Detection and Management of Abnormal Body Temperature
Edward F. Bell, MD
Peer Review Status: Internally Peer Reviewed
The normal axillary temperature of a newborn infant, if correctly measured for 5 minutes, is from 36.5 to 37.4°C (mean + 1.5 S.D.). This range should be applied to both the term and premature infant. If measured for a shorter period (less than 5 minutes), the normal range is somewhat lower but has not been clearly defined. In order to avoid the incorrect diagnosis of hypothermia, an axillary temperature below 36.5°C should only be recorded and reported to the physician if read after the thermometer has been held in place for a full 5 minutes.
If the axillary temperature is above 37.4°C (or rectal temperature above 37.5°C), it is important to decide whether the infant has a fever or environmental hyperthermia. With fever, as seen sometimes with infection, the hypothalamic set point is elevated and the infant uses his thermoregulatory control systems to maintain a high body temperature. In some situations this high temperature may help to fight the infection. A febrile infant often has peripheral vasoconstriction with cool skin and extremities.
An infant with a fever may be difficult to cool; in fact, it may be undesirable to lower axillary temperature to normal if the skin is already cool. First, it is important to record both skin (probe) and axillary temperature of a febrile infant as well as the air temperature for the infant in an incubator. If the skin temperature is 36.0 to 36.5°C and the axillary (or rectal) temperature is 38.0°C or less, the thermal environment should not be changed. If necessary, the skin temperature set point can be lowered to 35.5 or even 35.0°C in order to keep the axillary temperature below 38.0°C. If a skin temperature of less than 35.0°C is required to keep the axillary temperature below 38.5°C, the fellow or staff neonatologist should be consulted.
The infant with environmental hyperthermia should be cooled to a normal axillary temperature by decreasing environmental heating or reducing thermal insulation (blankets or clothing). A bath or cooling mattress should not be necessary to correct hyperthermia caused by environmental overheating.
An infant with hypothermia can be rewarmed by a radiant heat or an incubator with higher air temperature. The simplest way to avoid overheating during rewarming with a radiant warmer is to use the skin temperature servocontrol with a set point of 36.5°C. The rate of rewarming is probably not critical.
Mayfield SR, Bhatia J, Nakamura KT, Rios GR, Bell EF. Temperature measurement in term and preterm neonates. J Pediatr 1984;104:271-275.