Transcript History of Thermoregulation

History of Thermoregulation
 Incubation traced as far back as the
Egyptians
 Napoleon brought back to Parisian zoos
 1800’s used for premature infants
 1907 started use of temperature control
Basal Metabolic Rate
 Human body produces heat as by-product of
metabolism
Neutral Thermal Environment
 Narrow range of environmental temperature
 Infant is not required to adjust heat
production above natural resting levels
 Minimal oxygen consumption
 Ultimate goal
Shivering and Sweating
 Adults - Shivering is heat production from
voluntary and involuntary rhythmic muscle
activity. Sweating decreases heat by
vasodilation and evaporation.
 Neonates - Unable to produce heat by
shivering. Infants < 30 weeks cannot sweat,
and have 1/3 the response > 32 weeks.
Non-shivering Thermogenesis
Brown Fat Metabolism
 Brown Fat is Found:
 Around the great
vessels
 Adrenal glands
 Kidneys
 Axillas
 Nape of neck
 Between the scapulas
Brown Fat Metabolism
 Most important means of heat production in
neonates
 Present at 26 - 28 weeks gestation &
increases until 3 - 5 weeks postnatal
 Comprises 2.7% of total body weight in
term infant
 Cannot be replenished
Heat Transfer
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Conduction
Radiation
Convection
Evaporation
Conduction
 Transfer of heat between
solid objects in direct
contact
 Cold scale, circumcision
board, mattress
 Chemically activated
warmers, heated water
mattresses, skin-to-skin
 > on metals, < on cloth
Convection
 Transfer of heat to the
air moving across and
around the body
 Varies based on
temperature gradient,
body surface exposed
and speed of air
movement
Evaporation
 Heat loss by conversion of
liquid into vapor
 Mainly transepidermal
water loss (insensible)
 As relative humidity 
the water loss 
  with tachypnea,
activity, radiant warmers
and phototherapy
  as skin thickens and is
less permeable
Radiation
 Transfer of heat
between solid objects
that are not in direct
contact
 Surrounding walls and
windows, including
isolette walls
 Accounts for 64% of
the total dry heat loss
in premature infants
Hypothermia
 Short-term : Hypoglycemia, hypoxia,
metabolic acidosis (metabolism of brown
fat), anaerobic metabolism
 Long-term : Impaired weight gain, RDS,
heart failure, depletion of energy sources
 At risk : Premature infants, small for
gestational age, infants stressed due to
sepsis, RDS, asphyxia
Hyperthermia
 Causes : Overheating, phototherapy, sepsis,
CNS disorders, dehydration, maternal fever
RCNIC Guidelines
 Core temperature
 Axillary temperature
 Abdominal skin temp
36.2 - 37.5°C
36.2 - 37.5°C
36.0 - 36.5°C
 Temperature probes on abdomen or flanks
 Use hats & socks
Radiant Warmer
 Reflective covers on temperature probes
 Warm in non-servo (air-control) at
maximum heat before admission
 Servo control (patient control) with skin
temp set at 36.5 °C
Isolettes
 Servo control for < 1250 grams
 Non-servo control >1250 grams
 Avoid obstructing airflow
True Story
 When the transport team in Denver started
fixed wing air transport, they had difficulty
keeping infants warm.
 First trip: Full-term, preheated 37 °C
incubator.
Second Transport
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Added 50 % humidity
Increased incubator to 38 °C
Minimized time portholes were open
Preheated diapers and blankets
Third Transport
 Heated airplane cabin to 35 °C (95 °F)