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63 Cards in this Set
- Front
- Back
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What does Poikermothermic mean?
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Taking on the temperature of the environment
Ex. Reptiles (Humans act like reptiles under anesthesia. |
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What is the normal range for human temperature in humans?
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36-38 C
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Heat production =
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heat loss
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Energy is released in the cells by
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oxidation
It is used for work or stored as ATP |
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The % of energy released by oxidation of food appears in body as heat
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90%
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How is heat spread throughout the all tissues
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By the blood
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Hyperthermia: What are possible causes?
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Infections, Damage to hypothalmus, Malignant Hyperthermia (rxn to anesthesia r/t to Ca+ levels)
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Hypothermia: What are possible causes?
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Surgery, cold irrigating fluids, CABG induced
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Mechanisms for heat loss during Anesthesia:
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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 |
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Circadian Rhythms: Varies temperature by
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+/- 0.5 C (37C +/- .5)
Lowest in the AM Highest in the PM |
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Menstrual Cycle +/- 0.5 C: When is it the highest?
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Highest the 2nd 1/2 of the cycle
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Shell of the body is normally at what temp?
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32-35C
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What is the function of the intermediate zone in relation to maintaining body temp?
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Keeps the core temp at 37C (lies in bet shell & Core)
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What is the normal Core temp?
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37C
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The balance between heat production and loss?
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Heat = Metabolic Rate
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What is the mechansim for offloading heat?
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Shivering
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What are the effects of major shivering?
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Inc Energy & O2 requirement (02 by 500%)
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Conduction: What is a good conductor of heat?
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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.
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A substance that prevents movement of heat are
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Poor conductors & good insulators
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Where does heat transfer occur?
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Between regions of different temps, from higher to low temp.
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Materials in contact with the body act by?
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Conducting heat away from the skin.
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Air is a _____ conductor of heat
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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)
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Objects that emit energy in form of electromagnetic
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Radiation
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How much heat is lost by an uncovered body due to radiation?
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40-70%
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Heat travels by
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waves, no substance is needed to travel.
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The amount of heat radiated from the skin is dependent upon ______ of skin blood vessels
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dilation, More dilation
-> = more heat lost to radiation |
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Heat transfer by radiation depends upon _______ waves like light, infrared and UV
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Electromagnetic (the warmth of the sun)
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Evaporation: Insensible water loss
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heat lost constantly by evaporation (water diffuses up from deep layers of the skin to the surface -> evaporates.
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Sweating, how effective is it in heat loss
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Inc heat loss by 10 Fold. Effective cooling agent sm amt of water takes a large amount of heat to evaporate.
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Routes of Heat loss
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Radiation: 40-70%
Respiration: 10% (8% to humidify, 2% to warm) Convection: 30% (subsumes conduction) Evaporation: 20% (open wounds) |
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Ways to prevent heat loss: by respiration
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Humidifier
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Ways to prevent heat loss: by
Conduction |
Keep covered as long as possible
Drape as soon as possible |
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Ways to prevent heat loss: by
Radiation |
Surgical hat on Pt
Blankets |
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How does fat act as an insulator?
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Limits conduction from the core -> skin and only allows losses to come from skin.
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If the temp outside =15C
and the skin temp is 25C, the core temp is 37C What is the response of the blood vessels? |
Vasoconstriction
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If the temp outside =25C
and the skin temp is 35C, the core temp is 37C What is the response of the blood vessels? |
Vasodialation
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Hypothermia: For 1C dec in temp, metabolism dec by
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7%
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Hypothermia: If temp goes from 37-30 there is a ___% dec in O2 consumption
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50% (Used in CABG to be neuro protective)
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What is the most frequent cause of delayed awakening in anesthesia?
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Hypothermia:
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Hypothermia causes other effects in the body in relation to anesthesia
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Dec in liver blood flow (dec drug metab, difficult to reverse)
Increase solubility of gas in blood |
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Body's response to cold
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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) |
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Body's response to hot
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Vasodilation of skin vessels (inc rate of heat transfer to skin 8x)
Sweating |
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Heat loss w/ gen anesthesia: Phase one
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-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 |
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Heat loss w/ gen anesthesia: Phase Two (Period of Poikilothermia)
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Lose of .5C per hr for 3-4hr until 34.5 (passive dec temp toward ambient temp)
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Heat loss w/ gen anesthesia: Phase Three
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Below 34C
Active thermoregulation resumes Vasoconstriction dec heat loss 25% |
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Temp Measurement
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Temp scales (non electric)
Electrical Methods Clincial aspects |
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What how is temp measured in a convention mercury containing theromometer?
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Heat causes mercury to expand and it rises
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What are the freezing pt's in all three temperature scales?
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Freezing Pt= 0C, 32F, 273.15K
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What are the boiling pt's in all three temperature scales?
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Boiling pt: Vapor press= atmospheric pressure
100C, 212F, 373.15K |
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Temperature Scales
To convert to Kelvins |
K = C + 273
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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 |
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Temperature Scales
To convert to C |
(F-32) x 5/9 = C
(96.6 - 32) x 5/9 = 37C C = (F-32)/ 1.8 |
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Thermal expansion
Semiconductors are |
Metals that have properties in conducting electricity better when hotter. (used in thermometers (thermistors), PA Cath an example of thermistor)
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Mecrury Thermometer: how does it work
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-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. |
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Resistance formula
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Rt= Ro + RoaT
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Electrical measures of temp
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Resistance thermometers (metal heats resistance to electrical current)
-Thermister -Thermocouple |
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Electrical Measurements of Heat: Thermocouple
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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. |
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Putting many thermocouples together is called
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a thermopile
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Thermistors and temperature measurement
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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. |
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Liquid crystal probes
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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 |
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Liquid crystal probes measurement what form of temp
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skin temp only (not the same as core)
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Infared tympanic memb temp
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-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. |
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Infared tympanic memb temp
Advantange/disadvantage |
Must direct at TM otherwise get temp of bone and other parts of ear.
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