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Flashcards in Temperature and Humidity Deck (50)
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1

The mechanism by which most heat is lost during anaesthesia is radiation

True

2

NICE guidelines suggest the use of forced air warming for all surgery

False. NICE recommends the use of forced air warming if a patient is at higher risk or surgery is >30 min.

3

Hypothermia shifts the oxyhaemoglobin curve to the left, reducing tissue O2 delivery

True

4

The triple point of water is at 273.16°C

False. The triple point of water is at 273.16K (0.01°C).

5

Critical temperature is the temperature below which a vapour cannot be liquefied by any amount of pressure

False. Critical temperature is the temperature ABOVE which a vapour cannot be liquefied by any amount of pressure.

6

Thermocouples rely on the Seebeck effect

True. The Seebeck effect is the production of a voltage at the junction of 2 difference conductors. The magnitude of this voltage is dependant on the temperature of the junction.

7

1K is equal in magnitude to 1°C

True

8

If the oesophagus is used for measuring temperature, the upper third should be used for greatest accuracy

False. The lower third should be used.

9

Liquid crystal may be used in thermometers

True. They are used in chemical thermometers.

10

Resistance thermometers can only reliably be used for measuring large temperature changes

False. Resistance thermometers are extremely accurate and can be used for measuring small temperature differences.

11

Over one third of heat loss during anaesthesia is via conduction

False. 40-50% of heat loss is via radiation, 30% by convection, 20% by evaporation and 3% by conduction.

12

Maintaining the theatre environment at approximately 30% humidity is the ideal compromise between staff comfort and minimizing the patient’s heat loss

False. Relative humidity in theatres should be kept at around 50-60%. Higher humidity is uncomfortable for staff, lower increases the risk of sparks.

13

Hypothermia increases MAC

False. Hypothermia reduces MAC, i.e. less anaesthetic is required.

14

Infrared ear thermometers detect electromagnetic radioation emitted by the ear drum

True

15

Rectal temperaure tends to be lower than core temperature

False. Rectal temperature is usually 0.5-1°C higher than core temperature due to bacterial fermentation.

16

Thermistors Have a slow response time

False. They have a fast response time.

17

Thermistors Utilize the resistance properties of metal oxides

True. The resistance of metal oxide semiconductors fall exponentially with temperature.

18

Thermistors Are used in PA catheters

True. Thermistors can be made very small.

19

Thermistors Are often used with Wheatstone bridges

True. Wheatstone bridges are often used to improve accuracy.

20

Thermistors Depend on the Seebeck effect

False. Thermocouples rely on the Seebeck effect.

21

Mercury is more suitable than alcohol for measuring low temperatures

False. Alcohol is more suitable for measuring low temperatures as mercury solidifies at -39°C. Mercury is more suitable for high temperature as alcohol boils at 78.5°C

22

The Seebeck effect describes the non-linear fall in resistance seen when the temperature of a metal oxide rises

False. The Seebeck effect describes the production of voltage at the junction of two different conductors. The magnitude of this voltage is proportional to temperature. This principle is used in thermocouples. The non linear fall in resistance seen when the temperature of a metal oxide rises occurs in thermistors.

23

Bimetallic strips may be used in dial thermometers

True. Bimetallic strips containing two dissimilar metals with different coefficients of expansions are fixed together in a coil to make dial thermometers. (Volatile liquids can also be used). Bimetallic strips are also used to control the splitting ratios in Plenum vapourizers.

24

If the temperature (in K) of a volume of gas is doubled, the volume of the gas will double

True. This is Charles’s Law

25

The resistance of a metal increases exponentially with temperature

False. The resistance of a metal increases linearly with temperature. This is the principle behind resistance thermometers.

26

A hair hygrometer measures relative humidity

True

27

Relative humidity is equal to the absolute humidity divided by the saturated vapour pressure of water at that temperature

False. HME have one 15 mm and one 22 mm connector.

28

Relative humidity is equal to the absolute humidity divided by the saturated vapour pressure of water at that temperature

True. Relative humidity is the ratio of the mass of water vapour in a given volume of water (i.e. its absolute humidity) to the mass required to saturate that given voume of air at the same temperature (i.e. the SVP of water at that temperature).

29

HME (if not blocked) increase resistance to air flow by approximately 5cm H2O

False. HME increase reisitance to flow by 0.1-2 cm H2O.

30

The use of sodalime can achieve absolute humidity of 34 mg/L

False. The reaction of CO2 with soda lime can achieve an absolute humidity of 29 mg/L:
CO2 + H2O -> H2CO3
2NaOH + H2CO3 -> NaCO3 +2H2O + heat
Na2CO3 +Ca(OH)2 -> CaCO3 +2NaOH + heat
(34 mg/L is the absolute humidity in the upper airways )

31

Wet and dry bulb hygrometers are more accurate than hair or Reganult's hygrometers

False. Reganult's hygrometers are more accurate than wet and dry bulb hygrometers or hair hygrometers.

32

The same volume of water will produce a lower relative humidity in warmer air than in cooler air

True. Warmer air can hold more water when fully saturated; e.g. 17 g/m3 would produce a relative humidity of 100% at 20°C but only 38% at 37°C as air at this temperature can hold up to 44 g/m3.

33

Absolute humidity is the volume of water vapour present per unit volume of gas

False. Absolute humidity is the MASS of water vapour present per unit volume of gas (at a given temperature).

34

Fully saturated air at body temperature can hold 44 g/m3 of water

True

35

HME can achieve at best a relative humidity of 40-50%

False. HME can achieve relative humidity of 60-70%

36

A hair hygrometer is most accurate at relative humidities of 80-100%

False. Hair hygrometers are most accurate between relative humidities of 30-90%

37

Tables are required to interpret the reading of hair hygrometer

False.The change in humidity moves the hair directly over a scale. Tables are required for the interpretation of wet and dry bulb hygrometers and Reganult's hygrometers.

38

Wet and dry bulb hygrometers utilize the cooling effect of ether to measure relative humidity

False. Regnault’s hygrometers utilise the cooling effect of bubbling air through ether to measure relative humidity.

39

Reganult’s hygrometer can measure absolute and relative humidities

True

40

Wet and dry bulb hygrometers should only be used when there is minimal air movement around the thermometers

False. Wet and dry bulb hygrometers require air movement to allow the evaporation of water which cools the wet thermometer.

41

Bourdon Gauge can be used to measure humidity T/F

False. Bourdon gauges are used to measure pressure or temperature but not humidity.

42

Mass Spectrometry can be used to measure humidity T/F

True

43

UV Light can be used to measure humidity T/F

True. The absorption of UV light by water vapour can be used to measure humidity.

44

Transducers can be used to measure humidity T/F

True. The change in the resistance of capacitance of a substance when it absorbs water vapour can be used to measure humidity.

45

A Pitot Tube can be used to measure humidity T/F

False. Pitot tubes are used to improve the accuracy of pneumotachographs which are used to measure gas flow.

46

HME are most efficient with small tidal volumes

True. The humidifying efficiency of HMEs decreases with large tidal volumes.

47

The amount of water droplets that can be delivered by a nebulizer in a given volume of air is limited by temperature

True. The humidifying efficiency of HMEs decreases with large tidal volumes.

48

Gas driven (Jet) nebulisers rely on the Coanda effect

False. Gas driven nebulizers rely on the Venturi/Bernoulli effect.

49

Nebulized droplets of size 2-5 μm are deposited in the tracheo-bronchial tree

True

50

The upper airways humidify inhaled gases by the addition of up to 17 g/m3 of water

False. The upper airways increase the absolute humidity of inhaled air from 17 g/m3 at 20°C to 44 g/m3 at 37°C, an increase of 27 g/m3.