about neonatalthermoregulation

1. Neonatal thermoregulation
Dr T SASIDHAR
MODERATOR: DR MANDAKINI

2. history 1
• Art of incubation –ancient Egypt – for increasing poultry
production
• 1799 – Emperor Napoleon brought this concept of
incubation from Egypt to nurture the productivity of exotic
birds in captivity at Persia.
• 1830 – Tanier – French obstetrician- applied this principle
of graded incubation to premature infants in Paris.
• 1900 – Budin -- reported higher mortality In premature and
LBW due to hypothermia

3. • 1957- silverman and blanc – reported that the
premature infants housed in incubators
humidifed >80% had higher survival rates than
the babies in incubators humidified <60%
• 1959 – cross et al and hill – concept of
thermoneutral range
• 1969- sir Edmund hey and co workers – operated
the incubators warmed both by convection and
radiant heat.

4. Thermoregulation - goals
Maintain correct body temperature range in order
to:
• Maximize metabolic efficiency
• Reduce oxygen use
• Reduce calorie expenditure

5. Maintenance of body temp is a major task in newborn because
• 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 area to body mass of an adult
• Preterm infants and SGA infants have 4x the surface area 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

6. Definitions
Thermo neutral environment :
– This is defined as the range of ambient temperature within
which the baby can maintain normal core temperature with
minimal metabolic rate and oxygen consuption by vasomotor
activity alone.
– Above and below this temperature, compensatory mechanisms
are necessary to maintain normal temperature.
– In clinical setting, this temperature is regarded as the core
temperature between 36.5°C – 37.5°C and the skin temperature
does not change >0.3°C/hr while measured continuously 1.

7. • Hyperthermia 2: Axillary temperature >37.5°C
• Hypothermia 2 : Axillary temperature is <36.5°C
Cold stress 36.0-36.4°C
Moderate hypothermia 32-35.9°C
Severe hypothermia <32°C

8. How to measure the temperature?
• Recommended thermometer should have
measurement values till 30°C.
• Frequency of measurement
– Once daily in a term baby
– 2-3 times daily for a small baby (2.4-1.5 kg)
– Four times daily for very small babies (<1.5 kg)
– Every 2 hours for a sick baby
– Frequent assessment by mother using touch should
be encouraged.

9. Methods of temperature measurement
• Axillary – bulb of the thermometer placed against the roof of axilla
and baby’s arm s held close to the baby read after 3 minutes. It is
the standard method of temperature recording
• Rectal – direction is backwards and downwards- bulb is placed at a
depth of 3 cm from the anal opening- read after 2 minutes.
• Skin – using a probe called thermister attached to the skin over
upper abdomen- used for continuous monitoring of babies under
servo control, radiant warmer, incubators, etc.
• Human touch – temperature is felt at the abdomen, feet and hands
of the baby- a crude method.
– Abdomen, feet and hands are warm ----- normal
– Abdomen is warm but the feet and hands are cold ---- cold stress
– All are cold ----- hypothermia.

10. Factors effecting Thermoregulation
• Brown Adipose Tissue
• Body surface area
• Glycogen stores
• Body water content
• Posture
• Hypoxia
• Hypoglycemia
• Developmental
characteristics
• CNS
• Sedation
• sleep

11. Reasons of ↑susceptibility
– Large surface area
– Limited heat generating mechanisms
– Vulnerability to getting exposed due to dependent
nature of the baby
• Additional factors in the premature /lbw babies
are
– Decreased subcutaneous fat & brown fat
– More permeable skin
– Poor homeostatic response
– Even larger surface area

12. PHYSIOLOGY OF THERMOREGULATION
• Mammals are homeotherms
• Homeotherms: maintain near constant body temperature
even when subjected to wide range of environmental
temperature.
• Response to environmental temperature change include
sensory arm --- cns ------effector arm

13. Sensory arm
(skin and hypothalamus)
Once these receptors sense drop in temp.
Central thermostat in preoptic anterior hypothalamus
(near 3rd ventricle)
Effector arm - vasomotor&muscular response
- metabolic response
- sweating

14. • The vasomotor response:
– consists of a vasoconstriction of the peripheral vessels in an
attempt to conserve core temperature.
– This attempt to conserve heat is ineffective in the infant due to
poor insulation.
• Muscular response: there is an increase in voluntary
muscular activity in the neonate as an attempt at
nonshivering thermogenesis.
• An infant can limit heat loss by changes in the body posture
that reduce the skin surface area esposed to the
environment.

15. brown fat
• Important organ of nonshivering thermogenesis is
brown fat. The preferred fuel is free fatty acids.
• In full term infants brown fat is 4 % of body weight and
is laid down in the last trimester of pregnancy.
• It is well established by 22 wks of gestation and up to
90% of the total body fat by 29th wk of gestation.
• It generally disappears 3-6 months after birth, except in
cold stressed infants (where it will disappear sooner.)
• Hypoxia causes impairment of brown fat metabolism

17. Characteristics of brown fat
• It is so called because of increased presence of vascular
channels that in white adipose tissue.
• Places of brown adipose tissue are
Axilla, Groin, Interscapular area, Perirenal area, liver and para
aortic areas
• Microscopy:
– these cells have large rounded nucleus with a large
number of mitochondria and fat vacuoles.
– The mitochondria are rich in electron carriers and are
specialized to carry out an oxidation uncoupled from
phosphorelation.

18. • As environmental temperature decreases, an
increase in blood flow to the brown fat stores is
observed.
• Thyroid hormone is thought to facilitate the
response of the brown fat to norepinephrine.
• Nonshiveering thermogenesis is inhibited by
many anesthetic agents in experiental animals.

19. • It has long been known that brown fat is
responsible for heat production, containing a
protein (uncoupling protein 1).
• UCP 1 dissipates the proton gradient formed
across the mitochondrial inner membrane during
substrate oxidation.
• The magnitude of proton leak may be the major
contributor of metabolic rate.

20. • On stimulation of the cold receptors, norepinephrine is
released from the nerve endings and the effector
receptors in the brown fat are activated.
• This sets of a chain of steps and glycerol and fattyacids
being formed from the triglycerides and then oxidised
in an exothermic reaction.
• The heat so produced is distributed throughout the
body as a result of the brown fat’s proximity to the
blood vessels.

22. Differences between brown fat and
white fat
Features
Brown fat White fat
Vacuoles/cell Many one
Vascularity Good Poor
Nerve fibres many few
Mitochondria many few
stimulus for activation cold starvation
Function Heat production Nutrition

24. •When the air temperature around the baby is cool, thermo
receptors 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
•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.

25. Physics of heat transfer- four
methods

26. Conduction:
• It is transfer of heat between two solid objects of different temperatures
• Conductive heat loss can happen when baby placed on cold operating
table or radiography table etc.
• Conversely if baby placed close to heating pad, hot water bottle infant will
gain heat at rate directly proportional to temperature difference between
heat source and infant skin.
• 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 ward
– Skin to skin contact

27. Convection:
• Convective losses happen when the ambient air temperature is less than
baby’s skin temp.
• Air molecules in contact with skin are heated and they rise taking away
the heat
• If air flow is present heat losses are magnified
• 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

28. Radiant losses:
• It is heat loss at the speed of light from a warmer object to cooler one,
which is not in contact.
• When infants are placed near to windows or walls heat is lost by radiation,
even neonates placed in incubators losses heat to incubator walls
• Conversely the wall of incubator can act as greenhouse trapping heat from
sunshine and lead children warmer and even febrile
• 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 heat
• Wrapping tiny babies in saran or “bubble” wrap
•  environmental temperature

29. Evaporative losses:
• For every ml of water that evaporates from baby,580 calories
of heat are lost
• It depends on relative humidity of environment and
gestational age of infant.
• An infants evoperative loss accounts for 25% of heat
production, of this
• Respiratory tract-25%
• Trans epidermal water loss -75%
• It is not very significant in term infants, but it is very
significant in pre term and open surgical anomalies

30. Kangaroo Mother Care (KMC)
• Introduced in 1983 by Rey and Martinez in Colombia
– LBW infants nursed naked (wearing only cloth diaper)
between mothers’ breasts
– Data from other countries show infants nursed by KMC
have
• Fewer apnoeic episodes
• better blood oxygenation
• Lower infection rates
• Are alert longer and cry less
• Are breastfed longer and have better bonding
• Improved survival in low-resource settings

32. hypothermia
• Hypothermia 2 : Axillary temperature is <36.5°C
Cold stress 36.0-36.4°C
Moderate hypothermia 32-35.9°C
Severe hypothermia <32°C

33. hypothermia
Response to hypothermia
• Babies attempt to conserve heat by peripheral
vasoconstriction→ increased anaerobic
metabolism with acidosis → pulmonary
vasoconstriction → raised pulmonary arterial
pressure → further hypoxia with anaerobic
metabolism → a vicious cycle.

34. • With continued hypothermia, usually when
the temperature drops to 32°C, oxygen can
not be released from the hemoglobin,
resulting in the blood having a bright red
color, which should not be mistaken for good
perfusion.
• Free fatty acids released binds to albumin
displacing bilirubin → jaundice.

35. 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

36. 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

37. 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

38. 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.

39. 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.

40. 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)

41. 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

42. Signs and Symptoms of
Hypothermia
Poor weight gain occurs when:
• calories consumed
• brown fat stores are used to make body
heat.
Poor Feeding/Weight Loss

43. Consequences of Hypothermia
• Initially becomes restless,cries and may have increased
muscular activity to produce heat
• With increased heat loss bradycardia, fall in blood presuure
• Skin develops mottling
• Metabolic acidosis and right to left shunting with increased
hypoxia and hypoglycemia
• Sclerema, fat necrosis and disseminated hemorrhage
• Progressive brain damage and death

44. Prevention of hypothermia
Steps of warm chain
1. Warm delivery room
2. Warm resuscitation
3. Immediate drying
4. Skin to skin contact – kangaroo mother care.
5. Breastfeeding
6. Bathing postponed- during summer term babies can be sponged after
first 24 hours. During winter, for the sick or LBW babies this can be
postponed by several days usually until the umbilical cord falls off, often
by the end of first week.
7. Appropriate clothing – dressing the baby in layers of warm light
garments gives better insulation than single layer of heavy clothing
8. Mother and baby together
9. Professional alertness
10. Warm transportation – weakest link in the warm chain.

45. Incubators ad radiant warmers
• Incubator – baby Is warmed by circulating
warmed and humidified air around the baby
and the mechanism of heat transfer is by
convection.

47. • Radiant warmer – neonate lies on a waist high
bed and heated from above by a radiant
source. Compared to incubator, infants under
a radiant warmer have more insensible water
loss by evaporation which can be reduced by
using plastic sheets. It requires proper
cleaning and disinfection.

49. • Radiant warmers and incubators should be used in the servo
control mode with the abdominal skin temperature
maintained at 36.2°C -37 °C depending on the birth weight of
the neonate.
• Cheaper alternatives include
– Oil- fin radiators
– Warm air blowers
– Heaters
– 200 watt electricity bulb
• These lack servo control mechanism
• Carry risk of hypo/ hyperthermia.
Set temperature for incubators
Birth weight in
kg
Set temperature
(°C)
<1.0 37.0
1.0-1.5 36.8
1.5-2.0 36.6
2.0-2.5 36.4
>2.5 36.2

50. Management
• Methods for temperature maintenance include skin to skin contact, warm
room, radiant warmers, incubators and exposure to sources of heat.
Cold stress and moderate hypothermia:
• Remove baby from source causing hypothermia
• If mother is available and the baby condition allows, skin to skin contact
can be started, otherwise, baby should be dressed on warm clothes and
place in a warm room and warm bed. Alternatively a radiant warmer or
incubator can be used.
• The temperature should be measured every hour for first 3 hours
– If the raise of temperature is 0.5°C/hr then heating is adequate; now measure
2 hourly temperature till the normal temperature is attained, and thereafter 3
hourly for 12 hours, followed by routine frequency
– If the raise of temperature is not adequate, check heating technique. Sepsis
should be suspected in fluctuating temperatures with non responding
hypothermia.
• Supportive measures: maintain normoglycemia by frequent feeding.

51. Severe hypothermia
• Remove all wet clothing and place baby in a warm bed with warm clothes.
• Method of warming could be and incubator or a preheated radiant warmer or
thermostatically controlled heat mattress set at 37-38°C.
• Once baby’s temperature reaches 34°C, the rewarming process should be slowed
down.
• The temperature should be measured every hour for first 3 hours
– If the raise of temperature is 0.5°C/hr then heating is adequate; now measure 2 hourly
temperature till the normal temperature is attained, and thereafter 3 hourly for 12 hours,
followed by routine frequency
– If the raise of temperature is not adequate, check heating technique. Sepsis should be
suspected in fluctuating temperatures with non responding hypothermia.
• Supportive measures:
• Oxygen
• Empirical antibiotics (investigations to be sent to rule out sepsis)
• Saline bolus given if hypotension +
• Iv fluids for hypoglycemia correction and prevention
• Inj vit K 1 mg(0.5mg if weight <1 kg).

52. hyperthermia
• Defined as a rectal / axillary temperature greater than 37.5°c
(99.5°F)
• Predisposing factors are
– Immature thermoregulatory center
– Decreased ability to produce sweat
• Common reasons for hyperthermia are
– Over clothing
– Environmental exposure in summer
– Poor feeding
– Dehydration
– Direct sun exposure

53. Signs of Hyperthermia
• Tachypnea
• Tachycardia
• Flushing
• Hypotension
• Irritability
• Poor Feeding
• Skin Temp > Core Temp
53

54. Consequences of Hyperthermia
•  in Metabolic rate
•  oxygen consumption
• Dehydration from  insensible water loss
• Peripheral vasodilatation/ hypotension
• Fluid, electrolyte abnormalities
• seizures
54

55. Treatment of Hyperthermia
• Cool quickly but safely (undress, un-bundle, decrease
incubator temperature), tepid water sponge bath
• Possible sepsis work up or acetaminophen
55

56. Thank you

57. references
1. textbook of neonatal surgery by Dr D.
K.Gupta: first ed.2000
2. Ghai essential pediatrics: 7th ed.2009