Thermoregulation Flashcards
What is the neutral thermal environment?
an environment that is able to regulate heat production using minimal amounts of oxygen and glucose; the maintenance of a delicate balance between heat production and heat loss
What is the risk to the NTE at delivery?
an infant’s temp can drop 2-3degrees, putting the babe at risk for hypothermia with resultant hypoglycemia, neurologic sequelae and death
What is a neonate’s normal core temperature?
97.7-99.5
What are the classifications of hypothermia?
mild, moderate and severe
How is mild hypothermia defined?
96.8-97.6
How is moderate hypothermia defined?
89.6-96.6
How is severe hypothermia defined?
<89.6
In 1995, Beeram et al reported what consequences were a/w hypothermia?
an 11 fold increase in infant mortality when infants were born; hypothermia found in 60% of non-surviving infants
In 1999, Hulsey reported what neurologic implications a/w hypothermia?
surviving hypothermic infants had significantly more CNS disorders and rates of IVH
What are risk factors for temperature instability?
SGA, preterm, CNS abnormalities/damage, endocrine problems, hypoglycemia, cardiorespiratory abnormalities, abdominal wall defects, neuromuscular abnormalities, sepsis and spinal defects
How developed is shivering thermogenesis in the newborn?
very poorly developed
What is non-shivering thermogenesis?
metabolic pathway that is the main method of heat production for the newborn- utilizes brown fat metabolism
What is the only fx of brown fat?
to produce heat
What is required in the process of non-shivering thermogenesis?
O2 and glucose- this is why thermoregulation, a normal glucose level and adequate oxygenation are so closely linked
What is thermostability?
in an optimal situation, the newborn will maintain their core temp WNL within a wide range of ambient temp variation without increased O2 consumption or increased metabolic rate
Where is brown fat located?
axilla, nape of the neck, between the scapulas, mediastinum and around the kidneys
When do brown fat stores increase postnatally?
increase until 3-5 weeks postnatal life
What is the mechanism for non-shivering thermogenesis?
with the onset of cold stress, the hypothalamus detects this state and secretes epinephrine to produce vasoconstriction and to signal brown fat metabolism
What is responsible for temperature control?
the hypothalamus
What is the body’s method for regulating against hyperthermia?
peripheral vasodilation to allow heat to reach the skin’s surface, also results in insensible water losses that allows for the dissipation of heat; respiratory center is stimulated to increase RR to release heat via the lungs
What are the mechanisms for heat transfer?
conduction, convection, evaporation and radiation
What is conduction?
heat transfer by direct contact; degree of heat loss varies with exposed surface area
What factors increase an infant’s risk to heat loss via conduction?
decreased ability to flex extremities, decreased subQ fat and limited ability to vasoconstrictor peripheral blood vessels
How can heat loss via conduction be minimized?
swaddling, skin to skin, prewar all equipment before contact with infant’s skin
What is convection?
heat loss from air current that move heat away from the body; affected by ambient temperature, air flow velocity and relative humidity
How can heat loss via convection be accelerated?
when the environmental temperature is cooler and/or air flow velocity is higher
What are common ways that neonates loose heat via convection?
heat is swept away by drafts, air currents, AC, doors, windows, fans, open incubator portholes or “traffic” around the baby’s bed
How can heat loss via convection be minimized?
keep warmer sides up, cover with plastic, tx in preheated warmers, warm and humidify O2 prior to use, use incubator, move beds away from drafts or vents, dress and swaddle baby in pre warmed linens
What is evaporation?
liquid in converted into vapor, major source of heat loss at delivery and with bathing; heat is lost through the skin and respiratory tract (insensible water loss)
What is heat loss via evaporation dependent upon?
air speed and relative humidity
When does heat loss via evaporation occur?
when moisture on the surface of the skin or respiratory tract mucosa is converted into vapor- always accompanied with a cooling effect
What facilities heat loss via evaporation?
the cooler the ambient environment, the more rapid the heat loss
What is the effect of increasing incubator humidity?
decreases evaporative losses
How can heat loss via evaporation be minimized?
drying infant, then removing wet blankets, plastic bags at del, increase room temp, eliminate drafts/vents, heating and humidifying the incubator & O2, warming solutions prior to contact with bb, delay bath until body temp has stabilized
What is radiation?
transfer of radiant energy from the body to objects without direct contact
How can heat loss via radiation be minimized?
double walled incubators, pre warming the incubator, keeping incubator away from cooler exterior walls and windows, using isolette cover
How does radiant warmer heat gain occur?
when the surrounding surfaces are warmer than the infant’s skin temperature
What is the greenhouse effect?
heat is trapped bc plexiglass walls allow short wave radiation to penetrate the interior, baby will absorb all this short wave heat, but readmits heat as long wave radiation heat which cannot pass through the incubator wall. Long wave heat radiation can be reabsorbed by the infant, and if the cycle is not interrupted, the baby will become hyperthermic (c no incubator temp ∆)
What are the advantages of the radiant warmer?
quickly rewarm, allows direct access for procedures
What are the disadvantages of the radiant warmer?
risk for thermal burns and hyperthermia- ALWAYS USE ON SERVO MODE
What are the advantages of the incubator?
can be used on skin or servo mode, quieter environment, decreases insensible water losses
What are the disadvantages of the incubator?
limited access
What is the process of weaning an infant to the crib?
based on GA and/or weight; a baby hasn’t successfully weaned to the crib if they are wearing excessive amt of clothes
What are the benefits of skin to skin?
can be close to the breast for feeding, stabilize VS and oxygenation, improve sleeping patterns and direct social eye contact
What are contraindications for skin to skin?
physiologic instability
What is the clinical presentation of hypothermia?
pale, cool to the touch, acrocyanosis, respiratory distress, apnea, bradycardia, central cyanosis, irritability progressing into lethargy, progressive or chronic cold stress
What is the clinical progression of hypothermia?
progressive, peripheral vasoconstriction is the first response, then O2 consumption will increase, then progresses into A/B/central cyanosis
How does an infant present with chronic cold stress?
a weak cry, hypotonia, increased gastric residuals, abdominal dissension, poor feeding and poor weight gain
What is the physiologic response to cold stress?
vasoconstriction, brown fat metabolism and increased muscle activity and flexion
How will a term infant utilize muscle activity and flexion in a hypothermic state?
a term babe can increase muscles activity to increase heat and flex to decrease the surface area exposed to cooler environmental temperatures
How does vasoconstriction affect core body temperature?
shunting blood away from the skin surface into the body core, even with mild hypothermia
What happens to the metabolic rate in an infant with hypothermia?
metabolic rate increases in an effort to produce heat and conserve heat which in turn increases O2 consumption and glucose utilization; significant risk of conversion to anaerobic metabolism which will increase lactic acid built up
How is the respiratory system affected by hypothermia?
if already experiencing RDS, an increase in O2 demand may worsen distress and lead to hypoxemia
What conditions should be included in your differential diagnosis of temperature instability?
sepsis, hypothermia r/t prematurity and inappropriate environment, use of equipment, misuse of equipment
What is the recommended rate of rewarming an infant?
rate should be specific to each individual infant- depending on their tolerance; no evidence to give a specific rate; don’t exceed 0.5 degrees/hr
What should be monitored while rewarming an infant?
vital signs, level of consciousness, acid/base status
If utilizing a radiant warmer to rewarm an infant, what should be remembered?
with exposed skin, blood vessels are sensitive to heat (skin warms quicker than core), risk is warmer in response to cold baby temp will operate on full heat output
What is the risk of warming an infant too quickly?
rapid heating can cause vasodilation and a rapid drop in BP- if infant’s status begins to deteriorate, then the rate of warming needs to be ∆
What is the clinical presentation of hyperthermia?
warm to the touch, pink/ruddy (r/t vasodilation), tachypnea, apnea, tachycardia, weak cry, hypotonia, irritable, lethargic, poor feeding, sz, may have perspiration, hypotension
What is the etiology of hyperthermia in neonates?
equipment use/misuse, remove iatrogenic etiology- bundling, direct sunlight, phototx, etc; sepsis, CNS abnormalities or dehyradtion
What are common complications a/w hyperthermia?
increased insensible water losses, dehyradtion, hypotension and apnea
What is the infant’s response to hyperthemia?
thermal receptors sense overheating causing peripheral vasodilation and sweating occurs, which increases the evaporative losses
