The chance of survival of neonates is markedly enhanced by the successful prevention of excessive heat loss. For that purpose, the newborn infant must be kept under a neutral thermal environment. This is defined as the external temperature range within which metabolic rate and hence oxygen consumption are at a minimum while the infant maintains a normal body temperature (Figures 6–1 and 6–2 and Table 6–1). The normal skin temperature in the neonate is 36.0–36.5°C (96.8–97.7°F). Thenormal core (rectal) temperature is 36.5–37.5°C (97.7–99.5°F). Axillary temperature may be 0.5–1.0°C lower (95.9–98.6°F). A normal body temperature implies only a balance between heat production and heat loss and should not be interpreted as the equivalent of an optimal and minimal metabolic rate and oxygen consumption.
Neutral thermal environment during the first week of life, based on gestational age. (Reproduced, with permission, from Sauer PJJ et al: New standards for neutral thermal environment of healthy very low birthweight infants in week one of life. Arch Dis Child 1984;59:18.)
Neutral thermal environment from days 7 to 35 (in °C), based on body weight. (Reproduced, with permission, from Sauer PJJ et al: New standards for neutral thermal environment of healthy very low birthweight infants in week one of life. Arch Dis Child 1984;59:18.)
Table 6–1. APPROXIMATE NEUTRAL THERMAL ENVIRONMENT IN INFANTS WHO WEIGH >2500 g OR ARE >36 WEEKS' GESTATIONa |Favorite Table|Download (.pdf)
Table 6–1. APPROXIMATE NEUTRAL THERMAL ENVIRONMENT IN INFANTS WHO WEIGH >2500 g OR ARE >36 WEEKS' GESTATIONa
Data not establishedb
Hypothermia and excessive heat loss. Preterm infants are predisposed to heat loss because they have a high ratio of surface area to body weight, little subcutaneous fat, and reduced glycogen and brown fat stores. In addition, their hypotonic ("frog") posture limits their ability to curl up to reduce the skin area exposed to the colder environment.
Mechanisms of heat loss in the newborn include the following:
Radiation. Radiation is heat loss from the infant (warm object) to a colder nearby (not in contact) object.
Conduction. Conduction is direct heat loss from the infant to the surface with which he or she is in direct contact.
Convection. Convection is heat loss from the infant to the surrounding air.
Evaporation. Heat may be lost by water evaporation from ...
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