Temperature Monitoring Flashcards
Benefits of Warm Patients
- reduced wound infections
- reduced blood loss
- reduced cardiac events
- shortened hospital stays
- warming recoginzed as a standard of care by Medicare and SCIP
Dominant Thermoregulatory Site in Humans
- hypothalamus
- thermal input from skin is secondary mechanism that is also important
Processing of Thermal Regulation
- afferent thermal sensing - many cells in the body are temp sensors
- central regulation - set point vs thermoregulatory model
- efferent responses - sweating, peripheral cutaneous vasoconstriction, brown fat metabolism
more elaborate mechanisms: shivering, BP, and osmotic control adaptation
Indications for Temp Monitoring
- large volumes of cold fluids administered
- deliberate cooling/warming of pt
- pediatrics
- pts w known temp regulatory problems (MH)
- major surgical procedures
AANA/ASA Temp Standard
- every pt should have temp monitoring when body temp changes are anticipated, intended, or expected.
- you can chart “warm blankets applied, pt stats that are comfortable, temp monitoring available” during MAC cases
Thermoregulation During GA
- pts under GA are unable to activate behavioral responses and must rely on autonomic defenses and external temperature management
37 C +/- 0.2 degrees is normothermia
All anesthetics ______ autonomic thermoregulatory control
All anesthetics impair autonomic thermoregulatory control
Propofol, Alfentanil, Precedex, Iso, and Des
- increase sweating threshold minimally, if at all
- these help preserve warm defenses for some time
Propofol, Alfentanil and Precedex
produce a significant DECREASE in vasoconstriction and shivering thresholds
Iso and Des
- decrease the cold response threshold only slightly
Thermoregulation During Neuraxial Anesthesia
- Central Temp Control: slightly impaired by neuraxial anesthesia
- autonomic impairment compounded by an impairment in awareness by the patient that they are becoming hypothermic
- misperception that since pt awake they are able to regulate their temp… if they are numb, they can’t tell they are cold!
Why is core temp not usually monitored with neuraxial?
Because the pt is awake and core temp requires swan ganz or throat temp.
Axilla temp probe often used
4 Etiologies of Shivering During Neuraxial Anesthesia
- shivering in response to core hypothermia
- shivering in normothermic/hyperthermic pts developing a fever
- direct stimulation of cold receptors in the neuraxis by the injected LA
- non-thermoregulatory muscular activity that resembles thermoregulatory shivering (can let it run its course rather than give demerol 12.5 - 25 mg IV)
US Temp Standards (2002)
- max contact surface temp shall not exceed 48 C
- Average contact surface temp shall not exceed 46 C during normal conditions (max bair hugger temp is 42)
4 Temp Technologies
- thermistor
- thermocouple
- liquid crystal
- infrared
Thermistor
- composed of metal oxide placed into a wire - Advantages: small size, rapid response size, continuous readings, probes are interchangeable and disposable
Thermocouple
- electrical circuit w 2 metals, one remains at constant temp, other is exposed to area where temp is being measured
- Advantages: accurate, small size, rapid response time, continuous readings, stability, and probe interchangability
Liquid Crystal
- consists of a flexible adhesive backing w plastic encased in liquid
Advantages: safe, convenient, noninvasive, easy to apply, disposable, inexpensive
Disadvantages: not accurate (subjective and relies on observer interpretation), difficulty w adhesion to skin if wet or oily
Infrared
electronic instrument, accurate
Tympanic thermometer not useful or available in OR
Average Temperature Loss
- 0.5 and 1.5 in the first 30 minutes then 0.5 to 1 degree C per hour afterwards.
- Usually no more than 2-3 degrees per hour
Core Temperature
- deep, vital internal organs
- uniform: varies between 35.7 and 37.8 C
- core temp should be monitored when significant changes in temp are expected
Periphery
- normal thermoregulatory vasoconstriciton maintains a temp gradient between the core and periphery of 2 to 4 degrees C
- skin and axillary temps
- X degrees in the periphery means they are 2-4 degrees higher in the core
Pulmonary Artery
- measured via PA cath
- thought to be the best method to monitor temp
- not reliable during thoracotomy or cardiopulmonary bypass due to no blood flow through heart and lungs and temp of cardioplegia solution (cold)
Esophagus
- temps vary up to 4 degrees depending on location within esophagus (temp probe is curved - insert to curve)
- probe should be in lower third or fourth of esophagus
Nasopharynx
- location close to hypothalamus
- some studies show correlation w core temp (?)
- easily accessible during surgery
- may cause epistaxis
Temp Monitoring Graphic
Methods of Heat Loss
radiation > convection > evaporation > conduction
burn pts lose heat via evaporation
Each 1 degree C decrease in temp = metabolism decreases by _____
7%
so keep burn patients WARM!
Skin and Heat Loss
skin supports, insulates, and protects against heat loss
Radiation
- loss of electromagnetic energy through infrared rays from the warm body to colder objects in the room that do not contact the body.
- typically accounts for 65-70% of body’s heat loss
Convection
- second major heat loss mechanism
- transfer of heat to an air current
- determined by temperature gradient between body and air as well as air velocity
- most of this occurs prior to draping (surgical drapes prevent most convective heat loss during surgery)
Conduction
- lost via direct contact between pt and colder objects such as OR table, linens, surgical instruments, skin prep materials, irrigation, and IV fluids
- heat flow is proportional to the temp difference between the body and the colder object
- little lost to OR table pad, significant loss to cold prep and irrigation/IV solutions
Evaporation
- occur from skin, respiratory tract, open wounds, pneumoperitoneum, or wet towels/drapes that are in direct contact w the patients body
High Risk Hypothermia Populations
- geriatrics
- pediatrics
- hypothyroid
- pts w hypothalamic lesions
- hypothermia is the most common temp related disorder during anesthesia
Forced Air Warming Devices AKA Convection Warming Devices
- entrain ambient air through microbial filter
- air is warmed w thermostat controlled electric heater
- air is then blown through hose attached to an inflatable pt blanket
Advantages to Forced Air Warmers
- safe, simple, effective
- inexpensive
- variety of blankets (reusable, disposable)
- more calories to cost than other warming devices
- fiberoptic laryngoscopes can be warmed using forced air warming devices
- OR table can be warmed preoperatively
- can also be used to cool pts
Disadvantages to Forced Air Warmers
- electric power requirements make it unsuitable for field use
- cumbersome to transfer or set up in CT
- may need to be removed to expose covered areas
- most don’t permit concurrent use of multiple blankets without additional units
- risk of increased infections (debatable)
- interference w BIS and DOA moitors
Controversial Topic Re: Bair Hugger
- some say it spreads germs, blows dust into surgical sites
- key point: don’t turn on bair hugger until drapes are up!
- altermative to bair hugger is HotDog Patient Warming System
Review of the Literature Re: Temp Monitoring and Perioperative Thermoregulation
- GA > impairment than neuraxial anesthesia
- prolonged anesthesia = HYPERthermia (cause unknown)
- hypothermia post cardiac arrest shows little benefit despite trend years ago
MH
- Diagnosis made with unexplained signs of pyrexia, or tachycardia, or cyanosis, or rigidity, or failure of masseter muscle to relax (trismus)
- Defect in sarcoplasmic reticulum of skeletal muscle
- SR fails to sequester Ca++ and sustained muscle contractions occur w increased metabolism
- Tx w Dantrolene which acts on SR to decrease the release of Ca++
- Triggers: sux and halogenated inhaled agents
S/S of MH
- elevation of CO2 (earliest sign, it will double or triple)
- sympathetic hyperactivity manifested as increased HR
- Trismus (masster muscle spasm) appears in 50% of pts
- whole body rigidity in 75%
- cyanosis, unsatble BP, dysrhythmias, hyperkalemia
MH Prep
- remove circuit and bellows
- flush machine w 100% 02 for 30 minutes
- call work room engineer Steve and he will provide you with “non-triggering machine” with no gas and tape over it
- no sux in room! TIVA is appropriate
MH High Risk Pops
- Duchennes MD
- Native Americans
- Peds
- Kids of parents w MH
