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 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 36.2 - 37.5°C Axillary temperature 36.2 - 37.5°C Abdominal skin temp 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 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)