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Electrical safety . Dr. S. Parthasarathy MD., DA., DNB, MD ( Acu ), Dip. Diab . DCA, Dip. Software statistics PhD (physiology) Mahatma Gandhi medical college and research institute, puducherry , India . Problems ?? Why we should know?? . Anaesthesiologist is the team leader

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electrical safety

Electrical safety

Dr. S. Parthasarathy

MD., DA., DNB, MD (Acu),

Dip. Diab. DCA, Dip. Software statistics

PhD (physiology)

Mahatma Gandhi medical college and research institute, puducherry, India

problems why we should know
Problems ?? Why we should know??
  • Anaesthesiologist is the team leader

He/She only can handle

suction, OT lights, leads

ECG monitor and cautery

theatre contains equipments
Theatre contains equipments

The operating theatre is unusual as there are

numerous examples of the deliberate application of electrical equipment to the human body.

electrical hazards
Electrical Hazards
  • Fires
  • Burns
  • Electrical shock
  • Explosions
  • Power failure
the basics
The basics
  • understand and apply electrical engineering
  • analyze and avoid equipment hazards,
  • and to apply equipment safety standards,
  • Clinical engineering – new field
ohm s law
Ohm’ s law
  • Voltage /Current = Resistance
  • Voltage / Resistance = Current
  • Units
  • Volts , ohms , amperes
electrocution
Electrocution
  • The effects produced are dependent upon 4 factors:
  • (i) the amount of electricity that flows (current);
  • ii) where the current flows (current pathway)
  • (iii) the type of current (direct or alternating);
  • (iv) current duration.
resistance
Resistance
  • Dry skin = 1 mega ohm
  • Moist skin = 15 kiloohms
  • Electrode paste = 1,000 ohms
  • Needles and catheters = few hundred ohms
current and effects
Current and effects
  • 1 mA --- Tingling sensation
  • 15 mA---- Muscle tetany, pain and asphyxia
  • 75 mA ----- Ventricular fibrillation
  • : Let go current: less than 10 mA !!
  • Macro shock !! – what is that ??
macroshock and micro shock
Macroshock and micro shock
  • Macroshock is the type of electrocution where electricity enters through the skin and flows through a substantial portion of the body, only a fraction actually going through the heart
scenario is different
Scenario is different
  • when monitoring catheters, pacing wires, and dye injection catheters first began to be utilized inside the heart or the coronary arteries.– two differences
  • Rare scenario
  • Micro amperes are enough
  • Microshock
just that s enough
Just that’s enough !!
  • 10 µA as the maximum leakage of current allowable through electrodes or catheters contacting the heart.
  • Micro shock !!
grounding and un grounding
Grounding and un grounding
  • In electrical terminology, grounding is applied to two separate concepts.
  • The first is the grounding of electrical power, and the second is the grounding of electrical equipment.
  • (1) power can be grounded or ungrounded

(2) power can supply electrical devices that are themselves grounded or ungrounded

grounding and ungrounding
Grounding and Ungrounding
  • 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 Operating Room.
ot is electrically dangerous
OT is electrically dangerous
  • Numerous electronic devices, together with power cords and puddles of saline solutions on the floor, make the OR an electrically hazardous environment for both patients and personnel.
  • 40% of electrical accidents in hospitals occurred in the OR.
  • We don’t want macroshock ??
  • Ungrounded power supplies
in the or
In the OR
  • We need ungrounded power supplies
  • Hence
  • Isolation transformers
we need isolation transformer induction no direct connection to the secondary coil
We need isolation transformer- induction – no direct connection to the secondary coil

induction

what is a transformer
What is a transformer ??
  • A transformer is constructed by placing two coils close to each other.
  • An AC source is applied to one coil, and a current is induced in the other.
slide27
From the outlet - External case is grounded but the internal circuitry of the ECG monitor is ungrounded
internal arrangement of diathermy
Internal arrangement of diathermy

Isolation transformer

Earthed case

resistive and capacitative coupling
Resistive and capacitative coupling
  • The body can act as a connection if it comes into contact with the source of electricity and the earth directly or by touching an earthed object such as drip stand.
  • The body can also form a connection between an electrical source and earth by acting as one plate of a capacitor
  • Eg. MRI scanner
leakage currents
Leakage currents
  • All AC-operated power systems and electrical devices manifest some degree of capacitance..
  • 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 so-called leakage current partially ungrounds the isolated power system. This does not usually amount to more than a few 1 to 2 mA in an OR.
line isolation monitor
Line isolation monitor
  • The LIM continuously monitors the isolated power to ensure that it is indeed isolated from ground, and the device has a meter that displays a continuous indication of the integrity of the system
line isolation monitor1
Line isolation monitor
  • The reading on the LIM meter does not mean that current is actually flowing; rather, it indicates how much current would flow in the event of a first fault.
  • The LIM is set to alarm at 2 or 5 mA, depending on the age and brand of the system
classification of equipment according to their means of protection
classification of equipment according to their means of protection.
  • Class 1
  • Class 2
  • Class 3
class 1
Class 1

Any conducting part of Class I equipment accessible to the user, such as the metal casing, is connected to earth by an earth wire. This wire becomes the third pin of the plug connecting the equipment to the mains socket.

  • Class I equipment should have fuses at the equipment end of the mains supply lead, in both the live and neutral conductors
class 2
Class 2
  • Any accessible conducting parts of Class II equipment are protected from the live supply by either double or re-inforced insulation.
  • This should prevent any possibility of an accessible part becoming live and so an earth wire is not required.
class 3
Class 3
  • Class III equipment provides protection against electric shock by using voltages no higher than safety extra low voltage
  • SELV is defined as a voltage not > 25 V AC or 60 V DC.
  • Battery operated
what is in store next
What is in store next ??

The above classes of equipment – relate to electrocution

types for medical equipment
Types for medical equipment
  • Type B
  • The equipment may be of Class I, II or III but the maximum
  • leakage current must not exceed 100 μA. It is therefore not suitable for direct connection to the heart.
  • Type BF
  • As for type B, but uses an isolated (or floating) circuit
  • Type CF
  • These provide the highest degree of protection, using

isolated circuits and having a maximum leakage current

of < 10 μA.

  • suitable for direct cardiac connection,
  • e.g. ECG leads, pressure transducers and thermodilution
  • computers.
surgical diathermy
Surgical diathermy
  • Surgical diathermy equipment uses the heating effects of high frequency (kHz–MHz) electrical current to coagulate and cut tissues.
  • There are two basic types – monopolar and bipolar.
monopolar diathermy
Monopolar diathermy
  • generates electrical energy at 200 kHz to 6 MHz.
  • The energy is applied between two electrodes (neutral and active).
  • The neutral electrode has a large conductive

surface area producing a low current density with no measurable heating effect

  • Active – resistance – heat – effect
  • Cutting diathermy employs a sine waveform whilst coagulation uses a modulated waveform.
bipolar circuit completes in forceps
Bipolar – circuit completes in forceps
  • Bipolar diathermy operates with a much lower power output.
  • The output is applied between the points of a pair of specially designed forceps producing high local current density.
  • No current passes throughout the rest of the body.
  • No neutral plate
conductive flooring
Conductive Flooring
  • In past years, conductive flooring was mandated for ORs where flammable anesthetic agents were being administered.
  • This would minimize the buildup of static charges that could cause a flammable anesthetic agent to ignite.
  • The standards have now been changed to eliminate the necessity for conductive flooring in anesthetizing areas where flammable agents are no longer used.
electromagnetic interference
Electromagnetic Interference
  • telephones, cordless telephones, walkie-talkies, and wireless Internet access devices. :
  • they emit electromagnetic interference
  • 6.6 % incidence of pacemaker malfunction which returns to normal instantaneously.
  • The ECRI recommends that cellular telephones be maintained at a distance of 1 meter from medical devices, while walkie-talkies be kept at a distance of 6 to 8 meters.
  • Combination of walkie talkies and cell phones ??
fires factors
Fires – factors
  • Diathermy
  • Rugged insulation wires
  • Laser
  • Oxygen
  • Excessive friction of hot moving parts
  • Three devils
  • Fuel, igniting material, propagation
power failure
Power failure
  • 2 generators ready
  • Should be on in 10 seconds
  • Emergency lighting – to OR and Generator room ( keys ?? )
  • Which switches should be off? Or is it automatic !! (know the load )
what should we do
What should we do ??
  • All electrical equipment should be tested periodically by experienced personnel, usually a clinical bioengineering group associated with the operating rooms.
  • Anesthesiologists should verify that equipment has been maintained properly, that standards of performance have been met,
summary
Summary
  • Ohm’s law
  • Current and effects
  • Macroshock and microshock
  • Grounding and ungrounding
  • Line isolation monitor
  • classes and types
  • Surgical diathermy
  • EMI