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Principles I Test 4
Hypothermia
| Question | Answer |
|---|---|
| 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
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