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Primary FRCA MCQ > Physics and equipment > Flashcards

Physics and equipment Flashcards

1
Q

Which 2 factors affect the response time of a thermistor used in a temperature sensor

A

1- Size of thermistor (smaller is faster)

2- Material thermistor is made from

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2
Q

What percentage of heat loss is due to radiation intra-operatively

A

40%

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3
Q

What percentage of heat loss is due to convection intra-operatively

A

30%

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4
Q

What percentage of heat loss is due to evaporation intra-operatively

A

15%

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5
Q

What percentage of heat loss is due to respiratory losses intra-operatively

A

10%

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6
Q

What percentage of heat loss is due to conduction intra-operatively

A

5%

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7
Q

What volume of oxygen do size E cylinders hold

A

680L

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8
Q

What volume of oxygen do size HX cylinders hold

A

2300L

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9
Q

How do you calculate how much oxygen to take for patient transfer

A

MV X Fi02 x Time of transfer

X2

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10
Q

What volume of oxygen do size C cylinders hold

A

170L

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11
Q

What volume of oxygen do size CD cylinders hold

A

460L

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12
Q

What kind of ventilator is a Manley MP3

A

A Time-cycled pressure generator. A minute volume divider

Mapleson D

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13
Q

What volume of oxygen do size D cylinders hold

A

340L

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14
Q

What causes an over damped arterial line trace

A

Bubbles in system
Kinking of tubing
Blood clot in canula

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15
Q

What is the formula for Laplace’s law in alveoli

A

P = 2T/R

Pressure = 2 x surface tension/ radius

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16
Q

Define Avogadros law

A

The volume of a gas is directly proportional to the number of gas molecules at constant temperature and pressure

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17
Q

Define Dalton’s law

A

The total partial pressure of a mixture of gas is equal to the sum of the individual partial pressures of the gases in the mixture

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18
Q

Define Hooke’s law

A

The displacement or size deformation is proportional to the load or force of deformation. (elasticity)

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19
Q

Describe the function of a residual current device

A

A residual current device is a device that breaks a circuit if it detects current leakage. It monitors current in the live and neutral wire and uses a comparator to break the circuit if there is a difference.

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20
Q

Define Macroshock and how much current is typically required to cause this

A

Macroshock is the current required to cause VF from surface contact to skin.

typically 100mA

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21
Q

How is voltage of an AC current calculated

A

RMS - Root mean squared

Half the voltage is -ve so first the voltage measurements are squared. Then a mean is calculated. A square root of the mean is taken to get the voltage.

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22
Q

Which 3 wires are contained in a power point

A

1- Active (240V)
2- Neutral (0v relative to ground)
3- Earth- direct pathway into ground

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23
Q

Define critical temperature of a gas

A

The temperature at which a gas cannot be liquified no mater the pressure applied to it

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24
Q

Define a vapour

A

A gas below its critical temperature

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25
Q

Define SVP (Saturated vapour pressure)

A

The partial pressure generated by a vapour in equilibrium with its liquid form at a standard temperature and pressure

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26
Q

At what temperature is SVP of anaesthetic gases measured

A

20C

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27
Q

What is the SVP of Sevoflurane

A

21

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28
Q

What is the SVP of Isoflurane

A

33

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29
Q

What is the SVP of Desflurane

A

88

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30
Q

What is the SVP of Halothane

A

32

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31
Q

What is the SVP of Enflurane

A

22.9

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32
Q

What is the boiling point of Sevoflurane

A

58.6

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33
Q

What is the boiling point of Isoflurane

A

48.5

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34
Q

What is the boiling point of Desflurane

A

22.8

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35
Q

What is the boiling point of Halothane

A

50.2

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36
Q

What is the boiling point of Enflurane

A

56.2

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37
Q

Describe 3 methods used in vaporises to increase FGF saturation at high flow rates

A

1- Wicks- stick out from liquid vapour into chamber to increase surface area

2- Baffles- Channels that cause obstructions to direct flow making the FGF have direct contact with vapour more often

3- Bubbles- FGF can be bubbled through anaesthetic agent to increase surface area and saturation of the FGF.

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38
Q

Define latent heat of vapourisation

A

The energy required to change 1kg of liquid to gas at constant temperature

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39
Q

Define humidity

A

The amount of water vapour pressent within a gas

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40
Q

Define absolute humidity

A

The mass of water vapour (g) present per volume of air (metres cubed (m3))

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41
Q

Define relative humidity

A

Ratio of water vapour present in a gas relative to the maximum possible (100%saturated)

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42
Q

How does pressure affect humidity

A

The higher the ambient pressure the less water can be held in air

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43
Q

How does temperature affect humidity

A

The higher the temperature the more water can be held in air

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44
Q

Define dew point

A

The temperature below which water will begin to condense out of air (100% saturated)

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45
Q

Describe how a hair hygrometer works

A

Hair increases in length with increased humidity.

Piece of hair with weight to straighten it out. Increase in length of air makes pointer move and this reflects humidity

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46
Q

Describe how a wet and dry hygrometer works

A

2 thermometers one has bulb open to air the other is wrapped in a wet cloth.

For something to evaporate it requires heat so cools the surroundings.

If humidity is low water from wet bulb will evaporate cooling down the surroundings and dropping the temperature on the wet thermometer relative to dry.

If humidity is close to 100% water will not evaporate so no energy used and no cooling of surroundings so no relative temperature change in the 2 thermometers.

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47
Q

What is the SI unit of temperature

A

Kelvin

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48
Q

Define the measurement Kelvin

A

one kelvin is 1/273th of the thermodynamic temperature of the triple point of water (=0.01oC)

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49
Q

Define absolute zero in terms of temperature

A

The theoretical temperature at which all molecular movement stops

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50
Q

Define heat capacity

A

The amount of heat energy required to increase the temperature of an object by one degree C or K

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51
Q

What material is the resistance wire in resistance thermometers most commonly made from

A

Platinum

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52
Q

Describe how a thermocouple works to measure temperature

A

Two different metals meet at a junction. There is a voltmeter across the junction to measure voltage at the junction which varies with temperature due to Seebeck effect.

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53
Q

Describe what the ‘Seebeck’ effect is

A

When 2 dissimilar metals come together a voltage is produced at the junction. The voltage varies with temperature.

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54
Q

Describe how a bourdon gauge works to measure temperature

A

Bourdon gauge is a device normally used to measure pressure.

Charles’ law means that the volume of a gas will increase with temperature. So if we close the end of the tube in a bourdon gauge and add a small reservoir of gas to the end (this increases the volume of gas, so increases the volume change with temperature) then we’ve made a thermometer. As the temperture increases, the volume of gas in the tube increases and the tube will try to open, turning the gauge.

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55
Q

Define Boyle’s law

A

At a constant temperature, the volume of a fixed amount of gas is inversely proportional to its pressure

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56
Q

Define Charles law

A

At a constant pressure, Volume of a fixed amount of gas is proportional to its absolute temperature

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57
Q

Define Gay Lussac’s law

A

At constant volume, Pressure of a fixed volume of gas will increase in proportion to absolute temperature

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58
Q

Define Henry’s law

A

At constant temperature, the amount of gas dissolved in a liquid is directly proportional to the partial pressure of this gas in equilibrium with it

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59
Q

What is the function of a diode in a circuit

A

Allows current to flow in one direction

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60
Q

What is the unit for capacitance

A

Farad

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61
Q

Define a Farad

A

Farad is the unit for capacitance. A 1 farad capacitor when charged with 1 coulomb of charge has a potential difference of 1 volt between its plates.

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62
Q

Define the Isosbestic point

A

The wavelength at which light is absorbed by oxyhemoglobin and deoxyhaemoglobin equally

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63
Q

What is the Isobestic point of red light used in pulse oximeter

A

590nm

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64
Q

At what pressure is oxygen stored in a Vacuum-insulated evaporator (VIE)

A

7 Bar

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65
Q

Define resonance

A

Resonance is the ability of an object to oscillate in response to a movement

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66
Q

Define natural resonant frequency

A

The frequency which an object can resonate at with no energy needed to be applied

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67
Q

Define Damping

A

Damping is the ability of an object to resist oscillation in response to a force being applied to it

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68
Q

How does an over damped arterial line trace effect its reading in comparison to the true BP

A

The Reading is slow to react which means the waveform does not reach it’s maximal systolic and minimal diastolic pressure readings causing a squashed waveform. MAP is often correct despite this.

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69
Q

How does an under damped arterial line trace effect its reading in comparison to the true BP

A

Trace is hyper resonant and will show rapid response to the BP but also overshoot. This causes the readings to show an over read systolic and under read diastolic pressure. Waveform has spiked appearance. MAP is often correct despite this

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70
Q

Describe the Poynting effect in reference to Entonox

A

When liquid nitrous oxide and gaseous oxygen are mixed a gaseous mixture is formed. The mixture which is called Entonox will exhibit physical properties that are different from the individual gases, including its boiling point and critical temperature. Mixing reduces the critical temperature of N2O

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71
Q

Define sterilisation

A

The removal of all micro-organisms including spores, fungi and viruses

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72
Q

What is the Isosbestic point of Ifrared light used in pulse oximeter

A

805nm

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73
Q

What relative humidity can an HME filter achieve

A

60-70%

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74
Q

What is the pore size of a HME filter

A

0.2 micrometres

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75
Q

How long can a HME filter be used for

A

24 hours

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76
Q

Why does using the oxygen flush excessively risk causing awareness in a gas anaesthetic

A

Oxygen flush bypasses vaporisers and flow meters. This can reduce the concentration of anaesthetic gas in the breathing circuit if used excessively

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77
Q

At what pressure is Nitrous Oxide delivered

A

745 psi

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78
Q

What pressure is N20 stored in cylinders at

A

44 Bar

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79
Q

Why can’t pressure gauges be used in N20 cylinders to work out remaining volume

A

Nitrous oxide is stored in liquid form below its critical temperature. The pressure remains constant until all liquid has vaporised.

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80
Q

What is the filling ratio of Nitrous oxide (N20) in the UK

A

0.75

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81
Q

What is the filling ratio of Nitrous oxide (N20) in the hot countries

A

0.67

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82
Q

What is the weight of a size E N20 cylinder when empty

A

5.4kg

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83
Q

How can you calculate the remaining volume of N20 in a cylinder

A

Weight of cylinder currently - Weight of cylinder empty = weight of N20

Weight of N20 / molecular weight of N20 (44) =number of moles

Number of Moles x Avogadros number (22.4) = volume of gas

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84
Q

What is the critical temperature of Oxygen

A

-119C

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85
Q

What is the critical temperature of N2O

A

36.4

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86
Q

How do oxygen concentrators work

A

Room air is pressurised and passed through Zeolite towers containing 2 Ziolite lattices. These adsorb N20 and water vapour. Oxygen can be concentrated to 95%

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87
Q

Name a ventilator that uses an oxygen concentrator

A

Glostavent

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88
Q

What material are old medical gas cylinders made from

A

Molybdenum steel

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89
Q

What materials are modern medical gas cylinders made from

A

Aluminium wrapped in kevlar

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90
Q

Which gas has a blue shoulder on the cylinder

A

Nitrous oxide

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91
Q

Which gas has a white shoulder on the cylinder

A

oxygen

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92
Q

Which gas has a brown shoulder on the cylinder

A

Helium

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93
Q

Which gas has a grey shoulder on the cylinder

A

Carbon dioxide

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94
Q

Which gas has a black and white shoulder on the cylinder

A

Medical Air

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95
Q

Which gas has a blue and white shoulder on the cylinder

A

Entonox (nitrous oxide + oxygen)

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96
Q

Which gas has a brown and white shoulder on the cylinder

A

Helium + oxygen

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97
Q

What pressure are all molybdenum cylinders at temperature 15C

A

137Bar

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98
Q

What volume does 1 mole of gas occupy

A

22.4L

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99
Q

What is the pseudocritical temperature of entonox

A

-6C

Below this temperature the gasses separate with N20 at the bottom and 02 at the top

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100
Q

What is the purpose of a heat exchanger in a VIE

A

Warms up oxygen that leaves the tower

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101
Q

What is the purpose of a pressure rising vaporiser in a VIE

A

If demand of Oxygen exceeds supply this will warm up liquid oxygen to produce more vapour

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102
Q

What pressure are medical gases delivered at in theatre

A

4 Bar

7 Bar for surgical gasses used for equipment etc

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103
Q

What type of valve does a CD cylinder use

A

Integral

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104
Q

What type of valve does an E type cylinder use

A

Pin index

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105
Q

What type of valve does an HX type cylinder use

A

Integral

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106
Q

What type of valve does a c type cylinder use

A

Pin index

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107
Q

What type of valve does a ZX type cylinder use

A

Integral

(All double letter cylinders are new type which all use integral)

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108
Q

What volume of oxygen do size ZX cylinders hold

A

3970L

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109
Q

Why is Helium useful in airway obstruction

A

Reduction in airways radius with obstruction causes an increase in airways resistance, as demonstrated using the Hagen-Poiseuille equation. This results in an increased work of breathing with eventual fatigue, hypoxia and hypercapnia.

Helium is less dense than. oxygen/air so lowers Reynolds number which allows more laminar flow

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110
Q

List the 15 components of an anaesthetic work station

A

Fresh gas supply
Pressure gauges
Pressure regulating valves
Flow restrictors
Flow meters
Vapourisers
Common gas outlet
High flow oxygen flush
pressure relief valve
oxygen supply failure alarm
breathing system
ventilator
scavenging
suction
monitoring devices

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111
Q

What is the role of a fail safe valve in anaesthetic workstation

A

A fail safe in case the pressure regulator does not reduce the fresh gas pressure from cylinder/pipeline to a safe pressure

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112
Q

How do you calculate absolute pressure using a gauge pressure

A

Absolute pressure = Gauge pressure + atmospheric pressure (101kpa)

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113
Q

What is the Oxygen failure alarm also known as

A

The Ritchie whistle

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114
Q

How does an oxygen failure alarm work

A

A pressure sensitive valve that closes when O2 drops below 2 Bar form FGF. This closes the FGF to patient and vents it through a whistle/alarm. A new channel opens allowing atmospheric air to enter the system instead of FGF.

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115
Q

Which component on anaesthetic work station changes the intermediate pressure circuit to the low pressure circuit

A

Flow meter control valve (needle valve)

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116
Q

What makes the oxygen flowmeter different to the other gases

A

Oxygen is always on the left relative to the other gases
Oxygens knob is bigger
Oxygens Knob is a hexagonal shape

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117
Q

Why is oxygen flowmeter on the left compared to other gases

A

Boyle was left handed

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118
Q

What shape is the tube in a flowmeter

A

Conical

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119
Q

Do you take the reading from the top, middle or bottom of the conical shaped bobbin in a flowmeter

A

Top

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120
Q

What measure has been taken to stop bobbin from sticking in tube of flowmeter

A

Anti-static coating of tube

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121
Q

Why does the bobbin in a flowmeter spin

A

Veins etched into the bobbin makes it rotate

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122
Q

Why does the bobbin in a flowmeter shake around near the top of the tube at high flows

A

Towards the top of the tube the diameter is wider (due to conical shape). The wider diameter compared to length of the tube causes turbulent flow.

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123
Q

Which safety feature on the flowmeter prevents you from delivering 100% nitrous oxide

A

Bicycle chain ( Ohmeda “Link 25” system)

When turning N20 flowmeter up there is a chain joining it to the 02 flowmeter causing this to be turned up as well. Means you always deliver at least 25% 02 when using N20

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124
Q

What is the flow rate of the emergency Oxygen Flush

A

35L/min (matches average inspiratory flow rate)

125
Q

What is a safety feature of the emergency oxygen flush

A

Does not have a locking mechanism to avoid barotrauma

126
Q

Describe the pumping effect and how this can affect output concentration of vaporisers

A

The ventilator can causes cyclical pressure changes in the back bar (where vaporisers are) causing some saturated gas to move back in to the vaporiser and some passes through the bypass chamber giving a higher than expected output concentration

127
Q

Describe the pressurising effect and how this can affect output concentration of vaporisers

A

At very high flows or in large chambers the pressure of the gas passing through vaporiser is high. The concentration of agent vapour picked up is the same. When this gas reaches the common outlet it will expand to reduce pressure with the conc. of agent remaining the same. This results in dilution and causes a lower than expected output concentration

128
Q

What safety function does the Ohmeda selectatec system have on the back bar

A

The back bar is where you attach the vaporisers.

The selectatec system is a metal rod connecting the 2 vaporisers which will lock one of the vaporisers if the other is opened. Prevents 2 agents being used simultaneously.

129
Q

How do bimetallic strips allow for temperature compensation due to latent heat of vaporisation of agent

A

These devices use a bimetallic strip composed of two metal bands with different coefficients of expansion that bend according to the temperature inside the vaporization chamber. If temperature decreases they bend to allow more fresh gas flow (FGF) to enter vaporiser

130
Q

Why do you need to compensate for temperature drop due to latent heat of vaporisation

A

If temperature drops the SVP of an agent will fall which causes a reduction in the delivered concentration from the vapouriser

131
Q

How does a metal base of a vaporiser allow for temperature compensation due to latent heat of vaporisation of agent

A

Metal base allows vapouriser to be heated quickly from surrounding temperature of the room. This reduces the affect of temperature drop due to latent heat of vaporisation of agent.

132
Q

Does altitude affect output of volatile agent

A

SVP of agent only affected by temperature not pressure.

Concentration of agent at lower pressure would be increased.

Partial pressure of volatile agent is what causes anaesthesia not concentration of agent.

Partial pressure of volatile agent is unnafected by altitude due to Dalton’s law so altitude does not affect the efficacy of agent at constant temperature.

133
Q

Define an open breathing system

A

Respiratory tract is open to atmosphere and no rebreathing occurs

134
Q

Give an example of an open breathing system

A

Schimmelbusch mask

Gauze in a mask has anaesthetic agent drops added to it and patient breathes through this

135
Q

Define a semi-open breathing system

A

A system where volatiles are carried by fresh gas flow and can be diluted by room air

136
Q

Give an example of a semi-open breathing system

A

venturi mask

137
Q

Define semi-closed breathing system

A

A breathing system where volatiles are carried by fresh gas flow and can’t be diluted by room air

138
Q

What are the 3 sub classifications of semi-closed breathing systems

A

1- Rebreathing system without CO2 absorption
2- Rebreathing system with CO2 absorption
3- non-rebreathing system (Mapleson classification)

139
Q

Define a closed breathing system

A

A rebreathing system where the expiratory valve is closed

140
Q

What is soda lime composed of

A

80% CaOH
15% H2O
4% NaOH
1% KOH

Silicates
Indicator dye

141
Q

What is the role of KOH in soda lime

A

Accelerates rate of reaction

142
Q

Which dye in soda lime changes colour from red to white when saturated with CO2

A

Ethyl violet

143
Q

Which dye in soda lime changes colour from white to purple when saturated with CO2

A

Phenolphthalein

144
Q

What volume of CO2 does 1kg of soda lime typically absorb

145
Q

List the chemical reactions that occur in soda lime for CO2 absorption

A

H2O + CO2 -> H2CO3

H2CO3 + 2NaOH -> Na2CO3 + 2H2O + HEAT

Na2CO3 + Ca(OH)2 -> CaCO3 + 2NaOH

146
Q

Which byproduct is made in soda lime if using low flow anaesthesia with sevoflurane

A

Compound A

147
Q

Which material does not absorb infra red radiation and is used in measurement of end tidal Co2

148
Q

which 2 types of heat losses do forced air warmers prevent

A

Radiation
Convection

149
Q

What are the pin locations for a cylinder containing air

150
Q

What are the pin locations for a cylinder containing Oxygen

151
Q

What are the pin locations for a cylinder containing carbon dioxide

152
Q

What are the pin locations for a cylinder containing Nitrogen

153
Q

What are the pin locations for a cylinder containing Nitrous oxide

154
Q

What are the pin locations for a cylinder containing Heliox

155
Q

What are the pin locations for a cylinder containing Entonox

156
Q

What are the pin locations for a cylinder containing Helium

157
Q

Above which volume of fluid administration should you use a fluid warmer intra-operatively

158
Q

What does a IVC/Ao index <0.8 on ultrasound tell you

A

Patient is undefiled and needs fluids

159
Q

What does a IVC/Ao index > 1.2 on ultrasound tell you

A

Patient is likely fluid overloaded

160
Q

What are the 3 phases of hypothermia intra-operatively

A

1- Re-distribution phase
2- Linear phase
3- Plateau phase

161
Q

Which electrical component is used in a defibrillator to convert AC to DC

A

Rectifier

A type of diode (allows current to flow in one direction only)

162
Q

How is N20 manufactured

A

By heating ammonium nitrate at 250C

163
Q

Which wavelength of light is most absorbed by OxyHb

A

940nM (INFRARED)

164
Q

Which wavelength of light is most absorbed by deoxyHb

A

660nm (red light)

165
Q

How does a pulse oximeter calculate oxygen saturation

A

The ratio of 660nm compared to 940nm light absorbance. This ratio is cross-referenced to a table of absolute absorption

166
Q

Towards which value of SaO2 does Carboxyhaemoglobin (COHb) tend a pulse oximeter reading and why

A

100%

COHb absorbs the same amount of 660nm light as oxyHb

167
Q

Towards which value of SaO2 does Methaemoglobin (metHb) tend a pulse oximeter reading and why

A

85%

MetHb tends the ratio of 660nm/940nm towards 1 which gives Sats of 85%

MetHb equally absorbs 660nm and 940nm wavelengths

168
Q

What type of graph is visually seen on pulse-oximeter monitor

A

Photoplethysomgraph

169
Q

What is the Beer-lambert equation

A

I(trans) = I(in) x e ^c x α x l

Light out/transmitted = light in x e ^ concentration x molar extinction coefficient x length of path

170
Q

Describe how a polarographic (clark) electrode works in an ABG machine to measure PO2

A

Polarographic (clark) electrode is used to measure PO2 in blood gas.

O2 from blood passes through a membrane into canister with KCL electrolyte and a platinum cathode + Silver anode.

The circuit contains a battery which delivers 0.7v

Oxygen is reduced at the cathode causing current to flow through circuit

Current is measured by ammeter and is directly proportional to PO2

171
Q

Describe how the Ph electrode in an ABG machine works

A

Sensing electrode encased in hydrogen ion sensitive glass containing buffer solution of known H+ conc.

H+ ions contained in blood sample bind to glass and the difference in H+ conc of blood to the H+ conc. of buffer solution creates a potential difference.

Potential difference at sensing electrode is compared to reference electrode in circuit and voltmeter measure difference which is proportional to H+ of blood sample.

172
Q

Describe how the PCO2 (Severinghaus) electrode works in ABG machine

A

Modified H+ electrode.

CO2 can move across membrane encasing buffer solution around sensing electrode.

CO2 reacts with H20 to form H2CO3. The CO2 directly impacts the H+ conc. due to H2CO3 dissociation.

H+ is measured like in H+ electrode by causing a potential difference in circuit compared to reference electrode. Voltage is used to calculate pH.

Henderson hesselbalch equation used to calculate PCO2

173
Q

What type of ventilator is a VentiPac

A

VentiPac is a time cycled flow generator.

Flow is preset and pressure is limited. Any excess pressure is vented and not delivered to patient.

Ventilator essentially uses pressure from oxygen cylinder and released a set volume at a given time interval. Can be used for transfers. Normally gives Fi02 100% but can be switched onto Air mix setting where it will give FiO2 45%

174
Q

Define Coanda effect

A

The tendency of a jet of fluid to follow a convex surface.

When fluid passes through orifice it flows at high velocity but low pressure (Bernoulli principle) If the pressure is lower than atmospheric pressure it entrains air into the stream of fluid (like a vacuum effect) If the fluid passes close to a wall it will pull itself to the wall due to this vacuum effect

175
Q

What is the flow rate of a 16G cannula

176
Q

What is the flow rate of a 18G canola

177
Q

What effect does placing the arterial line transducer 10cm below the level of the heart have on BP

A

BP is measured 7.4mmHg higher than true value

178
Q

Give 2 physiochemical methods of measuring PO2

A

Polarographic (clark) electrode

galvanic fuel cell

179
Q

Give 2 Physical methods of measuring PO2

A

Paramagnetic

Mass spectrometry

180
Q

What are the 4 phases that occur in a mass spectrometer

A

Ionisation- sample is ionised into its components

Acceleration- Particles accelerated by magnet around a curve

Deflection- Heavy and light substances hit into wall of curve (depends on mass : charge ratio)

Detection- Number of particles of each type detected

181
Q

What is the gold standard for measuring gas concentration

A

Quadrapole mass spectrometer

182
Q

What is the cathode of a polarographic clark electrode made from

183
Q

What is the anode of a polarographic clark electrode made from

184
Q

What is the cathode of a Galvanic fuel cell made from

185
Q

What is the anode of a polarographic clark electrode made from

186
Q

What is the electrolyte used in a Galvanic fuel cell

187
Q

What is the electrolyte used in a polarographic Clark electrode

188
Q

What is the wavelength spectrum of visible light

189
Q

Define Collision Broadening

A

The phenomenon in which the spectral absorption peaks of one gas are changed (broadened) due to the collision or proximity of another gas

190
Q

Describe class I medical device in terms of electrical safety

A
  • Mains powered and earthed device
  • Uses isolating transformer
191
Q

Describe class II medical device in terms of electrical safety

A
  • Double insulated device
  • not earthed
193
Q

Define Bernoulli principle

A

An increase in velocity of a moving fluid results in simultaneous decrease in its pressure (and visa versa)

194
Q

Describe what happens to velocity and pressure of a fluid moving through a pipe which becomes constricted

A

Bernoulli’s principle

Velocity increases but pressure decreases

(like putting finger over hose pipe)

195
Q

What is the risk with using Venturi valve in patient with very high peak inspiratory flow rate (PIFR)

A

If PIFR exceeds the flow rate of the Venturi valve air is entrained around the mask which dilutes the 02 concentration.

196
Q

Define Fourier analysis

A

A mathematical operation that deconstructs a complex signal into its constituent frequencies.

The main waveform is known as the fundamental frequency

197
Q

Define natural frequency

A

The natural frequency of the system is the frequency at which it will oscillate freely (in the absence of sustained stimulus)

198
Q

Define resonance

A

Resonance is the amplification of signal when the driving frequency is close to the natural frequency of a system

199
Q

What does a damping co-efficient of <0.7 represent

A

Underdamped

200
Q

What does a damping co-efficient of 0.64 represent

A

Optimal damping

201
Q

What does a damping co-efficient of >0.7 represent

A

Overdamped

202
Q

What does a damping co-efficient of 1.0 repressent

A

Critical damping

203
Q

Define critical damping

A

When the damping coefficient is equal to the resonant frequency of the oscillator

Damping coefficient of 1.0

204
Q

How many times larger is the natural frequency of arterial line system compared to the natural frequency of the blood pressure wave

A

8X

Hr of 180bpm = frequency of 3hz

natural frequency of arterial line system is at least 24hz to avoid resonance which would amplify the waveform and make it inaccurate.

205
Q

What size filter is used in I.V drug giving set

A

0.2 micron

206
Q

What size filter is used in a blood giving set

A

200 micron

207
Q

Describe how IR absorption spectrophotometry is used to measure CO2, N20 and volatile gas concentrations

A

Bonds between dissimilar atoms absorb IR light causing them to vibrate. Each bond absorbs different wavelength. Using Beer Lambert law can work out concentration of each gas by looking at absorption peaks.

CO2 - 4.26 micrometers
N20- 4.5 Micrometers
Volatiles 3.3 micrometers

208
Q

What is the most common method of measuring anaesthetic gas concentrations

A

Infrared absorption spectrophotometry

209
Q

What is the gold standard method of measuring anaesthetic gas concentrations which clinical machines are calibrated with

A

Refractometry

210
Q

What is the 8 hour time weighted average concentration for N20 in the UK

211
Q

What effect does Ketamine have on BIS

A

Causes BIS number to go up due to a Gamma burst and increased Beta waves

212
Q

List 3 factors that cause a reduction in BIS

A

Hypothermia
Hypovolaemia
Neuromuscular blocking drugs

213
Q

What do Lundberg A waves indicate on ICP monitoring

A

Increase in ICP for 5-10 minutes (plateau waves)

Indicates reduced cerebral compliance and imminent herniation

214
Q

What do Lundberg B waves indicate on ICP monitoring

A

Oscilations of ICP at rate of 0.5-2 waves per second/ Hx

Indicates unstable ICP and possible vasospasm

215
Q

Outline the codes for pacemakers

A

Up to 5 letters

Position 1 = Chamber paced (Atria, Ventricles, Dual)

Position 2 = Chamber sensed (Atria, Ventricles, Dual)

Position 3 = Mode of response (Triggered, Inhibited, Dual)

Position 4 = Programmability (Programme, multi-programme, communicating, rate response)

Position 5 = Anti-tachycardia function (Pacind, shock dual)

216
Q

What is the average frequency of Delta waves on BIS

A

3Hz

Delta waves are long slow waves seen in sleep

217
Q

How can you calculate the natural frequency of an arterial line

A

Square wave test

Flush the arterial line - you get a flat square line

When you stop flushing you get multiple oscillations with decreasing amplitudes before it returns to normal trace

Calculate the period of one cycle (distance between 2 peaks next to each other in mm). (1 wavelength)

The speed at which the paper is running mm/s is divided by the period to give natural frequency

Frequency = Wave speed/ wavelength

218
Q

What is Corrected Flow Time (FTc) an indicator of on oesophageal doppler

219
Q

What is Peak Velocity (PV) an indicator of on oesophageal doppler

A

Contractility

220
Q

What 2 assumptions are made in oesophageal doppler

A

Descending aorta carries 70% of CO

Descending aorta cross sectional area based on demographical data

221
Q

What type of vacuum do you get in a Barometer with Mercury

A

A Torricellian vacuum

222
Q

What is 1 ATM equivalent to in mmHg

223
Q

What is 1 ATM equivalent to in cmH2O

224
Q

What is 1 ATM equivalent to in Kpa

225
Q

What is 1 ATM equivalent to in Bar

226
Q

List some of the properties of an ideal nerve stimulator device

A

Delivers constant current

Can deliver a supramaximal stimulus with current up to 80mA

Delivers a unipolar square wave of 0.1-0.3msecs

Has different stimulus settings: SF, TOF, DBS, Tetanus 50hz

227
Q

What does a TOF ratio of >0.9 mean in terms of neuromuscular blockade

A

Adequately reversed

228
Q

What is the pore size in a HME filter

A

0.2 micrometres

229
Q

What is the absolute humidity that a HME filter can provide

230
Q

What is the absolute humidity that a ultrasonic nebuliser can provide

231
Q

What is the absolute humidity that a cascade humidifier can provide

232
Q

What is the absolute humidity that a heated water bath humidifier can provide

233
Q

Describe what a class B electrical safety rating means in medical equipment

A

Medical device connected directly to patient which has a leakage current < 100mA

234
Q

Describe what a class BF electrical safety rating means in medical equipment

A

Medical device connected directly to patient which has a leakage current < 100mA and uses a floating circuit

235
Q

Describe what a class CF electrical safety rating means in medical equipment

A

Medical device connected directly to patient which has a leakage current < 10mA and uses a floating circuit

236
Q

Describe how Ohm’s law can be adapted for gas flow

A

Ohm’s Law ( V=IR )

Flow = change in pressure / Resistance (Q = ΔP/R)

237
Q

Describe how a pneumotachograph works

A

A measurement device in anaesthetic machine used for measuring flow.

A piece of tubing with a wider centre containing a mesh.

Mesh provides resistance to flow

Pressure measured before mesh and after mesh.

Can be used to calculate flow using Ohms law Flow = change in pressure / resistance

Bi-directional flow measurement

Widened centre to ensure laminar flow.

238
Q

Describe how a Wright respirometer works

A

A measurement device used to measure flow

FGF hits vanes causing them to spin. The spin is proportional to flow rate and hence volume.

Only unidirectional flow measurement.

Inertia of spinning vanes causes over-estimate of flow

239
Q

Which frequencies are used in surgical diathermy

A

in range of 1MHz

240
Q

Which type of diathermy requires a diathermy plate

A

Monopolar diathermy

241
Q

Which type of diathermy uses higher power

242
Q

Which gas is used to cool MRI scanners

243
Q

What effect does a Diamagnetic material have on magnetic flux

A

Decrease magnetic flux

244
Q

What effect does a ferromagnetic material have on magnetic flux

A

Increases magnetic flux

245
Q

What effect does a paramagnetic material have on magnetic flux

A

slightly increases magnetic flux

246
Q

Define Magnetic Flux

A

The magnetic field present in a material

247
Q

What is the unit for Magnetic Flux

A

Webber (Wb)

248
Q

What is the unit for Magnetic Flux Density

249
Q

What does a Galvanometer measure

250
Q

Which electrical wire is earthed at the substation

A

The neutral wire

251
Q

Define Impedence (Z)

A

The opposition to flow of A/C current due to the combination of resistance and reactance

Measured in Ohms

252
Q

What is the SI unit for Luminous intensity

253
Q

What are the SI units

A

M- metre
Kg- kilogram
s- second
A- ampere
mol- mole
K- kelvin
cd- candela

254
Q

Which gas cylinder size is used in manifolds and what is the volume

A

Size J

Volume 6800L

255
Q

Which size cylinder is used in anaesthetic machines and what is the volume

A

Size E

Volume 680L

256
Q

what pressure are Entonox cylinders stored at

A

13,700 kPa

257
Q

Which Vaporiser is specifically used with Desflurane

258
Q

What temperature and pressure does a TEC6 vaporiser use for Desflurane

A

39C

194 kPa

259
Q

What is a normal range of pulmonary artery wedge pressure

260
Q

What is the relationship between frequency of current and resistance of a capacitor

A

Frequency is inversely proportional to resistance

D.C current can’t pass through

261
Q

Which diathermy is safer for use in patients with a pacemaker

262
Q

Which type of diathermy requires a grounding plate

263
Q

What is the waveform used in cutting diathermy

A

A continues sine waveform with low voltage

264
Q

What is the waveform used in coagulation diathermy

A

Pulsed waveform with high voltage

265
Q

Which type of diathermy is more effective at coagulation than cutting

A

Bipolar diathermy

266
Q

What is a CO2 laser used for

A

Photocoagulation in ophthalmic procedures

267
Q

What is a Nd-YAG laser used for

A

Airway surgery

268
Q

What is an Argon laser used for

A

Retinal surgery and dermatology

269
Q

What is a yellow pulsed dye laser used for

A

Dermatology
- birth mark removal
- Port wine stain

270
Q

What is the critical temperature of oxygen

271
Q

What does the point of maximal amplitude oscillation of non-invasive blood pressure measurement relate to

272
Q

How do antistatic shoes prevent electrocution

A

Have high impedance so only very small current can flow. Allows current to enter earth so no static charge build up

273
Q

Describe what is meant by a T-piece breathing circuit

A

A circuit in which the FGF delivery is closest to the patient end of the circuit without valves or reservoir bags in between

274
Q

List the 3 breathing circuits which count as T-Piece circuits

A

Mapleson D
Mapleson E (Ayre’s T piece)
Mapleson F (Jackson Rees modification

275
Q

What size are epidural filters

A

0.2 micrometres

276
Q

What size are blood giving set filters

A

200 micrometres

277
Q

What is meant by transit time for ETCO2 measurement

A

time taken for the sample to reach the analyser

278
Q

What is meant by the rise time for ETCO2 measurement

A

The time it takes the analyser to process the sample once it has reached the analyser

279
Q

What principle does a DINAMAP use

A

Oscillometry

280
Q

How much energy is required in paediatric synchronised cardioversion

A

2 joules/kg

(4 if asynchronous)

281
Q

What is the critical temperature of oxygen

282
Q

What temperature is oxygen in a VIE

283
Q

What pressure are size E cylinders when full

284
Q

What is the unit of Inductance

285
Q

Define Beer’s law

A

The intensity of transmitted light decreases exponentially as the concentration of the substance it moves through increases

286
Q

Define Lambert’s law

A

The intensity of transmitted light decreases exponentially as the distance travelled through the substance increases

287
Q

What is the equation for Beer-Lambert law

A

A = εdc

Absorbance = molar extinction co-efficient x path length x molar concentration

288
Q

Is the oxygen in a VIE actively cooled

A

No

Latent heat of vaporisation of oxygen cools it and insulated by a vacuum

289
Q

Can zeolite columns in oxygen concentrators be re-used

A

Yes

Heating the zeolite column causes the trapped N2 and H2O to be released back into the atmosphere

290
Q

What are 2 safety features preventing you from connecting the wrong hose pipe to medical gas outlet

A

NIST- Non interchangeable screw thread on hose

Index collar on hose which only fits a particular diameter socket

Colour coded hose pipe and outlet

291
Q

Is a medical vacuum system

1- High flow, low pressure
2- Low flow, high pressure

A

2- low flow, high pressure

292
Q

Is a scanvenging system

1- High flow, low pressure
2- Low flow, high pressure

A

1- high flow, low pressure

293
Q

Which feature protects the central pipeline of a vacuum system from contamination

A

Suction trap

294
Q

What is the UK limit of environmental N2O concentration in theatre

A

100 ppm (parts per million) in 8 hours

295
Q

What is the UK limit of environmental isoflurane concentration in theatre

A

50 ppm (parts per million) in 8 hours

296
Q

Name a passive scavenging system

A

Cardiff Aldasorber

297
Q

How does a reservoir bag work

A

Fills with oxygen during expiration and can be drawn from during inspiration to meet patients peak inspiratory flow

298
Q

Match the colour to the vaporiser

Blue Sevoflurane
Orange Desflurane
Yellow Isoflurane
Purple Halothane
Red Enflurane

A

Blue Desflurane
Orange Enflurane
Yellow Sevoflurane
Purple Isoflurane
Red Halothane

299
Q

What is the weight cut off for using a Mapleson E circuit in paediatrics

A

Suitable up to 30kg

300
Q

What parameter should the volume of tubing in a Mapleson E circuit be matched

A

The patients tidal volume

If larger you get rebreathing

If smaller you get entrainment of air

301
Q

What is the voltage used in a clark polographic electrode

302
Q

Which anaesthetic gas causes the Clark Polographic electrode to over read

A

N2O

Is reduced at the cathode

303
Q

Which eponymous equation is used to calculate CO from a PiCCO device

A

Stewart-Hamilton equation

304
Q

Which volatiles can lead to production of carbon monoxide when they come into contact with dry Soda lime

A

Volatile agents that contain a -CHF2 molecule isoflurane, enflurane, desflurane

305
Q

What is the formula for energy stored in a capacitor

A

E = 1/2 X Q X V squared

Energy = 1/2 x charge x potential difference squared

306
Q

Which mode is most commonly used in ultrasound

307
Q

What is the max flow rate you can achieve with an oxygen concentrator

Primary FRCA MCQ (6 decks)

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