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

He/She only can handle suction, OT lights, leadsECG monitor and cautery

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

• Fires• Burns• Electrical shock• Explosions• Power failure

The basics

• understand and apply electrical engineering• analyze and avoid equipment hazards, • and to apply equipment safety standards,

• Clinical engineering – new field

• DC and the AC

Ohm’ s law

• Voltage /Current = Resistance

• Voltage / Resistance = Current

• Units • Volts , ohms , amperes

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

• Dry skin = 1 mega ohm • Moist skin = 15 kiloohms• Electrode paste = 1,000 ohms• Needles and catheters = few hundred ohms

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 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

• 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 !!

• 10 µA as the maximum leakage of current allowable through electrodes or catheters contacting the heart.

• Micro shock !! 

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

• 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.

Normal 3 plug grounding of home

Faulty equipment – shock

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

OT is electrically dangerous

OT is electrically dangerous

OT is electrically dangerous

In the OR

• We need ungrounded power supplies

• Hence • Isolation transformers

We need isolation transformer- induction – no direct connection to the secondary coil

induction

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.

Isolation transformer

From the outlet - External case is grounded but the internal circuitry of the ECG monitor is

ungrounded

Internal arrangement of diathermy

Earthed case Isolation transformer

Capacitor

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 • 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.

Leakage current and micro shock

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 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.

• Class 1

• Class 2

• Class 3

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

• 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 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 ??

The above classes of equipment – relate to electrocution

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.

Diathermy

This is symbolic

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• 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.

Patterns= modulated and sine forms

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

Electrosurgical unit

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• 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

• Diathermy • Rugged insulation wires • Laser • Oxygen • Excessive friction of hot moving parts• Three devils • Fuel, igniting material, propagation

Example –spirit, diathermy , oxygen

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 ??

• 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

• Ohm’s law• Current and effects • Macroshock and microshock • Grounding and ungrounding • Line isolation monitor • classes and types • Surgical diathermy • EMI

Thank you all