Physics and equipment Flashcards
(308 cards)
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
2
Q
What percentage of heat loss is due to radiation intra-operatively
A
40%
3
Q
What percentage of heat loss is due to convection intra-operatively
A
30%
4
Q
What percentage of heat loss is due to evaporation intra-operatively
A
15%
5
Q
What percentage of heat loss is due to respiratory losses intra-operatively
A
10%
6
Q
What percentage of heat loss is due to conduction intra-operatively
A
5%
7
Q
What volume of oxygen do size E cylinders hold
A
680L
8
Q
What volume of oxygen do size HX cylinders hold
A
2300L
9
Q
How do you calculate how much oxygen to take for patient transfer
A
MV X Fi02 x Time of transfer
X2
10
Q
What volume of oxygen do size C cylinders hold
A
170L
11
Q
What volume of oxygen do size CD cylinders hold
A
460L
12
Q
What kind of ventilator is a Manley MP3
A
A Time-cycled pressure generator. A minute volume divider
Mapleson D
13
Q
What volume of oxygen do size D cylinders hold
A
340L
14
Q
What causes an over damped arterial line trace
A
Bubbles in system
Kinking of tubing
Blood clot in canula
15
Q
What is the formula for Laplace’s law in alveoli
A
P = 2T/R
Pressure = 2 x surface tension/ radius
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
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
18
Q
Define Hooke’s law
A
The displacement or size deformation is proportional to the load or force of deformation. (elasticity)
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.
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
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.
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
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
24
Q
Define a vapour
A
A gas below its critical temperature
25
Define SVP (Saturated vapour pressure)
The partial pressure generated by a vapour in equilibrium with its liquid form at a standard temperature and pressure
26
At what temperature is SVP of anaesthetic gases measured
20C
27
What is the SVP of Sevoflurane
21
28
What is the SVP of Isoflurane
33
29
What is the SVP of Desflurane
88
30
What is the SVP of Halothane
32
31
What is the SVP of Enflurane
22.9
32
What is the boiling point of Sevoflurane
58.6
33
What is the boiling point of Isoflurane
48.5
34
What is the boiling point of Desflurane
22.8
35
What is the boiling point of Halothane
50.2
36
What is the boiling point of Enflurane
56.2
37
Describe 3 methods used in vaporises to increase FGF saturation at high flow rates
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.
38
Define latent heat of vapourisation
The energy required to change 1kg of liquid to gas at constant temperature
39
Define humidity
The amount of water vapour pressent within a gas
40
Define absolute humidity
The mass of water vapour (g) present per volume of air (metres cubed (m3))
41
Define relative humidity
Ratio of water vapour present in a gas relative to the maximum possible (100%saturated)
42
How does pressure affect humidity
The higher the ambient pressure the less water can be held in air
43
How does temperature affect humidity
The higher the temperature the more water can be held in air
44
Define dew point
The temperature below which water will begin to condense out of air (100% saturated)
45
Describe how a hair hygrometer works
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
46
Describe how a wet and dry hygrometer works
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.
47
What is the SI unit of temperature
Kelvin
48
Define the measurement Kelvin
one kelvin is 1/273th of the thermodynamic temperature of the triple point of water (=0.01oC)
49
Define absolute zero in terms of temperature
The theoretical temperature at which all molecular movement stops
50
Define heat capacity
The amount of heat energy required to increase the temperature of an object by one degree C or K
51
What material is the resistance wire in resistance thermometers most commonly made from
Platinum
52
Describe how a thermocouple works to measure temperature
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.
53
Describe what the 'Seebeck' effect is
When 2 dissimilar metals come together a voltage is produced at the junction. The voltage varies with temperature.
54
Describe how a bourdon gauge works to measure temperature
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.
55
Define Boyle's law
At a constant temperature, the volume of a fixed amount of gas is inversely proportional to its pressure
56
Define Charles law
At a constant pressure, Volume of a fixed amount of gas is proportional to its absolute temperature
57
Define Gay Lussac's law
At constant volume, Pressure of a fixed volume of gas will increase in proportion to absolute temperature
58
Define Henry's law
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
59
What is the function of a diode in a circuit
Allows current to flow in one direction
60
What is the unit for capacitance
Farad
61
Define a Farad
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.
62
Define the Isosbestic point
The wavelength at which light is absorbed by oxyhemoglobin and deoxyhaemoglobin equally
63
What is the Isobestic point of red light used in pulse oximeter
590nm
64
At what pressure is oxygen stored in a Vacuum-insulated evaporator (VIE)
7 Bar
65
Define resonance
Resonance is the ability of an object to oscillate in response to a movement
66
Define natural resonant frequency
The frequency which an object can resonate at with no energy needed to be applied
67
Define Damping
Damping is the ability of an object to resist oscillation in response to a force being applied to it
68
How does an over damped arterial line trace effect its reading in comparison to the true BP
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.
69
How does an under damped arterial line trace effect its reading in comparison to the true BP
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
70
Describe the Poynting effect in reference to Entonox
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
71
Define sterilisation
The removal of all micro-organisms including spores, fungi and viruses
72
What is the Isosbestic point of Ifrared light used in pulse oximeter
805nm
73
What relative humidity can an HME filter achieve
60-70%
74
What is the pore size of a HME filter
0.2 micrometres
75
How long can a HME filter be used for
24 hours
76
Why does using the oxygen flush excessively risk causing awareness in a gas anaesthetic
Oxygen flush bypasses vaporisers and flow meters. This can reduce the concentration of anaesthetic gas in the breathing circuit if used excessively
77
At what pressure is Nitrous Oxide delivered
745 psi
78
What pressure is N20 stored in cylinders at
44 Bar
79
Why can't pressure gauges be used in N20 cylinders to work out remaining volume
Nitrous oxide is stored in liquid form below its critical temperature. The pressure remains constant until all liquid has vaporised.
80
What is the filling ratio of Nitrous oxide (N20) in the UK
0.75
81
What is the filling ratio of Nitrous oxide (N20) in the hot countries
0.67
82
What is the weight of a size E N20 cylinder when empty
5.4kg
83
How can you calculate the remaining volume of N20 in a cylinder
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
84
What is the critical temperature of Oxygen
-119C
85
What is the critical temperature of N2O
36.4
86
How do oxygen concentrators work
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%
87
Name a ventilator that uses an oxygen concentrator
Glostavent
88
What material are old medical gas cylinders made from
Molybdenum steel
89
What materials are modern medical gas cylinders made from
Aluminium wrapped in kevlar
90
Which gas has a blue shoulder on the cylinder
Nitrous oxide
91
Which gas has a white shoulder on the cylinder
oxygen
92
Which gas has a brown shoulder on the cylinder
Helium
93
Which gas has a grey shoulder on the cylinder
Carbon dioxide
94
Which gas has a black and white shoulder on the cylinder
Medical Air
95
Which gas has a blue and white shoulder on the cylinder
Entonox (nitrous oxide + oxygen)
96
Which gas has a brown and white shoulder on the cylinder
Helium + oxygen
97
What pressure are all molybdenum cylinders at temperature 15C
137Bar
98
What volume does 1 mole of gas occupy
22.4L
99
What is the pseudocritical temperature of entonox
-6C
Below this temperature the gasses separate with N20 at the bottom and 02 at the top
100
What is the purpose of a heat exchanger in a VIE
Warms up oxygen that leaves the tower
101
What is the purpose of a pressure rising vaporiser in a VIE
If demand of Oxygen exceeds supply this will warm up liquid oxygen to produce more vapour
102
What pressure are medical gases delivered at in theatre
4 Bar
7 Bar for surgical gasses used for equipment etc
103
What type of valve does a CD cylinder use
Integral
104
What type of valve does an E type cylinder use
Pin index
105
What type of valve does an HX type cylinder use
Integral
106
What type of valve does a c type cylinder use
Pin index
107
What type of valve does a ZX type cylinder use
Integral
(All double letter cylinders are new type which all use integral)
108
What volume of oxygen do size ZX cylinders hold
3970L
109
Why is Helium useful in airway obstruction
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
110
List the 15 components of an anaesthetic work station
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
111
What is the role of a fail safe valve in anaesthetic workstation
A fail safe in case the pressure regulator does not reduce the fresh gas pressure from cylinder/pipeline to a safe pressure
112
How do you calculate absolute pressure using a gauge pressure
Absolute pressure = Gauge pressure + atmospheric pressure (101kpa)
113
What is the Oxygen failure alarm also known as
The Ritchie whistle
114
How does an oxygen failure alarm work
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.
115
Which component on anaesthetic work station changes the intermediate pressure circuit to the low pressure circuit
Flow meter control valve (needle valve)
116
What makes the oxygen flowmeter different to the other gases
Oxygen is always on the left relative to the other gases
Oxygens knob is bigger
Oxygens Knob is a hexagonal shape
117
Why is oxygen flowmeter on the left compared to other gases
Boyle was left handed
118
What shape is the tube in a flowmeter
Conical
119
Do you take the reading from the top, middle or bottom of the conical shaped bobbin in a flowmeter
Top
120
What measure has been taken to stop bobbin from sticking in tube of flowmeter
Anti-static coating of tube
121
Why does the bobbin in a flowmeter spin
Veins etched into the bobbin makes it rotate
122
Why does the bobbin in a flowmeter shake around near the top of the tube at high flows
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.
123
Which safety feature on the flowmeter prevents you from delivering 100% nitrous oxide
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
124
What is the flow rate of the emergency Oxygen Flush
35L/min (matches average inspiratory flow rate)
125
What is a safety feature of the emergency oxygen flush
Does not have a locking mechanism to avoid barotrauma
126
Describe the pumping effect and how this can affect output concentration of vaporisers
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
Describe the pressurising effect and how this can affect output concentration of vaporisers
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
What safety function does the Ohmeda selectatec system have on the back bar
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
How do bimetallic strips allow for temperature compensation due to latent heat of vaporisation of agent
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
Why do you need to compensate for temperature drop due to latent heat of vaporisation
If temperature drops the SVP of an agent will fall which causes a reduction in the delivered concentration from the vapouriser
131
How does a metal base of a vaporiser allow for temperature compensation due to latent heat of vaporisation of agent
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
Does altitude affect output of volatile agent
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
Define an open breathing system
Respiratory tract is open to atmosphere and no rebreathing occurs
134
Give an example of an open breathing system
Schimmelbusch mask
Gauze in a mask has anaesthetic agent drops added to it and patient breathes through this
135
Define a semi-open breathing system
A system where volatiles are carried by fresh gas flow and can be diluted by room air
136
Give an example of a semi-open breathing system
venturi mask
137
Define semi-closed breathing system
A breathing system where volatiles are carried by fresh gas flow and can't be diluted by room air
138
What are the 3 sub classifications of semi-closed breathing systems
1- Rebreathing system without CO2 absorption
2- Rebreathing system with CO2 absorption
3- non-rebreathing system (Mapleson classification)
139
Define a closed breathing system
A rebreathing system where the expiratory valve is closed
140
What is soda lime composed of
80% CaOH
15% H2O
4% NaOH
1% KOH
Silicates
Indicator dye
141
What is the role of KOH in soda lime
Accelerates rate of reaction
142
Which dye in soda lime changes colour from red to white when saturated with CO2
Ethyl violet
143
Which dye in soda lime changes colour from white to purple when saturated with CO2
Phenolphthalein
144
What volume of CO2 does 1kg of soda lime typically absorb
250L
145
List the chemical reactions that occur in soda lime for CO2 absorption
H2O + CO2 -> H2CO3
H2CO3 + 2NaOH -> Na2CO3 + 2H2O + HEAT
Na2CO3 + Ca(OH)2 -> CaCO3 + 2NaOH
146
Which byproduct is made in soda lime if using low flow anaesthesia with sevoflurane
Compound A
147
Which material does not absorb infra red radiation and is used in measurement of end tidal Co2
Sapphire
148
which 2 types of heat losses do forced air warmers prevent
Radiation
Convection
149
What are the pin locations for a cylinder containing air
1 and 5
150
What are the pin locations for a cylinder containing Oxygen
2 and 5
151
What are the pin locations for a cylinder containing carbon dioxide
1 and 6
152
What are the pin locations for a cylinder containing Nitrogen
1 and 4
153
What are the pin locations for a cylinder containing Nitrous oxide
3 and 5
154
What are the pin locations for a cylinder containing Heliox
2 and 4
155
What are the pin locations for a cylinder containing Entonox
7
156
What are the pin locations for a cylinder containing Helium
no pin
157
Above which volume of fluid administration should you use a fluid warmer intra-operatively
500ml
158
What does a IVC/Ao index <0.8 on ultrasound tell you
Patient is undefiled and needs fluids
159
What does a IVC/Ao index > 1.2 on ultrasound tell you
Patient is likely fluid overloaded
160
What are the 3 phases of hypothermia intra-operatively
1- Re-distribution phase
2- Linear phase
3- Plateau phase
161
Which electrical component is used in a defibrillator to convert AC to DC
Rectifier
A type of diode (allows current to flow in one direction only)
162
How is N20 manufactured
By heating ammonium nitrate at 250C
163
Which wavelength of light is most absorbed by OxyHb
940nM (INFRARED)
164
Which wavelength of light is most absorbed by deoxyHb
660nm (red light)
165
How does a pulse oximeter calculate oxygen saturation
The ratio of 660nm compared to 940nm light absorbance. This ratio is cross-referenced to a table of absolute absorption
166
Towards which value of SaO2 does Carboxyhaemoglobin (COHb) tend a pulse oximeter reading and why
100%
COHb absorbs the same amount of 660nm light as oxyHb
167
Towards which value of SaO2 does Methaemoglobin (metHb) tend a pulse oximeter reading and why
85%
MetHb tends the ratio of 660nm/940nm towards 1 which gives Sats of 85%
MetHb equally absorbs 660nm and 940nm wavelengths
168
What type of graph is visually seen on pulse-oximeter monitor
Photoplethysomgraph
169
What is the Beer-lambert equation
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
Describe how a polarographic (clark) electrode works in an ABG machine to measure PO2
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
Describe how the Ph electrode in an ABG machine works
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
Describe how the PCO2 (Severinghaus) electrode works in ABG machine
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
What type of ventilator is a VentiPac
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
Define Coanda effect
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
What is the flow rate of a 16G cannula
200ml/min
176
What is the flow rate of a 18G canola
100ml/min
177
What effect does placing the arterial line transducer 10cm below the level of the heart have on BP
BP is measured 7.4mmHg higher than true value
178
Give 2 physiochemical methods of measuring PO2
Polarographic (clark) electrode
galvanic fuel cell
179
Give 2 Physical methods of measuring PO2
Paramagnetic
Mass spectrometry
180
What are the 4 phases that occur in a mass spectrometer
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
What is the gold standard for measuring gas concentration
Quadrapole mass spectrometer
182
What is the cathode of a polarographic clark electrode made from
Platinum
183
What is the anode of a polarographic clark electrode made from
Silver
184
What is the cathode of a Galvanic fuel cell made from
Gold
185
What is the anode of a polarographic clark electrode made from
Ag/AgCl
186
What is the electrolyte used in a Galvanic fuel cell
KOH
187
What is the electrolyte used in a polarographic Clark electrode
KCL
188
What is the wavelength spectrum of visible light
400-700nm
189
Define Collision Broadening
The phenomenon in which the spectral absorption peaks of one gas are changed (broadened) due to the collision or proximity of another gas
190
Describe class I medical device in terms of electrical safety
- Mains powered and earthed device
- Uses isolating transformer
191
Describe class II medical device in terms of electrical safety
- Double insulated device
- not earthed
192
193
Define Bernoulli principle
An increase in velocity of a moving fluid results in simultaneous decrease in its pressure (and visa versa)
194
Describe what happens to velocity and pressure of a fluid moving through a pipe which becomes constricted
Bernoulli's principle
Velocity increases but pressure decreases
(like putting finger over hose pipe)
195
What is the risk with using Venturi valve in patient with very high peak inspiratory flow rate (PIFR)
If PIFR exceeds the flow rate of the Venturi valve air is entrained around the mask which dilutes the 02 concentration.
196
Define Fourier analysis
A mathematical operation that deconstructs a complex signal into its constituent frequencies.
The main waveform is known as the fundamental frequency
197
Define natural frequency
The natural frequency of the system is the frequency at which it will oscillate freely (in the absence of sustained stimulus)
198
Define resonance
Resonance is the amplification of signal when the driving frequency is close to the natural frequency of a system
199
What does a damping co-efficient of <0.7 represent
Underdamped
200
What does a damping co-efficient of 0.64 represent
Optimal damping
201
What does a damping co-efficient of >0.7 represent
Overdamped
202
What does a damping co-efficient of 1.0 repressent
Critical damping
203
Define critical damping
When the damping coefficient is equal to the resonant frequency of the oscillator
Damping coefficient of 1.0
204
How many times larger is the natural frequency of arterial line system compared to the natural frequency of the blood pressure wave
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
What size filter is used in I.V drug giving set
0.2 micron
206
What size filter is used in a blood giving set
200 micron
207
Describe how IR absorption spectrophotometry is used to measure CO2, N20 and volatile gas concentrations
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
What is the most common method of measuring anaesthetic gas concentrations
Infrared absorption spectrophotometry
209
What is the gold standard method of measuring anaesthetic gas concentrations which clinical machines are calibrated with
Refractometry
210
What is the 8 hour time weighted average concentration for N20 in the UK
100ppm
211
What effect does Ketamine have on BIS
Causes BIS number to go up due to a Gamma burst and increased Beta waves
212
List 3 factors that cause a reduction in BIS
Hypothermia
Hypovolaemia
Neuromuscular blocking drugs
213
What do Lundberg A waves indicate on ICP monitoring
Increase in ICP for 5-10 minutes (plateau waves)
Indicates reduced cerebral compliance and imminent herniation
214
What do Lundberg B waves indicate on ICP monitoring
Oscilations of ICP at rate of 0.5-2 waves per second/ Hx
Indicates unstable ICP and possible vasospasm
215
Outline the codes for pacemakers
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
What is the average frequency of Delta waves on BIS
3Hz
Delta waves are long slow waves seen in sleep
217
How can you calculate the natural frequency of an arterial line
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
What is Corrected Flow Time (FTc) an indicator of on oesophageal doppler
Preload
219
What is Peak Velocity (PV) an indicator of on oesophageal doppler
Contractility
220
What 2 assumptions are made in oesophageal doppler
Descending aorta carries 70% of CO
Descending aorta cross sectional area based on demographical data
221
What type of vacuum do you get in a Barometer with Mercury
A Torricellian vacuum
222
What is 1 ATM equivalent to in mmHg
760mmHg
223
What is 1 ATM equivalent to in cmH2O
1033cmH2O
224
What is 1 ATM equivalent to in Kpa
101.32Kpa
225
What is 1 ATM equivalent to in Bar
1.01Bar
226
List some of the properties of an ideal nerve stimulator device
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
What does a TOF ratio of >0.9 mean in terms of neuromuscular blockade
Adequately reversed
228
What is the pore size in a HME filter
0.2 micrometres
229
What is the absolute humidity that a HME filter can provide
30g/m3
230
What is the absolute humidity that a ultrasonic nebuliser can provide
90g/m3
231
What is the absolute humidity that a cascade humidifier can provide
60g/m3
232
What is the absolute humidity that a heated water bath humidifier can provide
40g/m3
233
Describe what a class B electrical safety rating means in medical equipment
Medical device connected directly to patient which has a leakage current < 100mA
234
Describe what a class BF electrical safety rating means in medical equipment
Medical device connected directly to patient which has a leakage current < 100mA and uses a floating circuit
235
Describe what a class CF electrical safety rating means in medical equipment
Medical device connected directly to patient which has a leakage current < 10mA and uses a floating circuit
236
Describe how Ohm's law can be adapted for gas flow
Ohm's Law ( V=IR )
Flow = change in pressure / Resistance (Q = ΔP/R)
237
Describe how a pneumotachograph works
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
Describe how a Wright respirometer works
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
Which frequencies are used in surgical diathermy
in range of 1MHz
240
Which type of diathermy requires a diathermy plate
Monopolar diathermy
241
Which type of diathermy uses higher power
Monopolar
242
Which gas is used to cool MRI scanners
Helium
243
What effect does a Diamagnetic material have on magnetic flux
Decrease magnetic flux
244
What effect does a ferromagnetic material have on magnetic flux
Increases magnetic flux
245
What effect does a paramagnetic material have on magnetic flux
slightly increases magnetic flux
246
Define Magnetic Flux
The magnetic field present in a material
247
What is the unit for Magnetic Flux
Webber (Wb)
248
What is the unit for Magnetic Flux Density
Tesla (T)
249
What does a Galvanometer measure
Current
250
Which electrical wire is earthed at the substation
The neutral wire
251
Define Impedence (Z)
The opposition to flow of A/C current due to the combination of resistance and reactance
Measured in Ohms
252
What is the SI unit for Luminous intensity
Candela
253
What are the SI units
M- metre
Kg- kilogram
s- second
A- ampere
mol- mole
K- kelvin
cd- candela
254
Which gas cylinder size is used in manifolds and what is the volume
Size J
Volume 6800L
255
Which size cylinder is used in anaesthetic machines and what is the volume
Size E
Volume 680L
256
what pressure are Entonox cylinders stored at
13,700 kPa
257
Which Vaporiser is specifically used with Desflurane
TEC6
258
What temperature and pressure does a TEC6 vaporiser use for Desflurane
39C
194 kPa
259
What is a normal range of pulmonary artery wedge pressure
6-12 mmHg
260
What is the relationship between frequency of current and resistance of a capacitor
Frequency is inversely proportional to resistance
D.C current can't pass through
261
Which diathermy is safer for use in patients with a pacemaker
Bipolar
262
Which type of diathermy requires a grounding plate
Monopolar
263
What is the waveform used in cutting diathermy
A continues sine waveform with low voltage
264
What is the waveform used in coagulation diathermy
Pulsed waveform with high voltage
265
Which type of diathermy is more effective at coagulation than cutting
Bipolar diathermy
266
What is a CO2 laser used for
Photocoagulation in ophthalmic procedures
267
What is a Nd-YAG laser used for
Airway surgery
268
What is an Argon laser used for
Retinal surgery and dermatology
269
What is a yellow pulsed dye laser used for
Dermatology
- birth mark removal
- Port wine stain
270
What is the critical temperature of oxygen
-119C
271
What does the point of maximal amplitude oscillation of non-invasive blood pressure measurement relate to
MAP
272
How do antistatic shoes prevent electrocution
Have high impedance so only very small current can flow. Allows current to enter earth so no static charge build up
273
Describe what is meant by a T-piece breathing circuit
A circuit in which the FGF delivery is closest to the patient end of the circuit without valves or reservoir bags in between
274
List the 3 breathing circuits which count as T-Piece circuits
Mapleson D
Mapleson E (Ayre's T piece)
Mapleson F (Jackson Rees modification
275
What size are epidural filters
0.2 micrometres
276
What size are blood giving set filters
200 micrometres
277
What is meant by transit time for ETCO2 measurement
time taken for the sample to reach the analyser
278
What is meant by the rise time for ETCO2 measurement
The time it takes the analyser to process the sample once it has reached the analyser
279
What principle does a DINAMAP use
Oscillometry
280
How much energy is required in paediatric synchronised cardioversion
2 joules/kg
(4 if asynchronous)
281
What is the critical temperature of oxygen
-119C
282
What temperature is oxygen in a VIE
-160C
283
What pressure are size E cylinders when full
13700 kPa
284
What is the unit of Inductance
Henry
285
Define Beer's law
The intensity of transmitted light decreases exponentially as the concentration of the substance it moves through increases
286
Define Lambert's law
The intensity of transmitted light decreases exponentially as the distance travelled through the substance increases
287
What is the equation for Beer-Lambert law
A = εdc
Absorbance = molar extinction co-efficient x path length x molar concentration
288
Is the oxygen in a VIE actively cooled
No
Latent heat of vaporisation of oxygen cools it and insulated by a vacuum
289
Can zeolite columns in oxygen concentrators be re-used
Yes
Heating the zeolite column causes the trapped N2 and H2O to be released back into the atmosphere
290
What are 2 safety features preventing you from connecting the wrong hose pipe to medical gas outlet
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
Is a medical vacuum system
1- High flow, low pressure
2- Low flow, high pressure
2- low flow, high pressure
292
Is a scanvenging system
1- High flow, low pressure
2- Low flow, high pressure
1- high flow, low pressure
293
Which feature protects the central pipeline of a vacuum system from contamination
Suction trap
294
What is the UK limit of environmental N2O concentration in theatre
100 ppm (parts per million) in 8 hours
295
What is the UK limit of environmental isoflurane concentration in theatre
50 ppm (parts per million) in 8 hours
296
Name a passive scavenging system
Cardiff Aldasorber
297
How does a reservoir bag work
Fills with oxygen during expiration and can be drawn from during inspiration to meet patients peak inspiratory flow
298
Match the colour to the vaporiser
Blue Sevoflurane
Orange Desflurane
Yellow Isoflurane
Purple Halothane
Red Enflurane
Blue Desflurane
Orange Enflurane
Yellow Sevoflurane
Purple Isoflurane
Red Halothane
299
What is the weight cut off for using a Mapleson E circuit in paediatrics
Suitable up to 30kg
300
What parameter should the volume of tubing in a Mapleson E circuit be matched
The patients tidal volume
If larger you get rebreathing
If smaller you get entrainment of air
301
What is the voltage used in a clark polographic electrode
0.6V
302
Which anaesthetic gas causes the Clark Polographic electrode to over read
N2O
Is reduced at the cathode
303
Which eponymous equation is used to calculate CO from a PiCCO device
Stewart-Hamilton equation
304
Which volatiles can lead to production of carbon monoxide when they come into contact with dry Soda lime
Volatile agents that contain a -CHF2 molecule isoflurane, enflurane, desflurane
305
What is the formula for energy stored in a capacitor
E = 1/2 X Q X V squared
Energy = 1/2 x charge x potential difference squared
306
Which mode is most commonly used in ultrasound
B- mode
307
What is the max flow rate you can achieve with an oxygen concentrator
5L/min
308
