Temperature and humidity Flashcards
Specific heat capacity:
the amount of heat required to raise the temperature of a unit mass of substance by 1K (J/Kg/K)
What is temperature?
property of a substance that determines whether it will transfer or receive heat to/from another substance. Heat energy will flow from an object of high temperature to one of low temperature
WHat is the triple point?
Triple point is the temperature and pressure at which the solid, liquid and gas phases of a substance exist in equilibrium (for H2O 273.16 K – 0.01°C, 611.2 Pa
What are STP?
0 degrees c (273.15K) 101.3kpa (760mmHg)
What is critical temperature
The temperature above which a vapour cannot be liquefied by any amount of pressure
What is latent heat
is the energy required to change the state of a substance without changing its temperature. It provides the energy needed to break the bonds holding the substance together.
Differences between mercury and alcohol in liquid expansion thermometers?
Alcohol better at low temps as mercury solidifies at -39
Alcohol less toxic + cheaper
Mercury better at high temps (alcohol boils at 78.5 degrees)
Adv/disadv of liquid expansion thermometers?
Adv:
Cheap, reliable, no power supply
Disadv- takes minutes to equiilibrate, non disposable, risk of break
How is heat lost from the body during anaesthesia
Radiation (40%)
COnvection 30%
Evaporation 20%
Conduction <5
10% is lost via respiration- heating of air + latent heat of vapourisation to humidify
Why is heat producition reduced duing anaesthesia ?
Peripheral mechanisms- reduced movement, less ability to shiver
Central mechanisms- drugs depress hypothalamic function so thermoregulatory responses are not initiated until a much lower temperature
Effects of hypothermia by system
CVS- reduced CO, increased blood viscositiy, vasoconstriction, J waves, arrhythmias
Resp- Left shift of curve, reduced O2 demand/CO2 production
Neuro- confusion/coma
ANaesthesia- less volatile needed, prolongs NMB
Other- acidosis, coagulopathy, diuresis, reduced emtabolic demand
Shivering post op can increase oxygen consumption by a factor of 10
Hiigh risk of hypothermia?
ASA 2 +
Low temp to start
combined ga/ra
intermediate/major surgery
risk of CVS complications
NICE guidelines for needing active warming?
FAWB if high risk or longer than 30mins, measure every 30 mins, fluids >500ml should be warmed
ABso;lute humidity
The mass of water vapour present per unit volume of gas at a given temp and pressure (mg/L or kg/m3
Relative humidity
Absolute humidity/the SVP of water at that temp, or,
The ratio of the mass of water vapour in a given volume of air compared with the mass that would be required to saturate that given volume of air at the same temp.
Dew point?
The temperature at which the relative humidity of the air exceeds 100% and water condenses out of the vapour phase to form liquid.
What is a hygrometer
MEasures humidity
What is hygroscopic material?
A material that attracts moisture from the atmosphere
Hair hygrometer uses
Simple measure of relative humidity btw 30-90%
Time lag of 5 minutes
HOw much water in air at 20 degrees
17g/m3
HOw much water can be held in the trachea at 34 degrees
34g/m3
How much water can be held by air at body temp 37degerres?
44g/m3
Methods of humidifying gases from least to most efficient?
Cold water bath
HME
Hot water bath
Bernoulli neb
Ultrasonic neb
Where are different sizes of nebuliser drop deposited?
20um- URT
2-5um- tracheobronchial tree
1um- alveloli (may impair gas exchange)
Smaller than this they are just exhaled again
WHat are the sizes of connector on HME filter?
15mm/22mm
Increase in resistance to flow by HME ?
0.1-0.2cmH20
abs humidity acheived by soda lime?
29mg/L
HOw much relative humidity can HME acheive?
60-70%
Most accurate hygrometer?
REganults
