Keeping Infants Warm
Neil McIntosh, DSc(Med)Andrew J. Lyon, MB
Child Life and Health
Reproductive and Developmental Medicine
Edinburgh EH9 1UW, Scotland
To the Editor.—
Neonatal management differs around the world. In the United States, small infants usually graduate from radiant heaters to incubators when they are no longer unwell, whereas in the United Kingdom small infants are usually managed in incubators and graduate out of these to cots.
Meyer et al1 compared the use of radiant heaters and incubators in preterm infants, concluding that the former may have advantages. However, the differences they report are only a reflection of their lack of understanding of how incubators should be used when admitting small, cold infants to their unit.
More than 50% of infants in each group had an admission temperature below 36°C. This high incidence of admission hypothermia/cold stress reflects poor delivery room practice. A radiant heater, using skin servo control, would be expected to rapidly raise the temperature of these cold infants. In contrast, the efficacy of warming in an incubator, using air mode control, depends on the starting air temperature—we were not informed as to what this was! In addition, raising the incubator temperature by only 0.1°C if the axillary temperature is cold, is homeopathic. This process, repeated only every 30 minutes, is guaranteed to prolong hypothermia with incubator management in their study.
This study should have considered 2 things to make a proper comparison of radiant heaters with incubators. First, the authors should have piloted their use of incubators to understand better their use. Second, although the discussion by the authors about why incubators should be used in air mode was true 20 years ago, it may not be true now (with double shells and proportional control). Certainly for this study both interventions should have been by servo control to make an appropriate comparison.
The major lesson that should be taken from this article is how important it is to manage very low birth weight infants in the delivery room to avoid cold stress, as temperature on admission is an independent marker of poor outcome in the very preterm infant.2
It is always interesting for incubator users to see the lengths that some use to turn radiant heaters into humidified incubators! With the careful use of humidity, it is unlikely that any significant difference in outcome would be found when comparing radiant heaters with correctly used and humidified incubators.
REFERENCES
- Meyer MP, Payton MJ, Salmon A, Hutchinson C, de Klerk A. A clinical comparison of radiant warmer and incubator care for preterm infants from birth to 1800 grams.
Pediatrics.2001; 108
:395
–401
[Abstract/Free Full Text] - Costeloe K, Hennessy E, Gibson AT, Marlow N, Wilkinson AR for the EPICure Study Group. The EPICure study: outcomes to discharge from hospital for infants born at the threshold of viability.
Pediatrics.2000; 106
:659
–671
[Abstract/Free Full Text]
Keeping Infants Warm
Michael Meyer, MDM. Payton, MD
South Auckland Health
Middlemore Hospital
Private Bag 93311 Otahuhu
Auckland, New Zealand
We have no doubt that keeping preterm infants warm on admission is extremely important. Drs McIntosh and Lyon state that a high incidence of low admission temperature reflects poor delivery room management. According to this, many units around the world suffer from poor technique, eg, in the United Kingdom, the EPICure Study found that of preterm infants 24 and 25 weeks’ gestation, 36% had admission temperatures <35°C.1 In another study, nearly 50% of infants < 32 weeks’ gestation had an admission temperature of 36°C or below when managed according to the Neonatal Resuscitation Program protocol. 2 Although undesirable, the point is that being cold on arrival to the nursery is common for small preterm infants. The low temperature is partly preventable (by polyethylene wrapping2) and, on the basis of 2 studies, more rapidly corrected by radiant heating than incubator nursing.3,4
Drs McIntosh and Lyon wrongly assume we were predominantly radiant warmer users before the study—our neonatal nurses used primarily incubator care. In fact, we did run a pilot study, but it was on the use of the radiant warmer! Their assertion that the changes we made to the set temperatures of both the radiant warmers and incubators were too small needs clarification. These changes were for infants who had been in a stable thermal environment; gradual reductions in set temperature were essential with increasing postnatal age, as we stated in the article. We did not want to create thermal stress by rapid changes in set temperature!
We did not describe our management when a cold infant was admitted to an incubator and a neutral thermal environment had not been obtained. The starting incubator air temperature depended on birth weight5—the range was, in fact, stated in the "Methods." If the abdominal skin temperature was low with the incubator approaching the set air temperature, the air temperature was increased by the nurses by 0.5°C to 2°C, depending on the difference between the desired and actual abdominal skin temperature. The air temperature was then adjusted by smaller amounts to find the air temperature required to maintain abdominal skin temperature.
We disagree that abdominal servo should have been used instead of air mode in the incubator group. Greater thermal instability has been noted with abdominal servo (even with modern incubators). We are not aware of any published evidence to refute this, and as recently as 1997, Lyon et al6 themselves stated they use air mode "because of known increased thermal stress caused by servo control driven by a set abdominal skin temperature."
Drs McIntosh and Lyon suggest there is no difference in outcome between incubators and radiant warmers. However, Dr McIntosh’s research has shown the effects of nursing procedures on temperature (in)stability with incubators.7 According to Dr McIntosh’s group,7 "the change in temperature is often substantial—as much as 2.4°C centrally and 3.0°C peripherally—with slow recovery to normal" and this "may influence ultimate outcome." The slow recovery is because convective air heating in an incubator is relatively inefficient. On a radiant warmer, temperature loss associated with procedures, eg, temporary removal of humidification, is rapidly corrected because radiant heat directly warms subcutaneous tissues. In our study this resulted in a greater percentage of abdominal temperatures in the desired range on day 1 and low temperature in the first 12 hours affects mortality rates.8
Because of the effectiveness of radiant heat, a radiant warmer with humidity is not at all the same as a humidified incubator when the environment is disturbed, as it frequently is in first few days of life of a sick preterm infant. Perhaps the USA practice of initially using radiant heaters has merit.
REFERENCES
- Costeloe K, Hennessy F, Gibson AT, Marlow N, Wilkinson AR for the EPICure Study Group. The EPICure study: outcomes to discharge from hospital for infants born at the threshold of viability. Pediatrics.2000; 106 :659 –671
- Vohra S, Frent G, Campbell V, Abbott M, Whyte R. Effect of polyethylene occlusive skin wrapping on heat loss in very low birth weight infants at delivery: a randomized trial. J Pediatr.1999; 134 :547 –51[CrossRef][Web of Science][Medline]
- Meyer MP, Payton MJ, Salmon A, Hutchinson C, deKlerk A. A clinical comparison of radiant warmer and incubator care for preterm infants from birth to 1800 grams. Pediatrics.2001; 108 :395 –401
- Robinson RO, Jones R. Advantages and disadvantages of overhead radiant heaters. Proc Roy Soc Med.1977; 70 :209 –211[Medline]
- Rutter N. Temperature control and its disorders. In:Roberton NRC, ed. Textbook of Neonatology. Edinburgh, Scotland: Churchill Livingstone; 1986:148–161
- Lyon AJ, Pikaar ME, Badger P, McIntosh N. Temperature control in very low birthweight infants during first five days of life. Arch Dis Child.1997; 76 :F47 –F50[CrossRef][Web of Science]
- Mok Q, Bass CA, Ducker DA, McIntosh N. Temperature instability during nursing procedures in preterm infants.
Arch Dis Child.1991; 66
:783
–786
[Abstract/Free Full Text] - Richardson DK, Corcoran JD, Escobar GJ, Lee SK. SNAP-II and SNAPPE-II: simplified newborn illness severity and mortality risk scores. J Pediatr.2001; 138 :92 –100[CrossRef][Web of Science][Medline]
PEDIATRICS (ISSN 1098-4275). ©2002 by the American Academy of Pediatrics
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