ground connects to chassis)

40. Worst Case Scenario: Hot shorts to chassis, ground broken
(short circuit)
! ! !
___!_______________
/ | \ _____
_____Hot______/____|___/\/\/\/\ \ // \\
| | | Patient | * * |
__Neutral____|_________/\/\/\/\| | wants >| ^ |<
| | toast: \ O / /
| | | \_____/ /
| T o a s t e r | |_____|_____/
___________|_______________________| |
/ | Patient
Broken Ground ______________ /.\ is
\ | O.R. table |-----towel-- / \ toast
/ \__________/ / \
/ | / \
/ | Ground wire _/ \_
\ ground |
10 amps
10 amps
Notice role of ground.
How is the circuit completed?
Grounded vs. ungrounded demo

41. Safe Scenario: Hot shorts to chassis, ground intact
(short circuit)
! ! !
___!_______________
/ | \ _____
_____Hot______/____|___/\/\/\/\ \ // \\
| | | Patient | * * |
__Neutral____|_________/\/\/\/\| | wants >| ^ |<
| | toast: \ / /
| | | \_____/ /
| T o a s t e r | |_____|_____/
___________|_______________________| |
/ | Fuse
| ______________ /.\ blows
\ | O.R. table |-----towel-- / \ before
/ \__________/ / \ patient
/ | / \
/ | Ground wire _/ \_
\ ground |
30 amps
30 amps
Notice role of ground.
How is the circuit completed?

42. Microshock hazard: Neutral shorts, ground wire intact
___________________
/ \ _____
_____Hot______/________/\/\/\/\ \ // \\
| | | Patient | * * |
__Neutral____|_________/\/\/\/\| | wants >| ^ |<
| | | toast: \ / /
| | | | \_____/ /
| | T o a s t e r | |_____|_____/
___________|__|____________________| |
/ Short!! | Patient
| /.\ is
\ | O.R. table |-----towel-- / \ OK
| /ft \__________/ / \
| | / \
/ | Ground wire _/ \_
\ ground |
10 amps
5 amps
5 amps
V=I R = 5 A   = 320 mV, even though the chassis is properly grounded!

43. Microshock Current delivered directly to heart
10 A will cause fibrillation
The chassis voltage from a neutral-ground short carrying 5 amps, 320 mV, exceeds the microshock threshold. Since the line isolation monitor will sense this, the monitor is able to provide some protection against microshock.

44. Microshock
Voltage to induce VF through intracardiac pacing electrode: 5 mV
Chassis voltage with neutral short to ground in conventional circuit: 320 mV
Chassis voltage with neutral short to ground with functioning line isolation monitor: mV

45. Grounded Power

46. Grounded Electrocution if I have a CVP

47. Why is equipment grounded?
Stray Capacitance/Capacitive Coupling:
Defective appliance current diversion to ground wire.
Remember all equipment leaks a small amount of current
All OR equipment has 3 prong plug
Equipment ground wire is attached to the case of the instrument to allow the small amount of current to have a low resistance path to ground and reduce risk of macroshock (think carpet static electricity)

48. Ungrounding The OR has many perils that make grounding less ideal.
Saline puddles
Power cords w/ tears in their insulation (colored part of cord)
Numerous electronic devices that  risk

49. Ungrounding This is where the questions are derived:
OR uses ungrounded power that is derived from Grounded utilities
ISOLATION TRANSFORMER is the answer…

50. Isolated and Ungrounded

52. Ungrounding: Isolated Power
Power source does not have a ground, the equipment is grounded
Isolated Power System provides protection from Macroshock.
Faulty equipment plugged into an isolated power system does not present a shock hazard.

53. Summary Macroshock: Microshock: Electrocautery:
80 mA can induce VF across an arm-arm circuit
Hard with dry skin, easier with wet skin
Isolation transformer makes it impossible to complete circuit to ground in OR, provided ground wires are attached.
Microshock:
10 A can induce VF on the heart
Isolation monitor limits the ability of any grounded chassis to come up to adequate voltage to induce microshock
Electrocautery:
Correct placement and function of return electrode prevents burns at site where current exits the body.

54. Ungrounded Safety

55. LIM (Line Isolation Monitor)
Continuously monitors the potential for current flow from the isolated power supply to ground.
Determines the degree of isolation b\w 2 power wires and the ground.
Predicts the current flow.

57. LIM (Line Isolation Monitor)
Alarm is activated if 2mA-5mA of current is detected.
Remember Macroshock vs. Microshock?

58. Figure A faulty piece of equipment plugged into the isolated power system does not present a shock hazard. It merely converts the isolated power system into a grounded power system. The figure insert illustrates that the isolated power system is now identical to the grounded power system. The dashed line indicates current flow in the ground wire.

59. Figure When a faulty piece of equipment is plugged into the isolated power system, it will markedly decrease the impedance from line 1 or line 2 to ground. This will be detected by the LIM, which will sound an alarm.

60. Application: Electrical Shock
What levels of current (mA) is dangerous?
<1 mA = imperceptable to touch
Ventricular Fibrillation can be induced by:
100 mA of macroshock
100 μA (microamperes)of microshock current

61. Electrical Shock
SO L.I.M. DOES NOT PROTECT AGAINST MICROSHOCK SINCE IT DETECTS 2mA-5mA

62. LIM (Line Isolation Monitor)
Indicates the existence of a single problem (SINGLE FAULT)
Namely there is a problem with the ungrounded system becoming grounded
So we are back to regular home power
No shock with single fault

63. LIM (Line Isolation Monitor)
A second problem (TWO FAULTS) are required for SHOCK to occur.
A faulty piece of equipment-very likely at HH
Unsafe environment like electric device + pool of normal saline.

64. Boards
LIM DOES NOT protect from MICROSHOCK, it warns of a POTENTIAL problem
If an LIM goes off, remove the last piece of equipment that was plugged in
In OR power source is ungrounded and equipment is grounded

65. QUESTIONS
The isolation monitor (LIM) on the wall of the operating room is to alert one to
Faulty drainage of static electricity from equipment to the conductive floor
The presence of equipment with a broken ground wire connection
An excessive load on the isolation transformer supplying the room
An excessive electrical leakage from either side of the power line to ground
Too low conductance in the floor.

66. Answer
The isolation monitor (LIM) on the wall of the operating room is to alert one to
D - An excessive electrical leakage from either side of the power line to ground

67. QUESTION
Electrocautery machines do not cause VF because the current they deliver differs from the electric current supplied by wall electrical outlets primarily by being:
DC instead of AC
Lower in voltage
Lower in frequency
Higher in frequency

68. Answer
Electrocautery machines do not cause VF because the current they deliver differs from the electric current supplied by wall electrical outlets primarily by being:
D - Higher in frequency

69. QUESTION The LIM (line isolation monitor)
Measures leakage current flowing from patient to ground
Measures leakage current flowing from the electrical equipment to the patient
Sounds an alarm if the leakage current exceeds 50 mA
Measures the impedance between AC wiring and ground
Cuts off power to the circuit if a faulty piece of equipment is connected

70. Answer D
The LIM measures the impedance from the AC wiring of an isolated power system to ground and only sounds an alarm if current in excess of 2-5 mA could flow to ground.

71. QUESTION The isolated power supply system used in OR’s requires that:
The metal portions of the OR table be connected to earth ground
The patient be insulated from the metal portions of the OR table
Conductive flooring be used in the OR
A transformer be connected between electrical equipment in the OR and the electric power supplied by the utility company

72. Answer The isolated power supply system used in OR’s requires that:
D - A transformer be connected between electrical equipment in the OR and the electric power supplied by the utility company

73. QUESTION Microshock hazard is increased in patients:
With a temporary pacing wire in place
In electrically operated beds
Receiving TPN via CVC
Who are in rooms with isolation transformers

74. Answer B
Both 1 and 3 can conduct electricity close to the heart and bypass the high resistance of the skin
100 mA for VF in MACROSHOCK
100 μA (microamperes) for VF in MICROSHOCK

75. QUESTION Operating rooms use an isolated power supply because:
Grounding cannot occur
Contact with both wires of the isolation transformer would cause no shock
Leakage current is zero
It affords protection against high amperage electrocution

76. Answer Operating rooms use an isolated power supply because:
4 - It affords protection against high amperage electrocution
Remember LIM’s detect 2-5 mA (milli Ampres), a small amount of current

77. QUESTION A ground fault circuit interrupter:
Is almost never used in OR
Is foolproof method for preventing serious electrical shock
May be used in a grounded electrical system
Has both audio and visual alarms to indicate the presence of a ground fault

78. Answer B
A GFCI prevents current from flowing in a circuit when there is an imbalance in the current flowing in the two sides of the circuit.
Not used in OR b\c it would turn off life support equipment

79. QUESTION Leakage current: Is harmless
Occurs b\c of the magnitude of the inductance b\w electrical conductors supplying equipment
Is of the DC type
Is unintentional flow of current from the internal wiring of a device largely a result of capacitance and AC current

80. Answer Leakage current
4 - Is unintentional flow of current from the internal wiring of a device

81. QUESTION
The current delivered to a pt by an electrocautery device differs from the current supplied by an electrical utility in its
Capacitance
Frequency
Amperage
Voltage
Power

82. Answer B
USA electricity is 60 Hertz and electrocautery is > 10,00000 Hertz
Hertz = frequency-remember bovie uses high frequency to prevent tissue damage

83. Electrocautery

84. Electrocautery with Poor Contact

85. Electrocautery Return Electrodes
If the return electrode is broken, current will find alternative path back to electrocautery unit.
ECG Electrodes
Twitch Monitor (case of 3rd degree facial burn at VA)
Be suspicious if standard settings are not producing an adequate spark
Electrocautery example

86. Electrocautery Return Electrodes
Place the return electrode close to surgical site
If an ECG electrode is closer, it may still take some of the current
Don’t place over metal implants
Function as internal lightening rods, focusing current on a small area near the implant, and the return electrode

87. Bipolar electrocautery
No return electrode, current just flows between two poles
Useful for laparoscopy, because current doesn’t flow through bowel, risking burning the intestine

88. The hospital-grade plug pattern conforms to the NEMA 5-15 standard; however, (1) the blades are usually solid instead of folded brass, (2) the blades are normally nickel-plated, and (3) the plug includes a cable retention device or strain relief to prevent any stress to the plug's internal connections. It is imperative that the ground connection be reliably maintained to protect the patient and medical staff. Although many hospitals prefer that the plug be clear so that internal connections can be inspected visually .

91. Summary Macroshock: Microshock: Electrocautery:
80 mA can induce VF across an arm-arm circuit
Hard with dry skin, easier with wet skin
Isolation transformer makes it impossible to complete circuit to ground in OR, provided ground wires are attached.
Microshock:
10 A can induce VF on the heart
Isolation monitor limits the ability of any grounded chassis to come up to adequate voltage to induce microshock
Electrocautery:
Correct placement and function of return electrode prevents burns at site where current exits the body.