1. Dip. Diab. DCA, Dip. Software statistics
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

2. Problems ?? Why we should know??
Anaesthesiologist is the team leader
He/She only can handle
suction, OT lights, leads
ECG monitor and cautery

3. Theatre contains equipments
The operating theatre is unusual as there are
numerous examples of the deliberate application of electrical equipment to the human body.

4. Electrical Hazards Fires Burns Electrical shock Explosions
Power failure

5. The basics Clinical engineering – new field
understand and apply electrical engineering
analyze and avoid equipment hazards,
and to apply equipment safety standards,
Clinical engineering – new field

6. DC and the AC

7. Ohm’ s law Voltage /Current = Resistance
Voltage / Resistance = Current
Units
Volts , ohms , amperes

8. 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.

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

10. 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 ??

11. 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

12. 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

13. Just that’s enough !!
10 µA as the maximum leakage of current allowable through electrodes or catheters contacting the heart.
Micro shock !!

14. 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

15. 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.

16. Normal 3 plug grounding of home

17. Faulty equipment – shock

18. 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

19. OT is electrically dangerous

20. OT is electrically dangerous

21. OT is electrically dangerous

22. In the OR We need ungrounded power supplies Hence
Isolation transformers

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

24. 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.

25. Isolation transformer

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

28. Internal arrangement of diathermy
Isolation transformer
Earthed case

29. Capacitor

30. Capacitative coupling

31. 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

32. 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.

34. Leakage current and micro shock

35. 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

36. 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

37. classification of equipment according to their means of protection.

38. 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

39. 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.

40. 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

41. The above classes of equipment – relate to electrocution
What is in store next ??
The above classes of equipment – relate to electrocution

42. 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.

43. Diathermy

44. This is symbolic

46. 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.

47. 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.

48. Patterns= modulated and sine forms

49. 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

50. Electrosurgical unit

51. 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.

52. 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 ??

53. Fires – factors Diathermy Rugged insulation wires Laser Oxygen
Excessive friction of hot moving parts
Three devils
Fuel, igniting material, propagation

54. Example –spirit, diathermy , oxygen

55. 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 )

56. 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,

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

58. Thank you all