NICU breast milk warming practices and the physiological effects of breast milk feeding temperatures on preterm infants

Effects of the thawing rate and heating temperature on immunoglobulin A and lysozyme activity in human milk

Background

The percentage of infants receiving frozen human milk (HM) is increasing. The effects of thawing and warming on the secretory immunoglobulin A (SIgA) level and lysozyme activity in frozen HM should be investigated to identify optimal methods for preserving immune factors in frozen HM.

Methods

Milk samples were collected from 40 mothers with healthy full-term infants who had been lactating for one to six months. The baseline samples were analyzed within 24 h after collection, and the other samples were frozen at -18 °C before analyses. We compared two methods: placing the container overnight in a refrigerator at 4 °C before warming (slow thawing) and immediately thawing in warm water after removing the sample from the freezer (rapid thawing). Additionally, we investigated the effects of the warming temperature by comparing room temperature (25 °C) and physiological temperature (37 °C). The SIgA concentrations and lysozyme activities in the milk samples were determined using ELISA kits and fluorometric lysozyme activity assay kits, respectively.

Results

The SIgA concentrations and lysozyme activity in frozen HM were 16.5–52.1% and 16.8–39.3% lower than those in fresh HM, respectively. The SIgA concentrations in frozen HM were stable during slow thawing at 37 °C (p = 0.072) compared with those in fresh HM. The SIgA concentrations and lysozyme activity were maintained at significantly higher levels during slow thawing than during rapid thawing at 25 °C (p = 0.002 and p < 0.001, respectively). Slow thawing preserved higher SIgA concentrations and lysozyme activity than rapid thawing at 37 °C, but the difference was not significant.

Conclusions

The SIgA level in HM frozen at -18 °C for two months was stable after overnight thawing in the refrigerator (4 °C for 12 h) before warming to 37 °C compared with that in fresh milk. The thawing of HM in the refrigerator overnight (and then warming to 25 °C or 37 °C for 30 min) has the potential to preserve the SIgA concentration and lysozyme activity to a greater extent than heating immediately after removal from the freezer. Broader temperature ranges should be analyzed to determine the temperature that minimizes the losses in SIgA concentration and lysozyme activity in HM.

The Effect of a Continuous Milk Warming System on Weight Gain in Very Low Birth-Weight Infants: A Randomized Controlled Trial

BACKGROUND

Few studies support the practice of warming human milk before feeding. No studies have compared the method of warming milk and its effect on growth, particularly in preterm infants.

PURPOSE

To evaluate growth in preterm infants receiving continuously warmed human milk as compared with infants receiving human milk warmed in a hot water bath before feeding.

METHODS

Forty-four infants less than 32 weeks' gestation admitted to a regional referral level IV neonatal intensive care unit in south central United States were randomly assigned to either the experimental group (continuous warming: n = 22) or the control group (hot water bath: n =22) for 10 days. All infants were on full human milk feedings (120-130 kcal/kg/d) as part of a standardized feeding protocol. Tolerance and weight gain over the 10-day period were used to evaluate the effectiveness of continuous milk warming.

RESULTS

There was a significant difference in weight gain for infants receiving continuously warmed milk compared with infants receiving standard warmed milk (203.73 ± 70.71 vs 271.95 ± 67.40, P = .002).

IMPLICATIONS FOR PRACTICE

The use of continuous milk warming improves weight gain in very low birth-weight infants.

An Experimental Study on Human Milk Rheology: Behavior Changes from External Factors

The influence of external factors, including temperature, storage, aging, time, and shear rate, on the general rheological behavior of raw human milk is investigated. Rotational and oscillatory experiments were performed. Human milk showed non-Newtonian, shear-thinning, thixotropic behavior with both yield and flow stresses. Storage and aging increased milk density and decreased viscosity. In general, increases in temperature lowered density and viscosity with periods of inconsistent behavior noted between 6–16 ∘ C and over 40 ∘ C. Non-homogeneous breakdown between the yield and flow stresses was found which, when coupled with thixotropy, helps identify the source of nutrient losses during tube feeding.

Preterm Infants May Better Tolerate Feeds at Temperatures Closer to Freshly Expressed Breast Milk: A Randomized Controlled Trial

PURPOSE

Feeding intolerance is one of the most frequent problems among preterm infants. These infants are fed with expressed breast milk or preterm formulas of which the temperature is not routinely measured. In this study, we aimed to examine the effects of feeds with warm milk versus room temperature milk in preterm infants.

MATERIALS AND METHODS

Infants with a birth weight ≤1,500 g or gestational age ≤34 weeks were included in the study and assigned to two different feeding temperature groups (22-24°C and 32-34°C). Some infants in both groups were exclusively breast milk-fed, and some received breast milk and artificial milk (mixed feeding). Feeding tolerance of infants in both groups and the consequences were evaluated.

RESULTS

In total, 80 preterm infants (group 1 fed with milk at 22-24°C, n = 40; group 2 fed with milk at 32-34°C, n = 40) were prospectively included in the study. There was a slight decrease in gastric residual frequency in infants fed with breast milk in group 2. Apnea was significantly more frequent in group 1 (p = 0.006), and these infants needed more anti-reflux treatment (p = 0.013).

CONCLUSION

According to our results, warming enteral feeds close to body temperature are encouraging especially due to the decrease in gastric residual frequency, apnea of prematurity, and need for anti-reflux treatment. More studies may confirm the positive effect of warm enteral feeds on feeding tolerance in preterm infants.

Human Milk Warming Temperatures Using a Simulation of Currently Available Storage and Warming Methods

Human milk handling guidelines are very demanding, based upon solid scientific evidence that handling methods can make a real difference in infant health and nutrition. Indeed, properly stored milk maintains many of its unique qualities and continues to be the second and third best infant feeding alternatives, much superior to artificial feeding. Container type and shape, mode of steering, amount of air exposure and storage temperature may adversely affect milk stability and composition. Heating above physiological temperatures significantly impacts nutritional and immunological properties of milk. In spite of this knowledge, there are no strict guidelines regarding milk warming. Human milk is often heated in electrical-based bottle warmers that can exceed 80°C, a temperature at which many beneficial human milk properties disappear. High temperatures can also induce fat profile variations as compared with fresh human milk. In this manuscript we estimate the amount of damage due to overheating during warming using a heat flow simulation of a regular water based bottle warmer. To do so, we carried out a series of warming simulations which provided us with dynamic temperature fields within bottled milk. We simulated the use of a hot water-bath at 80°C to heat bottled refrigerated milk (60 ml and 178 ml) to demonstrate that large milk portions are overheated (above 40°C). It seems that the contemporary storage method (upright feeding tool, i.e. bottle) and bottle warming device, are not optimize to preserve the unique properties of human milk. Health workers and parents should be aware of this problem especially when it relates to sick neonates and preemies that cannot be directly fed at the breast.