TEMPERATURE CONTROL IN THE NEWBORN INFANT
I. Why Keep the Baby Warm?
A. Cooling of the newborn infant results in increased metabolic demands
B. A decreased body temperature may cause:
1. acidosis
2. hypoglycemia
3. hypoxia
4. pulmonary hypertension
5. apnea and bradycardia
II. How Warm Should We Keep the Newborn Infant?
A. Neutral Thermal Environment (NTE)
1. Definition: the NTE is that environment or skin temperature which allows the metabolic rate of the infant to be at a minimum.
2. In an incubator, air temperature is used as an index of NTE and should be obtained from the bedside nurse flowchart.
3. In an overhead warmer, skin temperature is used as an index of NTE and should be maintained between 36.2 and 37oC.
A. Incubator
1. Remember that the air temperature settings in the charts are only approximations.
2. In the very small baby it is suggested that an abdominal skin temperature be monitored until it is determined that the air temperature setting is appropriate.
3. When infants are clothed (“cot nursed”), lower incubator temperatures may be required to prevent overheating.
4. Humidified incubators are available and should be used for use in all infants < 1000 grams birth weight in the first 7 days of life. Typical humidity settings should be 70% - 80% for this group of infants. After 7 days the humidity setting should be lowered to 50% until 14 days of life. For infants 1.0-1.5 kg birth weight, utilize 50% humidity upon admission.
B. Radiant Warmer
1. Respiratory gases should be isothermic and humidified for babies under radiant warmers.
2. The radiant warmer regulates the temperature on the principle of patient servocontrol.
a. always check the probe to see that it is firmly attached to the skin
b. attach the probe with a single piece of clear tape
c. the probe should always be in an area which is exposed to the radiant heat.
3. The energy cost of evaporative fluid loss is 0.58 cal/cc. For a very small infant on a radiant warmer (not what we usually do), use of a polyethylene occlusive barrier over the infant may aid in reducing free H2O losses. Apply it so that there is no air flow (eliminate convection losses). Keratinization of skin occurs enough to prevent excessive free water losses after the first 5-7 days of life in the very small infant. The use of a polyethylene occlusive barrier should be reserved only for those infants < 1000 grams who cannot be moved to a maximally humidified incubator.
4. Optimal temperature probe placement is on the side of the infant facing up. If the probe is trapped between the infant and the bed, there is a high probability that the baby will be overheated.
C. General
The trigeminal area of the face is particularly sensitive to changes in the environmental temperature.
1. Therefore, respiratory gases must be heated and humidified.
2. A temperature of between 35o and 37oC or approximately the same as indicated for NTE is usually appropriate.
3. The application of over-heated gases in an oxyhood may cause apnea, tachypnea and/or overheating.
4. Remember that it takes 5 times as much energy to humidify as it does to heat gas, therefore always humidify respiratory gases.
IV. Radiant Warmer versus Incubators
It has been shown that both radiant warmers and incubators can maintain a thermoneutral environment. The indications as to which device to use will depend on the clinical situation of the baby.
A. Indications for use of a radiant warmer
1. In general, all new admissions should be placed into an appropriately pre-heated and humidified incubator unless it is determined that the need for better patient access is required for immediate invasive procedures such as umbilical lines.
2. As the baby becomes more stable he should be moved to an incubator.
B. Indications for an incubator
1. Any baby who does not require radiant warmer should be maintained in an incubator at the appropriate environmental temperature.
2. Humidified incubators are to be utilized for smaller infants with birth weight < 1.0 kg. Humidification should be maintained between 70%-80%. Higher levels will fog up the incubator.
3. Humidified incubators are to be utilized for infants with birth weight 1.0 – 1.5 kg. Humidification should be maintained at 50%.
V. Weaning From an Incubator
A. The weaning process should begin at 32 weeks PCA. Infants should be clothed (“cot nursed”) at this time and the incubator should be placed on Air Servo Control. The air temperature should be set and adjusted with the use of the NTE (Neutral Thermal Environment) Chart.
B. Weight loss at adequate caloric intake may indicate weaning that has begun too early. Poor feeding, general lethargy, acidosis, or increased frequency of apnea and bradycardia may also indicate an immature temperature regulation capacity. Alternatively, these signs and symptoms are also associated with the onset of sepsis.
VI. Re-warming Following Delivery or Admission from Home
A. Need to provide a heat-gaining environment to stop any ongoing heat losses
1. Rapid re-warming at > 1º C per hour has been associated with metabolic acidosis, severe IVH and higher mortality in the VLBW infant. Therefore, re-warming should be regulated carefully and should occur very slowly. Body temperature should increase at approximately 1º C per hour.
2. Make sure infant becomes increasingly warmer (measure frequent body temps)
3. Minimize evaporative loss by increasing humidity (esp. in new admission or ELBW infant)
4. Minimize radiant losses by protecting incubator walls from excess cooling.
5. Place the cold infant on Air Servo Control with the set point at approx. 0.5 - 1º C over the current body temperature of the infant. Each hour, adjust the set point higher by 0.5 - 1ºC. When the infant’s body temperature is normal, place the incubator into Patient Servo Control mode with the set point at the usual 36.5º C.
B. Check for routes of heat loss.
C. Swaddling or external radiant lamps.
D. Watch for apnea with hypothermia or rapid warming. Also remember that temperature instability may be a sign of infection in any neonate.