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63 Cards in this Set

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  • Back
What does Poikermothermic mean?
Taking on the temperature of the environment
Ex. Reptiles (Humans act like reptiles under anesthesia.
What is the normal range for human temperature in humans?
36-38 C
Heat production =
heat loss
Energy is released in the cells by
It is used for work or stored as ATP
The % of energy released by oxidation of food appears in body as heat
How is heat spread throughout the all tissues
By the blood
Hyperthermia: What are possible causes?
Infections, Damage to hypothalmus, Malignant Hyperthermia (rxn to anesthesia r/t to Ca+ levels)
Hypothermia: What are possible causes?
Surgery, cold irrigating fluids, CABG induced
Mechanisms for heat loss during Anesthesia:
1) Gen Anesth depresses thermoregulatory center
2) Both Gen + Reg Anesth cause Periph Vasodilation
3) Surgery: Inc area of pt exposed
4) Cold gases
5) Cold IV Fluids
Circadian Rhythms: Varies temperature by
+/- 0.5 C (37C +/- .5)
Lowest in the AM
Highest in the PM
Menstrual Cycle +/- 0.5 C: When is it the highest?
Highest the 2nd 1/2 of the cycle
Shell of the body is normally at what temp?
What is the function of the intermediate zone in relation to maintaining body temp?
Keeps the core temp at 37C (lies in bet shell & Core)
What is the normal Core temp?
The balance between heat production and loss?
Heat = Metabolic Rate
What is the mechansim for offloading heat?
What are the effects of major shivering?
Inc Energy & O2 requirement (02 by 500%)
Conduction: What is a good conductor of heat?
Substances that heat is easily passed through (metals & crystals) Hold a metal rod in your hand it feels cold because heat from hand is conducted to the cool metal object.
A substance that prevents movement of heat are
Poor conductors & good insulators
Where does heat transfer occur?
Between regions of different temps, from higher to low temp.
Materials in contact with the body act by?
Conducting heat away from the skin.
Air is a _____ conductor of heat
Poor. Layer of air bet clothing and skin acts as an insulator. (ex. several layers more effective than one have layer due to air trapping in each layer)
Objects that emit energy in form of electromagnetic
How much heat is lost by an uncovered body due to radiation?
Heat travels by
waves, no substance is needed to travel.
The amount of heat radiated from the skin is dependent upon ______ of skin blood vessels
dilation, More dilation
-> = more heat lost to radiation
Heat transfer by radiation depends upon _______ waves like light, infrared and UV
Electromagnetic (the warmth of the sun)
Evaporation: Insensible water loss
heat lost constantly by evaporation (water diffuses up from deep layers of the skin to the surface -> evaporates.
Sweating, how effective is it in heat loss
Inc heat loss by 10 Fold. Effective cooling agent sm amt of water takes a large amount of heat to evaporate.
Routes of Heat loss
Radiation: 40-70%
Respiration: 10% (8% to humidify, 2% to warm)
Convection: 30% (subsumes conduction)
Evaporation: 20% (open wounds)
Ways to prevent heat loss: by respiration
Ways to prevent heat loss: by
Keep covered as long as possible
Drape as soon as possible
Ways to prevent heat loss: by
Surgical hat on Pt
How does fat act as an insulator?
Limits conduction from the core -> skin and only allows losses to come from skin.
If the temp outside =15C
and the skin temp is 25C, the core temp is 37C What is the response of the blood vessels?
If the temp outside =25C
and the skin temp is 35C, the core temp is 37C What is the response of the blood vessels?
Hypothermia: For 1C dec in temp, metabolism dec by
Hypothermia: If temp goes from 37-30 there is a ___% dec in O2 consumption
50% (Used in CABG to be neuro protective)
What is the most frequent cause of delayed awakening in anesthesia?
Hypothermia causes other effects in the body in relation to anesthesia
Dec in liver blood flow (dec drug metab, difficult to reverse)
Increase solubility of gas in blood
Body's response to cold
vasoconstriction skin vessels (dec blood flow to skin dec loss by convection)
Shiver- (contractions of muscles to convert energy to heat and mech energy)
Piloerection- (hairs caputure layer of air = insulator)
SNS stimulation- (cells inc heat production)
Body's response to hot
Vasodilation of skin vessels (inc rate of heat transfer to skin 8x)
Heat loss w/ gen anesthesia: Phase one
-Rapid dec in temp 1.5C in 1st hour
-Redistribute blood and heat to the core
(takes 30 min of convetive blankets to inc temp to 38C
Heat loss w/ gen anesthesia: Phase Two (Period of Poikilothermia)
Lose of .5C per hr for 3-4hr until 34.5 (passive dec temp toward ambient temp)
Heat loss w/ gen anesthesia: Phase Three
Below 34C
Active thermoregulation resumes
Vasoconstriction dec heat loss 25%
Temp Measurement
Temp scales (non electric)
Electrical Methods
Clincial aspects
What how is temp measured in a convention mercury containing theromometer?
Heat causes mercury to expand and it rises
What are the freezing pt's in all three temperature scales?
Freezing Pt= 0C, 32F, 273.15K
What are the boiling pt's in all three temperature scales?
Boiling pt: Vapor press= atmospheric pressure
100C, 212F, 373.15K
Temperature Scales
To convert to Kelvins
K = C + 273
Temperature Scales
To convert to F
C x 9/5 + 32 = F
(37 x 9/5 + 32 =98.6 F
9/5 = 1.8
F = (C X 1.8) + 32
Temperature Scales
To convert to C
(F-32) x 5/9 = C
(96.6 - 32) x 5/9 = 37C

C = (F-32)/ 1.8
Thermal expansion
Semiconductors are
Metals that have properties in conducting electricity better when hotter. (used in thermometers (thermistors), PA Cath an example of thermistor)
Mecrury Thermometer: how does it work
-Bulb & Narrow tube
-Glass wall allows heat to pass
-tube is calibrated
-Constriction above bulb of mercury prevents mercury from receding when removed from pt.
Resistance formula
Rt= Ro + RoaT
Electrical measures of temp
Resistance thermometers (metal heats resistance to electrical current)
Electrical Measurements of Heat: Thermocouple
Using two wires of diff metal
-The temperatures at each wire unconnected ends are the same.
- Heat the place where the two wires are joined = a tiny voltage, proportional to the diff of temperature at the junction and the reference temp.
Putting many thermocouples together is called
a thermopile
Thermistors and temperature measurement
Thermistors are metals that change elec resist w/ gain or lose of heat
-can be placed in body cavity
-heat travels to the termistor and it heats up
- temp rises -> resist falls
-resistance is the measure of temp
-Reach thermo equilib quick and accurate measure temp.
Liquid crystal probes
coiled stacks of lengthy molecules that twist and untwist in relation to temp.
-crystals heat r/t conduction of heat from body
-Colors of different patches of crystals changes
-cheap, ??accuracy
Liquid crystal probes measurement what form of temp
skin temp only (not the same as core)
Infared tympanic memb temp
-measures infrared radiation from tympanic memb. (site chosen due to prox of ICarotid)
-Sensor grp of thermocouples
-exposed to radiation of TM
-heats up thermopile->voltage prop to diff bet reference juction and the measuring junction temp.
Infared tympanic memb temp
Must direct at TM otherwise get temp of bone and other parts of ear.