1
Q
Describe the differences in the relative effects of viscosity and density on laminar and turbulent flow.
A
Laminar: viscosity has a greater effect than density
Turbulent: density has a greater effect than viscosity
2
Q
What is paramagnetism and which gases are paramagnetic?
A
Paramagnetic gases are attracted by a magnetic field (and can be analysed by a paramagnetic analyser) due to the presence of unpaired outer orbital electrons.
Examples: oxygen, nitric oxide
3
Q
What is the critical temperature of a substance?
A
A substance above its critical temperature cannot be liquified irrespective of the pressure applied to it.
4
Q
What is the critical temperature of oxygen?
A
-118 degrees
5
Q
What is a sieving coefficient?
A
It provides a measure of how different molecules move across a semi-permeable membrane. In renal replacement therapy, it is the ratio of the concentration of a molecule in the ultrafiltrate compared to the concentration in the blood.
Smaller molecules equilibrate across the membrane more readily and have a coefficient around 1.
6
Q
Briefly explain how a pulse oximeter works.
A
In pulse oximetry, red (660nm) and infrared (940nm) LEDs blink on and off 30 times per second. The degree of absorbance of these wavelengths by a photodetector is measured, and is correlated with known data to provide an estimate of oxygen saturations.
Oxygenated haemoglobin absorbs infrared (940nm) light to a greater degree than deoxygenated haemoglobin. The reverse is true of red light.
The off:off signal allows for the photodetector to establish the degree of ambient light which is then subtracted from the received signal.
7
Q
What is a purpose of a diode?
A
Convert AC to DC current
(known as rectification)
May also be referred to as a rectifier.
8
Q
What is the saturated vapour pressure of water at 37 degrees?
A
6.3 kPa
9
Q
How much does pressure increase by as you go underwater?
A
1 atmosphere for every 10 m of depth
10
Q
Define:
latent heat of vaporisation
A
Energy required to change one unit of mass from liquid to gas
e.g. water boiling
11
Q
Define:
latent heat
A
Energy required to transform matter from one state to another.
12
Q
Define:
latent heat of fusion
A
Energy required to change one unit of mass from solid to liquid.
e.g. when ice melts
13
Q
Define:
specific heat capacity
A
Determines the energy needed to raise 1 kg of the substance by a temperature of 1 degree.
14
Q
State the equation that determines the energy required to change the temperature of a material.
A
Q = cmΔT
Q: energy required
c: specific heat capacity
m: mass
ΔT: temperature change
15
Q
What is the specific heat capacity of water?
A
4.18 J/g/C
16
Q
Why doesn’t the temperature of water go above 100 degrees in a kettle?
A
The SVP is equal to atmospheric pressure meaning that bubbles can form within the bulk of the water and escape into the vapour phase.
At this point, no further increase in kinetic energy is required - instead, the thermal energy is used to break hydrogen bonds.
This absorbs energy meaning that the average kinetic energy (hence, temperature) does not rise any further.
17
Q
What is the triple point with regards to phases of matter?
A
Pressure and temperature where all three states can coexist.
18
Q
Define:
critical pressure
A
Minimum pressure required to liquefy the gas at the critical temperature.
19
Q
Define:
vapour
(as opposed to gas)
A
Any substance in the gas phase at a temperature lower than its critical temperature.
This means that vapours can be condensed into a liquid or to a solid by increasing the pressure without reducing the temperature.
20
Q
Define:
solid, liquid and gas
A
Solid: A state of matter with a fixed shape and volume, where particles are tightly packed and vibrate in place.
Liquid: A state of matter with a fixed volume but no fixed shape, allowing it to flow while particles move more freely than in a solid.
Gas: A state of matter with no fixed shape or volume, where particles move rapidly and spread out to fill any container.
21
Q
State Newton’s first law.
A
Constant velocity: objects move in a straight line at constant speed or remain stationary unless a force acts upon the object.
22
Q
State Newton’s second law.
A
Acceleration of a body is proportional to the force applied and inversely proportional to the mass of the object.
F = m x a
23
Q
Define:
pressure
A
Force applied to an object per unit area
P = F/A
24
Q
State Hooke’s law.
A
There is a linear relationship between the force applied and the extension of a spring within the elastic limits for that spring.
F = -kx
F: force
k: spring constant
x: extension
A spring is a device that stores mechanical energy when deformed and exerts a restoring force that returns it to its original shape.
25
# Define:
spring constant
The degree of stiffness or springiness.
## Footnote
The higher the spring constant the more difficult it is for the spring to extend.
The amount of displacement from equilibrium can be positive (extension) or negative (compression) - the negative sign, therefore, indicates that the spring exerts a force in the opposite direction to the displacement.
26
# Define:
boiling point in relation to saturated vapour pressure
Temperature at which the saturated vapour pressure is **equal to atmospheric pressure**.
## Footnote
At boiling point, further heat does NOT increase the temperature but provides the latent heat of vaporisation which makes gas molecules evaporate from the liquid phase.
27
Why is boiling point defined as the temperature at which **SVP equals atmospheric pressure**?
Atmospheric pressure pushes down on the liquid, preventing vaporisation.
When the liquid's saturated vapour pressure matches the atmospheric pressure, the gas molecules inside the liquid can form stable bubbles without being crushed by external pressure.
These bubbles rise and escape, leading to boiling.
## Footnote
This is why the boiling point is lower at higher altitudes.
28
# Define:
saturated vapour pressure
Pressure exerted by the vapour phase of a substance when in equilibrium with the liquid phase (i.e. molecules entering liquid phase are equal to molecules leaving it).
29
How does SVP **relate** to volatility?
A higher SVP means that the agent will more readily vaporise.
## Footnote
A standard temperature must be set when comparing SVP.
30
# Define:
viscosity
A measure of a fluid's resistance to flow due to **internal friction**.
31
What is a **Newtonian fluid**?
Constant viscosity regardless of flow rate.
## Footnote
Non-Newtonian fluids can become more or less viscous with increasing flow rate.
32
What is **surface tension** and what causes it?
**Force per unit length** acting along the surface of a liquid that resists external force.
Hydrogen bonds between water molecules on the surface of a liquid are stronger than those in the middle as there are fewer surrounding molecules.
This pulls neighbouring molecules as close to each other as possible (causing the bubble shape).
33
State the **law of Laplace**.
The larger the radius of the vessel, the greater the wall tension required to withstand a given internal fluid pressure.
34
State the **equations** that reflect the law of Laplace in spherical bubbles and in cylinders.
**Sphere**: ΔP = 2T/R
**Cylinder**: ΔP = T/R
## Footnote
Wall tension and surface tension are measured in force per unit length (N/m)
35
Why do **aortic aneurysms** often form spheres?
Initially, it looks like a cylinder and the increase in radius leads to increasing wall tension in a vicious cycle.
If it bulges towards a more cylindrical shape, the tension will decrease because the wall tension of a sphere is half that of a cylinder for the same difference in pressure and radius.
36
How does the role of surfactant in alveoli relate back to the law of Laplace?
**ΔP = 2T/R**
Smaller alveoli have a higher pressure for a given surface tension. This means that smaller alveoli are harder to inflate and would empty into larger alveoli.
Surfactant (made mainly of DPPC) reduces surface tension and is present in greater concentrations in smaller alveoli.
37
# Define:
work in the context of physics
Product of the force applied and the distance the object is moved.
**Work = Force x Distance**
38
# Define:
energy
Capacity for doing work.
39
# Define:
power in the context of physics
Rate at which work is being done (or the rate of energy transfer).
Power = Work Done/Time Taken
40
What is a **joule**?
The amount of energy required to exert a force of one newton through a distance of one metre
## Footnote
A calorie is another unit for energy and is approximately 4.2 J.
41
What is the **unit for power**?
Watt
| (1 watt = 1 joule per second)
42
Derive how the work done by a ventilator is equal to **pressure x volume**.
Work Done = Force x Distance
Force = Pressure x Area
Work Done = Pressure x Area x Distance
Volume = Area x Distance
Work Done = Pressure x Volume
43
What is a **COBRA Perilaryngeal Airway**?
A **supraglottic airway device** used for ventilation during general anesthesia, designed to seal the upper airway and facilitate breathing.
## Footnote
The COBRA airway has a ramp which helps to guide tracheal tubes towards the larynx.
44
What features of a circle system **minimise** rebreathing?
**Unidirectional valves** are between the patient and the reservoir bag on both inspiratory and expiratory limb.
Fresh gas flow introduced between soda lime and the inspiratory valve.
APL valve between expiratory valve and soda lime.
The ventilator is typically located between the unidirectional valve in the expiratory limb and the soda lime.
45
What does a **circle system layout** illustrate?
A circle system layout illustrates the arrangement of components in a **closed circuit** for anesthesia delivery, ensuring **efficient gas flow** and **minimizing rebreathing**.
## Footnote
This system typically includes unidirectional valves, a reservoir bag, and a carbon dioxide absorbent.
46
What **features** of a plenum vaporiser are there to enhance safety?
* A **long inlet port** into the vaporising chamber ensures that the bypass channel is not contaminated by retrograde flow (creates increased resistance to backflow).
* **Downstream flow restrictors** maintain vaporiser at a pressure greater than at the gas outlet.
* **Downstream pressure relief valves** act to prevent back pressure being transmitted to the ventilator.
* **Anti-spill valves** prevent contamination of the breathing circuit.
* **Wicks and baffles** are used to ensure gas leaving the vaporisation chamber is fully saturated with vapour.
47
What **stimulus** is used by peripheral nerve stimulators and why?
A **supramaximal stimulus of 50 mA** is used in peripheral nerve stimulators.
This is 25-50% higher than that needed to produce a maximal response which ensures all motor fibres depolarise simultaneously and eliminates variation due to impedance and position of electrodes.
48
What are the main advantages and disadvantages of a **mainstream gas analyser**?
**Advantages**: no sampling tube, reduced chance of obstruction, no lag time, no pollution, no effect due to changes in water vapour pressure.
**Disadvantages**: sensor windows clog with secretions, bulky, increased risk of patient cross-contamination.
49
What are the main advantages and disadvantages of a **sidestream gas analyser**?
**Advantages**:
* easy to connect
* no problem with sterilisation
* can be used in awake patients
* easy to use in unusual patient position (e.g. prone, lightweight, robust.)
**Disadvantages**:
* lag time
* possible sampling tube obstruction
* water vapour pressure can change ETCO2 concentrations
* sampled gas vented to atmosphere or returned to circle system
* moisture trap required to dry gas
* pressure drop along sampling tube affects ETCO2 concentrations
50
What is a hypoxic guard on a **rotameter flowmeter**?
It makes it impossible to deliver an oxygen concentration below 25%.
## Footnote
E.g. when nitrous oxide is turned up to 9 L/min, the oxygen flow rate will increase to 3 L/min to achieve a concentration of 25%
51
What are the two main bundles of optical fibres in a flexible fibreoptic endoscope?
* Coherent bundle (to transmit image)
* Non-coherent/illumination bundle (to transmit light)
## Footnote
A working channel surrounded by a flexible steel braid, angulation wires and a protective sheath.
52
What is the approximate diameter of fibres of the coherent bundle of a **fibreoptic endoscope**?
The coherent sheath can consist of as many as 10,000 fibres of diameter 5-20 μm.
53
What are some **features** of an ideal microbial filter.
* Low penetration rate
* Effective bidirectionally
* Small internal volume (minimise dead space)
* Minimal resistance to gas flow
* Effective when wet or dry
* Disposable
* Cheap
* Transparent and lightweight
54
State the **equation** for calculating total resistance in parallel circuits.
1 / Rₜₒₜ = 1 / R₁ + 1 / R₂ + 1 / R₃ + … + 1 / Rₙ
## Footnote
n = number of parallel branches
55
What is the **composition** of soda lime?
* 90-95% calcium hydroxide
* 2-5% sodium hydroxide
* Silica and zeolite – varying amounts
* Indicator dye
## Footnote
pH is 13.5 with a moisture content of 14-19%. Calcium carbonate is formed during the series of reactions between carbon dioxide and the constituents of soda lime.
56
State **Gay-Lussac law**.
Pressure and temperature are directly proportional.
57
State **Charles' law**.
Volume and temperature are directly proportional.
58
State **Boyle's law**.
Product of pressure and volume is constant (k=PV). Therefore, P1V1 = P2V2 in a closed system.
59
State **Henry's law**.
At a given temperature, the amount of gas dissolved in a liquid is **directly proportional to the partial pressure** of gas in equilibrium with the liquid.
## Footnote
Increasing the temperature will decrease solubility of gas dissolved in the fluid causing bubbles to form.
60
State **Graham's law**.
Describes how the rate of diffusion of a substance is inversely proportional to its molecular weight.
61
What is post-tetanic stimulation on a **peripheral nerve stimulator**?
5 second tetanic stimulus (50 Hz) followed by a 3 second pause and then 20 stimuli at a rate of 1 Hz.
## Footnote
During the period of stimulation, **pre-synaptic receptors are activated** which leads to the **synthesis and mobilisation of additional acetylcholine**.
This explains why twitches appear following tetanic stimulation, yet did not appear with the conventional train of four.
Used for deep neuromuscular block
62
# Define:
damping
Decrease in the amplitude of an oscillation as a result of **energy loss in a system due to frictional or resistive forces**. The damping coefficient gives a measure of how quickly an oscillating system will come to rest at a new value.
63
What damping coefficient does an **optimally damped system** have?
0.64
64
What is the theoretical minimum fresh gas flow required for a **circle system**?
250 mL/min to meet basal oxygen consumption.
65
# Define:
a Coulomb
One coulomb is the amount of charge transported by a current of one ampere in one second.
1 C = 1 A x 1 s
Equals: 6.24 × 10¹⁸ electrons
66
What is the purpose of the **Selectatec interlock system** on anaesthetic machines?
Ensures that only one vaporiser % control dial may be turned on at any time through the use of interlocking extension rods.
67
What is the volume of oxygen within a **full size E cylinder**?
680 L
Pressure of 137 bar
## Footnote
\ Internal volume is 5 L (in terms of how much water it can hold).
68
What is the volume of oxygen within a **full size D cylinder**?
340 L
69
What is the volume of oxygen within a **full size CD cylinder**?
460 L
## Footnote
These cylinders are at 230 bar (rather than 137 bar).
70
What is the **difference** between resistance, reactance and impedance in electrical circuits?
* **Resistance** describes the opposition to flow of direct current.
* **Reactance** is used when the current is alternating.
* **Impedance** (Z) is the sum of resistive and reactive components.
## Footnote
All are measured in ohms.
71
What is the **zeroth law** of thermodynamics?
If two thermodynamic systems are in equilibrium with a third then they are also in equilibrium with each other.
72
What is the **first law** of thermodynamics?
Energy can neither be created nor destroyed only converted from one form to another.
73
What is the **second law** of thermodynamics?
Entropy tends to increase with time.
## Footnote
i.e. a measure of unavailable energy
74
What is the **third law** of thermodynamics?
As a system approaches absolute zero (-273.15ºC) all processes cease and entropy approaches a minimum.
75
Why is a biphasic current used in **defibrillation**?
* Allows compensation for wide variations in thoracic impedance by electronically adjusting waveform magnitude and duration
* Lower peak current delivered (20 A vs 40 A)
* Less energy required for defibrillation
* Improved safety profile
## Footnote
Biphasic means that current flows in one direction before reversing.
76
How does a **Haemocue** provide a point-of-care estimate of haemoglobin concentration?
**1**. Sodium deoxycholate haemolyses erythrocytes releasing Hb.
**2**. Sodium nitrite converts Hb to MetHb which then reacts with sodium azide to give azidemethaemoglobin.
**3**. Absorbance is measured at two wavelengths (570 nm and 880 nm). Degree of absorbance is relative to Hb concentration so estimate is generated.
**4**. After each reading, photometer zeros itself and checks the intensity of the light source and photocell.
77
What is a **Wright respirometer**?
Small, compact device used to measure tidal volume and minute volume of expiratory flow.
## Footnote
Vane turns 150 times per L of gas
Needs minimum flow rate of 2 L/min (up to 25 L/min)
Resistance to breathing is 2 cm H2O.
78
How much carbon dioxide can **100 g of soda lime** absorb?
25 L of CO₂
79
What are the 3 subclasses of **domestic electrical equipment**?
* **Class 1**: a mains powered device enclosed WITH EARTHING
* **Class 2**: double insulated electrical device, NO EARTHING
* **Class 3**: SELV (safety extra low voltage) of typically 24V (AC) to 50V (DC). These devices may be battery powered or connected to mains via a transformer.
80
What are the 3 subclasses of **medical electrical equipment**?
* **Type B**: touches skin but does not penetrate (e.g. ECG)
* **Type BF**: part that touches the patient is electrically isolated from the rest of the device (e.g. thermometer)
* **Type CF**: for equipment that touches the heart or is inserted into the body (e.g. pacing wires)
81
What is an **RC circuit**?
Where a resistor and capacitor are placed in series as a circuit. It acts as a low pass filter i.e. allows frequencies below a certain value to pass.
82
What is **Avogadro's law**?
Equal volumes of an ideal gas at standard temperature and pressure will contain an equal number of molecules, and that one mole of an ideal gas at standard temperature and pressure occupies **22.4 litres**.
83
What is the **triple point** of water?
273.16 K, and sub-atmospheric pressure (611 Pa)
## Footnote
This is the point at which it exists in solid, liquid and gas phases at equilibrium.
Kelvin is 1/273.16 of the thermodynamic temperature of the triple point of water.
84
What are the anode and cathode made of in a **Clark electrode**?
**Anode**: Silver
**Cathode**: Platinum
85
What does '**relaxation**' mean in the context of MRI?
Radiofrequency (RF) energy is applied perpendicularly to the applied magnetic field at the Larmor frequency which rotates the net magnetisation of hydrogen ions in tissue. When the RF energy is switched off, net magnetisation returns to equilibrium and energy is lost to surrounding tissue. This is relaxation.
86
Which aspect of a current that passes through a body during electrocution is the most important factor in causing **ventricular fibrillation**?
Frequency of the current (at 50-60 Hz the sensitivity of biological tissues to unwanted electrical stimulus is maximal).
87
What is the normal range for systemic vascular resistance on a **LiDCO**?
800-1200 dynes.sec.cm⁻⁵
## Footnote
Pulmonary vascular resistance is around 20-130 dynes/s/cm5
88
What **stroke volume variation** on a LiDCO would suggest that the patient is unlikely to be fluid responsive?
< 10%
89
Why might a Wrist respirometer **overestimate** minute volume?
Momentum of the vanes can cause an overestimation.
90
Why is it **important** that an HME filter has as low a volume as possible?
Minimise dead space and prevent rebreathing.
## Footnote
Tidal volume should be at least 5 times the internal filter volume.
91
Which **Mapleson system** is this?
**Mapleson A (Magill)**
FGF is near the reservoir bag and APL valve is near the patient.
## Footnote
Efficient for spontaneous breathing.
92
Which **Mapleson system** is this?
**Mapleson D**
FGF near the patient.
APL valve near the bag.
## Footnote
Efficient for controlled.
Inefficient for spontaneous.
93
What is **collision broadening** in end-tidal CO₂ measurement?
Overlap of absorption spectra of CO₂ (**4.3 μm**) and nitrous oxide (**4.5 μm**) can lead to overestimation of end-tidal CO₂ by IR spectroscopy.
## Footnote
CO₂ also absorbs IR at **2.7** and **15 µm**.
94
What are the **different indicator dyes** used in soda lime canisters and their respective colour changes?
* **Ethyl violet** – white to purple
* **Phenolphthalein** – pink/red to white
* **Clayton yellow** – pink/red to yellow/cream
* **Ethyl orange** – orange to yellow
* **Mimosa Z** – red to white
95
What mechanism enables gas driven nebulisers to humidify the gas?
Air is passed through a constriction leading to an **increase in velocity** and **decrease in pressure** (conservation of energy) as described by the **Bernoulli effect**.
This reduction of pressure leads to **entrainment** of water via the **Venturi effect**.
96
Describe the parts of a **Tuohy needle**.
* Usually **16G**
* **Huber tip**: blunt leading edge, angled tip for catheter passage
* **Lee's lines**: measure depth
* **Macintosh wings**: stabilize needle
* **Stylet**: prevents tissue coring
## Footnote
A loss of resistance syringe is used for epidurals, but is not part of the Tuohy needle.
97
How to interpret a **TEG**?
* **Prolonged R Time**: anticoagulant or clotting factor deficiency
* **Low Alpha Angle**: fibrinogen issue
* **High K Time**: fibrinogen or platelet issue
* **Low Max Amplitude**: weak clot, ineffective platelet function
* **Short Lysis Time + High CL30**: overactive fibrinolytic system
98
What are **epidural filters** made of?
**0.22 micron mesh** to prevent the passage of bacteria, viruses and foreign bodies into the epidural space.
99
What is the **difference** between absolute and relative humidity?
**Absolute**: mass of water vapour in a given volume of gas at a given temperature and pressure (g/m3)
**Relative**: ratio of actual mass of water vapour compared to maximum amount of water vapour the gas could contain at the same temp and pressure
100
What is the **absolute humidity** of fully saturated air at 20 degrees Celsius at atmospheric pressure?
17 g/m³
## Footnote
At 34 degrees it is 34 g/m³ (in the upper trachea)
101
What **factors** affect the natural frequency of an invasive blood pressure monitoring system?
NF is proportional to √(r²/clρ)
## Footnote
r = radius of the tubing
c = compliance
l = length
ρ = density of the fluid
102
What **measures** are taken to ensure that invasive arterial blood pressure monitoring systems don't resonate?
* Has a natural frequency 10x higher than the fundamental frequency (sine wave 1-2 Hz, corresponds to heart rate 60-120 bpm)
* Frequency range of 0.5 to 40 Hz to include the first 10 harmonics of the heart rate
103
What happens if the frequency of the driving force in an invasive arterial blood pressure monitoring system coincides with the resonant frequency of the system?
A resonant sine wave will be superimposed on the pressure wave.
## Footnote
This will raise the systolic blood pressure, reduce the diastolic blood pressure, but should have no effect on the mean arterial pressure.
104
What is a **resistance wire thermometer**?
As temperature increases, resistance through a thin piece of metal **increases linearly**.
## Footnote
Slow response time and fragile.
Needs Wheatstone bridge to increase sensitivity.
105
# fhumi
What is a **thermistor**?
Consists of a **semiconductor** for which there is a **non-linear relationship between resistance and temperature** (resistance decreases with temperature).
## Footnote
Cheap and small so can be used for invasive monitors (e.g. pulmonary artery flotation catheter).
Respond quickly to changes but can have calibration error.
106
What is a **semiconductor**?
A material whose electrical conductivity is between a conductor and an insulator.
## Footnote
Conductivity can be controlled by adding impurities (doping), applying electrical fields or increasing the temperature.
107
Describe how the **nuclear arrangement** of semiconductors are responsible for their properties.
In a semiconductor, electrons exist in two energy bands:
- **Valence Band**: electrons are bound tightly to atoms and can't move freely
- **Conduction Band**: electrons are free to move enabling conduction
## Footnote
At room temperature, most electrons are in the valence band, however, applying energy (e.g. heat) enables the electrons to jump across the band gap to the conduction band so it can conduct electricity.
108
What is a **thermocouple**?
They rely on the **Seebeck (thermoelectric) effect**. At the junction of two dissimilar metals, a voltage will be produced in **proportion to the temperature difference** between two such junctions. Typically copper and constantan are the metals used. The response is nearly linear and passes through the origin as a temperature difference of zero produces zero output voltage.
## Footnote
Multiple thermocouples in series produce a thermopile which will increase sensitivity.
109
State **Poiseuille's law**.
## Footnote
r = radius
ΔP = pressure gradient
n = viscosity
l = length
Q = flow rate
110
How is Poiseuille's law related to **Ohm's law**?
This is analogous to Ohm’s law (**V = IR –> I = V/R**), where voltage is represented by the pressure gradient, current is represented by the flow rate, and resistance is given by 8nl/πr⁴.
111
What is the **difference** between the flow at the bottom compared to the top of a rotameter?
At the **bottom** (low-flow), the space between the bobbin and wall is narrow. Gas flow is laminar and **dependent on viscosity**.
At the **top** (high flows) the space between the bobbin and wall is wider. Gas flow is more turbulent and **dependent on density**.
## Footnote
The pressure difference across the bobbin is constant at all points in the rotameter.
112
Why is flow at the bottom of a rotameter dependent on **viscosity**, whereas at the top it is dependent on **density**?
At the **bottom** of a rotameter, the gap between the bobbin and tube is narrow, so flow is laminar and mainly affected by viscosity — the internal friction of the gas.
At the **top**, the gap is wider, flow becomes turbulent, and is mainly influenced by density, which affects the inertia and turbulence of the gas.
113
What is a **Goldman vaporiser**?
* 30 mL in circuit draw-over variable bypass vaporiser
* NOT temperature compensated
* Small, cheap, lightweight
* Variable output
114
What is an **Oxford miniature vaporiser**?
* Variable bypass draw-over vaporiser
* NOT actively temperature compensated but incorporates an ethylene glycol heat sink
* Any anaesthetic agent can be used by changing a removable scale on the dial
115
What is the **difference** between state and response entropy in depth of anaesthesia monitoring?
**State Entropy**: calculated from low frequency range waves
**Response Entropy**: calculated from high frequency waves including EMG activity from frontalis muscle
## Footnote
As a patient wakes, the difference between SE and RE increases due to diminishing effect of drugs affecting the central nervous system and the increased contribution of EMG values from the frontalis muscle. RE increases more quickly than SE.
116
What is **co-oximetry**?
Requires a blood sample to be taken and spectrophotometric techniques are then performed that are able to provide information regarding oxyhaemoglobin, deoxyhaemoglobin, methaemoglobin and carboxyhaemoglobin.
117
What will be the **effect** on freezing and boiling points of adding one mole of solute to 1 kg of water?
* Increase the boiling point by 0.51ºc (ebullioscopic constant)
* Decrease the freezing point by 1.86ºc (cryoscopic constant)
* Increase the osmotic pressure
118
Why does adding solute to a solvent **increase** boiling point?
Boiling occurs when vapour pressure = atmospheric pressure.
Solute particles get in the way of water molecules escaping into the gas phase, thereby lowering the vapour pressure for a given temperature.
This means you have to heat the solution to a higher temperature to boil.
119
Why does adding solute to a solvent **decrease** freezing point?
Freezing happens when water molecules arrange into a solid crystal structure.
Solute particles disrupt this orderly arrangement, making it harder for water to freeze.
Therefore, you must lower the temperature further to freeze the solution → freezing point goes down.
120
Describe the **Manley MP3 ventilator**.
**Pressure generator, time-cycled, minute volume divider.**
Two knobs are able to change from controlled to manual and to adjust the inspiratory time. The inflation pressure is adjusted by sliding a weight to a different position on top of the main bellows. Fresh gas flow drives the ventilator.
In inspiration a small bellows receives FGF and the main bellows deliver their content to the patient. During expiration the small bellows delivers their content to the main bellows until a predetermined tidal volume is reached.
121
What are **colligative properties**?
Physical properties that are dependent on **number of dissolved particles** rather than the identity of the solute.
Includes elevation of boiling point, reduction of freezing point, reduction in vapour pressure and change in osmotic pressure.
## Footnote
This is how an osmometer works.
122
How many drops of clear fluid or blood are equal to 1 mL in a **giving set**?
**Clear Fluid**: 20 drops
**Blood**: 15 Drops
123
What is the **Finapres method** of blood pressure measurement?
Method of continuous, non-invasive blood pressure measurement.
## Footnote
A small cuff placed around the finger is inflated or deflated by a controller system to keep the blood volume in the finger constant (as measured by photoplethysmography). The applied pressure to keep blood volume constant is comparative to arterial blood pressure.
124
Why is it **important** that oxygen is the last gas added to a mixture that is delivered to a patient?
If it was added earlier to the mixture, a crack in an adjacent flowmeter will mean that the oxygen follows the path of least resistance and escapes via the cracked flowmeter rather than to the patient - thereby delivering a hypoxic mixture.
125
Why do **diathermy circuits** operate at frequencies in the mega Hertz?
Avoid the risk of inducing ventricular fibrillation.
Risk is highest around **50-60 Hz**, which is the frequency of mains electricity.
126
Why is **medical vacuum suction** considered a high pressure, low flow system?
The pump used to generate vacuum should be able to generate a negative pressure of **-400 mmHg or 53 kPa**.
The minimum requirement of suction is to generate a vacuum of 500 mmHg in 10 seconds with a displacement of air of 25 L/min as such it is considered a HIGH pressure, LOW flow system.
Generated by 2 or more mains-powered vane pumps that provide a high vacuum, high displacement system
127
What **current** is used by nerve stimulator needles when performing a peripheral nerve block?
Initially a high output of 1-3 mA is chosen and the needle advanced slowly towards the nerve until contraction is noted.
The output is then reduced until maximal stimulation is achieved with minimum output from the nerve stimulator.
Typically 0.3-0.5 mA suggests the needle tip is touching or very close to the nerve.
If contraction occurs at ≤ 0.2mA it suggests that the needle tip is intraneural and should be withdrawn.
128
What is represented by the area within a **magnetic hysteresis curve**?
Heat energy lost
## Footnote
When a ferromagnetic material is placed in a magnetic field, it will become magnetised (O to A).
When the field is removed, it remains weakly magnetised (A to B)
Area within the loop is heat loss.
129
State the **ideal gas law**.
**PV = nRT**
## Footnote
P = pressure (Pa)
V = volume of gas (m³)
n = number of moles (mole)
R = ideal gas constant (8.31 J/K/mol)
T = temperature (Kelvin)
130
What is the **difference** between electromotive force and voltage?
**EMF** describes the driving voltage of a battery.
**Voltage** is known as potential difference and represents the difference in electric potential between two points in a circuit.
131
# Define:
disinfection
Process of rendering an object free from all pathogenic organisms **excluding bacterial spores**.
132
What is **Pasteurisation**?
Method of disinfection that uses temperatures of 70 °C for 30 minutes.
133
Which Mapleson system is used with a **Manley MP3 ventilator**?
Mapleson D
134
# Define:
resonance
| (in the context of MRI)
Absorption of energy by an oscillating or precessing system.
Precession refers to the movement of nuclei around a magnetic field.
135
# Define:
magnetic flux
Measurement of total magnetic field passing through a given area.
## Footnote
When divided by the size of the area, it is called magnetic flux density.
136
What are the **units** of magnetic flux and flux density?
**Magnetic Flux**: Weber (Wb)
**Magnetic Flux Density**: 1 Tesla = 10,000 Gauss
## Footnote
1 Tesla = 1 Wb/m²
137
What is the **purpose** of the pressure bag in invasive arterial monitoring?
Normal saline is pressurised to **300 mmHg** and runs at a rate of **2-4 mL/hr** via a flushing device.
This prevents clot formation, keeping the arterial line patent and reducing damping.
138
What is a **notch filter** in electronics?
Removes a specific frequency from a signal.
139
Why is a *high common mode rejection ratio* desirable for operational amplifiers?
It neutralises upstream circuit noise (i.e. rejects signals common to both inputs).
This prevents mains interference with ECGs via a differential amplifier - it cancels out mains noise common to both inputs.
140
What is the **purpose** of the non-return pressure relief valve on the back bar of the anaesthetic machine?
Obstruction of the common gas outlet can cause rising pressure within the circuit that can transmit gases back into the anaesthetic machine causing damage and contamination.
This valve opens at 35-40 kPa of pressure.
141
What **current**, if electrocuted, can lead to respiratory muscle contraction and asphyxia?
50 mA
142
What **current**, if electrocuted, can lead to ventricular fibrillation?
100 mA
143
What **current**, if electrocuted, can lead to charring and extensive burns?
1000 mA
## Footnote
1 mA is a tingle, 5 mA is pain
144
State the equation describing the **impedance of a capacitor**.
**Z = d/fa**
## Footnote
Z = impedance
d = distance between the plates
f = frequency of current
a = area of plates
145
What pressure and flow rate does the **oxygen flush** deliver?
* Flow of 35-75 L/min
* Pressure of 4 bar
* Bypassing the flowmeters and vaporiser
146
Describe the **colour-coding system** used for filters on anaesthetic machines.
* **Yellow** – breathing filters for viruses, bacteria and particulate matter.
* **Blue** – heat and moisture exchange.
* **Green** – heat and moisture exchange and filter.
147
What is the purpose of the **Nernst equation**?
Calculates the electrical potential for an **INDIVIDUAL** ion, and thus allows for the estimation of how each ion affects the membrane potential.
148
State the **Nernst equation**.
Membrane potential = nRT/F x ln
| (extracellular concentration/intracellular concentration)
## Footnote
n = valence
R = universal gas constant
T = temperature (Kelvin)
F = Faraday’s constant
ln = natural logarithm
This equation can only be applied when a membrane is permeable to the ion in question.
149
What is the **mechanical equivalent** of heat?
The theory that mechanical work may be transferred to heat energy and heat energy to work, the magnitude of one being proportional to the other. This is the principle used in the generation of electricity in coal power stations.
150
What is the **Severinghaus electrode** designed to detect?
**pCO2 in blood**
## Footnote
Consists of a measuring electrode (silver/silver chloride) and reference electrode (mercury/mercury chloride) surrounded by film of NaHCO3 and permeable Teflon membrane allowing CO2 to diffuse from sample to solution.
In solution, CO2 is converted to H+ via CA.
H+ interacts with buffer around reference electrode leading to potential difference between two electrodes which leads to voltage that correlates with pCO2.
151
What is the **absolute pressure** of an oxygen cylinder at sea level?
13700 kPa (137 bar) + 101 kPa (≈1 bar) = 13800 kPa
## Footnote
Once filled, if taking up Mount Everest, the absolute pressure does not change because it is sealed.
152
# Define:
sterilisation
The process of rendering an object free from all pathogenic organisms **including bacterial spores.**
153
# Define:
decontamination
The process of removing contaminants such that they are unable to reach a site in sufficient quantities to initiate an infection.
## Footnote
Consists of cleaning, disinfection and sterilisation.
154
How do you size a **blood pressure cuff**?
* **Length**: >80% arm circumference
* **Width**: >40% circumference, >20% diameter
155
What is the gold standard non-EEG technique for detecting awareness in **intravenous anaesthesia**?
Isolated forearm technique
## Footnote
The forearm is isolated with a tourniquet prior to injection of muscle relaxant. This means if the patient is aware but ‘paralysed’ they would still be able to indicate using this hand.
156
What current and frequency is used for **train-of-four monitoring**?
4 x 50 mA stimuli being delivered at a rate of 2 Hz
157
What **metals** are used to construct the electrodes in a pH electrode?
* Silver
* Mercury
158
What is the **correct order** of steps in cell salvage?
* Retrieval (via a low pressure suction)
* Filter (150 microns)
* Centrifuge
* Disposal of waste
* Wash and resuspension
* Reinfusion (solution with haematocrit 60%)
159
How does a **Ritchie whistle oxygen alarm** work?
Pneumatically powered oxygen failure alarm based on a single stage regulator.
When oxygen pressure falls, the force pushing up on the diaphragm reduces to less than the opposing force of the spring. This opens the poppet valve allowing oxygen to flow through the whistle.
Must have auditory sound of **at least 60 dB lasting 7 seconds**.
160
What triggers the **oxygen alarm** on modern ventilators?
When oxygen pressure falls **below 200 kPa**.
161
How does **pressure** swing adsorption work to produce oxygen for patient use?
* Ambient air is filtered and pressurised to 137 kPa.
* It enters one of the parallel towers on either side of the mix tank.
* Air is forced through a molecular sieve made from zeolite (aluminium and silica crystals) which attracts nitrogen but allows oxygen to pass.
## Footnote
A changeover switch is operated to pressurise the alternate tower and nitrogen is removed from the first tower by using a vacuum allowing the zeolite to regenerate.
162
Which **formula** describes the relationship between the frequency and wavelength of electromagnetic radiation?
**c = f λ**
## Footnote
c = speed of light (m/s)
f = frequency (Hz)
λ = wavelength (m)
163
Which **formula** is used to calculate the energy of a form of electromagnetic radiation?
**E = h f**
## Footnote
where h is Planck’s constant
164
What are the **different signal frequencies** that are allowed through in diagnostic and monitoring ECGs?
**Monitoring**: 0.5 to 40 Hz
**Diagnostic**: 0.05 to 100 Hz
165
List some mechanisms of **sterilising equipment**.
* Steam (gold-standard) via an autoclave
* Ethylene oxide
* Hydrogen peroxide gas plasma
* Ozone
* Ionising radiation
* Dry hot air
166
How is **steam sterilisation** performed?
Conducted in an **autoclave**; effective, non-toxic, and inexpensive.
Four variables: steam, pressure, temperature, and time.
Sterilisation occurs at 121 ºC for 30 minutes or 132 ºC for 4 minutes at 2.25 bar. Heat-labile materials like plastics may not be sterilised.
167
Explain how **piezoelectric quartz crystal oscillation** can be used to monitor the concentration of anaesthetic gases.
Quartz crystals exhibit a natural resonant frequency when stimulated.
Two crystals are used, one of which is coated in a lipid layer. The lipid layer is able to absorb volatile anaesthetic agents which will change the resonant frequency.
The change of frequency is directly proportional to the partial pressure of volatile.
168
State the **equation** for Beer-Lambert law.
The absorbance of light is equal to **log(I0/I1) = αlc**
## Footnote
α = extinction coefficient
l = path length
c = sample concentration
169
What is the **difference** between osmolarity and osmolality?
**Osmolarity** is a measure of the number of osmoles (osmotically active particles) per litre of solution.
**Osmolality** is the number of osmoles per kg of solvent.
## Footnote
Osmolality is preferred as the volume of solvent changes slightly with temperature, however its weight does not.
170
What is the **absolute humidity** of fully saturated air at 20 degrees centigrade?
17 g/m³
171
What is the **absolute humidity** of fully saturated air at 36.5 degrees centigrade?
44 g/m³
172
Describe how the size of **nebulised droplets** affects their penetration into the airways.
* Upper airway: 40 μm
* Bronchi/bronchioles: 8-15 μm
* Peripheral conducting airway: 3-5 μm
* Alveoli: 0.8-3 μm
173
What is the **difference** in the capacity of a size E nitrous oxide cylinder vs a size E oxygen cylinder?
**Nitrous Oxide**: 1800 L
**Oxygen**: 680 L
## Footnote
As nitrous oxide is a liquid, it can store more.
174
What is the **pressure** of a size E nitrous oxide cylinder at 20 degrees?
52 bar
## Footnote
This is the saturated vapour pressure of nitrous oxide at 20 ºc, and is therefore the cylinder pressure of a full nitrous oxide cylinder. At 15 degrees the answer would be 44 bar.
175
What is the **critical pressure** of nitrous oxide?
72 bar
176
Write the **equations** that take place in the Clark electrode.
**Cathode reaction (platinum)**: O2 + 2H2O + 4e– -> 4OH–
**Electrolyte reaction**: 4NaCl + 4OH– -> 4NaOH + 4Cl–
**Anode reaction (silver)**: 4Ag + 4Cl– -> AgCl + 4e–
177
What **feature** of an endotracheal tube facilitates a good view of the glottis?
**Left facing bevel** allows an optimal view of the glottis and the tip of the endotracheal tube together.
## Footnote
As the tube is inserted from the right side of the mouth, a left facing bevel means the tip of the tube can be more easily visualised as it is sited between the vocal cords.
178
Why is bipolar diathermy **safer** in patients with permanent pacemakers?
The current travelling between the two electrodes minimises the risk of the current travelling through the pacemaker.
179
Which **details** of a gas cylinder are engraved on the side?
* Date of test
* Test pressure
* Chemical formula for gas
* Tare weight
180
How does a **Regnault's hygrometer** work?
Consists of a silver tube filled with ether with a thermometer.
Air is bubbled through the ether causing a drop in temperature (**latent heat of vaporisation**).
Condensation forms on the silver tube at the **dew point**. The temperature at which this occurs may be used to calculate the relative humidity using look up tables.
181
State **Stevin's formula**.
**P = ρghA**
## Footnote
P = pressure
ρ = density of the fluid
g = acceleration due to gravity
h = height (depth) of the fluid column
A = cross‑sectional area
182
What is an **elastomeric pump**?
Single-use, balloon-type infusion pump for continuous drug delivery.
## Footnote
Consists of:
* Balloon (100–600 mL) filled and stretched; recoil pushes drug out.
* Flow restrictor sets rate (~5–10 mL/h).
* Optional squeeze chamber allows patient to give extra bolus (PCA); refilling time = lock-out.
183
What are the **7 SI units**?
**SMMACKK**
* **Seconds** (s) – time
* **Mole** (mol) – amount/quantity of substance
* **Metre** (m) – length
* **Ampere** (A) – electrical current
* **Candela** (cd) – intensity of illumination
* **Kelvin** (K) – thermodynamic temperature
* **Kilogram** (kg) – mass
184
Describe the **absorption spectra** of oxy- and deoxyhaemoglobin.
* **660 nm**: oxy absorbs less than deoxy
* **590 and 805 nm**: isobestic point
* **940 nm**: oxy absorbs more than deoxy
185
Describe the **five mechanisms of filtration** and their particle size efficiencies.
* **Interception**: > 1 µm
* **Inertial impaction**: 0.5-1 µm
* **Gravitational settling**: > 5 µm
* **Brownian diffusion**: < 0.5 µm
* **Electrostatic interaction**: Charged particles attract to oppositely charged fibres.
186
What is the **Seebeck effect**?
Aka thermoelectric effect
The generation of a voltage at the junction of two dissimilar metals which varies according to temperature.
187
What **features** of an **endotracheal tube** aid insertion and ensure patient safety?
* **Left-facing bevel**: improves view of tip
* **Murphy's eye**: allows ventilation if tip is obstructed
* **Magill curve**: follows upper airway anatomy
## Footnote
Low-pressure, high-volume cuff
Vocal cord guide
188
State the **flow rates** for different sizes of cannula.
* **14G (orange)**: 270 ml/min
* **16G (grey)**: 180 ml/min
* **18G (green)**: 80 ml/min
* **20G (pink)**: 54 ml/min
* **22G (blue)**: 31 ml/min
189
What does this symbol represent in an **electrical circuit**?
Transformer
## Footnote
It is used in a defibrillator circuit to step up the voltage
190
# Define:
**ultrafiltration**
A process that allows the basic removal of plasma water (ultrafiltrate) from the blood together with very small molecules via solute drag. It is primarily used to correct volume overload and does not require replacement of body fluid.
## Footnote
Typical pore size is approximately 20 kDa.
191
What is the main purpose of a **catheter mount**?
Prevent transmission of accidental movements of the breathing system to the endotracheal tube.
192
State some **adaptations** of the theatre environment that are designed to reduce the risk of electrical sparks.
* Antistatic flooring (mean resistance of 20-50 kiloohms)
* Theatre crocs are antistatic
* Rotameters on machine are antistatic
* Relative humidity kept above 50%
193
List some **contraindications** for intra-aortic balloon pumps.
* Severe aortic regurgitation
* Aortic dissection
* Sepsis
* Severe peripheral vascular disease
194
What are some **complications** associated with intra-aortic balloon pumps?
* Limb ischaemia (thromboembolism or mechanical obstruction)
* Bleeding
* Infection
* Balloon rupture
195
What does this symbol represent in an **electrical circuit** and what is its unit of measurement?
Inductor
One Henry is the inductance when one ampere flowing in a coil generates a magnetic field strength of one weber i.e. H = Wb/A.
196
What is an **inductor** in electronics?
An electrical component that **stores energy in a magnetic field** when current flows through it.
## Footnote
It opposes any change in the current flowing through it which is useful for smoothing out surges. It opposes AC.
197
Explain how a **Wheatstone bridge** works.
A Wheatstone bridge measures an unknown resistance (Rx) by balancing two resistor ratios: R3/R1 = Rx/R2.
When balanced, the voltage between branches is zero. This high sensitivity allows precise detection of small changes, like in arterial line transducers where it filters out common noise.
198
Describe the efficiency of a **Mapleson A system**.
**Spontaneous**: efficient
- FGF must equal the minute volume
**Controlled**: inefficient
- high pressure forces fresh gas out of the APL, FGF of 2-3 x minute volume needed to prevent rebreathing
199
What **property of an atom** will enable it to exhibit spin?
The nucleus contains an uneven number of protons and neutrons.
The direction of spin is perpendicular to the axis of rotation.
200
What **factors** affect the performance of an HME filter?
* Water vapour content of expired gas
* Inspiratory and expiratory flow rates (slower means more time that gas is in contact with HMEF material)
* Volume of HMEF material (larger = more efficient)
* Thermal conductivity (low conductivity maintains greater temperature difference between either side of the HMEF and enables more heat and moisture to be transferred)
201
What **relative humidity** is achieved by a heat and moisture exchange filter?
60-70%
202
What is the **time delay** on pulse oximetry and capnography?
**Pulse oximetry**: 20 seconds
**Capnography**: 3.8 seconds
203
What **factors** would affect the accuracy of a pneumotacograph?
* Location in the breathing circuit
* Gas composition
* Gas temperature
* Humidity
* Dead space
204
How is it possible for ultrasonic humidifiers to **achieve** a relative humidity of over 100%?
Supersaturation
## Footnote
A temporary state where water vapour exceeds saturation because there are ultrafine water droplets in addition to water vapour
205
What are the **key components** of a signal processing circuit?
* **Amplifier**: amplifies small biological signals
* **Filters**: isolate relevant frequency ranges (exclude artefacts)
* **Analogue-to-digital** converters
* **Microprocessors**: interpret and display data
206
What is the **minimum efficiency size** of a filter in an anaesthetic circuit?
0.3 µm
## Footnote
Efficiency size refers to the particle size that is hardest for the filter to capture because it's too small for interception, inertial impaction and gravitational settling, and too large for Brownian motion.
207
What is a **CR circuit** and what is it used for?
A CR circuit consists of a capacitor and resistor in series. It acts as a **high-pass filter**, allowing high-frequency signals to pass while blocking low-frequency signals (like DC). It's commonly used in signal processing to remove unwanted low-frequency noise.
208
List **different lasing mediums** and their respective wavelengths.
* **Argon (400-600 nm)**: visible blue/green lasers. Used in ophthalmic surgery. Aka Excimer.
* **Nd:YAG (1060 nm)**: near infrared and used for endoscopic surgery
* **CO2 (10,600 nm)**: far infrared, poor tissue penetration, used for superficial airway surgery
209
How does a **Tec 6 vaporiser** work?
Dual-circuit, gas-vapour injection vaporiser designed for desflurane.
Has a sealed, heated vaporising chamber (39 degrees at 2 atmospheres) to keep desflurane in vapour form.
It injects precise amounts of desflurane into the FGF downstream.
A differential pressure transducer sense FGF pressure and two pressure regulating resistors adjust internal desflurane vapour pressure to match FGF pressure (enables reliable injection of desflurane).
The second resistor sets the output concentration.
210
Why is a **crystal window** used in an infrared carbon dioxide analyser?
Glass absorbs infrared radiation and would decrease the amount of infrared reaching the detector.
211
What is **relaxation** in the context of MRIs and how are T1 and T2 relaxation different?
In MRI, relaxation refers to the process by which net magnetisation returns to equilibrium after the radiofrequency (RF) pulse is turned off. This occurs through two mechanisms:
* **T1 relaxation (spin-lattice)**: the time taken for magnetisation to realign with the main magnetic field by releasing energy to surrounding tissue.
* **T2 relaxation (spin-spin)**: the time taken for protons to lose phase coherence with each other in the transverse plane.
## Footnote
T1 reflects recovery of alignment; T2 reflects loss of synchrony. Both are negative exponential processes and vary by tissue type.
212
Why does a **Mapleson F circuit** lead to high level of volatile gases in the theatre environment?
Mapleson F (Jackson-Rees modification of Ayre’s T-piece) **cannot be attached to scavenging**, and therefore exhaled gas will exit through the end of the reservoir bag directly into the environment.
213
What does '**cycling**' mean with regards to ventilators?
The method of cycling determines when a ventilator changes from its inspiratory phase to expiratory phase.
## Footnote
Most commonly time cycled ventilators are used, i.e. the expiratory phase begins after a pre-set inspiratory time is reached.
Flow cycling is less common in newer machines.
214
Why might nitrous oxide **cause** an over-estimation of the carbon dioxide content measured by mass spectrometry?
Both nitrous oxide and carbon dioxide have the same molar mass (44 g/mol) and so will have the same mass/charge ratio leading to overlap in detection and a falsely high reading.
215
What is the **Larmor frequency**?
* Product of the gyromagnetic ratio of the isotope and the magnetic field strength
* Determines the rate of precession of an object about an external magnetic field
216
What are the **features** of a proseal LMA?
* Detachable handle for insertion along the hard palate
* Gastric tube lumen
* Integrated bite block
* Pilot balloon
* Cuff inflation line
* Inflatable cuff
* Dorsal cuff to improve seal pressure to 35 cm H2O
217
What is the **formula** for sizing endotracheal tubes in children?
Size = age/4 + 4
218
How much is **1 atmosphere** in bar, PSI, kPa, cm H2O and mm Hg?
1.01 bar
14.69 psi
101.3 kPa
1033 cm H2O
760 mm Hg
219
What are some **safety features** of the oxygen rotameter on an anaesthetic machine?
* Oxygen knob is always furthest to the left
* Colour coded (white) as per pipeline oxygen
* Slightly larger
* Ridged texture
* Hypoxic guard (linking oxygen and nitrous oxide valves so that minimum deliverable oxygen concentration when nitrous is used is 25%)
220
Describe how a **left-sided double lumen endobronchial tube** works.
Refers to which main bronchus the endobronchial tube enters.
Has two openings. A **proximal opening** to the trachea above the carina, and a **distal opening** which is located in the left main bronchus. These openings correspond to the proximal lumens: clear for trachea, blue for bronchial.
If the tracheal cuff is inflated and the clear lumen connected to the breathing circuit then both lungs can be ventilated. When the blue cuff (endobronchial cuff) is also inflated and the breathing circuit connected to the clear lumen, then only the right lung will be ventilated. If the breathing circuit were connected to the blue lumen (with both cuffs inflated) only the left lung would be ventilated.
221
What is the **R time** on a TEG?
R time (reaction time) is the time taken between beginning an assay and point when the amplitude is 2 mm.
## Footnote
This represents the time for fibrin formation to begin.
222
What is the **K time** on a TEG?
Time from the R time to when the amplitude is 20mm wide.
## Footnote
This is used as a measure of clot strengthening.
223
What is the **alpha angle** on a TEG?
Angle to the horizontal made by straight line between the R time and K time.
## Footnote
This represents how quickly a clot forms.
224
What does the **MA** represent on a TEG?
The maximum amplitude of the graph and represents the maximum strength of clot.
## Footnote
This is primarily influenced by platelet count and function, and fibrin.
225
What does the **CL30** represent on a TEG?
Width of the graph 30 minutes after maximum amplitude. It represents fibrinolysis.
226
What are the **benefits** of a fenestrated tracheostomy tube?
* Allow movement of air via the nasal and oral route enabling speaking and coughing
* Improved weaning from ventilator
227
Outline the **Spaulding Classification** of medical devices.
* **Critical Items**: Enter sterile field or vascular system; high infection risk; must be sterilized (e.g., catheters).
* **Semi-Critical Items**: Contact mucous membranes or broken skin; intermediate infection risk; require high-level disinfection (e.g., laryngoscopes).
* **Non-Critical Items**: Contact intact skin; low infection risk; require low-level disinfection (e.g., blood pressure cuffs, tympanic thermometers).
228
# Define:
fluorescence
When energy is supplied to an atom it results in electrons being raised to a higher energy level. When these spontaneously fall back to ground state a photon of energy is released which is fluorescence.
229
Which **harmful byproduct** can be formed when volatiles with a CHF2 side-chain (desflurane, isoflurane and enflurane) react with soda lime?
Carbon monoxide
230
What is the **maximum safe dose** of prilocaine?
6 mg/kg
231
What **colour coding** is used for anaesthetic vapours?
* Red – halothane
* Purple – isoflurane
* Yellow – sevoflurane
* Blue – desflurane
* Orange – enflurane
232
What are the different brain waves and frequencies measured by a **BIS**?
* Delta 0-4 Hz, deep sleep
* Theta 4-8 Hz, deep relaxation
* Alpha 8-13 Hz, relaxation
* Beta 13-30 Hz, conscious thought
233
What is the **spectral edge frequency**?
* Frequency below which 95% of brain wave activity occurs
* Provides a single value indicating the dominant frequency range in the EEG signal
234
How does an **oscillotonometer** measure blood pressure?
1. A sensing/occluding cuff is inflated over systolic blood pressure and slowly deflated
2. Oscillations in the cuff are measured
## Footnote
Oscillations start = systolic
Maximal oscillations = MAP
Oscillations stop = diastolic
235
Which **type of filter** is most appropriate for a patient that's intubated and ventilated on ITU?
Pleated hydrophobic filter with heat and moisture exchanger
## Footnote
Pleated hydrophobic filters are more efficient than electrostatic filters.
236
What is a **Cardiff aldasorber**?
A **passive scavenging device** that removes volatile anaesthetic agents from waste gases via charcoal absorption. It connects directly to scavenging tubing but does not absorb carbon dioxide or nitrous oxide.
## Footnote
It must be replaced every 12 hours, and exhaustion is indicated only by increased canister weight. Heating the aldasorber can release the absorbed volatile agents.
Cannot be used in a circle system.
237
What is an **underdamped system**?
System is **unable to prevent oscillations** in response to a step change. The new value is reached quickly but the system oscillates before eventually settling at the new value. Typical damping coefficient is 0-0.3.
238
What is an **overdamped system**?
Has a **blunted response to a step change**. A long time is taken to reach the new value but there is no overshoot. The damping coefficient is >1.
239
What is a **critically damped system**?
Has a damping coefficient of 1. This provides quickest attainment of the new input value with no overshoot. This is still slower than optimal damping.
240
What is an **optimally damped system**?
Has a damping coefficient of 0.64.
This is the **best combination of rapid response to a stepped change in input and minimal overshoot**. There are no more than 2 oscillations prior to attaining the new value.
This means it can accurately track changes in arterial pressure without delays or overshoots.
241
Describe the **efficiency** of a coaxial Mapleson D circuit (Bain) for spontaneous and controlled ventilation.
* **Spontaneous** = Inefficient (FGF = 2 x MV)
* **Controlled** = Efficient (FGF = MV)
242
List the **entrainment ratios** for different venturi masks.
* 24% – 1:25
* 28% – 1:10
* 35% – 1:4.6
* 40% – 1:3.1
* 60% – 1:1
Primary FRCA
flashcards
Decks in class (17)
# Cards
-
Anatomy for Anaesthesia223
-
Physiology: Respiratory303
-
Physiology: Cardiovascular179
-
Physiology: Renal, Hepatic & GI63
-
Physiology: Neuro, Endo, & Haem237
-
Pharmacokinetics and Pharmacodynamics213
-
Pharmacology: Inhalational & Intravenous Agents232
-
Pharmacology: Analgesics & Muscle Relaxants160
-
Pharmacology: Emergency & Miscellaneous Drugs251
-
Part 1: Physics & Equipment242
-
Part 2: Physics & Equipment227
-
Part 3: Physics & Equipment232
-
Part 4: Physics & Equipment217
-
Statistics & Evidence-Based Practice36
-
Part 1: Applied Clinical Anaesthesia165
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Part 2: Applied Clinical Anaesthesia169
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Part 3: Applied Clinical Anaesthesia157
