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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
Microshock definition
Skin is breached and currents are delivered directly to myocardium Higher current densities are generated near the myocardium
26
Currents in microshocks that can cause dangerous dysrhythmias when delivered near the myocardium
100 microA
27
Current threshold below which microshock is unlikely to cause harm
44 microA
28
Factors which increase risk of microshock induced ventricular arrhythmias
Site of stimulation - ventricles more sensitive Increased area of stimulation Longer duration of current passage
29
Equipment which predisposes patients to microshock
Saline filled (electrically conductive) CVC Pacing wires Oesophageal doppler probes
30
Classification of electrical equipment - according to degree of protection: Definition
Designated by the type and quantified by its permissible leakage under Normal Conditions (NC) and Single Fault Conditions (SFC)
31
Classification of electrical equipment - according to degree of protection
Type B Type BF Type CF Defibrillator-safe BF Defibrillator-safe CF
32
Type B electrical equipment + logo
May be class I, II or III Not generally suitable for direct patient connection
33
Type B electrical equipment maximum leakage currents
Type 1 equipment: NC < 0.1 mA SFC < 0.5 mA Type 2 equipment: NC < 0.1 mA SFC < 0.1 mA
34
Type BF electrical equipment + logo
May be class I, II or II Has an isolated (floating) circuit - therefore suitable for direct patient connection
35
Type BF electrical equipment maximum leakage currents
Type 1 equipment: NC < 0.1 mA SFC < 0.5 mA Type 2 equipment: NC < 0.1 mA SFC < 0.1 mA
36
Type CF electrical equipment + logo
May be class I, II or III High degree of protection against shock Suitable for direct cardiac connection
37
Type CF electrical equipment maximum leakage currents
All equipment: NC < 0.01 mA SFC < 0.05 mA
38
Defibrillator-safe BF electrical equipment + logo
Same specification as for Type BF but is defibrillator safe I.e. may be left in contact with patient during defibrillation
39
Defibrillator-safe CF electrical equipment + logo
Same specification as Type CF but is defibrillator safe I.e. may be left in contact with patient during defibrillation
40
Floating circuit definition
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
Line isolation monitor
Should be fitted to floating circuits to ensure it has not accidentally become earthed
42
Why aren't floating circuits used in all electrical equipment everywhere
Expensive
43
Earth leakage circuit breakers (ELCBs)
Electromechanical devices which disconnect the power supply to faulty electrical equipment when current flows down earth wire May be voltage or current operated
44
Typical rating of medical infusion pumps
Type CF Suitable for direct connection to heart because they may be connected to heart via column of electrolyte solution
45
Diathermy mechanism
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
Current density definition
Amount of current flowing per unit area Diathermy uses high frequency currents to minimise risk of inducing dangerous dysrhythmias
47
Types of diathermy
Monopolar Bipolar
48
Monopolar diathermy mechanism
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
Monopolar diathermy power used
100 - 200 Watts
50
Bipolar diathermy mechanism
Uses 2 electrodes to create a local circuit High current density applied between bipolar forceps Little effect on nearby tissue
51
Bipolar diathermy power used
< 100 Watts
52
Advantages of bipolar diathermy
Lower power used Lower chance of current travelling via alternate pathway compared to monopolar diathermy
53
Microscopic effects of diathermy
Coagulation - higher temps and current density Desiccation - lower temps and current density
54
Macroscopic effects of diathermy
Vaporisation - causes cutting of tissues Tissue destruction
55
Diathermy waveform which achieves cutting
Continuous higher frequency (~ 400 Hz) Lower voltage (400 - 1000V) Higher power (> 100 Watts)
56
Diathermy waveform which achieves coagulation
Interrupted / modulated current Lower frequency (250 - 400 Hz) Higher voltages (up to 9 kV) Lower power (< 100 Watts)
57
Diathermy waveform which achieves blended cutting and coagulation
Blend of both
58
Electrical safety mechanism with monopolar diathermy
Use of isolating capacitor
59
Electrical safety mechanism with bipolar diathermy
Earth free circuit used
60
Which type of diathermy should be used in patients with pacemakers
Bipolar

Anaesthetic FRCA Primary - eLFH Equipment (4 decks)

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