History of Thermoregulation

Incubation traced as far back as the Egyptians

Napoleon brought back to Parisian zoos1800’s used for premature infants1907 started use of temperature control

Basal Metabolic Rate

Human body produces heat as by-product of metabolism

Neutral Thermal Environment

Narrow range of environmental temperatureInfant is not required to adjust heat

production above natural resting levelsMinimal oxygen consumptionUltimate 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 glandsKidneys

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

ConductionRadiationConvectionEvaporation

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

EvaporationHeat loss by conversion of

liquid into vaporMainly transepidermal

water loss (insensible) As relative humidity

the water loss with tachypnea,

activity, radiant warmers and phototherapy

as skin thickens and is less permeable

RadiationTransfer 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 36.2 - 37.5°CAxillary temperature 36.2 - 37.5°CAbdominal skin temp 36.0 - 36.5°C

Temperature probes on abdomen or flanksUse hats & socks

Radiant Warmer

Reflective covers on temperature probesWarm in non-servo (air-control) at

maximum heat before admissionServo control (patient control) with skin

temp set at 36.5 °C

Isolettes

Servo control for < 1250 gramsNon-servo control >1250 gramsAvoid 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

Added 50 % humidity Increased incubator to 38 °CMinimized time portholes were openPreheated diapers and blankets

Third Transport

Heated airplane cabin to 35 °C (95 °F)