What Is Known/What Is New
What Is Known
- Nutrient losses are more associated with continuous than bolus feeds.
- Fat losses constitute a significant amount of the nutrients lost.
What Is New
- Adjusting the method of milk delivery significantly reduces these losses.
- Fat losses are significantly diminished in this new method.
Extrauterine growth restriction remains one of the most common morbidities in extremely low-birth-weight (ELBW) infants. Optimizing nutrition for this critical group has focused on different approaches to fortification. These have ranged from using higher protein intake (1), enhancing feeds with human milk-derived cream (2), and usage of exclusive human donor milk (HDM) fortifiers (3). HDM has gained increased utilization in ELBW infants as its usage has been associated with a decreased incidence of necrotizing enterocolitis (4). HDM may offer the advantage of known protein content and comes in different caloric concentrations. Similarly, to expressed breastmilk (EBM), HDM is also fortified when offered to ELBW infants. To optimize nutritional contents of delivered milk soon after birth, different practices have looked at early fortification (5,6). Although there remains a wide range of practices on when to fortify human milk and how to diversify the nutritional content of the prepared human milk, preventative approaches looked at ways to maintain the quality and minimize nutrient losses during the preparation or the delivery of human milk. More than half a century ago, milk fat has been shown to adsorb to tube delivery systems causing a significant drop in both fat and caloric contents of delivered milk (7). To address this issue among others, bolus feeds as compared with continuous feeds have been recommended as the method associated with a lower loss of fat content (3,8).
During continuous feeds in our practice, the syringe is positioned vertically pointing upwards. It is common to develop a precipitate by the end of the feed especially when a human milk fortifier (HMF) was being used as a supplement (Fig. 1). This precipitate was the last volume to be infused and would typically end up being wasted as connector feeding tubes were discarded after the end of feedings. We thus hypothesized that during continuous feeds, including the precipitate as part of the targeted delivered volume should significantly minimize macronutrient losses. Our objective was to compare our standard way of delivery with a new method whereby the left-over milk in the tube is pushed towards the infant at the end of the feeding.
This was an in vitro model conducted at the Regional One Health Hospital neonatal intensive care unit (NICU), Memphis, TN. The study protocol was approved by the Institutional Review Board at the University of Tennessee Health Science Center and was deemed exempt as it did not involve human subjects.
The study was designed to evaluate macronutrient losses during tube feedings in the smallest ELBW infants. For an infant weighing 450 g feeding at 150 mL/kg, a schedule of 8 mL of milk delivered every 3 hours would be ordered. Human milk was thawed and homogenized by gentle stirring. Similac Human Milk Fortifier Powder (Abbot Nutrition, Columbus, OH) was added to prepare a 24 kcal/oz product at a ratio of 1 packet (5 mL) to every 25 mL of human milk. Milk was analyzed using the SpectraStar Near-Infrared Analyzer (Unity Scientific, Columbia, MD). An infusion pump (Medfusion 3500) was attached to a pole with the infusion syringe (Covidien Monojet 12 mL Enteral Syringe with Tip Cap) placed in vertical position with tip of syringe pointing up. The syringe was attached to extension tubing (Covidien Kangaroo Extension Set 152.4 cm) with end of the tubing pointing into glass collection cup. Plastic wrap was placed on top of collection cup to prevent evaporative losses.
In the standard method, 11 mL of milk were drawn up into a syringe. The syringe cap was placed back on, and the contents of syringe were gently stirred. The syringe cap was removed and 1 mL of breast milk was emptied into the testing plate of human milk analyzer to get baseline measurements of macronutrient contents. Of the remaining 10 mL in the syringe, 2 mL were used to prime the extension tubing leaving 8 mL left in the syringe. The infusion pump was then set to run at 2.67 mL/hour, thus delivering 8 mL over 3 hours.
The 8 mL delivered milk was collected in a glass cup. It was rewarmed again by dipping the cup in warm water for 3–5 minutes while stirring gently. One milliliter was analyzed. This analysis represented the macronutrient content of delivered milk to an infant. The milk that remained in the extension tubing was also analyzed. In our practice, this milk would be discarded. This whole process was repeated 10 times; 5 samples were EBM and 5 were HDM.
In the new method, 9 mL of fortified milk were prepared similar to the procedures used for the standard method. One milliliter of breast milk was analyzed for macronutrient content. Of the remaining 8 mL in the syringe, 2 mL were used to prime the extension tubing. The infusion pump was then set to run at 2.67 mL/hour and would typically finish infusing the 6 mL milk in about 2 hours and 15 minutes as there would be no milk left in the syringe. The syringe would then be removed from the extension tubing and 2 mL of air would be pulled back into the syringe. The syringe would then be attached back into the extension tubing and the 2 mL of air would be slowly pushed, therefore, pushing the 2 mL leftover milk in the tubing, and thus, completing the delivery of the entire 8 mL of prepared BM into the glass collection container. Milk was then rewarmed and 1 mL of the collected milk was analyzed. Similarly, this whole process was repeated 10 times. Five samples were EBM, and 5 samples were HDM.
SAS V.9.3 was used for the statistical evaluation. A Wilcoxon-Mann-Whitney test was used to compare the continuous variables between nutrient levels in milk prepared by the 2 different methods. Wilcoxon signed rank sum test was used to measure differences within the same method of preparation between prepared, delivered, and leftover milk. All tests were 2-sided; P < 0.05 was considered as statistically significant. Data are presented as mean ± SD.
A total of 50 samples were analyzed; 30 were collected from milk delivered by standard method and 20 from milk delivered by the new method. There were no differences in macronutrient and caloric contents between milk samples prepared for each procedure, Table 1 (A vs B). Both methods were associated with significant losses in fat and calories, but only the standard method was associated with a significant amount of protein loss (A vs C and B vs D). When comparing the quantity of losses between the 2 methods, the deficiency in nutrient content was much more substantial when milk was delivered by the standard method (C vs D). Fat, protein, and calorie losses were 16.7%, 3.4%, and 9.2%, respectively, using the standard method compared with 8.2%, 0%, and 3.3% using the new method. The significant losses in nutrients using the standard method were predominantly explained by the significant nutrient content gains in the left over milk as compared with baseline prepared milk (A vs E).
Despite improvements and variations in delivery methods, a decrease in fat content of prepared milk because of tubing losses remains a decade-old problem that continues to be investigated (7,8). The main etiology of this problem stems from the fact that fat adsorbs to the syringe walls and the connection tubes. Even fat added as a fortifier in the form of medium chain triglyceride oil also adheres to the tubing (9). Towards the end of a feeding, it is postulated that the moving plunger dislodges some of the fat adsorbed to the walls releasing a significant bolus of fat (7,10).
With this in mind, several interventions have been recommended to ameliorate these losses. Decreasing the contact time between fat and tubing walls by using bolus feedings as compared with continuous feeding was associated with significant success (10–12). A Cochrane review analysis, however demonstrated that both methods are not significantly different in their effects on long-term growth outcomes (13). Other interventions included ultrasonic homogenization of human milk whereby there is less fat separation (14), periodic agitation of the syringe to keep fat suspended (15,16), positioning the syringe vertically with tip upwards to cause fat to float and be delivered earlier in the feeding before it adsorbs to the walls (10,16), moving the tip of the syringe from a central to a peripheral position to leverage the use of the syringe in the horizontal position (17), and using a flat polypropylene plunger head instead of the classical conical rubber head as fat adsorbs more to rubber than polypropylene (17). All of these interventions have been associated with varied degrees of success. The strength of this study lies in the simplicity of a cost free intervention (with minimal labor cost for RN time) leading to a significant reduction in nutrient losses. Furthermore, it is likely that combining the new method with other methods will decrease fat losses even further.
The idea of recovering adsorbed fat from feeding tubing is not totally new. Brooke was the first to report that up to a 24% of fat is lost in tubing of feedings; washing the tubing showed some recovery of the fat content (7). Narayanan et al.(15) recommended complete emptying of the syringe at the end of each feed as left over milk had a high nutrient content. Both of these approaches are not applicable anymore. It is not practical to wash the tubing with distilled water to recover fat (7). Syringes have become more efficient with an insignificant dead space volume. An approach that overlaps with our findings was that of Greer et al (10) who recommended infusing air into the tubing after the end of the feeds.
Studies have predominantly found that fat was the main macronutrient lost. Our study was started simply because of the intrigue developed after noting that a precipitate forms towards the end of the infusion when HMF was mixed with human milk. Our findings show that the standard method of delivering milk was associated with a loss in protein delivered as noted by a statistical difference between the prepared and delivered milk. We speculate that clinical studies using the new method may show significant improvements in all 3 growth parameters. This is because the precipitate was significantly rich in protein, and when reintroduced back as is proposed in the new method, significant losses of protein were eliminated. Although not measured, a significant portion of the precipitate is likely rich in calcium and phosphorous, a finding that has been reported with continuous feeds (3).
The main limitation of this study is the small sample size in each arm. This was because of the fact that the milk analyzer was only available for a short period for research purposes. However, this small sample size is unlikely to have significantly affected the results. Baseline data about nutrient losses found in this study using the standard method were similar to what has been previously reported. Furthermore, the new method as a stand alone intervention had such a substantial enhancement to the delivered milk that significant differences between the 2 methods were apparent with a small sample size. The findings of our study helped push a practice change in our unit, and feeding delivery guidelines changed from primarily continuous to bolus feeds. Still, continuous feeds remain a common practice as they anecdotally seem to be associated with less bradycardia and desaturation events in some of the extremely premature infants. They are also much better tolerated in infants with short bowel syndrome. A 2 mL leftover volume may be associated with lower losses when volumes greater than 8 mL are being delivered. However, larger volumes will have more net fat to adsorb to the larger syringe size used. Larger volumes also may be associated with a more concentrated precipitate and leftover milk. The effect of changing the type of fortifier, liquid versus powder or intact versus hydrolyzed protein, may change the results of the study. Similarly, changing the syringe type or using syringes with different plunger heads may be associated with different results as well. Future research on both practices may help understand and improve fortified milk delivery methods.
Minimizing significant nutrients’ cause of losses by delivery methods remains one of the most important interventions to improve the nutritional content of delivered milk for ELBW infants. Traditional continuous delivery methods of human milk are associated with significant losses of fat and protein. By preparing the exact amount of ordered milk and then pushing through the residual milk left in the tubing with a small amount of air, this study offers a simple intervention that would significantly decrease these losses.
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