Thermoregulation Flashcards
Thermoregulation
Process of maintaining core body temperature at a near constant value
Normothermia
36.2-37.6 de reefs Celsius
97-100 F
Hypothermia
Less than 36.2 C
Mild-34-36C (93.2-96.8F)
Moderate- 30-34C (86-93F)
Severe- less than 30C (less than 86F)
Accidental- left out in cold, fall into river or lake, not wearing enough clothes
Therapeutic- decreased perfusion with MI or injury; kept in mild hypothermia to slow down body processes because they use less oxygen
Hyperthermia
Greater than 37.6 C
Body temp rises with unchanged hypothalamic set point
Natural ability to get rid of heat is impaired
Environment can be too hot
Genetic- malignant hyperthermia
Drugs can cause- narcotics, anything that increases metabolic rate (e.g., amphetamines), some antibiotics, antihistamines
Hyperpyrexia
Extremely high temperature greater than 41.5 C
Hypothalamus
Controls physiological adjustments
Uses the negative feedback loop to help regulate temperature
Fever
Increase in hypothalamic set point where the negative feedback loop works to cool the body down with a higher temperature
Infants and toddlers
Increased risk for hypothermia
Lack ability to conserve heat and immature body processes
Have large body surface area compared to mass which is also why they dehydrate faster
Decreased subcutaneous fat which acts as an insulator
Unable to correct changes/dependent on caregivers- cannot put on more clothes or take them off
Rule of thumb: have one more layer of clothing than what adults need. EX: if an adult has a sweatshirt on, the infant should have a t-shirt and a sweatshirt
Elderly
Risk for hyperthermia
Sweat glands decrease- decreased ability to perspire and use evaporation to cool selves
Reduced circulation can cause peripheral problems
Decreased vasoconstrictive response to cold- they can get cold faster as they continue to dilate esp. if they are on meds that cause vasodilation
Reduced shivering response as the muscles don’t respond as well and are cold more often
Slower metabolic rate- cold more often
Reduced perception of heat and cold so they may not recognize when they are cold or hot
Other populations at risk
Low socioeconomic status- if they cannot afford heat or cooling systems, warm clothing, etc.
Homeless- no protection from the elements
Risk factor: cognition
Dementia may cause inability to recognize if it’s too hot or too cold. They may wander out into the elements without wearing proper clothing.
Substance abuse- alcoholics who are drunk may not notice the changes from the elements.
Risk factor: health condition
CHF & DM patients have poor perfusion and a decreased ability to vasoconstrict or vasodilate, peripheral neuropathies where they are unable to feel the hot or cold as much
Traumatic brain injury- any injury to the hypothalamus can be chronically hot or cold
Poor nutritional status- if not maintaining glucose levels, can cause problems with heat or cold if glucose is not being used to cause shivering, etc.
Risk factor: genetics
Malignant hyperthermia
Risk factor: recreational or occupational exposure
Skiing or working in the cold, construction workers, running, exercising in the heat, etc.
How we gain heat
BMR
Muscular activity
Hormones (e.g., thyroid hormone)
Dietary-induced thermogenesis (we eat a lot, we get warm)
Postural changes (can gain heat by curling up into a ball which provides less surface area to lose heat)
Environment (external heat)
How we lose heat
Radiation
Conduction
Convection
Evaporation
Muscles
Respirations
Heat production and conservation
Produced through metabolic activity:
Ingestion and metabolism of food will create heat and keep us warm.
BMR- the higher the BMR, the warmer we typically are.
Amount of heat is dependent on amount of food, physical activity, and hormone levels. With physical activity, the more active we are, the more we create heat and normal hormone levels.
Chemical thermogenesis:
Epinephrine will make us warm and great more heat.
Conservation through peripheral vasoconstriction:
Heat is conserved through peripheral vasoconstriction; if I take my blood and stick it centrally in my body, I have less available at the surface and less available to lose heat. This makes vasoconstriction a good heat conserved.
Radiation heat loss
Electromagnetic waves that emit heat from the skin surface to the air
More skin exposed, the more heat lost
Vasoconstriction or dilation can help hold onto or lose heat by making blood readily available or pulling blood centrally
Conduction heat loss
Heat travels through something solid with direct contact
EX: our body sits on something cool, looses heat to cooler surface. This cools the body down. This is why we put a warming blanket down for older adults or put infants in a warmer- so they do not lose heat to the surface of the bed
Convection heat loss
Loss of heat by air currents
The flow of heat from the body surface to cooler surrounding air. Eliminate drafts such as windows or AC to reduce heat loss by convection
Naturally happens with the more exposed skin
Warm air (from skin) rises, will go away from our skin and cool air will enter and replace the warm air. This happens even without drafts. If there are drafts, heat loss by convection increases
Vasodilation heat loss
More convection can happen with this
Evaporation heat loss
Perspiration creates energy
When a liquid is converted into gas, it requires energy. It will take energy heat from the skin to cause evaporation. It produces cooling. We can promote that by using convection which increases evaporation rates.
Muscle activity heat loss
When the body itself is too hot, muscle tone will decrease
This decreases BMR and decreases our heat
This explains when it’s too hot, you feel tired and don’t feel like moving. Moving takes effort because the body is decreasing muscle tone.
Respiration heat loss
With ambient, cool air, this air is breathed in, the body warms it, used it for energy, then exhales the warm air which can cool our body
This only works if the ambient air is cooler than our body temperature
Temperature control
Hypothalamus and the negative feedback loop
Heat production and conservation with endocrine and sympathetic action: hypothalamic pituitary thyroid
Heat production with hypothermia
When thermoreceptors in the skin, spinal cord, and abdominal organs detect that our temperature is too low, heat production occurs
The hypothyroid stimulating hormone releasing hormone- the TSH, rh, and the hypothalamus sends the message to the pituitary which releases thyroid stimulating hormones which tells the thyroid gland to make T4 which goes to the kidney adrenal medulla to produce epinephrine. Epinephrine increases BMR starting with glycolysis (increase our glucose). This provides more energy to muscles to increase muscle tone, causing vasoconstriction to conserve heat, and increases muscle tone and shivering
Sympathetic nervous system: Cholinergic neural changes
Sweat glands
Heat loss by evaporation
Sympathetic nervous system: Alpha adrenergic neural changes
Blood vessels
Internal flow of heat from core to skin
Sympathetic nervous system: Beta adrenergic neural changes
Brown fat
Non-shivering thermogenesis in infants
Somatic nervous system: cholinergic neural changes
Skeletal muscle
Heat production by shivering
Hyperthermia consequences
Sweating leads to dehydration and sodium loss
Vasodilation: hypotension, tachycardia, decreased CO, coagulation due to thicker/viscous blood, CV collapse
Cerebral edema: CNS degeneration starts with confusion leading to seizures and stupor and leading to death
Renal necrosis r/t lack of perfusion
Hyperthermia exam
Vasodilation: flushed, red skin
Diaphoresis: clammy, sweating
Dehydration: dry skin, dry mucous membranes, decreased urine output, increased urine specific gravity, electrolyte imbalance (low sodium, high potassium- hemoconcentrated from sodium loss)
Neuro: confusion leading to stupor, coma, and death
Hyperthermia interventions
Remove clothing (cotton breathes better than polyester or synthetics)
Monitor CO with vasodilation and tachycardia
Hydrate with isotonic solution
Cool packs where arteries are closest to the surface allowing for more central cooling. Good locations: axilla, in the groin on top of the femoral arteries, behind the knees, sides of the neck. Don’t want too cold that it’s causing shivering because this will increase their temperature.
Gastric or colonic lavage in severe cases- run cold water through the stomach and through the rectum
When fever occurs
When microorganisms invade:
endogenous pyrogens are released into the bloodstream; these substances travel to the hypothalamus where they trigger the production and release of prostaglandins; prostaglandins initiate a fever response
Fever is typically a reaction to a microorganism. It is a therapeutic method by the body to attempt to kill microorganisms.
Leaving a temperature may help kill a virus faster.
Fever risks
Diminished immune response
Very young, very old
Adolescents who practice risky behavior resulting in infections, neurological trauma, alcohol/drug abusers
Children in daycare
The under or unvaccinated
Sustained fever
Constant above 38C (100.4 F) with little fluctuation
Intermittent fever
Fever spikes interspersed with usual temperature levels
Remittent fever
Fever spikes and falls without a return to normal temperature levels
Go up and down without reaching normal levels. EX: 102, then 100, then 103, etc.
Relapsing fever
Periods of febrile episodes and periods with acceptable temperature values
Fever treatment
Antipyretics- NSAIDs and Tylenol are most common. NSAIDs are best to cover inflammation and fever.
No aspirin for children and adolescents due to risk of Reye’s syndrome which causes a pneumonia production which can cause permanent brain damage leading to death.
Take off clothing, ice packs (be careful they do not shiver)
Febrile seizures
Usually occur in children from a rapid rise in temperature above 39C (102F) in association with acute viral or bacterial illness. Not about how high it goes but how fast it gets there.
No intracranial infection or other defined cause is found. Still, assess for neuro S/S indicative of meningitis or encephalitis. Immature neurology puts kids at risk.
Usually between 3 months to 5 years old. They usually will grow out of it by the time they’re 5-6 years old.
Often have family history
Children who have had one are 30-50% more likely to have another. The lower convulsive threshold of infants may explain this type of seizure.
Teach parents to monitor seizures ans give Tylenol or NSAIDs to keep temperature down
Tests for pediatric fevers
Under 29 days, will perform LP on febrile patients due to the risk of meningitis or encephalitis that could have been passed from mom during birth.
Blood tests: CBC with differential and blood culture
Urine test: urinalysis and culture
Stool tests: culture and fecal WBC count if diarrhea present
Chest radiography
Malignant hyperthermia
Inherited muscle disorder
Reaction to general anesthesia and succinylcholine
Massive amounts of muscle contraction cause a high serum calcium and potassium
Sustained muscle contraction (rigidity) increases our BMR. Temperatures can go up into the 40-41C range very quickly
Observe for a rapid rise in temperature, tachycardia, hypertension, and increased muscle contractions
Quick action is necessary or the patient will die
Treat: terminate inhaled gas, IV therapy, quick cooling with ice, Dantrolene IV is the only effective drug
Treating malignant hyperthermia
Stop all anesthesia
Dantrolene 2-3mg/kg is the only drug for this. It’s a major muscle relaxant which stops muscle contractions and hyperthermia
Access acidosis: hang bicarb quickly
Insulin for hyperkalemia
Cooling blanket/saline infusion/ ice/ lavage
Foley to get good urine output to monitor for kidney ischemia
Treat dyrhythmias
Look at family history: may use other forms of anesthesia if this condition is possible from family history. If S/S of it occur, stop all anesthesia
Will try to book their surgery first thing in the morning so there isn’t any residual anesthesia gases in the machines
Hypothermia consequences
Dependent on severity and duration
Tissue ischemia- skin is low tolerant to not being perfumed well; fingers, toes,smaller appendages, and nose are common areas for frostbite
As vasoconstriction fails to warm the body, vasodilation occurs. This is more dangerous because the patient feels warm and may even take clothes off
Temperature under 28C- ice crystals form in our cells and begin bursting cells causing cellular death, decreased perfusion, ischemia, and necrosis
Hypothermia exam
Vasoconstriction: cool, pale skin
Muscle rigidity and shivering as the body increases BMR to make heat (muscles feel tight)
Cognition decreased because of colder, slower perfusion of blood to the brain: fatigue, lethargy, confusion
Dysrhythmias because heart isn’t being perfumed as well
Slower metabolic rate and poor perfusion: decreased urine output a d CV collapse
Hypothermia interventions
Passive external warming: dry clothing, warm drinks, exercise; heating pads (careful not to cause burns); warm bath
Active core rewarding: warm fluid IV, peritoneal and gastric lavage, inhaled warm oxygen
Don’t warm too quickly. Fast warming can cause ice crystals to burst more cells. Cold: put them in tap water that is not too hot. If it’s stinging, it’s too warm. Slowly reward to avoid ischemia
Hyperthyroid S/S (SPEED UP)
Skin- diaphoresis, moist, sweaty, thinning hair
CV- tachycardia, HTN
Respiratory- tachypnea
GI- wt. loss/diarrhea , hunger r/t increased BMR
Neuro- irritability, exopthalamous (bulging eyes), blurry vision
Hyper metabolism- fever
Other- manic, goiter
Labs- decreased TSH, production of too much thyroid hormones T3 and T4
Large amount of T3 & T4 tell the pituitary not to make thyroid stimulating hormone (TSH), making TSH low because T3 and T4 are high. If there is a hypothalamus problem where it is overstimulating the thyroid stimulating hormone releasing hormone, then T3 and T4 will typically be high.
Goiter- big neck from thyroid overproducing
Hyperthyroid treatment
Meds inhibit new production by blocking iodine binding sites in the thyroid: Propythiouricil (PTU)- look at concerns with liver damage; Methimazole can cause birth defects
Thyroid has a very high affinity for iodine
Radioactive iodine- take a radioactive solution that tags onto iodine. As the body ingests the iodine, the body uptakes it and the radiation destroys the thyroid tissue. They are radioactive after and should not be around babies who are more risk for radiation
Thyroidectomy- may do partial or full
Risks for radioactive iodine and thyroidectomy is hypoglycemia as we are destroying thyroid tissue
Thyroid storm
Excessive hormone release. Can be an essential problem- pituitary tissue. Can be a problem with the thyroid tissue itself
Fever. Tachycardia, HTN
Anxious to confused to psychosis
May lead to death
Treat S/S of hyper metabolism: need massive amount of fluid because of diuresis and diarrhea; need antipyretics for the high fever; beta blockers and calcium channel blockers to treat tachycardia; labetalol to treat HTN
Treat symptomatically until thyroid can be under control
PTU is typically done to start blocking the thyroid production
Hypothyroid S/S (SLOW DOWN)
Skin- dry, brittle, hair loss
CV- bradycardia, hypotension
Metabolic- wt. gain, cold r/t inability to produce heat
Psych- depression
GI- constipation, anorexia
Neuro- lethargy, paresthesias
Other- edema, bradypnea, myxedema (head and neck; can cause airway problems)
Labs- increase TSH; decreased T3 and T4
Myxedema- untreated hypothyroid
Decreased CO from poor heart muscle contraction increases edema
Hypothermia (30-32C)
Treatment: warming mattress, IV levothyroxine (looking at T3), IV glucose (metabolism is lower), corticosteroids (increase epinephrine to heat the body up)
Measuring temperature
Oral- most common; wait at least half an hour since smoking, eating, or drinking
Axillary- preferred site in infants, developmentally delayed, or cognitively impaired; ensure skin-to-skin contact in both sides. May be inaccurate with hypothermia; usually 0.5C (0.9F) lower than oral
Rectal- stick in by an inch; don’t do on immunocompromised, bleeding disorder, neonates, or reveal surgery; usually 0.5C (0.9F) higher than oral
Tympanic- high degree of user errors based on cooperation, exact angle of insertion, etc.
Temporal artery- high degree of user error. It needs to catch the temporal artery in two different places: across and down the forehead
In the ICU, temperature-probes can be built into the foley or ET tube to measure core samples
Neonatal physiology
Predisposes to poor thermal control
Wet skin at birth and high surface area to body ratio- lost heat via skin surface
Immature hypothalamus- does not react as well or as quickly to temperatures that are too hot or too cold
At term baby has more brown fat than the adult which is is used to create heat. Pre-term babies are at high risk for hypothermia because they have not yet developed brown fat. They use this brown fat for non-shivering thermogenesis. Term babies lack subcutaneous fat which acts as an insulator so they are also at risk for hypothermia, but not as severe as the preterm baby
Drying and wrapping or skin to skin contact with a hat is required for temperature control
Effects of cold
Decreased surfactant efficiency: the cooler they are, the less surfactant works; they are then unable to open their airways and breathe effectively
Increased oxygen consumption- using more oxygen to stay warm
Respiratory distress
Increased utilization of calories as BMR increases because they are trying to maintain heat
Reserves- hypoglycemia
Increased postnatal weight loss
Thermal care
Monitor temperature and observe for instability
Skin to skin contact, cover/wrap, hats to keep baby warm and prevent heat loss
Plastic wrapping for preterm neonates in delivery suite and then humidification to decrease loss of perspiration
Maintain the neutral thermal environment
