Thermoregulation

Published on 03/06/2015 by admin

Filed under Neonatal - Perinatal Medicine

Last modified 22/04/2025

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CHAPTER 8 Thermoregulation

David Cartwright

Background

• Temperature regulation is critical to survival of preterm babies. They have few mechanisms for losing heat if too warm, a high surface-area-to-volume ratio making heat loss easy, and few mechanisms for increasing body temperature when cool.

• Preterm babies have much lower body fat stores than term babies, particularly of ‘brown fat’ which is a good energy store that is able to be converted to heat readily.

• Very preterm babies have very thin, permeable skin, which allows increased water loss across the skin. This evaporative water loss is also a potent source of heat loss. Some units use a plastic wrap to ameliorate this heat loss before admission to the nursery.

• It is best to avoid hyperthermia.

While there are good data showing that the long-term management of preterm babies in suboptimal environmental temperatures is associated with poorer survival, and there are data showing an association between low admission body temperature and poorer survival, there are no data which show that admission hypothermia and the subsequent short-term hypothermia that occurs in the intensive care unit are causative of that poorer outcome. Admission hypothermia could simply be a marker for sicker infants who have already required more than usual intervention and who will have poorer outcomes. It cannot be assumed that making babies warmer at admission will improve their survival — more research is needed to determine a causal link between transient hypothermia and poor outcome, and whether improving admission temperatures is an effective intervention.

Techniques

The ‘thermo-neutral range’ for environmental temperature (i.e. the environmental temperature at which a baby’s energy expenditure is lowest) is generally higher and narrower the more immature the baby. We need to provide warmth and minimise radiant and evaporative heat losses.

1. Provide warmth — generally an incubator or open bed with radiant warmer is used.

We recommend using incubators exclusively for all preterm babies; be aware of the slightly increased difficulty in performing vascular access procedures that comes with that. These procedures really can be performed very readily inside incubators, particularly the more modern, roomier ones. Some units, however, prefer to initially nurse a baby under a radiant warmer. The use of radiant warmers increases evaporative fluid losses.

2. Minimise radiant heat losses — have the room in which the babies are kept warmed to 24–26°C. A double-walled incubator also assists in reducing radiant heat losses.

3. Minimise evaporative heat losses — use an incubator rather than an open bed with a radiant warmer. Provide high humidity — many of the newer incubators can do this very efficiently. Use as much humidity as is possible while avoiding ‘rainout’ in the incubator — in the order of 60–80%.

4. The heat outputs of both incubators and radiant warmers can be servo-controlled to the baby’s skin temperature, which is a more sensitive indicator of a cool infant than its core temperature. A baby in a suboptimal thermal environment will maintain its core temperature longer than its skin temperature, but this will be at the expense of energy that should be used for breathing and growing. Skin servo-control can be a very efficient method of allowing the baby to determine its own neutral thermal environment: set the skin temperature 0.5–1°C below core temperature, e.g. 36.2–36.5°C.

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