Download - thermoregulation 2012
Temperature Control in the Neonate
Physiology of Thermoregulation in the Neonate
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Over view
Fetal thermoregulation
Perinatal transition
Neural control of thermoregulation
Non shivering thermiogenesis
Mechanics of heat loss
Strategies for conservation of heat
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What do we know?
Appropriate thermal care
Better survival
Growth
Fluid electrolyte balance
( Silverman et al 1958,1966)
Thermoregulation is one of the greatest challenges in the care of newborn babies especially premature newborns
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Fetus as poikilothermic animal
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Thermoregulation in fetus
Metabolic rate of fetus per tissue wt. higher than adult
Fetal temp consistently 0.3-0.5 deg C higher than mothers (always in parallel)
Heat clamp: tight linkage of maternal and fetal temperature that prevent fetus from independently regulating its own temperature.
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Inhibited non shivering thermiogenesis
Fetal adipose tissue
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Fetal adipose tissue
adenosine
hypoxia
PGE2
Transition from the warmth of womb to the cold exterior
Delivery room
the first thermal stress a newborn has to face
37C
25C
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Modes of heat loss at birth
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Modes of heat loss at birth
Energy in watt/m2
Hammarlund et al, 1980
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Susceptibility to Heat Loss
The higher ratio of body surface
The higher proportional surface area of the head
Thin non-keratinized skin
Lack of thermogenic brown adipose tissue
The low amount of musculature and the inability to shiver
A lack of thermal insulation, e.g., subcutaneous fat
Immature nervous system
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Thermal regulation in delivery room
Hypothermia @ NICU admission- independent risk factor for mortality
Costoloea K, EPICure study, Ped 2000
Watkinson M, Clin Perinatology, 2006
In babies with birth weight > 3250 gm
body temperature by 09 C in 15 min
Hummarlund et al
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Modes of heat generation
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Heat generation
Metabolic process
Peripheral vasoconstriction
Non shivering thermiogenesis
Voluntary muscle activity
Biocybernetic concept
environment
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Controllers
Effectors
Sensors
Controller Model (Sensors)
Peripheral
Thermoreceptors in skin (cold and warm receptors)
Cold receptors
Cold menthol receptor 1
20 35 C
Warm receptors
Vallinoid receptor (VR, VLR 1)
40- 45 C
Ant Lat Spinothalamic pathway
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Other Sensors
Ant hypothalamus (thermosensitive)
Preoptic nucleus (thermosensitive)
Spinal cord
Medulla
Dorsal abdominal wall?
Muscles ?
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Core vs. peripheral temperature
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Normal neonatal thermograph
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Controller Model
Integrator (thermoresponsive neurons)
Post Hypothalamus
Ant hypothalamus
Preoptic nucleus
Effectors
Shivering
Non shivering : Brown fat
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Integration of thermal inputs
www.mona.uwi.edu
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Thermoregulatory effectors system
3 receptors
receptors
M3 receptor
Nm receptor
Bruck K: In Schmidt RF, Thews G, Human Physiology.Springer-Verlag
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CNS
ANS
Brown adipose tissue
Vasomotor system
Somatosensory cortex
Skeletal musculature
Sweat glands
Voluntary movement system
Non shivering thermiogenesis
Thermal insulation
Sweat secretion
Shivering thermiogenesis
Behavioral response
Non Shivering Thermogenesis
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26-36 wk
4-6 month
10-15%
Brown adipose tissue
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Sites of brown fat
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Klaus et al
Biochemical mechanism of response to cold
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Cold response at genomic level
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Strategies to prevent heat loss
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Strategies to prevent heat loss:
CONVECTIVE HEAT LOSS can be prevented by:
Providing warm ambient air temperature
Placing infants less than 1500 grams in incubators
Keeping portholes of the incubator closed
Warming all inspired oxygen
On open warmers keeping sides up and covering infant if possible
Using Infant Servo Temperature Control
Cochrane Review by Sinclair JC
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Strategies to prevent heat loss:
RADIANT HEAT LOSS can be prevented by:
Avoiding placement of incubators, warming tables and bassinets near cold windows, walls, air conditioners, etc..
Placing a knit hat on the infants head
environmental temperature
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Strategies to prevent heat loss:
CONDUCTIVE HEAT LOSS can be prevented by:
Placing a warm diaper or blanket between the neonate and cold surfaces
Placing infant on pre-warmed table at time of delivery
Warming all objects that come in contact with the neonate
Admitting infant to a pre-warmed
Skin to skin contact eg.KMC
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Strategies to prevent heat loss:
EVAPORATIVE HEAT LOSS can be prevented by:
Keeping the neonate and his/her environment dry.
Drying the baby immediately after delivery.
Placing preterm or SGA infant in occlusive wrap/bag at delivery
Delay bath until temperature is stable
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Cochrane database review
Plastic barriers effective in reducing heat loss in newborns