temperature monit
TRANSCRIPT
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TEMPERATURE
MONITORING
Moderator : Dr Raktima Anand
Presenter : Dr Prashanth S
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Terms
Normal regulation
Indications
Monitoring sites
Technologies
Guidelines
Overview
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CORE BODY TEMPERATURE
Well perfused tissues
Uniform temperature
2 to 4 degrees warmer
Trunk,Head, CNS
PERIPHERAL BODYTEMPERATURE
Variable perfusion
Varies with Environment,Core,Vasomotion
Cooler
Arms and Legs
Core temperature, although by no means completelycharacterizing body heat content and distribution, is the bestsingle indicator of thermal status in humans.
TERMS
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Threshold temperatureCentral temperature that elicits a regulating effect, e.g., vasoconstriction,vasodilatation, shivering, sweating, nonshivering thermogenesis
Inter threshold rangeTemperature range over which no regulatory response occurs
Mean body temperature
Physiologically weighted average temperature from various tissues
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Nonshivering thermogenesisHeat production (above basal metabolism) not associated withmuscle activity
Shivering thermogenesisHeat production through voluntary muscle activity
Dietar y thermogenesisHeat production through metabolism of nutrients
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PHYSIOLOGY OF
THERMOREGULATION
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1.C
onduction 3% 2.Evaporation 24% 3.C
onvection 34% 4. Radiation 39%
MECHANISMS OF HEAT LOSS
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Afferent input
Central Response
Thresholds
Efferent Response
THERMOREGULATION
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To quantify hypo or hyperthermia, detectmalignant hyperthermia
Patient is deliberately cooled or warmedPediatric surgeryInfusion of large volume of iv fluids or blood
WHY SHOULD WE MONITOR?
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1st phase: shortly after induction core temp. dec. by 0.5-1c- vasodilation inc. heat loss-metabolic heat prodn. remains constt.-redistribution
2nd phase: heat loss> metabolic heat prodn.
3rd phase: plateau
- thermal steady state- centrally impaired- prevented by nerve blocks
HEAT LOSS UNDERGENERAL ANAESTHESIA
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CHANGES DURING ANAESTHESIA
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NEURAXI AL ANESTHESI A
Vasoconstriction and shivering thresholds reducedR
esponse intensity is half normalBehavioral thermoregulation impaired
³ shivering patient who denies feeling cold´
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Myocardial ischemia:-postop. Shivering-inc. oxygen consumption-ischemia??
-cardiac irritability & ventricular arrhythmias
Coagulopathy:fall in core temperature by 1.3°C increases blood loss by30%
-increased incidence of allogenic blood transfusion-impaired platelet function-impaired clotting factor enzyme function
Complications due to
Hypothermia
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Wound infections & healingThermoregulatory vasoconstriction dec. oxygendelivery
Impairs immune function
-T cell mediated antibody function
-neutrophil function
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Pharmacokinetics & pharmacodynamics :
-Duration of action of muscle relaxants -Core hypothermia per se Twitch strength by 10-15%
-MAC of volatile anaesthetics by 5%/ c
Recovery duration & thermal discomfort:- solubility of volatile anesthetics & dec. metabolism of iv-prolongs emergence
BENEFIT:
Potection against ischemia and hypoxia
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CORE TEMPERATURE
1. Pulmonary artery cathetersConsidered gold standardIncorporated thermocouple or thermistor Special considerations in Cardiac Bypass
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2. Esophageal temperature
Can be placed into esophageal stethoscopesThermistor or thermocouple
3. Nasopharyngeal temperatureCan be measured with an esophageal probe
positioned above the palateReasonably close to brain and core temperature.
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1. Bladder temperature
Measured with a Foley catheter with an attachedthermistor or thermocouple. Accuracy decreases with low urine output
and during surgical procedures of the lower abdomen
NEAR CORE TEMPERATURESITES
2. Rectal temperatureReadings affected by the presence of stool and of bacteria that
generate heat
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3. Oral temperatureEasily accessible, acceptable to patientsInaccurate in mouth breathers,ingestion of hot or cold fluids
4. Axillary temperature
Probe should overlie axillary artery Acceptable to awake patients
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Skin-temperature
Confounded by Core-to-peripheral redistribution andvasomotion Ambient temperature
Used in Neuromuscular monitoring
Temporal artery thermometersUse infra red waves at approximately 10 Hz
Presumption that temporal artery correlateswith core temperatureInaccurate for clinical use
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Technologies
Thermistor - composed of a metal oxide sintered into a wire / fused into a rod/bead .- needs a source of current and a means to measure that current.- Resistance and temperature inversely proportional
- Advantages : small size,rapid response time,continuous readings,sensitivity to small changesInexpensive.Interchangeable and disposable.
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THERMOC
OUPLE:
- electrical circuit with 2 dissimilar metals welded together - 1 of the two metal junctions at a constant temperature- Voltage difference measured and converted to a reading.- Advantages : accuracy
small size,rapid response time,continuous readings,Stability,Inexpensive, disposable.
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Platinum Wire
- Electrical resistance varies almost linearly with temperature.- Resistance is measured in a manner similar to a thermistor.- Accurate ,gives continuous readings.- Probes interchangeable
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Liquid Crystal
- organic compounds in thermal transformation from a solid to aliquid state pass through an intermediate phase that exhibitsanisotropic properties .- Flexible adhesive backing with plastic-encased crystals.- Safe, convenient, noninvasive, easy to apply and read,
disposable, nonirritating, and inexpensive, give fast, continuousreadings .- Disadvantages of liquid crystal thermometers include the needfor subjective observer interpretation ,reduced accuracy.
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Infrared thermometers
- measurement of a portion of the infrared radiation from surfaces.- Otoscopelike probe with disposable probe covers- The probe placed firmly as far as possible into the ear canal.- Good patient compliance,no trauma, rapid measurement
- Often used in the postanesthesia care units , critical care areas.- Poor penetration, improper aiming, and obstructions, intermittent.- Not useful for monitoring in the operating room.
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Damage to monitoring sites
Burns
Incorrect information
Hazards of thermometry
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GUIDELINES
GA for>30 minRegional anaesthesia when changes in body
temp. are intended or anticipatedUnless hypothermia indicated, maintain coretemp. >36c