THERMOREGULATION IN NEONATES.pptx

TEMPERATURE REGULATION IN
NEONATES
DR. S KUNAL TEJUS
PEDIATRIC RESIDENT

History
• 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

• 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

BACKGROUND.
• Neonatal hypothermia after delivery is a worldwide issue,
occurs in all climates, and if prolonged can cause harm and
affect survival.
• During pregnancy, maternal mechanisms maintain
intrauterine temperature.
• After birth, newborns adapt to relatively cold environment
by the metabolic production of heat.
• Neonates are not able to generate an adequate shivering
response.
(Thermoregulation in adults is achieved by both metabolic
and muscular activity (e.g., shivering).)

Factors that increase risk for hypothermia include
1. prematurity,
2. intrauterine growth restriction,
3. asphyxia, and
4. congenital anomalies (e.g., abdominal wall defects, central
nervous system [CNS] anomalies).
5. hypothyroidism. Infants with persistent, unexplained
hypothermia should be evaluated for hypothyroidism.

The Fetal Thermal Equilibrium
• Generates heat in the processes of tissue proliferation,
metabolism and muscular movement.
• Fetal (and neonatal) heat production per unit weight is
higher than in the adult.
• Temperature gradient between the fetus and the mother
is about 0.5°C and the heat being dissipated mainly via the
placental circulation.

Neonatal Thermoregulation
• Exposure to cold, clamping of the umbilical cord, and the
general “stress of being born” induce a thermal response.
• It is part of a homeostatic system that is aimed at
preserving body temperature.
• Shivering thermogenesis is non-operative in the normal to
near-normal body temperature range.
• Cold-exposed infant thus depends on chemical
thermogenesis to avoid hypothermia.

THERMOREGULATION IN NEONATES.pptx

BROWN FAT AND NON-SHIVERING
THERMOGENESIS
Brown fat is a source for thermogenesis in term newborns.
1. highly vascularized and numerous capillaries.
2. composed of many mitochondria, lipid vacuoles,
3. innervated by sympathetic neurons.

- nape of the neck (mc)
- interscapular region
- axillary and groin region
- peri-renal areas.

• Decrease in temperature leads to increased blood flow to
Brown fat.
• Exposure to cold induces a sympathetic surge
(Norepinephrine is released) that acts on receptors in
brown fat stores stimulating lipolysis.
• The stimulation of the sympathetic pathways also causes a
surge in thyrotropin which leads to the release of thyroxine
(T4) and triiodothyronine (T3).
• T3 causes upregulation of thermogenin which, like
norepinephrine, acts on brown fat to initiate chemical
thermogenesis.

• The presence of the protein thermogenin in brown fat
uncouples β-oxidation (uncoupling of adenosine
triphosphate and fatty acid oxidation)
• Resulting in metabolic production of heat, in the form of
proton from mitochondrial inner membrane, instead of
adenosine triphosphate.
• Heat produced warms the organs and blood directly
leading to an elevation in body temperature.

The cost of heat production implies that even a slight long-
term exposure to cold will increase thermogenesis,
1. consume oxygen and substrate stores,
2. hypoglycemisa
3. impact negatively on growth.

Preterm infants have a limited thermogenic capacity due
1. to scarce fat stores
2. suboptimal nutritional provision.

TEMPERATURE MAINTENANCE
A. Premature infants experience increased mechanisms of
heat loss combined with decreased heat production
capabilities.
Compared with term infants, premature infants have the
following:
1. A higher ratio of skin surface area to weight and a relatively
large head which is a prominent source of heat loss
2. Highly permeable skin which leads to increased
transepidermal water loss and increased evaporative heat
loss.

3. Decreased subcutaneous fat, an effective source of
insulation.
4. Decreased ability to maintain a flexed posture to minimize
heat loss.
5. Less-developed stores of brown fat (1% to 2% of body
weight of preterm infant vs. 4% of body weight of term) and
decreased glycogen stores.
6. Poor vasomotor control.

7. Low levels of thermogenin and 5,3-monodeiodinase.
8. Lower surge of thyrotropin (especially infants <30 weeks)
9. Inadequate caloric intake to provide nutrients for
thermogenesis and growth.

• Axillary normal temperature is 36.5°C to 37.5°C
• According WHO,termometer kept for at least 3 mins.
Hypothermia is <36.5°C
1. Cold stress: 36 - 36.4°C
2. Moderate hypothermia: 32C - 35.9°C
3. Severe hypothermia: <32°C

• The use of low-reading thermometers (from 29.4°C
[85.0°F]) is recommended
• Temperature readings less than 34.4°C (94.0°F) can go
undetected with routine thermometers.

To distinguish cold stress from hypothermia
1. central core body and peripheries are warm: no
hypothermia
2. central core body is warm but peripheries are cold +/-
acrocyanosis: cold stress.
3. cental core body and peripheries are cold: hypothermia
(moderate or severe)

B. Cold stress.
In the setting of resuscitation, newborn infants are subject to
acute hypothermia respond with a cycle of peripheral
vasoconstriction, causing
1. anaerobic metabolism,
2. metabolic acidosis,
3. Hypoxemia,
4. pulmonary vasoconstriction.
Hypoxemia further compromises the infant’s response to
cold.

C. Neonatal cold injury
• Rare, extreme form of hypothermia, seen in low birth
weight (LBW) infants and term infants with CNS disorders.
• Core temperature can fall below 32.2°C (90°F).
• More often in home deliveries, emergency deliveries, and
settings where there is inadequate thermoregulatory
support.

Signs may include
1. hypotension;
2. bradycardia;
3. slow, shallow, irregular respiration;
4. poor sucking reflex;
5. abdominal distention or vomiting;
6. decreased activity;
7. decreased response to stimulus; and
8. decreased reflexes.

• These infants may have a bright red color because of the
failure of oxyhemoglobin to dissociate at low temperature.
• They may have central pallor or cyanosis
• Skin may show edema and sclerema.
• Metabolic acidosis, hypoglycemia, hyperkalemia, azotemia,
and oliguria can be present.
• Generalized bleeding, including pulmonary hemorrhage.

D. Hyperthermia, defined as an elevated core body
temperature, may be caused by a
1. relatively hot environment,
2. infection,
3. dehydration,
4. CNS dysfunction,
5. medications.

Environmental contributors such as phototherapy, incubators
or warming table settings, or proximity to sunlight should be
considered.
1. If environmental temperature is the cause of
hyperthermia, the trunk and extremities are the same
temperature and appears vasodilated.
2. In contrast, infants with sepsis are often vasoconstricted
and the extremities are cooler than the trunk.

E. Induced hypothermia.
• Induction of controlled hypothermia can reduce neuronal
loss and subsequent brain injury after a hypoxic-ischemic
insult,
• Therapeutic hypothermia is now standard of care.
• It is a time-sensitive therapy and needs to be instituted
within the first 6 hours after birth to be most effective.

1. History of an acute perinatal event (nonreassuring fetal
heart tracings, cord prolapse, placental abruption),
2. pH less than 7.0, base deficit more than or equal to 16 on
cord gas or gas obtained within 1 hour of life,
3. 10-minute Apgar score less than or equal 5,
4. Assisted ventilation initiated at birth and continued for at
least 10 minutes.
Target temperature range is 32.5° to 34.5°C.
Core temperature should be monitored every 15 minutes.

The Modes of Heat Exchange
1. Convection
• Air movement causes warm air close to the skin to move
away, resulting in heat loss.
• Magnitude of heat loss through convection is similar in
term and preterm infants.
• Convective heat loss is much increased when air velocity is
high (forced convection).

Prevention
1. Place preterm infant in incubator
2. Keep portholes of the incubator closed
3. Warm all inspired air
4. Use servo control for skin temperature

Radiation
• Radiant heat transfer occurs from the infant to
surrounding cooler surfaces.
• Cold walls near infant but not in direct contact with infant
or Cold doors and windows nearby
• The magnitude of heat exchange depends on the
temperatures of the surfaces and the body surface area
exposed.
• Most important route of heat loss in preterm infants
greater than 28 weeks’ gestation

Prevention
• Avoid placement of incubators or bassinets near cold
windows or air conditioners
• Place a hat on the infant’s head
• Place extremely preterm infant in bag or surround with
plastic wrap
• Increase environmental temperature
• Use double-walled incubators

Evaporation
• Evaporation of fluid from the skin surface implies loss of
heat (approximately 2.4 kJ/g water).
• Very immature infants have poor skin barrier function,
leading to large losses of water and heat for several days to
weeks after birth.
• Wet skin and hair after birth or after a bath, Wet clothes
and skin after emesis, Wet diaper and Insensible water loss
from lungs and skin

Prevention
• Dry the infant immediately after delivery
• Keep the infant and clothing dry
• Place preterm or small-for–gestational age infant in occlusive
wrap/bag at delivery
• Delay bath until temperature is stable
• Place infant in an environment with 60% humidity (will
substantially decrease evaporative losses)

• Most important route of heat loss in extremely preterm
infants less than 28 weeks’ gestation
• High loss in extremely preterm infants due to immature
skin
• Even when dry, evaporative loss continues, especially if low
humidity environment.

Conduction
• Contact with cold objects such as scales or cold blanket
• Negligible in most care situations, because mattresses used
in incubators and cots are made of insulating material like
a gel mattress such as those used in some radiant warmer
beds
Prevention
• Place a warm diaper or blanket between the infant and
cold surfaces
• Place infant on prewarmed table at time of delivery
• Warm all objects that are in contact with the infant
• Hold infant skin to skin
• Use exothermic mattress

• Conductive heat delivery (e.g., heated mattress or skin-
toskin care, placing on prewarmed mattres at time of
delivery) is a simple and effective way to rewarm infants
and stabilize body temperature.

Respiratory Loss of Heat
• Respiratory water and heat exchange take place by the
combined processes of evaporation and convection.
• These processes occur as the temperature and vapor
pressure of the inspired air rapidly equilibrates in the
airway.
• The losses are related to air temperature and humidity
and directly proportional to the rate of breathing.
• Provision of a warm and humid environment (e.g.,
humidified incubator) and/or assisted ventilation with
use of adequately warmed and humidified (saturated at
≥37.0°C) gas will reduce respiratory loss of water and
heat to a minimum and aid temperature stability.

IV. THERMONEUTRAL ENVIRONMENT.
• This “thermoneutral zone” is defined as the range of
temperature within which the infant can maintain a
normal body temperature at minimal metabolic rate with
use of non-evaporative processes (vasoconstriction,
vasodilation, and/or changes in posture) only.
• Outside this range, body temperature might still be
maintained at the cost of an increased metabolism.

Central (“Core”) Body Temperature
• Probe inserted into a body cavity (e.g., rectum, esophagus)
• Esophageal temperature measurements represent true
core temperature
• Recommended when very strict thermal monitoring is
needed and body surface measurements are unreliable
(i.e., during therapeutic hypothermia).
• Rectal temperature measurements do not reliably reflect
core temperature,
• Pose unnecessary risks of repeated trauma to the rectal
mucosa, and their use should be limited

V. MANAGEMENT TO PREVENT HEAT LOSS
A. Healthy term infant
1. Standard thermal care guidelines include
• maintaining the delivery room temperature at 23° to
25°C (Neonatal Resuscitation Program)/25°C
(World Health organization),
• immediately drying the infant (especially the head),
• applying a hat if available to prevent significant heat
loss through the scalp,
• removing wet blankets,
• wrapping the newborn in prewarmed blankets,
• prewarm contact surfaces and minimize drafts.

2. Examination in the delivery room should be performed
with the infant under a radiant warmer.
A skin probe with servo control to keep skin temperature at
37°C (98.6°F) should be used for prolonged examinations.

3. Skin-to-skin care during the first 1 to 2 hours of life offers a
practical and effective approach to achieving a neutral
thermal environment.
Thismethod has the added benefit of promoting early
breastfeeding.

Warm chain
Set of ten interlinked steps.
1. Warm delivery room –25 to 28°C
2. Warm resuscitation
3. Immediate drying with warm linen
4. Skin-to-skin contact
5. Breast feeding
6. Postpone bath
7. Appropriate clothing and bedding
8. Rooming in – mother and baby together
9. Warm transportation
10. Training of health personnel and awareness raising

B. Premature infant
1. Standard thermal care guidelines should be followed.
the practice of delayed cord clamping has not been found to
contribute to hypothermia.
2. Additional interventions immediately after birth can
optimize thermoregulation.
a. Barriers to prevent heat loss should be used in extremely
premature infants. These infants should be placed in a
polyethylene bag immediately after birth; Plastic wraps and
bags which are inexpensive are also effective.

b. Gel mattresses have been found to be as effective as the
plastic bags and wraps.
c. A radiant warmer should be used during resuscitation and
stabilization, and the servo-controlled temperature probes
should be placed promptly on the infant.
d. A heated incubator should be used for transport.

3. In the neonatal intensive care unit (NICU), infants require a
thermoneutral environment to minimize energy expenditure
and optimizegrowth;
skin mode or servo control can be set so that the incubator’s
internal thermostat responds to changes in the infant’s skin
temperature to ensure a normal temperature despite any
environmental fluctuation.
If a skin probe cannot be used due to the potential damage to
skin in small premature infants, the incubator should be kept
at an appropriate temperature on air mode.

• once the baby is discharged from NICU, parents are taught
to assess baby’s temperature by touching abdomen and
feet with dorsum of thier hands.
• if cold, that indicates environment is cold and baby is
wrapped and assessed after 30 mins.

4. Humidification of incubators has been shown to reduce
evaporative heat loss and decrease insensible water loss,
typically used for patients less than 1,200 g or 30 to 32
weeks’ gestation for the first 10 to 14 days after birth.

Risks and concerns for possible bacterial contamination have
been addressed in current incubator designs which include
heating devices that elevate the water temperature to a level
that destroys most organisms.
Notably, the water transforms into a gaseous vapor and not a
mist, thus eliminating the airborne water droplet as a
medium for infection.

5. Servo-controlled open warmer beds may be used for very
sick infants.
The use of a tent made of plastic wrap prevent both
convection heat loss and insensible water loss
6. Incubators are designed to decrease all four forms of heat
loss.
Double-walled incubators further decrease heat loss
primarily due to radiation and, to a lesser degree, conduction.

7. Current technology includes hybrid devices they offer the
features of both a traditional radiant warmer bed and an
incubator in a single device with the added capacity to
provide blended oxygen to the neonate.
8. Premature infants in relatively stable condition can be
dressed in clothes and caps and covered with a blanket.
• Kangaroo care should be given in stable preterm babies.
• Heart rate and respiration should be continuously
monitored.
• Cocoon warmer can keep babies warm in between KC
sessions.

Management of hypothermia
Cold stress and moderate hypothemia
Remove cold, wet clothings and place baby in warmer
environment. start skin to skin. if not improved, consider
warmer or incubator.

Severe Hypothermia
• Remove cold, wet clothings and place baby in an incubator
with temperature set at 35-36C
• Rewarming rate: Target temperature elevation by
0.5C/hour with hourly monitoring for 3 hours.
• once temperature reaches 34C, slow rewarming with 2nd
hourly monitoring till normal axillary temperature is
attained.
• thereafter continue 3rdly monitoring for next 12 hours.
• consider INJ. VITAMIN K.

In addition to rewarming, hypoglycemia should be corrected.
The infant may benefit from a normal saline bolus (10 to 20
mL/kg), supplemental oxygen, and correction of metabolic
acidosis.
These infants should not be fed until euthermic and should be
carefully evaluated and treated for possible infection,
bleeding, or injury.

VI. HAZARDS OF TEMPERATURE CONTROL
METHODS
A. Hyperthermia.
A servo-controlled warmer can generate excess heat, which
can cause severe hyperthermia if the probe becomes
detached from the infant’s skin. Temperature alarms are
subject to mechanical failure.
• Look for possible cause
• Check room temperature (maintain at 25-28°C)
• Look for signs of infection
• Look for signs of dehydration

Predisposing factors
• Immature thermoregulatory center
• decreased ability to produce sweat
Common reasons are
• over clothing
• environmental exposure in summer
• poor feeding
• dehydration
• direct sun exposure

Signs of Hyperthermia
• Tachypnea
• Tachycardia
• Flushing
• Hypotension
• Irritability
• Poor feeding
Signs of dehydration
• Sunken eyes, or
• Depressed fontanelle, or
• Loss of skin elasticity, or
• Dry tongue and mucous membrane

• Keep baby away from source of heat (warmer, heater,
sunlight)
• Remove extra clothes
• Decrease environmental temperature (if needed)
• Recheck baby's temperature every 1 hour till normal
• If >39°C, sponge the baby with luke warm water Treat
underlying cause
• Ensure adequate feeding or fluids
• Treat dehydration, if present
• Measure blood glucose; if < 45mg/dL, treat for
hypoglycemia
• Do not give antipyretic

B. Undetected infections.
Servo control of temperature may mask the hypothermia,
hyperthermia, or temperature instability associated with
infection.
A record of both environmental and core temperatures, along
with observation for other signs of sepsis, will help detect
infections.

C. Volume depletion.
Radiant warmers can cause increased insensible water loss.
Body weight, urine output, and fluid balance should be closely
monitored in infants cared for on radiant warmers.

THERMOREGULATION IN NEONATES.pptx

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