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Principles I Test 4

Hypothermia

QuestionAnswer
Define thermolysis. Loss of heat (how patients loose heat in the OR)
What are the four major components of thermolysis? conduction, evaporation, radiation, convection
Define thermogenesis. creating heat (how patients generate heat in the OR)
What are the 4 major components of thermogenesis? non-shivering, shivering, diet induced, basal metabolic rate
What type of signals do C fibers carry? unmyelinated fibers that carry warm temperature signals and dull pain signals
What type of signals do A Delta fibers carry? myelinated fibers that carry cold temperature signals and sharp pain signals
When the perception of pain in blocked with anesthetic agents, the ability to perceive __________ is also blocked hot and cold (temperature)
What is the path of both the C and A Delta fibers? they both sense temperature information from thermally sensitive cells, their signal travels through either the C or A Delta fiber to the substantia gelatinosa of the spinal cord to the hypothalamus
What is the major temperature regulating center of the brain? the hypothalamus
What is the body's first and most consistent response to hypothermia? Is it metabolically costly or energy efficient? vasoconstriction; energy efficient when compared to shivering
How much can vasoconstriction decrease heat loss? by 25 - 50%
This method of heat conservation is inefficient and does not occur in newborns and premature infants. shivering
Shivering can cause a _______ increase in whole-body O2 consumption. 2 - 5 fold
What is the most important insulator against heat loss? intact skin
Basal metabolic rate peaks at age 2. For every 1 degree Fahrenheit change in body temperature, BMR changes by _____ 7% (increases if body temp increases, decreases if body temp decreases)
This doubles the heat production in infants, but increases heat production only slightly in adults. Non shivering thermogenesis
How does non shivering thermogenesis work? ANS fibers (beta receptors) innervate brown fat found predominately in infants (located in scapula, neck, back, viscera); lipolysis is stimulated with temperature decrease which causes heat release
What is the temperature range for normothermia? > 36 Celsius (96.8 F)
What is the temperature range for mild hypothermia? 34 - 35.9 Celsius
What is the temperature range for moderate hypothermia? 32 - 33.9 Celsius
What is the temperature range for severe hypothermia? < 32 Celsius
What is the major contributing type of heat loss in both the awake and anesthetized patient? radiation
Define radiation. electromagnetic heat waves emanate from all surfaces; an increased rate of radiation occurs when temperatures of the body are higher than surrounding air temperature
Define convection. loss of heat to air currents; normally, hair on our bodies traps air in on the surface layer of the skin and counters convection forces
What 2 methods of heat loss do forced air convection units, like the Bair Hugger device, combat? heat loss from both radiation and convection
In the OR, radiation and convection account for what percentage of total heat loss in the anesthetized patient? 70%
Define evaporation. loss of heat via water loss from the skin and mucous membranes
Though sweating during general anesthesia is rare, evaporation heat loss from the anesthetized patient in the OR can occur. How? heat loss from open surgical wounds or burn wounds; this is a significant source of heat loss in children (r/t large BSA) and burn patients
Define conduction. the transfer of heat between two adjacent surfaces (unlike radiation, the surfaces must be touching)
Why is conduction heat loss typically negligible in the anesthetized patient in the OR? because patients directly contact only the foam pad, which is a great thermal insulator
Why does a patient become poikilothermic during surgery? anesthesia increases the internal temperature threshold range about 20 fold, meaning thermoregulatory defenses are not triggered
How long does Phase I of heat loss during anesthesia last and what occurs during this phase? 1 hour; steep drop in temperature (~1-2 C) due to redistribution of core temperature to periphery (vasodilation)
What occurs during Phase II of heat loss during anesthesia and how long does it last? gradual decline of temperature (~0.5-1 C) over the next 2 to 3 hours due to heat loss to the environment exceeding heat production
What occurs during Phase III of heat loss during anesthesia and how long does it last? occurrence of a steady state after about 4 hours where heat loss matches heat production
______________ is a standard of care in pediatric anesthesia and should be monitored in all pediatric cases. Temperature monitoring; axillary is usually sufficient, rectal or esophageal for big cases
What are some important methods of heat loss prevention in pediatric cases? adjust room temp > 24 Celsius, overhead radiant heaters, forced air warming devices, heating blankets, keep neonates in incubator, keep the head covered, warm fluids, warm skin prep solution, dry off excess skin prep solution
What are 3 consequences of post-op shivering? increased O2 consumption by as much as 5x, increased ICP, increased IOP
Hypothermia _________ blood loss and need for transfusions. increases
Cold induced defect in platelet function is seen as a significant effect at what temperature? < 34 Celsius
Hypothermia _______ the incidence of morbid cardiac outcomes. triples
Hypothermia _______ the incidence of surgical wound infections and delays wound healing. triples
What type of EKG change is seen in 80% of adult and teenage patients whose body temperature dips below 35 Celsius? J wave (Osborn wave)
What does the J wave (Osborn wave) seen on an EKG represent? it is a deflection at the J point in the same direction as the QRS complex that represents an inter ventricular conduction defect
Other than J waves (Osborn waves), what are some EKG abnormalities seen in hypothermic patients? lengthened intervals (PR, RR, QRS, QT), sinus brady (babies mostly), heart block, v-fib
Hypothermia shifts the oxyhemoglobin dissociation curve to the ____. left
What account for the increased duration of drugs in hypothermic patients? most metabolic enzymes are temperature sensitive; also volatile anesthetic drugs are more soluble at colder body temperatures
The duration of vecuronium more than ________ with a 2 degrees Celsius reduction in temperature doubled
The duration of atracurium increased by ______ with a 2 degree Celsius reduction in temperature 60%
MAC decreases ____ for every 1 degree Celsius decrease in temperature 5%
What percentage of heat loss is from extremities? 60%
What percentage of heat loss is from the thorax/abdomen? 20%
What percentage of heat is lost from the head? 10%
What percentage of heat is lost from the respiratory tract? 10%
Cutaneous heat loss is directly proportional to ______________ surface area
True or False: the areas of skin that are covered are more important than the total amount of skin covered. False! the amount of skin covered is more important than which surfaces are covered
Blankets provide passive insulation to skin surface. A single layer of blanket reduced heat loss by _____ 30%
A single layer blanket re-warms the body at what rate? 1.5 C/hour
A Bair Hugger or other warmed forced air device rewarms at what rate? 2.5 C/hour
What should the OR temperature be (ideally) to prevent heat loss? > 72 F (23 C) for adults and > 26 C for infants
At a room temperature less than ____ all anesthetized patients become hypothermic 70 F
Why would an inhalation induction conserve body heat more than an IV induction? IV induction agents cause massive vasodilation which means heat loss; though volatiles also can cause vasodilation, IV anesthetics are worse
Hypothermia decreases cerebral metabolic rate by ___ and cerebral blood flow by ___ for each 1 C drop in temperature. 8%; 7%
______________ is more difficult to trigger and less severe in patients kept slightly hypothermic. malignant hyperthermia
Reduced core temperature is recommended for surgeries where tissue ischemia can be anticipated. What are some of these surgeries? carotid surgery, neurosurgery, patients with traumatic brain injury, cardiac bypass surgery
Created by: Mary Beth