Transcript Electrical safety mgmc

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, leads
ECG 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
i
n
d
u
c
t
i
o
n
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