Primary FRCA Course Measurement and Monitoring Exam Prep Questions Flashcards
In pulse oximetry:
The SpO2 is determined by the absorbance of light of wavelengths 660nm and 940nm
True. Pulse oximetry relies on measuring the relative absorbance at two wavelengths (660nm and 940nm). Reduced haemoglobin has greater absorbance at 660nm and oxyhaemoglobin greater at 940nm. The ratio is the determined and the SpO2 is then calculated
In pulse oximetry:
Methaemoglobinaemia causes the SpO2 to approach 85%
True. Carboxyhaemoglobin causes an increase in SpO2 equal to its concentration, but methaemoglobin absorbs light equally at both 660nm and 940nm so the saturation tends towards a value of 85%
In pulse oximetry:
Oxyhaemoglobin absorbs better at the longer wavelength
True. Pulse oximetry relies on measuring the relative absorbance at two wavelengths (660nm and 940nm). Reduced haemoglobin has greater absorbance at 660nm and oxyhaemoglobin greater at 940nm. The ratio is the determined and the SpO2 is then calculated
In pulse oximetry:
Fetal haemoglobin gives an inaccurately high reading of saturation
False. Fetal haemoglobin does not affect the accuracy of pulse oximetry
In pulse oximetry:
The pulse oximeter is less accurate at low rather than high saturations
True. The monitor is accurate to within 3% at values of over 70%, but less accurate as the saturation falls
Regarding pulse oximetry:
The arterial a.c (pulsatile) component of the signal is approximately 20% of the total absorption
False. The pulsatile component is typically 2% of the total absorption.
Regarding pulse oximetry:
Functional saturation is defined as the ratio of oxyhaemoglobin to oxyhaemoglobin plus reduced haemoglobin
True. Functional saturation is the ratio of O2HB to (O2Hb + Hb), it is Fractional saturation that includes other haemoglobins.
Regarding pulse oximetry:
Beer’s law relates the intensity of transmitted light to the path length
False. Beer’s law relates the absorption of transmitted light to the concentration of the substance whereas Lamberts law relates it to path length.
Regarding pulse oximetry:
Infrared light is only absorbed by small molecules with symmetric bonds
False. Infrared light is absorbed by small molecules with asymmetric bonds so that vibration can occur.
Regarding pulse oximetry:
Motion artefacts produces a high a.c. to d.c. signal ratio
True. Motion will produce an increase in a.c. components however this is noise and therefore the signal to noise ratio will be lower
Causes of inaccuracies on pulse oximetry include:
Methaemoglobinaemia
True. MetHb, hypothermia (causing vasoconstriction) and extraneous lighting can all affect pulse oximetry accuracy.
Causes of inaccuracies on pulse oximetry include:
Fetal haemoglobin
False. Fetal haemoglobin does not have a significant effect.
Causes of inaccuracies on pulse oximetry include:
Hypothermia
True. MetHb, hypothermia (causing vasoconstriction) and extraneous lighting can all affect pulse oximetry accuracy.
Causes of inaccuracies on pulse oximetry include:
Blue nail polish
True. Blue nail varnish absorbs red light and can affect readings. Similarly the use of blue dyes for sentinel node biopsy can lead to reduction in recorded oxygen saturation using a pulse oximeter
Causes of inaccuracies on pulse oximetry include:
Extraneous lighting
True. MetHb, hypothermia (causing vasoconstriction) and extraneous lighting can all affect pulse oximetry accuracy.
Concerning the measurement of oxygen:
A Clark electrode requires a polarising voltage
True. The Clark electrode is a polarographic electrode and needs a polarising voltage.
Concerning the measurement of oxygen:
Fuel cells can be affected by the presence of nitrous oxide
True. Some fuel cells are affected by N2O.
Concerning the measurement of oxygen:
A paramagnetic analyser has a slower response time than a Clark electrode
False. Modern paramagnetic analysers have a fast response time.
Concerning the measurement of oxygen:
A polarographic technique is used in normal blood gas analysers
True. Oxygen is measured by a polarographic technique in most blood gas analysers.
Concerning the measurement of oxygen:
Oxygen saturation is directly measured using a co-oximeter
False. A CO-oximeter measures the concentrations of different haemoglobins and calculates the oxygen saturation from the relevant percentages.
The following are directly measured in a standard blood gas analyser:
pH
False!!? A blood gas analyser directly measures hydrogen ion concentration using a glass electrode. pH is calculated mathematically as the negative Log of the hydrogen ion concentration and therefore not directly measured! Small but important point if asked in the exam.
The following are directly measured in a standard blood gas analyser:
Bicarbonate concentration
A blood gas analyser directly measures hydrogen ion concentration using a glass electrode, the tension of oxygen using a polarographic electrode and carbon dioxide indirectly through a modification of the glass electrode. Bicarbonate is extrapolated using the HH equation.
The following are directly measured in a standard blood gas analyser:
Oxygen tension
True. A blood gas analyser directly measures hydrogen ion concentration using a glass electrode, the tension of oxygen using a polarographic electrode and carbon dioxide indirectly through a modification of the glass electrode.
The following are directly measured in a standard blood gas analyser:
Partial pressure of carbon dioxide
False. A blood gas analyser directly measures hydrogen ion concentration using a glass electrode, the tension of oxygen using a polarographic electrode, and carbon dioxide indirectly through a modification of the glass electrode. Partial pressures are derived by measuring the atmospheric pressure.
The following are directly measured in a standard blood gas analyser:
Oxygen saturation
False. A blood gas analyser directly measures hydrogen ion concentration using a glass electrode, the tension of oxygen using a polarographic electrode, and carbon dioxide indirectly through a modification of the glass electrode. Oxygen saturation may be derived but is not directly measured
Arterial blood gas samples:
Storage at room temperature causes a rise in pH
False. Blood gas samples become acidotic with time so the pH falls.
Arterial blood gas samples:
A hypothermic patient will have an inaccurately high pO2 if temperature-correction is not employed
True. If temperature-correction is not applied then hypothermic patients will have an inaccurately high PO2 reading.
Arterial blood gas samples:
Air bubbles in the sample may lead to a fall in the pCO2
True. Air bubbles contain no CO2 so will reduce the reading of pCO2.
Arterial blood gas samples:
Excessive heparin will cause an inaccurately high pH
False. Heparin is acidic so will reduce the pH.
Arterial blood gas samples:
Storage at room temperature causes a fall in pO2
True. At room temperature white cells metabolise oxygen and pO2 falls.
The oxygen electrode in a blood gas analyser:
Incorporates on a lead anode
False. The anode is typically silver and the cathode platinum, the electrolyte solution is a potassium chloride solution.
The oxygen electrode in a blood gas analyser:
The cathode is usually platinum
True. The anode is typically silver and the cathode platinum, the electrolyte solution is a potassium chloride solution.
The oxygen electrode in a blood gas analyser:
Potassium hydroxide is the usual electrolyte in the electrode
False. The anode is typically silver and the cathode platinum, the electrolyte solution is a potassium chloride solution.
The oxygen electrode in a blood gas analyser:
Current flow depends on oxygen tension at the cathode
True. Current flow depends on the oxygen tension at the cathode. The more oxygen there is the greater the current (this is the principle of an amperometric sensor). At the cathode a reductive reaction occurs and oxygen is consumed with the gain of electrons to form hydroxide ions.
The oxygen electrode in a blood gas analyser:
Is of the fuel cell type
False. Fuel cells are not used in blood gas analysers. The polarographic (Clark) Electrode is used in blood gas analysers.
The fuel cell:
Contains a lead anode
True. A fuel cell contain a lead anode and gold mesh cathode.
The fuel cell:
Has a faster response time than a polarographic electrode
False. They both have relatively slow response time as it is they are electrochemical processes.
The fuel cell:
Is not affected by temperature
False. It is affected by temperature as a chemical reaction takes place.
The fuel cell:
Nitrous oxide in the gas mixture reacts with the anode to produce nitrogen
True. Nitrous oxide is broken down to nitrogen at the anode.
The fuel cell:
Is used to measure oxygen tension in a blood gas analyser
False. Typically a Clark polarographic electrode is used in a blood gas analyser.
Concerning the Clark PO2 electrode:
Is composed of a platinum cathode and a gold anode
False. The Clark electrode has a platinum cathode and SILVER anode. A fuel cell has gold cathode.
Concerning the Clark PO2 electrode:
An oxygen consuming electrochemical reaction takes place at the anode
False. The oxygen consuming reaction takes place at the cathode where there is gain of electrons (reduction).
Concerning the Clark PO2 electrode:
It can be used to measure oxygen partial pressure in gases and liquids
True. A Clark electrode can be used in both gases and liquids.
Concerning the Clark PO2 electrode:
It requires a voltage of 0.6 V to be applied between its electrodes
True. Typically a polarising voltage of 0.6 V is used.
Concerning the Clark PO2 electrode:
It is sensitive to changes in temperature
True. As with all electrochemical electrodes it is sensitive to changes in temperature.
The Severinghaus carbon dioxide electrode:
Incorporates KCL and NaHCO3 in the electrolyte solution
True. KCl and NaHCO3 are in the electrolyte solution
The Severinghaus carbon dioxide electrode:
Directly measures the PaCO2
False. The electrode is a modification of the glass electrode and measures the hydrogen ion concentration in the bicarbonate solution. It is therefore an indirect measure of PaCO2.
The Severinghaus carbon dioxide electrode:
Incorporates hydrogen ion sensitive glass
True. The pH electrode incorporates hydrogen ion sensitive glass which generates a potential difference across the glass in the presence of hydrogen ions.
The Severinghaus carbon dioxide electrode:
Incorporates a platinum wire cathode
False. It is the oxygen electrode that has a platinum cathode.
The Severinghaus carbon dioxide electrode:
Is affected by temperature
True. All electrochemical electrodes are affected by temperature
Recognised methods of measuring anaesthetic vapour concentration include:
Raman scattering
True.
Recognised methods of measuring anaesthetic vapour concentration include:
Paramagnetism
False. Paramagnetism is used for oxygen analysis as oxygen does not absorb infrared light
Recognised methods of measuring anaesthetic vapour concentration include:
Ultraviolet absorption
True. UV absorption is a recognised method of historical interest only.
Recognised methods of measuring anaesthetic vapour concentration include:
Mass spectrometry
True.
Recognised methods of measuring anaesthetic vapour concentration include:
Photoacoustic spectrophotometry
True. The main method of measuring anaesthetic vapour concentration is Infrared Absorption Spectrophotometry. Photoacoustic spectrometry is similar but measures sound generated rather that light absorbed.
The following can be used to measure carbon dioxide in expired gases (capnography):
Clark polarographic electrode
False. Capnography is usually undertaken using infrared absorption spectrophotometry. Mass spectrometry and Raman scattering can also be used. Paramagnetic analysers and the Clark electrode measure oxygen
The following can be used to measure carbon dioxide in expired gases (capnography):
Paramagnetic analyser
False. Capnography is usually undertaken using infrared absorption spectrophotometry. Mass spectrometry and Raman scattering can also be used. Paramagnetic analysers and the Clark electrode measure oxygen
The following can be used to measure carbon dioxide in expired gases (capnography):
Infrared absorption spectrometry
True. Capnography is usually undertaken using infrared absorption spectrophotometry. Mass spectrometry and Raman scattering can also be used. Paramagnetic analysers and the Clark electrode measure oxygen
The following can be used to measure carbon dioxide in expired gases (capnography):
Mass spectrometry
True. Capnography is usually undertaken using infrared absorption spectrophotometry. Mass spectrometry and Raman scattering can also be used. Paramagnetic analysers and the Clark electrode measure oxygen
The following can be used to measure carbon dioxide in expired gases (capnography):
Raman analyser
True. Capnography is usually undertaken using infrared absorption spectrophotometry. Mass spectrometry and Raman scattering can also be used. Paramagnetic analysers and the Clark electrode measure oxygen
The following have infrared absorption spectra which overlap with that of carbon dioxide:
Water vapour
True. Water vapour, sevoflurane and nitrous oxide all have infrared absorption spectra which overlap with that of CO2.
The following have infrared absorption spectra which overlap with that of carbon dioxide:
Sevoflurane
True. Water vapour, sevoflurane and nitrous oxide all have infrared absorption spectra which overlap with that of CO2.
The following have infrared absorption spectra which overlap with that of carbon dioxide:
Nitrous oxide
True. Water vapour, sevoflurane and nitrous oxide all have infrared absorption spectra which overlap with that of CO2.
The following have infrared absorption spectra which overlap with that of carbon dioxide:
Nitrogen
False. Nitrogen does not absorb infrared light as it only has symmetric bonds
The following have infrared absorption spectra which overlap with that of carbon dioxide:
Helium
False. Helium does not absorb infrared light as it only has symmetric bonds
Concerning the measurement of expired carbon dioxide using the infrared absorption technique:
The wavelength of infrared light used is 4.3 micrometres
True.
Concerning the measurement of expired carbon dioxide using the infrared absorption technique:
The absorption of infrared light by carbon dioxide is based on the Beer-Lambert law
True. Absorption follows the Beer-Lambert law with absorption being dependant on concentration and path length.
Concerning the measurement of expired carbon dioxide using the infrared absorption technique:
The windows on the sample chamber are made of lead crystal glass
False. The windows are made of a material that is transparent to infrared, lead crystal glass is not.
Concerning the measurement of expired carbon dioxide using the infrared absorption technique:
Nitrous oxide interferes with infrared absorption by carbon dioxide
True. N2O, and volatile agents interfere with the measurement due to collision broadening which is a physical interaction between the different molecules.
Concerning the measurement of expired carbon dioxide using the infrared absorption technique:
Oxygen interferes with infrared absorption by carbon dioxide
True. Oxygen can interfere with the measurement though it does not absorb infrared light
Concerning spectrophotometric absorption spectra of reduced and oxygenated haemoglobin:
At the isosbestic point, the absorption coefficient is the same
True. The isobestic, or as it more properly written, isosbestic point for oxy and deoxyhaemaglobin is approximately 805nm and is the point at which both molecules absorb equally.
Concerning spectrophotometric absorption spectra of reduced and oxygenated haemoglobin:
The isosbestic point occurs at a wavelength around 650 nm
False. The isobestic, or as it more properly written, isosbestic point for oxy and deoxyhaemaglobin is approximately 805nm and is the point at which both molecules absorb equally.
Concerning spectrophotometric absorption spectra of reduced and oxygenated haemoglobin:
The amount of oxygenated haemoglobin is directly proportional to the shift in the isosbestic point
False. The isosbestic does not shift with respect to differing proportions of oxy and deoxyhaemoglobin.
Concerning spectrophotometric absorption spectra of reduced and oxygenated haemoglobin:
The maximum difference in the absorption of the two forms of haemoglobin occurs at a wavelength around 940 nm
False. The maximum difference in the absorption of the two forms of haemoglobin occurs at a wavelength of about 650 nm.
Concerning spectrophotometric absorption spectra of reduced and oxygenated haemoglobin:
The pulse oximeter uses the difference between the absorption spectra of the two forms of Hb to quantify their relative concentrations
True.
Refractometers:
Are capable of measuring vapour concentration in gas mixture
True. Refractometers are typically used to measure vapour concentrations in gas mixtures by measuring the bending of light waves due to the change in gas composition.
Refractometers:
Require calibration
True.
Refractometers:
Directly measure the vapour concentration
False. They measure vapour concentration INDIRECTLY.
Refractometers:
Are not influenced by water vapour
False. They are influenced by water vapour.
Refractometers:
Are used to calibrate vaporisers
True.
Blood-gas analysis:
The base excess is the amount of strong acid required to return the pH of 1 litre of blood to 7.40 at a PCO2 of 5.3 kPa and 37°C
True. Base excess is used to assess the metabolic component of the blood-gas analysis.
Blood-gas analysis:
Too much heparinised saline tends to cause a falsely low reading of the PCO2
True. Errors can occur due to excessive heparin either due to the dilutional effect of excessive saline (low pCO2 and low pO2, though the pH is little effected), or due to the heparin itself (high potassium measurement)
Blood-gas analysis:
Too much heparin tends to cause a falsely low reading of potassium concentration
False. Errors can occur due to excessive heparin either due to the dilutional effect of excessive saline (low pCO2 and low pO2, though the pH is little effected), or due to the heparin itself (high potassium measurement).
Blood-gas analysis:
A Clark electrode requires a battery
True. It is the fuel cell that does not
Blood-gas analysis:
Prolonged storage at 4°C may lead to a falsely low value for PO2
True. Prolonged storage even at 4°C can lead to either a falsely low reading of pO2 (due to ongoing metabolism in white blood cells) or a falsely high reading (due to bubbles dissolving).
The following statements are correct:
Visible light has a wavelength between 400 and 700 nanometers
True. Visible light is between 400 (Blue) and 700 (Red) nm.
The following statements are correct:
Carbon dioxide has a peak absorption at 4.3 micrometers
True. CO2 has an absorption peak at 4.3 micrometres.
The following statements are correct:
3.3 micrometers is the common absorption peak for volatile anaesthetic agents
True. Volatile agents have absorption peaks close to 3.3 micrometres.
The following statements are correct:
Methane interferes with gas analysis in the 9-11 micrometer band
False. Methane absorbs in the 3-4 micrometre range and can build up in circle breathing systems. There is a second volatile agent peak at 9-11 micrometers that is not affected by methane.
The following statements are correct:
Collision broadening alters the wavelengths at which infrared absorption by carbon dioxide takes place
True. Collision broadening widens the range of wavelengths absorbed by CO2.
Concerning mass spectrometry:
The analysing chamber operated at atmospheric pressure
False. The chamber in a mass spectrometer operates at near vacuum pressures and requires a pump to maintain this pressure.
Concerning mass spectrometry:
The ions are accelerated by an anode plate
False. The ions are accelerated by a cathode plate.
Concerning mass spectrometry:
In a quadruple mass spectrometer there are two large electromagnets
False. A quadrupole mass spectrometer has 4 electromagnets that produce the ion gate.
Concerning mass spectrometry:
The sample from a mass spectrometer can be returned to a circle system to allow low flow anaesthesia
False. Samples from a mass spectrometer are ionised and cannot be returned to the breathing circuit.
Concerning mass spectrometry:
Mass spectrometry is less accurate than infrared absorption spectrophotometry
False. Mass spectrometers the gold standard of gas analysers.
The following statements are correct:
Fuel cells are suitable for breath to breath analysis of oxygen concentration
False. Both fuel cells and the polarographic electrode are not suitable for breath to breath analysis due to their slow response time
The following statements are correct:
Unpaired electrons are responsible for oxygen’s paramagnetic property
True. Oxygen and Nitric Oxide are paramagnetic due to unpaired electrons in their outer rings
The following statements are correct:
Damping coefficient is inversely proportional to the amplitude ratio in invasive arterial pressure measurement
True. A high amplitude ratio suggests little damping and therefore a low damping coefficient
The following statements are correct:
The natural frequency of a mass-string dynamic oscillator is directly proportional to its mass
False. It is inversely proportional to the square root of the mass
The following statements are correct:
Fourier Transformation is a mathematical operation that deconstructs a complex signal into its constituent frequencies
True. This is the definition of Fourier Transformation.
