Neurohormonal of
Thermoregulation
Dr. Dini Sri Damayanti,MKes
Body Temperature
Shell temperature:
Temperature closer to skin
Oral temperature
36.6o-37.0oC (97.9o-98.6oF)
Core temperature:
Most important temperature
Temperature of “core” (organs in cranial, thoracic
and abdominal cavities)
Rectal temperature
37.2o-37.6oC (99.0o-99.7oF)
Heat Production
Exergonic reactions:
Oxidation and ATP use.
Most heat generated by brain, heart,
liver and glands at rest.
Skeletal muscles 20-30% at rest. Can
increase 30-40 times during exercise.
Thermoregulatory Center
Hypothalamus:
Preoptic area neurons: hypothalamic
thermostat:
Heat-losing center
Heat-promoting center
Monitors temperature of blood and receives
signals from peripheral thermoreceptors.
Negative feedback loops
Thermoregulatory Center
Heat-losing center (hipotalamus anterior):
Activates heat losing mechanisms:
Dilation of dermal arterioles: increase
blood flow to skin.
Sweating.
Increased respiration through mouth.
Behavioral: remove clothing.
Inhibits heat-promoting center.
Thermoregulatory Center
Heat-promoting center ( hipotalamus posterior
):
Activates heat generating mechanisms:
SNS:
Vasoconstriction of dermal arterioles: decrease blood
flow to skin
Stimulates arrector pili muscles: hair stands on end
Shivering thermogenesis: spinal reflex of alternating
contractions in antagonistic muscles
Nonshivering thermogenesis:
Long-term mechanism stimulating thyroid hormone
release T3 and T4.
Inhibits heat-loss center.
Nonshivering Thermogenesis
Temperature sensors are in
the skin (in newborns
particularly the face), the
spinal cord and the
hypothalamus.
Temperature information is
processed in the
hypothalamus.
Norepinephrine (NE) is
released in response to
cold stress.
Result: Vasoconstriction
and increased metabolic
activity.
Nonshivering Thermogenesis
Vasoconstriction also occurs in infants but the
primary response is increasing heat production
from brown fat metabolism.
Brown fat mechanism is known as nonshivering
thermogenesis
NE stimulates receptors on brown fat cells;
activates lipase which releases intracellular fatty
acids.
Conversion of T4 to T3 inside brown fat cells. T3
cellular metabolic rate
Uncoupling protein uncouples mitochondrial oxidative phosphorylation.
H+ gradient
heat rather than ATP
Result: Large increase in heat production and O2 consumption.
In case of hypoxia, temperature because of
O2
Mechanisms of Heat
Transfer
Radiation:
Infrared radiation.
Conduction:
Direct transfer of energy through physical contact.
Convection:
Heat loss to air around the human body.
Evaporation:
Energy change in water molecule from liquid to
vapor.
Core
body
temperat
ure
>37°C
Thermoreceptors
© 2008 Paul Billiet ODWS
Blood
NEGATI
temperature
VE
FEEDBA
CK Muscles
of skin
Thermoreceptors
arteriole
walls
Sweat
Bod
relax
Hypothalamus nerv glands
y
es increas
lose
e
s
Muscle
secreti
heat
s
on
reduce
activity
Retur
n to
37°C
Core
body
temperat
ure
<37°C
Thermoreceptors
© 2008 Paul Billiet ODWS
Blood
NEGATI
temperature
VE
FEEDBAMuscles
CK of skin
arteriole
Thermoreceptors
walls
Bod
nerv
constric
y
Sweat
es
t
lose
Hypothalamus
glands
s
decreas
less
e
heat
Bod
secreti
Muscle
y
on
s
nerv
gain
shiveri
es
s
ng
heat
Retur
n to
37°C
Goal of Thermoregulation
Maintain correct body temperature range
in order to:
maximize metabolic efficiency
reduce oxygen use
protect enzyme function
reduce calorie expenditure
14
THERMOREGULATION IN THE
NEONATE
15
Challenges of thermoregulation
in Neonatal care
Prior to delivery infants do not maintain
A temperature independently
Infant’s in-utero temp is generally
0.5˚C higher than mother’s temp
Rapid cooling occurs after delivery
16
Neurologic adaptation:
Thermoregulation
Maintenance of body temp is a major task
Skin is thin & blood vessels are close to the surface
Have little subcutaneous fat to serve as barrier to
heat loss
Term Infants have 3x the surface to body mass of an
adult
Preterm infants and SGA infants have 4x the surface
mass to body mass of an adult
Preterm infants are especially susceptible to heat loss
due to poor tone,  fat and thinner skin than term
infants
17
Neutral Thermal
Temperature
A neutral thermal temperature is
the body temperature at which an
individual's oxygen use and energy
expenditure are minimized.
Minimal metabolic rate
Minimal oxygen consumption
18
Body temperature in the
newborn infant
Classification of hypothermia is based on core
temperature
NORMAL – 36.5 to 37.3˚C (97.7 –99.2˚F)
Cold Stress 36.0 to 36.4˚C (96.8 – 97.6 ˚F)
Cause for concern
Moderate hypothermia 32 –35.9˚C (89.6-96.6˚F)
Danger, warm infant
Severe hypothermia – below 32˚C (89.6 ˚F)
Outlook grave, skilled care urgently needed
19
Neutral Thermal
Environment (NTE)
The air temperature
surrounding the baby
supports maintenance
of a neutral thermal
body temperature.
20
Thermoneutrality
When the air temperature
is in the correct range and
the infant’s body maintains
a neutral thermal
temperature, we have
achieved thermoneutrality
21
Why Are Infants At
Greater Risk for
Thermoregulation
Problems?
22
Thermoregulation Risk
Factors
Premature
SGA
Neuro problems
Endocrine
Cardiac / respiratory problems
Large open areas in the skin
Sedated Infants
Drug exposure
23
Why are they at Risk???
Brown Adipose
Tissue
Body surface area
SQ Fat
Glycogen stores
Body water content
Posture
Hypoxia
Hypoglycemia
Anomalies
CNS
Sedation
24
What Do We Know?
Infants have more skin surface per
pound of body weight than older
children or adults
More skin means more radiant heat and
more insensible water loss.
25
Risk factors for Preterm
Infants
• less brown fat and glycogen stores
• decreased ability to maintain flexion
• increased body surface area compared to
weight
26
What Do We Know?
The majority of an infant’s
thermal receptors are found
in the face, neck, and shoulder
area.
Stimulation of these
receptors will result in chilling
and calorie expenditure
27
What Do We Know?
Shivering, which is the
main way in which older
children and adults
generate heat, is
impossible or not
effective in infants.
Neonates and young
infants generate heat by
burning brown fat.
28
Production of Heat
Metabolic Processes
Voluntary Muscle Activity
Peripheral Vasoconstriction
Nonshivering Thermogenesis
29
Metabolic Process
Heat Generation by
Oxidative metabolism
Glucose
Fats
Protein
Metabolic Energy
Brain
Heart
Adrenal Gland
30
Voluntary Muscle Activity
Postural changes
Restless movements
Limited use to Newborn
31
Peripheral Vasoconstriction
Reduces skin blood flow
Decreases loss of heat from the body
32
Nonshivering
Thermogenesis
Metabolism of brown adipose tissue
Initiated in hypothalamus
Sympathetic nervous system
Norepinephrine release at the site of
brown fat
33
What is Brown Fat?
Brown fat is an energy source for
infants
It can be found:
Near Kidneys and adrenals
Neck, mediastinum, scapular,
and the axilla areas.
Can not be replaced once used
34
35
Brown Fat
In full term infants brown fat is 4 % -10% of adipose
deposits.
In preterm infants, brown fat will not be found until
26-30 weeks gestation, and then only in small
amounts.
Brown fat generally disappears 3-6 months after birth,
except in cold stressed infants (where it will disappear
sooner.)
Hypoxia causes impairment of brown fat metabolism
36
So What?
When the air temperature
around the baby is cool,
thermoreceptors in the
skin are stimulated. Nonshivering thermogenesis
is initiated and brown fat is
burned for energy to keep
the body temperature stable.
This is the infant’s initial response.
37
What Next?
Conversion of brown fat
uses oxygen and glucose,
therefore, the cold stressed
infant will become hypoxic
and hypoglycemic.
Blood gas and glucose levels
are affected.
Growth is affected as calories
are used to stay warm
rather than grow.
38
What are the Signs
and Symptoms of
Thermal
Instability?
39
Methods of heat loss
Peripheral Vasodilatation
 blood flow
facilitates heat transfer from periphery
to environment
Sweating
 evaporative heat loss
 postnatal age increases the ability to sweat
Appears first on term newborn head
40
Healthy Vs. Sick Neonate
Healthy Newborn
Brown adipose tissue
Produces heat and
loses heat as needed
Sick or Low birth wt
infants
Increased energy
demand
Decreased energy
store
Vulnerable to heat
stress
41
Hypothermia – Signs/symptoms
Body cool to touch
Mottling or pallor
Central cyanosis
Acrocyanosis
Poor Feeding
Abdominal distension
Hypotonia
Hypoglycemia
gastric residuals
Bradycardia
Tachypnea
Restlessness
Shallow or Irregular
Respirations
Apnea
Lethargy
42
Signs and Symptoms of
Hypothermia in Infants
Vasoconstriction
Peripheral vasoconstriction occurs in an
effort to limit heat loss via blood vessels
close to the skin surface.
Pallor and cool skin may be noted, due to
poor peripheral perfusion
43
Signs and Symptoms of
Hypothermia in Infants
Increased Respiratory Rate
Pulmonary vasoconstriction occurs
secondary to metabolic acidosis.
Increasing Respiratory Distress
Related to decreased surfactant
production, hypoxia, & acidosis
44
Signs and Symptoms of
Hypothermia in Infants
Restlessness
Restlessness may be a type of behavioral
thermoregulation used to generate heat through
muscle movement.
The first sign may be an alteration in sleep
patterns.
Restlessness also indicates a change in
mental status as cerebral blood flow
diminishes, due to vasoconstriction.
45
Signs and Symptoms of
Hypothermia in Infants
Lethargy
If thermo-instability goes unrecognized,
the infant will become more lethargic,
as cerebral blood flow continues to
diminish and hypoxemia and
hypoglycemia become more
pronounced.
46
Signs and Symptoms of
Hypothermia cont.
Metabolic Disturbances
Metabolic acidosis
Hypoxemia
Hypoglycemia
progress due to continued metabolism of
brown fat, release of fatty acids and anaerobic
metabolism (lactic acid)
47
Signs and Symptoms of
Hypothermia
Cardiac
As central blood volume increases, initially
the heart rate and blood pressure increase
Arrhythmias
May result from depressed myocardial
contractility and irritability caused by
hypothermia
48
Signs and Symptoms of
Hypothermia
Poor Feeding/Weight Loss
Poor weight gain occurs
when:
calories consumed
brown fat stores are used
to make body heat.
49
Even the smallest
weight loss may take
days or even weeks
to recover, as
infants
are limited in the
volume of food they
can eat and number
of calories they can
tolerate.
50
Consequences of
Hypothermia
Hypoxemia from  Oxygen consumption
Hypoglycemia from  glucose
metabolism
Respiratory & metabolic acidosis
secondary to anaerobic metabolism
Inhibition of surfactant production
related to  acidosis
51
Consequences of
Hypothermia
 pulmonary blood flow related to
pulmonary vasoconstriction in response
to  body temperature
 pulmonary vascular resistance
compromises the delivery of oxygen at
the cell level
 risk of developing PPHN in the near
term, term or post term infant
52
Prevention of Hypothermia
Hypothermia can be prevented by
maintaining a neutral thermal
environment and reducing heat loss.
A neonate is in a neutral thermal
environment when the axillary
temperature remains at 36.5° - 37.3°
(97.7° - 99.2° F) with minimal oxygen
and calorie consumption
53
Prevention of Hypothermia
Reduction of heat loss
Consider the four ways by which the
neonate experiences heat loss and
intervene appropriately.
54
Prevention of Hypothermia
Prevention of hypothermia is the best
treatment but if it occurs anyway, the
following is a list of what you can do to
relieve the cold stress.
Increase ambient air temperature
Apply external heat sources
Warm hat
Warm blankets or diapers
Chemical mattress
55
Prevention of Hypothermia
Avoid stressing the baby
Monitor skin temperature carefully and
when it normalizes remove the external
heat sources one at a time to prevent
rebound hypothermia
56
Hyperthermia
57
Hyperthermia
HYPERTHERMIA also has negative
consequences for the neonate.
Defined as a rectal / axillary
temperature greater than 37.3°c
(99.2°F)
58
Risk factors for
Hyperthermia
Excessive environmental temp
Sepsis
Dehydration
Alterations in the hypothalamic control
mechanism
Birth Trauma
Anomalies
Drugs
59
Signs of
Hyperthermia
Tachypnea
Apnea
Tachycardia
Flushing
Hypotension
Irritability
Poor Feeding
Skin Temp > Core Temp
60
Consequences of Hyperthermia
 in Metabolic rate
 oxygen consumption
Dehydration from  insensible water
loss
Peripheral vasodilatation/ hypotension
Fluid, electrolyte abnormalities
seizures
61
There Are a Lot of
Factors to Consider.
How Can I Be Sure
My Patient Maintains
Thermoneutrality?
62
It Is Important
to Review and
Understand the
Four Methods
of Heat
Transfer
63
Possible Sources
of Heat Loss
64
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
65
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 infant’s head
Wrapping tiny babies in saran or “bubble”
wrap
 environmental temperature
66
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
67
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
68
69
Interventions for at Risk Infants
Pre-warmed radiant warmer bed
Pre-warmed incubator
Do not leave a warmer bed or incubator in the
manual mode
Servo mode allows the baby to control the heat
output of the warmer units
Heated water pad
Heat lamp
Warm and humidify inspired gases
Occlusive wrap/bag at delivery
70
Interventions for at Risk
Infants
Open incubator portholes and doors
only when necessary
Blanket over incubator
Cluster care
71
Interventions to Consider
Cover thermoreceptor-rich areas, such as the
head.
Dry well after baths, especially the head and neck
area.
Dress and cover infants, when in cribs, to prevent
them from chilling.
Warm fluids prior to dressing changes
Rewarm slowly to prevent a potential subsequent
drop in blood pressure.
72
Rewarming the Hypothermic Infant
Always be prepared to intervene
Rewarm slowly (0.5˚C per hour)
Monitor closely (vital signs every 15 – 30min)
Core temp
Skin temp will be higher than axillary
Blood pressure
Rewarming may lead to vasodilation - hypotension
Heart rate and rhythm
Bradycardia & arrhythmias common with hypothermia
73
Rewarming
Monitor Respiratory rate and effort
Increased distress
Apnea
Oxygen saturations
Hypoxemia / desaturations
Be prepared for  need for respiratory support
Monitor acid/base status
Blood glucose
Monitor- infant at increase risk for hypoglycemia
74
Guidelines for Rewarming
Incubator better control than warmer
Set temp 1 – 1.5˚C above core temp
Assess infant temp every 15-30 minutes
As infants core temp reaches set temp
and infant is not showing signs of
deterioration increase set temp again.
Continue process until temp within
normal range
75
Signs of Deterioration during
rewarming
Tachycardia – due to in cardiac output
Cardiac arrhythmia
Hypotension
Hypoxemia / Desaturations
Worsening respiratory distress
Worsening acidosis
76
Cooling the overheated
neonate
Extended position- not flexed
Expose skin- remove clothing
Keep active temp reduction methods to
a minimum to prevent dramatic heat
loss
Monitor temperature and VS every 15 –
30minutes
Be prepared to intervene
77
Conclusions
Hypothermia in the newborn is due more to a
lack of knowledge than to lack of equipment.
Hypothermia is a preventable condition that
has well documented impact on morbidity
and mortality.
Therefore, assisting the infant to maintain a
normal body temperature and preventing
hypothermia during stabilization is critical
78