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