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ELECTRICAL SAFETY IN OPERATING ROOM
Presenter: Dr. Sabin Bhandari
Moderator: Dr. Asish Ghimire
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.
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
• Principles of Electricity • Electrical Shock Hazards• Grounding• The line isolation monitor• Ground fault circuit interrupter• Electrosurgery• Electromagnetic interference(EMI)
OUTLINE
Electricity is the flow of electrons
PRINCIPLES OF ELECTRICITY
Conductor- Any substance that permit flow of electrons
Insulator- Any substance that does not allow the flow of electrons
DC- Electrons flow in one direction
PRINCIPLES OF ELECTRICITY…DIRECT AND ALTERNATING CURRENTS
Note: Current leaves the source and returns to the source
AC- Electron flow switches direction at
regular interval.120
times/sec for 60 Hz current
Ohm's law:
V OR E = I × Rwhere,
E is electromotive force (in volts), I is current (in
amperes),R is resistance (in
ohms).
PRINCIPLES OF ELECTRICITY…
Ohm’s law for fluidPressure = Flow * ResistanceBasis for the physiologic equation
B.P. = CO * SVRWhere, B.P. is blood pressureCO is cardiac outputSVR is systemic vascular resistance
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 × RNote: power can also be thought as a measure of heat produced
PRINCIPLES OF ELECTRICITY…
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
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
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
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.
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
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…
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
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…
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-
• Principles of Electricity• Electrical Shock Hazards• Grounding• The line isolation monitor• Ground fault circuit interrupter• Electrosurgery• Electromagnetic interference(EMI)
If electrical system are not properly wired, persons can be electrocuted
• DC – less dangerous
• AC – 3 times as dangerous as DC
ELECTRICAL SHOCK HAZARDS
Why electricity is particularly dangerous in the operating room ??
1. Operating rooms
are full of electrical equipment.
ELECTRICAL SHOCK HAZARDS
2. Anaesthetized patients are "helpless" and can't move away from a shock.
3. Operating rooms are full of fluids
4. Electrical current is invisible
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.
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 ?
TRANSFORMERS
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.
• 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.
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
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.
Wires carrying a low voltage have higher losses than wires carrying an high voltageTo minimize losses, the power company transmits electricity at high voltages.
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.
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
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.
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
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.
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.
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.
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.
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.
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.
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
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
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
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.
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
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
Current Effect
100 μA (0.1 mA) Ventricular fibrillation
10 μA (0.01 mA) Recommended maximum 60-Hz leakage current
MICRO SHOCK
• Principles of Electricity• Electrical Shock Hazards• Grounding• The line isolation monitor• Ground fault circuit
interrupter• Electrosurgery• Electromagnetic
interference(EMI)
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
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
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?
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.
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.
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
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.
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
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.
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
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
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.
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 hazardNo need for grounding, thus increasing the safety margin.
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.
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".
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.
Faulty equipment plugged into an isolated power system does not present a shock hazard
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.
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).
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.
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…
• Principles of Electricity• Electrical Shock Hazards• Grounding• The line isolation monitor• Ground fault circuit
interrupter• Electrosurgery• Electromagnetic
interference(EMI)
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
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
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/IZ = (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.
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
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
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
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.
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
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 !!!!!
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.
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 ????
• Principles of Electricity• Electrical Shock Hazards• Grounding• The line isolation monitor• Ground fault circuit interrupter• Electrocautery• Electromagnetic interference(EMI)
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
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.
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
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
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.
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
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
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.
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
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.
• Principles of Electricity• Electrical Shock Hazards• Grounding• The line isolation monitor• Ground fault circuit
interrupter• Electrosurgery• Electromagnetic
interference(EMI)
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.
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
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
SYSTEM COMPONENTS
1. Generator (electrosurgical unit)
2. Inactive dispersive electrode (grounding pad)
3. Active electrode (“Bovie” pencil)
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
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
TYPES OF ESU UNITS
Monopolar
Bipolar
(Some ESU units have both monopolar & bipolar capability)
MONO-POLAR (FLOW OF CURRENT)• Generator (ESU unit)
• Active electrode (cautery pencil)
• Patient
• Dispersive cautery pad (ground plate)
• Generator
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
MONOPOLAR MODES
Electrosurgical generators are able to produce a variety of electrical waveforms.
Cut
Coag
Blend- produces cutting effect with hemostasis
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
COAGULATIONWhen 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
BLENDA “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.
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
BIPOLAR ELECTROSURGERY
• Generator (ESU unit)
• Active electrode (cautery pencil)
• Patient
• Electrode tip
• Generator
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
1. Burn
2. Low frequency “stray” current
3. Explosion hazards
4. Electrosurgical smoke
SAFETY CONCERNS
Place dispersive pad over a well-vascularized muscle mass
Avoid placing grounding pad over bony prominences, hairy sites, scar tissue, excess adipose tissuePlace 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 siteAvoid any tenting or gaps where parts of the pad are not in contact with the patient
SAFETY MEASURES
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
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
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
• Principles of Electricity• Electrical Shock Hazards• Grounding• The line isolation monitor• Ground fault circuit interrupter• Electrosurgery• Electromagnetic interference(EMI)
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
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.
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, walkie-talkies 6 to 8 meters.
THANK YOU
Any questions ???
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/electricalsafety.html#why
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