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Anaesthetic FRCA Primary - eLFH Equipment > eLFH - Electrical Safety and Diathermy > Flashcards

eLFH - Electrical Safety and Diathermy Flashcards

1
Q

UK mains supply current type

A

Alternating current (AC)

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2
Q

UK mains supply frequency

A

50 Hz

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3
Q

UK mains supply voltage

A

Oscillates between +340 V and -340 V

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4
Q

Root mean square definition

A

Generates more meaningful ‘average’ voltage for sinusoidal waves

Especially when they oscillate around zero volts as the mean will = 0 V

Therefore the waveform is squared to make the negative values positive

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5
Q

Root mean square voltage (rms) of UK mains supply

A

240 V rms

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6
Q

Calculation for root mean square of sinusoidal waveforms

A
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7
Q

Ohm’s law

A

V = IR

Voltage = Current x Resistance

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8
Q

Equation for Power generated by a current flowing across a resistor (or a person)

A

P = I^2 x R

Power = Current squared x Resistance

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9
Q

3 ways that electricity can cause harm to patients

A

Electrocution

Burns

Interference with monitoring

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10
Q

Electrocution definition

A

Occurs when current passes along an unintended path, causing either tissue or electrophysiological abnormalities

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11
Q

Factors which impact the effects of current flow in electrocution

A

How much current flows (A)
Type of current (DC vs AC)
Frequency of current
Current pathway
Current density
Duration of current flow

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12
Q

Effect of current flowing at 1-5 mA

A

Tingling sensation

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13
Q

Effect of current flowing at 5-10 mA

A

Pain

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14
Q

Effect of current flowing at 15 mA

A

No-let-go threshold

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15
Q

Effect of current flowing at 50 mA

A

Respiratory arrest

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16
Q

Effect of current flowing at 100 mA

A

Ventricular fibrillation

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17
Q

Classification of electrical equipment - according to means by which it provides electrical safety

A

Class I

Class II

Class III

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18
Q

Class I electrical equipment definition

A

Accessible conductive parts are connected to earth by and earth wire which maintains the exposed metalwork at zero potential

Provides low resistance path for current to return to local electricity substation in the event of a fault

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19
Q

Class I electrical equipment - process in event of a fault

A

Live component touches earthed casing

Casing also becomes live

Current flows via all paths to earth proportional to their relative resistances

Very low earth resistance reduces current flowing through person if they touch the casing

Total current flow also increases causing fuse to blow and breaks the circuit

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20
Q

Class II electrical equipment definition

A

Protected by double or reinforced insulation / case

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21
Q

Why class II electrical equipment don’t require an earth wire

A

Minimal chance of person coming in contact with faulty live component, so earth wire not required

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22
Q

Class III electrical equipment definition

A

Powered internally by a battery or by SELV (safety extra low voltage)

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23
Q

Specifications for SELV (safety extra low voltage)

A

Voltage not greater than 25 V AC or 60 V DC

No earth connection (usually floating circuit)

Low risk of accidental contact with higher voltage

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24
Q

Macroshock definition

A

Current flow from intact skin to skin

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25
Q

Microshock definition

A

Skin is breached and currents are delivered directly to myocardium

Higher current densities are generated near the myocardium

26
Q

Currents in microshocks that can cause dangerous dysrhythmias when delivered near the myocardium

A

100 microA

27
Q

Current threshold below which microshock is unlikely to cause harm

A

44 microA

28
Q

Factors which increase risk of microshock induced ventricular arrhythmias

A

Site of stimulation - ventricles more sensitive

Increased area of stimulation

Longer duration of current passage

29
Q

Equipment which predisposes patients to microshock

A

Saline filled (electrically conductive) CVC

Pacing wires

Oesophageal doppler probes

30
Q

Classification of electrical equipment - according to degree of protection: Definition

A

Designated by the type and quantified by its permissible leakage under Normal Conditions (NC) and Single Fault Conditions (SFC)

31
Q

Classification of electrical equipment - according to degree of protection

A

Type B

Type BF

Type CF

Defibrillator-safe BF

Defibrillator-safe CF

32
Q

Type B electrical equipment + logo

A

May be class I, II or III

Not generally suitable for direct patient connection

33
Q

Type B electrical equipment maximum leakage currents

A

Type 1 equipment:
NC < 0.1 mA
SFC < 0.5 mA

Type 2 equipment:
NC < 0.1 mA
SFC < 0.1 mA

34
Q

Type BF electrical equipment + logo

A

May be class I, II or II

Has an isolated (floating) circuit - therefore suitable for direct patient connection

35
Q

Type BF electrical equipment maximum leakage currents

A

Type 1 equipment:
NC < 0.1 mA
SFC < 0.5 mA

Type 2 equipment:
NC < 0.1 mA
SFC < 0.1 mA

36
Q

Type CF electrical equipment + logo

A

May be class I, II or III

High degree of protection against shock

Suitable for direct cardiac connection

37
Q

Type CF electrical equipment maximum leakage currents

A

All equipment:
NC < 0.01 mA
SFC < 0.05 mA

38
Q

Defibrillator-safe BF electrical equipment + logo

A

Same specification as for Type BF but is defibrillator safe

I.e. may be left in contact with patient during defibrillation

39
Q

Defibrillator-safe CF electrical equipment + logo

A

Same specification as Type CF but is defibrillator safe

I.e. may be left in contact with patient during defibrillation

40
Q

Floating circuit definition

A

Earth free circuit

Further means of protection against electrical shock

Equipment separated from the earthed mains supply by an isolating transformer - transfers power from substation by magnetic field

41
Q

Line isolation monitor

A

Should be fitted to floating circuits to ensure it has not accidentally become earthed

42
Q

Why aren’t floating circuits used in all electrical equipment everywhere

A

Expensive

43
Q

Earth leakage circuit breakers (ELCBs)

A

Electromechanical devices which disconnect the power supply to faulty electrical equipment when current flows down earth wire

May be voltage or current operated

44
Q

Typical rating of medical infusion pumps

A

Type CF

Suitable for direct connection to heart because they may be connected to heart via column of electrolyte solution

45
Q

Diathermy mechanism

A

High frequency alternating current

Current passing through any conductor dissipates power causing a heating effect

The heating effect (H) is proportional to the square of the current, and inversely proportional to the area through which it passes

Heating effect is also proportional to current density

46
Q

Current density definition

A

Amount of current flowing per unit area

Diathermy uses high frequency currents to minimise risk of inducing dangerous dysrhythmias

47
Q

Types of diathermy

A

Monopolar

Bipolar

48
Q

Monopolar diathermy mechanism

A

Small active electrode at site of surgery relative to the ground electrode

Circuit formed by active electrode, ground electrode and patient’s tissue

Same current flows through both active and ground electrodes - ground plate has much lower current density due to larger area

49
Q

Monopolar diathermy power used

A

100 - 200 Watts

50
Q

Bipolar diathermy mechanism

A

Uses 2 electrodes to create a local circuit

High current density applied between bipolar forceps

Little effect on nearby tissue

51
Q

Bipolar diathermy power used

A

< 100 Watts

52
Q

Advantages of bipolar diathermy

A

Lower power used

Lower chance of current travelling via alternate pathway compared to monopolar diathermy

53
Q

Microscopic effects of diathermy

A

Coagulation - higher temps and current density

Desiccation - lower temps and current density

54
Q

Macroscopic effects of diathermy

A

Vaporisation - causes cutting of tissues

Tissue destruction

55
Q

Diathermy waveform which achieves cutting

A

Continuous higher frequency (~ 400 Hz)

Lower voltage (400 - 1000V)

Higher power (> 100 Watts)

56
Q

Diathermy waveform which achieves coagulation

A

Interrupted / modulated current

Lower frequency (250 - 400 Hz)

Higher voltages (up to 9 kV)

Lower power (< 100 Watts)

57
Q

Diathermy waveform which achieves blended cutting and coagulation

A

Blend of both

58
Q

Electrical safety mechanism with monopolar diathermy

A

Use of isolating capacitor

59
Q

Electrical safety mechanism with bipolar diathermy

A

Earth free circuit used

60
Q

Which type of diathermy should be used in patients with pacemakers

A

Bipolar

Anaesthetic FRCA Primary - eLFH Equipment (4 decks)

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