RCOA Guide to the FRCA Examination The Primary (fourth edition) - Physics, Equipment & Monitoring, and Statistics MTF Flashcards
When measuring central venous pressure:
A catheter inserted in an adult at the antecubital fossa should be passed no more than 20 cm up the vein
False. The tip of the catheter should be within superior vena cava and that distance will vary between patients.
When measuring central venous pressure:
The optimum internal diameter for the catheter is 0.25 mm
False. The usual adult size catheters are 14-16 Gauge, corresponding to 1.63 and 13 mm diameter.
When measuring central venous pressure:
Direct subclavian vein catheterisation can be used
True. Either internal jugular or subclavian vein could be used as long as the catheter tip is located in the superior vena cava.
When measuring central venous pressure:
Microshock is a potential hazard
True. Microshock is a term describing the induction of ventricular fibrillation by small electrical currents (below the threshold of skin sensation, i.e. below 1 mA) when applied to very small areas of ventricular muscle, usually by vascular catheters or wires. It requires a small area of contact with heart muscle so that the current density is high despite low current.
When measuring central venous pressure:
The zero level should be set at the level of the angle of Louis
whatever the position of the patient
False. It is usually set at the point where the fourth intercostal space and mid-axillary line cross each other. This allows the measurement to be as close to the right atrium as possible with the patient in a supine position.
A liquid inhalational anaesthetic agent is allowed to come into equilibrium with a mixture of gases. Under these conditions, the partial pressure of the agent in the resulting gas mixture depends on:
The atmospheric pressure
False. At this point an inhalational agent will be at its saturated vapour pressure (SVP). It is only the temperature of the liquid that influences the SVP. The higher the temperature, the higher the SVP.
A liquid inhalational anaesthetic agent is allowed to come into equilibrium with a mixture of gases. Under these conditions, the partial pressure of the agent in the resulting gas mixture depends on:
The surface area of the liquid
False. At this point an inhalational agent will be at its saturated vapour pressure (SVP). It is only the temperature of the liquid that influences the SVP. The higher the temperature, the higher the SVP.
A liquid inhalational anaesthetic agent is allowed to come into equilibrium with a mixture of gases. Under these conditions, the partial pressure of the agent in the resulting gas mixture depends on:
The volume of the liquid
False. At this point an inhalational agent will be at its saturated vapour pressure (SVP). It is only the temperature of the liquid that influences the SVP. The higher the temperature, the higher the SVP.
A liquid inhalational anaesthetic agent is allowed to come into equilibrium with a mixture of gases. Under these conditions, the partial pressure of the agent in the resulting gas mixture depends on:
The composition of the gas mixture
False. At this point an inhalational agent will be at its saturated vapour pressure (SVP). It is only the temperature of the liquid that influences the SVP. The higher the temperature, the higher the SVP.
A liquid inhalational anaesthetic agent is allowed to come into equilibrium with a mixture of gases. Under these conditions, the partial pressure of the agent in the resulting gas mixture depends on:
The temperature of the liquid
True. At this point an inhalational agent will be at its saturated vapour pressure (SVP). It is only the temperature of the liquid that influences the SVP. The higher the temperature, the higher the SVP.
The correct SI unit for:
Force is the pascal
False. Pascal is the Sl unit of pressure. 1Pa = 1N/m^2.
Force is expressed in Newtons. 1N=1kg.m.s^-2: A force of 1 N will give a mass of 1 kg an acceleration of 1 m per second.
The correct SI unit for:
Mass is the gram
False. The Sl unit of mass is the kilogram.
The correct SI unit for:
Time is the second
True
The correct SI unit for:
Length is the metre
True
The correct SI unit for:
Energy is the watt
False. Watt is a derived unit of power (the rate of doing work, J S^-1).
The unit of energy is Joule. 1J = 1 N.m. One Joule is the energy expended when the point of application of a force of 1N moves 1 m in the direction of the force.
The following are true of critical temperature:
Critical temperature is the temperature above which a substance cannot be liquefied however much pressure is applied
True. This is a definition of critical temperature.
The following are true of critical temperature:
The critical temperature of oxygen is -119°C
True.
The following are true of critical temperature:
Nitrous oxide cylinders always contain liquid nitrous oxide
False. At the very end of its use, there is no liquid left in the cylinder only vapour. This is when the pressure in the cylinder starts to drop rapidly. In addition, at temperatures above its critical temperature the cylinder will contain only gas.
The following are true of critical temperature:
The critical temperature of nitrous oxide is 48.5°C
False. The critical temperature of nitrous oxide is 36.5°C.
The following are true of critical temperature:
Critical pressure is the vapour pressure of a substance at its critical temperature
False. The critical pressure of a substance is the pressure required to liquefy a gas at its critical temperature.
According to laws of physics:
Boyle’s Law assumes that molecular size is unimportant
True. Boyle’s Law is an ideal gas law and assumes among other things that molecular size is unimportant.
According to laws of physics:
Boyle’s Law states that the volume of a gas varies inversely with pressure
True. This is the definition of Boyle’s Law
According to laws of physics:
Charles Law predicts that as the temperature of a mass of gas is raised from 10°C to 20°C its volume will double.
False. Charles Law states that at a constant pressure, the volume of a given mass of gas varies directly to its absolute temperature. Absolute temperature is measured in Kelvin. 0°C = 273K. Hence, 10°C= 10+273=283K and 20°C=20+273=293K. So, when temperature rises from 10 to 20°C the pressure only goes up by 3.5% (it does not double). The temperature change in Kelvin is only 10K (10K is 3.5% of the initial 283K).
According to laws of physics:
Dalton’s Law states that a gas dissolves in proportion to its partial pressure
False. Dalton’s Law states that in a mixture of gases, the pressure exerted by each gas is equal to the pressure which would be exerted if that gas alone were present. Hence, the total pressure exerted by the mixture of gases is equal to the sum of the partial pressures of individual gases.
According to laws of physics:
Laplace’s Law suggests that large alveoli should collapse
False. Laplace’s Law for spheres reads P= 2T/r, where P is the pressure gradient across the wall, T is the tangential force acting along the length of the wall and r is the radius. So in large alveoli, the radius will be larger and consequently the resultant pressure gradient across the wall will be smaller. That is why large alveoli do not collapse and there is a tendency of small alveoli to empty into large alveoli. In normal lungs this does not occur due to the presence of surfactant lining the alveoli.
The Doppler effect:
Applies to both electromagnetic radiation and sound
True. The Doppler effect for electromagnetic waves such as light is invaluable in astronomy. It has been used to measure the speed at which stars and galaxies are approaching or receeding from us.
The Doppler effect:
Changes the velocity of reflected ultrasound
False. It is the change of frequency of a signal that is key to the Doppler effect.
The Doppler effect:
Depends on the piezo-electric properties of some crystals
False. That is the true of clinical ultrasound but not the Doppler effect.
The Doppler effect:
Shows a shift to lower frequency if the source is moving away from the receiver
True. And the opposite is correct showing the shift to a higher frequency if the source is moving towards the receiver.
The Doppler effect:
Can indicate the velocity of red blood cells
True. The sound waves reflect from surfaces of the red blood cells as they approach and move away. Analysis of the reflected frequencies allows determination of velocity of flow.
Sevoflurane vapour:
Concentration can be measured using a refractometer
True. The refractometer, sometimes called the interferometer can measure the concentration of any inhalational agent. It measures the extent to which light is bent (i.e. refracted) when it moves from air into a sample.
Sevoflurane vapour:
Is less dense than air
False.
Sevoflurane vapour:
Absorbs ultraviolet radiation
False. It absorbs infrared radiation.
Sevoflurane vapour:
Can be measured by absorption of infrared radiation
True. That is the principle of infrared analyser when used to measure the concentration of sevoflurane and other substances containing two dissimilar atoms in a molecule.
Sevoflurane vapour:
Can be measured by mass spectrometry
True. Mass spectrometry works by ionising chemical compounds to generate charged molecules or molecular fragments. Their mass-to-charge ratios are then measured.
The Bain coaxial breathing system:
Delivers the fresh gas flow in the outer tube
False. The inner tube carries the fresh gas flow. By contrast, the coaxial Mapleson A system (Lack) carries the fresh gas flow in the outer tube.
The Bain coaxial breathing system:
Requires a fresh gas flow equal to the patient’s minute volume to prevent rebreathing with spontaneous respiration
False. Rebreathing would definitely occur at a fresh gas flow equal to minute ventilation. To prevent rebreathing, a fresh gas flow of 2-4 times per minute ventilation is usually quoted.
The Bain coaxial breathing system:
Can be used in a child weighing 20 kg
True. In fact, it has been safely used in children weighing less than 20 kg.
The Bain coaxial breathing system:
Has a dead space which is increased if the inner tube is dislodged at the machine end
True. Apparatus dead space is that volume of a breathing system that contains alveolar gases that are inhaled on a subsequent breath. Following this disconnection, it is increased. Alveolar gases would be pushed towards (rather than away from) the patient by the fresh gas flow risking dangerous accumulation of carbon dioxide.
The Bain coaxial breathing system:
Can function as a Mapleson C system
False. It is Mapleson D. The Mapleson classification is specific about the spatial relationship between fresh gas flow input, reservoir bag, APL valve and tubing in the system.
