A neutral thermal environment is one in which the infant’s core temperature is maintained while minimizing the metabolic rate and oxygen consumption. Mechanisms of heat loss include:

Conduction:  transfer of heat between solid objects through surface contact

Convection:  heat transfer by movement of a transmitting fluid (air)

Radiation:  direct heat transfer by electromagnetic radiation

Evaporation:  loss of heat via the conversion of fluid to water vapor

General Guidelines:

The normal range for axillary temperature is 36.5 – 37.5°C. Servo-controlled abdominal skin temperature should be maintained at 36.2 - 36.5°C.

Axillary temperature should be taken every 2-4 hours. If the temp is outside the normal range, it should be taken hourly until it returns to normal.

Document the bed type and the infant’s temperature. Bed, heated mist temperatures, and humidity temperatures should be recorded hourly. Skin temperature should be recorded hourly when using the servo control mode. Record any type of cold stress event, i.e. resuscitation, line placement, procedures, etc.

Parents should be taught the rationale for thermoregulation procedures and how to take their baby’s temperature.

1. The skin probe should be attached using a hydrogel probe cover. Use the servo control setting. Positioning the infant on the temp probe may cause heat trapping.
2. A knitted or stockinette cap should be placed on the head unless otherwise indicated.
3. Warm hands and stethoscope before handling infant.
4. Change wet diapers as soon as possible to prevent heat loss by conduction and evaporation.
5. Socks or booties may be worn unless an umbilical artery catheter is in place.
6. Dry quickly after bathing.
7. The infant should be well wrapped in blankets when held by parents.

Special considerations for the <1500 g infant (and especially the <1000g infant)

1. Inbed scales are recommended.
2. A Giraffe bed is ideal; however, if a Giraffe is not available, use a Plexibox and plastic tent to decrease convective and evaporative losses.
3. Use heated mist for at least the first 2 weeks of life. The heated mist temperature should correlate very closely with the bed temperature or slightly higher. A small opening should be made in the tent to prevent rainout. (Macrocondensation increases water-borne organisms in the environment and the risk of nosocomial sepsis.) Otherwise, the tent should be secured to prevent drafts and to maintain humidity. The infant should be kept dry.
4. Burn sheets may be used on infants with fragile or impaired skin.
5. Aquaphor should be applied to the skin of <1000g infants for the first 4 days of life.

By decreasing transepidermal water loss, it decreases evaporative heat loss.

Incubators

1. Move the premature neonate to an incubator from an open bed warmer as soon as clinically indicated.
2. A double-walled incubator is recommended to decrease radiant heat loss.
3. The standard incubator temperature chart may be used to find a starting air temperature for the incubator.
4. When humidity is used, fill with distilled water only. Humidity of 60 – 80% will allow the incubator temp to be decreased.
5. A knitted or stockinette cap, shirt, and/or socks may be worn.
6. The infant should be dressed in a shirt and cap and well wrapped in blankets when out of the incubator.

1. Growing premature infants should wean to a crib or bassinet when clinically indicated. Assessment of readiness should be evaluated around 1600g. Postnatal age should also be considered.
2. Infants should be dressed. A cap should be worn.

Other measures to minimize heat loss and support heat production:

1. Use contact material of low thermal conductivity e.g. gelfoam mattress.
2. Prevent contact with cool surfaces e.g. be aware of enhanced conductive heat loss when weighing an infant on a cold metal scale.
3. Use preheated sterile drapes during stabilization procedures.
4. Prevent exposure to air currents, such as cold drafts from air-conditioning vents.
5. Prevent fluctuations in ambient temperature e.g. frequent opening of portholes of an incubator for various procedures can lead to a precipitous drop in ambient temperature and enhanced convective heat loss.
6. Maintain normal oxygenation. A hypoxic state is detrimental to normal metabolic activity.
7. Maintain adequate caloric and nutrient intake. Adequate substrate is necessary as fuel for normal metabolic activity.

The above guidelines can also be found in the NICU Nursing Guidelines Manual, #40:08.17 and the NICU Manual 2001.

References:

Baumgart S. Thermal regulation in the fetus and newborn. Intensive Care of the Fetus and Neonate. Mosby, 1996.

Flenady VJ, Woodgate PG. Radiant warmer vs incubators in newborn infants. Cochrane Systematic Reveiws. http://www.nichd.nih.gov/cochraneneonatal/Flenady2/Flenady.htm