To warm or not to warm infant feedings is not really the question. Obviously, refrigerated milk is likely to have an impact on the temperature of a very low birth weight infant, although the extent of that impact will depend on the temperature and volume of the milk. However, what temperature is best for milk delivery remains without extensive research.
Research about milk warming started as far back as 1957. Gibson a community pediatrician, looked at infant’s acceptance of cool or cold feedings.1 Most infants (67%) accepted cold feedings and no difference in growth patterns was found between the groups fed cold, cool or warm milk. These infants were bigger, healthier infants than what we see in the NICU today. They were at home and fed the designated temperature (warmed or not with no specific temperature) by their mother.
One study found no matter what the milk temperature was, body temperature increased. This is likely related to the increase in metabolic rate following feeding. Is this also true in premature infants, and does it extend to very premature infants? Likely, the small feedings we give to the very premature infant does not cause this increase in metabolic rate and therefore body temperature.
There are several theoretical reasons to warm the milk prior to feeding, including (and probably the most significant) the potential effect on the body temperature of the very low birth weight infant. Studies have attempted to show effects of feeding temperature variations and effect on metabolic rate, residuals, effect on body temperature and growth patterns. Gonzales did show an increase in residuals related to cold feedings but this has not been replicated since and was a fairly small sample size.2 Many other practices have changed as well since that time.
So, the benefit of warming feedings and to what ideal temperature is still without good evidence. There is, however, no evidence that this is harmful. As such, the accepted practice is to warm to some as-yet-undefined temperature. The Human Milk Banking Association advocates warming feeds to body temperature for premature infants, particularly those at risk for necrotizing enterocolitis (NEC).3 This generally applies to those under 1500 grams. For term infants, feedings may be given at body temperature, room temperature or straight from the refrigerator.
Two studies have been published in which milk warmed with a warm water bath was evaluated for exact temperature.3, 4 Dumm et al demonstrated a range of milk temperature from 21.8°C to 36.2°C, ranging from less than normal room temperature to low infant body temperature.3 Lawlor-Klean, Lefaiver, Weisbrock demonstrated a range of milk temperature from 22°C to 46.4°C, low room temperature to (72 F) to the temperature of very hot coffee!4 Over-warming may be as detrimental as under warming, deteriorating nutrients, antibodies and more as well as potentially burning an infant.
Thawing and warming may occur in a variety of methods. Clear recommendations have been adopted regarding avoidance of microwave warming or thawing.3 Thawing at room temperature, in the refrigerator or in warm water, are all used. If milk is thawed in warm water, it often reaches room temperature or warmer before taken from the water bath. Once the milk has been warmed to room temperature or beyond, it should not be returned to the refrigerator and therefore, must be used within 4 hours.5 Thawing in the refrigerator or with a controlled mechanism such as is now available on the market should be done to avoid warming. The refrigerator method of thawing requires an extended amount of time for thawing to take place, especially with large amounts of milk.
Regarding milk warming for feeding, either a warm water bath or one of the mechanical methods are commonly used. While the warm water bath is often used, concerns include an unreliable end temperature as already mentioned, as well as possible contamination of the feeding. The issue of contamination is worth discussion. Tap water often contains an “acceptable” level of bacteria that in the normal, healthy population is not of concern. However, contamination of a feeding to be given to a high risk neonate could certainly cause a problem. Tap water often contains an “acceptable” level of pseudomonas and other bacteria we recognize as lethal in the NICU. Even a small amount of these bacteria can be life-threatening to our high-risk infants. Avoidance of feeding contamination is important since translocation of bacteria colonized in the gut has been shown to lead to blood stream infection.
Finally, if the temperature of the milk is indeed important in preventing feeding intolerance and necrotizing enterocolitis, and possibly enhancing growth, what effect does the extended hang time of a continuous feed or feed over time have on the ultimate temperature of the milk when it reaches the infant? If milk is infusing over 30 minutes to 4 hours with tubing extending from the pump to the feeding tube both inside and outside the incubator, temperature will change over this time period, more or less, depending on room temperature, length of infusion time and incubator temperature.
We often think of feeding babies as a simple, almost mindless task in the NICU. As we find out more and more about their nutritional needs and preparation for feeding, we know this, as much as the delicacy of gas exchange during lung disease, requires finesse and attention. The proper nutrition at the proper time is critical for tiny babies whose brains are requiring the majority of the nutrition.
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Read a previous post, The Neonatal Microbiome.
1. Gibson JP. Reaction of 150 infants to cold formulas. J Pediatr. 1958; 52: 404–406
2. Gonzales, I, DurveaEJ, Vasquez E, Garahty N Effect of enteral feeding temperature on feeding tolerance in preterm infants. Neonatal Network. 1995;14(3):39-43.
3. The Human Milk Banking Association of North America, Inc. (2011). Best Practice for Expressing, Storing and Handling Human Milk in Hospitals, Homes and Child Care Settings. HMBANA: West Hartford, CT.
3. Dumm M, Hamms M, Sutton J, Ryan-Wenger N. NICU breast milk warming practices and the physiological effects of breast milk feeding temperatures on preterm infants. Advances in Neonatal Care. 2013;13(4):279-287.
4. Lawlor-Klean P, Lefaiver CA, Wiesbrock J. Nurses’ perception of milk temperature at delivery compared to actual practice in the neonatal intensive care unit. Advances in Neonatal Care. 2013;13(5):E1-E10.
5. Robbins S, Meyers R. Pediatric Nutrition Practice Group. (2011). Infant feedings: Guidelines for preparation of human milk and formula in health care facilities 2nd ed. American Dietetic Association.