Temperature Monit

8/8/2019 Temperature Monit

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TEMPERATURE

MONITORING

Moderator : Dr Raktima Anand

Presenter : Dr Prashanth S



Terms

Normal regulation

Indications

Monitoring sites

Technologies

Guidelines

Overview



TERMS



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



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



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



PHYSIOLOGY OF

THERMOREGULATION



THERMAL PATHWAY



1.C

onduction 3% 2.Evaporation 24% 3.C

onvection 34% 4. Radiation 39%

MECHANISMS OF HEAT LOSS



Afferent input

Central Response

Thresholds

Efferent Response

THERMOREGULATION



INDIC ATIONS



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?





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





CHANGES DURING ANAESTHESIA



NEURAXI AL ANESTHESI A

Vasoconstriction and shivering thresholds reducedR

esponse intensity is half normalBehavioral thermoregulation impaired

³ shivering patient who denies feeling cold´



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



Wound infections & healingThermoregulatory vasoconstriction dec. oxygendelivery

Impairs immune function

-T cell mediated antibody function

-neutrophil function



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



MONITORINGSITES



CORE TEMPERATURE

1. Pulmonary artery cathetersConsidered gold standardIncorporated thermocouple or thermistor Special considerations in Cardiac Bypass



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.





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



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



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



TECHNOLOGIES



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.



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.



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



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.



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.



Damage to monitoring sites

Burns

Incorrect information

Hazards of thermometry



GUIDELINES

GA for>30 minRegional anaesthesia when changes in body

temp. are intended or anticipatedUnless hypothermia indicated, maintain coretemp. >36c



Temperature Monit

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