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Iowa Neonatology Handbook: Temperature
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.
Reference:
Mayfield SR, Bhatia J, Nakamura KT, Rios GR, Bell EF. Temperature
measurement in term and preterm neonates. J Pediatr 1984;104:271-275.
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