Week 2 - Temp Flashcards
What is temperature? What is heat? How do they differ?
temp: measurement of the thermal state of an object
heat: thermal energy
Temperature is the quantitative measurement of that energy.
How does increasing heat tend to increase entropy?
Entropy is the universe’s trend to equilibrate things. It is the unidirectional movement of energy from high concentrations to lower concentrations.
Heat and energy are the same. Heat loss (energy loss) is unidirectional from higher concentrations to lower concentrations or from hotter to colder.
Increasing heat would increase entropy because it would cause a larger gradient.
How do manometers work?
The manometer balances the pressure to be measured against the pressure exerted by a vertical column of liquid of known density, for example, mercury and water.
By what methods do patients lose heat?
radiation
convection
conduction
evaporation
What is radiation?
the transfer of heat energy by emission of infra-red radiation to the surrounding walls, equipment, floor, etc
What is convection?
the transfer of thermal energy by heating air adjacent to the skin, it increases kinetic energy, expands, becoming less dense and then carrying that heat away
(Shore’s example: you’re in a cold pool. if you stay in one spot, you eventually get warm. then you move away and you get cold again since the warm water around you was replaced by cold water)
What is conduction?
heat loss by direct contact with less hot substances
What is evaporation?
the loss of heat of vaporization of moisture on the skin
(This is limited by the gradient of skin H2O to the atmospheric H2O difference. Sweating increases the gradient and thus increases heat loss)
By which method is the majority of heat lost? By which method is the least amount of heat lost?
most - radiation
least - evaporation
(however, burn patients are more susceptible to evaporative heat loss)
When does the greatest amount of heat loss in the operating room occur?
in the first hour
due to vasodilation from VAA
What are some ways to prevent heat loss in the operating room?
blankets on their body or on their head
bair hugger
lower carrier gas flows and use of in-line humidification to decrease evaporation
What is the humidity at saturation in the alveoli? (worded strangely, but this was in the study guide)
By passing through the vascular nasal passages, inhaled air is warmed, filtered, and reaches near 100% relative humidity
What is the partial pressure of H2O vapor in the alveoli?
47mmHg
Inhaled air has a low partial pressure of H2O (3.7mmHg) but as it is warmed and humidified, this value increases to 47mmHg
What is the percent of atmospheric pressure of water vapor in the alveoli?
At the alveoli, the PP of water is 47 mmHg.
47 So, ------ = 0.0618 or 6.18% 760
How do spontaneous breathing patients humidify respiratory gases?
Simple: Spontaneous breathing patients breathe through the nose, circulating air humidifying the air.
(More Complex Anesthesia School Answer: In the nose we have sebaceous glands and coarse hairs, also known as vibrissae. Thanks to these guys, the mucus producing epithelium of the nose, and the rich arterial supply of the nose, a variety of functions can occur in the nose including filtration, humidification, and heating of inspired air. As long as air isn’t terribly cold, the nose can warm it to nearly body temperature and moisten air to nearly 100% relative humidity. (Remember, relative humidity is the percent of humidity in partial pressure compared to the maximum air can be humidified at a certain temperature. )
How do we humidify gases for mechanically ventilated patients?
HME- heat and moisture exchanger humidifiers
heated water vaporizers and humidifiers are used to deliver a relative humidity higher than that delivered by HME
What is the ideal humidity in the operating room?
Back in the day, Ether was very flammable and static electricity could ignite a flame. So humidity used to be set at 50%. However, since this is no longer really a concern, it’s followed less.
What instrument measures humidity?
a hygrometer
What is latent heat of vaporization?
“Latent heat vaporization is the amount of heat energy per unit mass required to convert a liquid into the vapor phase.”
600 calories (2500 joules) is withdrawn from the environment to convert 1gm of H2O into vapor.
Example: cleaning skin with alcohol, iodine or chlorhexadine gluconate.
What is the formula to convert degrees F to degrees C?
F = 1.8 (C) + 32
or
9
F = —- (C) + 32
5
What is the formula to convert degrees C to Kelvin?
K = C + 273.15
Heat is a product of what?
metabolism
Metabolic rate increases by how much for each 1 degree C increase?
6 - 7 % / each degree C
Cardiac output increases by how much for each 1 degree C increase?
3 L/min / each degree C
Shivering can increase oxygen consumption by how much?
400 - 500 %
Which reaction takes heat to run the reaction: endothermic or exothermic?
an endothermic reaction
Which reaction creates heat during a reaction: endothermic or exothermic?
an exothermic reaction
Define absolute humidity.
the mass of water vapor in a given volume of air (measured in grams)
Define relative humidity.
the ratio of the mass of water vapor in a given volume of air to the mass required to saturate that given volume of air at the same temp.
mass of water vapor = ----------------------------------- mass necessary for saturation
(any number greater than 1 = condensation)
(ie. cold air has less saturation, hot air can hold more saturation)
Fully saturated air at 37 degrees C contains how much water vapor?
44 mg/L
