Equipment safety features

Classification of devices

•  Classification by class: Class I, II, III

•  Classification by type: Type B,BF,CF

•  Classification by suitability for use in flammable atmosphere: AP and APG

•  Protection against ingress of water: IPX classification

•  Class-I –  Basic insulation –  Earth

•  Class – II –  Double insulation

•  Class – III –  Safety Electrical Low Voltage (S.E.L.V) no > 25V for

A.C and 60V for D.C

Class-I and III

Classification by type

•  All diagnostic,therapeutic,life supporting or patient handling equipment must comply with type B, BF or CF specifications.

•  Classified on the basis of permissible leakage currents.

Leakage current L

N

E

The current that does not return back via the neutral is the ‘leakage current’

A P A P G

Type B Type BF Type CF

Class II Anaesthetic Proof

Anaesthetic Proof G

Type - B •  May have applied parts

•  Maximum permissible leakage currents below the thresholds for skin sensation (500µA), unlikely to cause any pain or injury

•  e.g; thermometers, manometers, gas analysers and ventilator alarms

Type - BF

Type-F isolated circuits, suitable for applications where surface electrodes are used, diminishing the safety factor provided by normal skin resistance

Maximum permissible leakage currents (500µA), similar to those of type-B

e.g Forced Air warmers, Blood warmers, Nerve stimulators etc

Type - CF Most stringent protection against shock hazard Intended for applications where an intra-cardiac connections is likely

Maximum permissible patient leakage current set at 1/10 (<50 µA) of that for type B or BF devices

e.g ECG, EMG, EEG , pacemakers and devices likely to be connected to cardiac catheters (such as syringe drivers and pressure transducers)

T

0-5 cms

5-25 cms

A P

A P G

Zones of Risk

Suitability for use in flammable atmosphere

May be used in zone of risk 5-25 cm from an enclosed medical gas system

Device must not be capable of igniting any mixture of explosive anaesthetic agent with air in normal use

Standards met by prevention of static sparks, restriction of temperatures (<200oC) and energy levels, and by fireproof enclosures

AP

Suitability for use in flammable atmosphere

May be used within the gas system itself or in the zone of maximum risk 0-5 cm from the gas system

No device must be capable of igniting mixtures of explosive anaesthetic agents with oxygen or nitrous oxide, in both normal and first fault conditions

Surface temp not > 900C

AP G

IPX Classification

Drip Proof Splash Proof Water tight

IPX - 1 IPX – 4 IPX - 7

Summary

•  Macro and micro shock •  Safety features in prevention of shock •  How the equipment are made safe. •  Safety classification of equipment

Electrical hazards can be minimised but not eliminated

Surgical Diathermy

Electrical Hazards

Diathermy

•  High frq current: – 300KHz – 3 MHz

•  Current flow through patient : – 200 – 400 mA – Nearly 2 Amps (when used in Urology)

Diathermy

•  Cutting – High Frq oscillation – Sine wave pattern

•  Coagulation – Bursts of Lower Frq – Damped , pulsed sine wave pattern

Diathermy waveforms

Time

V

Cutting

Time

V

coagulation

Time

V

Blended

Dessication and Coag

•  Coag, when used on low power Dessication

•  Relatively slow drying out of tissues by current that does not produce sparks

Fulgration and Coag

•  Coag with high power setting Fulgration

•  High power setting generates sparks

intermittent heating of tissue cells to dry

out quickly rather than explode into steam

Power settings

Power = Current 2 x Resistance ( R ) P= I2 X R

Low Power < 30 watts

•  Dermatology •  Laproscopy (Monopolar and Bipolar) •  Neurosurgery (Monopolar and Bipolar) •  Oral surgery •  Plastic surgery •  Vasectomies

Medium Power Cutting 30 to 100 Watts

Coagulation 30 to 70 Watts

•  Gen Surgery •  Head and neck (ENT) •  Laparotomy •  Orthopaedics Surgery (Major) •  Thoracic Surgery •  Vascular surgery

High Power Cutting > 100 Watts

Coagulation > 70 Watts

•  Ablative cancer surgery, mastectomies cut 180 – 300 watts, coag 70 – 120

•  Thoracotomy ( heavy fulguration 70 – 120 watts)

•  Transurethral resections ( cut 100 – 170 watts, coag 70 – 120 watts)

Active electrode

Indifferent Electrode/

Plate

Current density

High Density

Low Density

Diathermy machine

Active Electrode

Bipolar

Diathermy machine

Active Electrode

Indifferent Electrode (Plate)

Monopolar

Electrode •  Current flow: between Active electrode &

indifferent electrode ( Plate )

•  Plate electrode connected in the machine in various ways.

1.  Directly to the earth

2.  Isolation Capacitor

3.  Isolated Circuit

Earthed Plate

Diathermy machine

Active Electrode

Indifferent Electrode (Plate)

Problems with earthed plate

Diathermy machine

Diathermy machine

120/80 mmHg

Isolating Capacitor

0.01 µF Reactance At diathermy frq20Ω

At 50 to 60 Hz 300,000Ω

Diathermy machine Isolation capacitor

Diathermy machine

Diathermy machine

Isolated Diathermy

Floating Diathermy

Active Electrode

Indifferent Electrode (Plate) Isolated diathermy

Active Electrode

Indifferent Electrode (Plate) Isolated diathermy

No contact

No current flow

No diathermy

Active Electrode

Indifferent Electrode (Plate) Isolated diathermy

Plate Monitor

Diathermy and pacemakers

Dangers and precautions

Pacemaker interference

Depends on •  The type of pacing electrodes (i.e., unipolar or

bipolar) in the patient

•  How well the pacemaker circuitry is shielded and

•  The strength and the proximity of the discharge from the electrosurgical unit.

Diathermy and pacemakers

PROBLEMS WITH USING DIATHERMY IN PATIENTS WITH

PACEMAKERS

DIRECT EFFECT OF THE DIATHERMY (MONOPOLAR)

EFFECTS OF CAPACITANCE DUE TO HIGH FREQUENCY

CURRENT ( DIATHERMY UNIT ITSELF, RF CURRENT

GENERATOR)

PACEMAKER UNIT

DIATHERMY UNIT

Direct effects

Capacitive effects

Diathermy noise ( RF )

•  Inhibit or turn off any pacemaker Complete Heart Block and no pacing

•  Disrupt the pacing program in a programmable pacemaker Severe tachycardia

Diathermy and Pacemakers

•  A preoperative consultation with a cardiologist.

•  Be prepared to reset a pacemaker to the asynchronous mode (i.e., regular, uninhibited pacing).

For complex pacemakers or patients

•  Have a cardiologist and appropriate pacemaker programming equipment present or immediately available during surgery.

•  External pacing equipment ( trans-cut or temp pacing)

•  Isoprenaline (pharmacologic pacer, conc of 1 µg/mL for small bolus injections t ½ : 7mins) Dose : 0.5 – 8.0 µg/min

Unipolar diathermy and Pacemakers

•  Earth pads: As far away as possible from the pacemaker and its wires.

•  The path from the earth pad to the diathermy tip should not traverse the pacemaker circuit.

Conclusion: Diathermy and pacemakers

•  Avoid as far as possible.

•  Use bipolar

•  If using monopolar – Place the plate distant from the pacemaker. – Do not apply the current across the chest – Strength and duration of use should be

minimal