Gastrointestinal function and its ontogeny: how should we feed the preterm infant?

Development of the Gastrointestinal Tract in Newborns as a Challenge for an Appropriate Nutrition: A Narrative Review

The second and third trimesters of pregnancy are crucial for the anatomical and functional development of the gastrointestinal (GI) tract. If premature birth occurs, the immaturity of the digestive and absorptive processes and of GI motility represent a critical challenge to meet adequate nutritional needs, leading to poor extrauterine growth and to other critical complications. Knowledge of the main developmental stages of the processes involved in the digestion and absorption of proteins, carbohydrates, and lipids, as well as of the maturational phases underlying the development of GI motility, may aid clinicians to optimize the nutritional management of preterm infants. The immaturity of these GI systems and functions may negatively influence the patterns of gut colonization, predisposing to an abnormal microbiome. This, in turn, further contributes to alter the functional, immune, and neural development of the GI tract and, especially in preterm infants, has been associated with an increased risk of severe GI complications, such as necrotizing enterocolitis. Deeper understanding of the physiological colonization patterns in term and preterm infants may support the promotion of these patterns and the avoidance of microbial perturbations associated with the development of several diseases throughout life. This review aims to provide a global overview on the maturational features of the main GI functions and on their implications following preterm birth. We will particularly focus on the developmental differences in intestinal digestion and absorption functionality, motility, gut–brain axis interaction, and microbiomes.

Impact of early aggressive nutrition on retinal development in premature infants

The normal retinal development is interrupted by preterm birth and a retinopathy of prematurity (ROP) may develop as its consequence. ROP is characterized by aberrant vessel formation in the retina as a response to multiple risk factors influencing the process of retinal angiogenesis. Insulin-like growth factor I (IGF-1) and vascular endothelial growth factor (VEGF) play an important role in the process of normal retinal vascularization. Insufficient nutrition during the first 4 postnatal weeks results in low serum levels of IGF-1, which is essential for correct retinal vessels formation, ensuring survival of the newly formed endothelial cells. Low IGF-1 level results in stop of angiogenesis in the retina, leaving it avascular and prompting the onset of ROP. Keeping the newborns in a positive energetic balance by providing enough nutrients and energy has a beneficial impact on their growth, neurodevelopment and decreased incidence of ROP. The best way to achieve this is the early parenteral nutrition with the high content of nutrients combined with early enteral feeding by the own mother´s breast milk. Multiple studies confirmed the safety and efficacy of early aggressive nutrition but information about its long-term effects on the metabolism, growth and development is still needed.

Two-hourly versus 3-hourly feeding for very low birthweight infants: a randomised controlled trial

OBJECTIVE

To determine whether feeding with 2-hourly or 3-hourly feeding interval reduces the time to achieve full enteral feeding and to compare their outcome in very low birthweight preterm infants.

DESIGN

Parallel-group randomised controlled trial with a 1:1 allocation ratio.

SETTING

Two regional tertiary neonatal intensive care units.

PATIENTS

150 preterm infants less than 35 weeks gestation with birth weight between 1.0 and 1.5 kg were recruited.

INTERVENTIONS

Infants were enrolled to either 2-hourly or 3-hourly interval feeding after randomisation. Blinding was not possible due to the nature of the intervention.

MAIN OUTCOME MEASURES

The primary outcome was time to achieve full enteral feeding (≥100 mL/kg/day). Secondary outcomes include time to regain birth weight, episode of feeding intolerance, peak serum bilirubin levels, duration of phototherapy, episode of necrotising enterocolitis, nosocomial sepsis and gastro-oesophageal reflux.

RESULTS

72 infants were available for primary outcome analysis in each group as three were excluded due to death-three deaths in each group. The mean time to full enteral feeding was 11.3 days in the 3-hourly group and 10.2 days in the 2-hourly group (mean difference 1.1 days; 95% CI -0.4 to 2.5; p=0.14). The mean time to regain birth weight was shorter in 3-hourly group (12.9 vs 14.8 days, p=0.04). Other subgroup analyses did not reveal additional significant results. No difference in adverse events was found between the groups.

CONCLUSION

3-hourly feeding was comparable with 2-hourly feeding to achieve full enteral feeding without any evidence of increased adverse events.

TRIAL REGISTRATION NUMBER

ACTRN12611000676910, pre-result.

Gastric emptying in premature newborns with acute respiratory distress

OBJECTIVES

The authors hypothesized that acute respiratory distress (ARD) delays gastric emptying. The objective was to test this hypothesis by assessing gastric emptying on the second and seventh days of life in premature infants with ARD resulting from pulmonary disease.

METHODS

Thirty-nine newborns with ARD starting on the first day of life were selected and paired with 39 healthy control newborns matched by weight (within 250 g). Gestational age was <or =35 weeks and birth weight was < or =1750 g for all subjects. Gastric emptying was assessed at 48.0 +/- 24.0 hours and at 168.0 +/- 24.0 hours of life. A test meal consisting of 3 mL/kg of 5% glucose in water labeled with phenol red was administered by gastric tube over 1 minute and gastric retention was determined as percent test meal remaining in the stomach 30 minutes after administration.

RESULTS

Gastric retention at 30 minutes varied considerably in both groups and was significantly higher (P < 0.01) in newborns with ARD (61.4%) than controls (51.8%) at 48.0 +/- 24.0 hours, decreasing significantly after partial or full remission of ARD at 168 +/- 24 hours of life. Gastric retention was 60.2% in newborns with feeding intolerance and 36.8% in tolerant newborns (P < 0.001) at 168 hours. ARD and periventricular or intraventricular hemorrhage were predictors of gastric retention at 48 +/- 24 hours of life, whereas feeding intolerance and gestational age were predictors of gastric retention at 168 +/- 24 hours. Gastric retention was inversely correlated with gestational age.

CONCLUSION

Gastric emptying is delayed in premature infants with ARD during the first 72 hours of life and may impair the initiation of enteral feeding.

Nutritional modulation of neonatal outcomes

In humans, growth and development continues until early adulthood when bone, muscle, and nervous tissue reaches final stages of maturity. Adequate levels of nutritional intake and utilization are critical to optimize ongoing growth. The goal of nutritional therapy for premature or ill neonates has been to provide sufficient nutrients to allow growth to continue at rates seen in utero. Functional immaturity of the gut in the premature infant makes absorption and utilization of nutritional substrates difficult. Premature infants are at risk for developing necrotizing enterocolitis, a potentially lethal bowel disorder. The etiology of necrotizing enterocolitis is not well understood, and a number of theories of causation have been proposed. Breast milk, the optimal source of nutrition for the neonate, is believed to confer some protection against necrotizing enterocolitis. A number of breast milk components have been credited with antiinflammatory properties. Breast milk is recognized for its benefits, yet for preterm infants breast milk alone does not promote adequate growth. A number of breast milk supplements have been investigated to facilitate growth and development and to prevent necrotizing enterocolitis. This article addresses development of the fetal gastrointestinal system, focusing on the biological mediators for normal function and the role of human breast milk and its additives in optimizing neonatal growth. The possible etiologies of necrotizing enterocolitis are discussed in terms of the relationship between this disease and enteral feeding practices.

Early aggressive nutrition in preterm infants

Increasingly, neonatologists are realizing that current feeding practices for preterm infants are insufficient to produce reasonable rates of growth, and earlier and larger quantities of both parenteral and enteral feeding should be provided to these infants. Unfortunately, there is very little outcome data to recommend any particular nutritional strategy to achieve better growth. Instead, the rationale for feeding regimens in many nurseries has been quite variably extrapolated from animal data and human studies conducted in gestationally more mature and/or stable neonates. Additionally, there are no well-controlled, prospective studies that validate any nutritional regimen for the very preterm and or sick, unstable neonate. The goal of this review is to present available data to help define the risks and benefits of early parenteral and enteral nutrition, particularly in very preterm neonates, concluding with a more aggressive approach to feeding these infants than has been customary practice.

Gastric electrical activity and gastric emptying in preterm newborns fed standard and hydrolysate formulas

BACKGROUND

Because infant formulas containing hydrolyzed cow milk protein are used to reduce feeding intolerance and to improve gastric emptying, the effect on gastrointestinal motility of a hydrolysate formula was compared with that of a standard preterm formula.

METHODS

Thirty-six preterm newborns with a gestational age of 32.2 +/- 2.3 weeks were assigned randomly to standard formula or hydrolyzed formula. Cutaneous electrogastrography and ultrasound examination of gastric emptying were performed simultaneously to evaluate gastrointestinal motility before and after the test meal. All recording sessions were performed 1 week after infants had reached full enteral feeding.

RESULTS

No significant difference in gastrointestinal symptoms was noted in the newborns fed the different formulas. In particular, regurgitation and vomiting were observed in 78% versus 64% of preterm newborns after standard and hydrolyzed formula, respectively (Fisher exact test, not significant). No differences were found in terms of gastric electrical activity and gastric emptying time between the two groups.

CONCLUSIONS

It seems unnecessary to use hydrolysate formulas to improve motility in preterm infants.

Gastric electrical activity and gastric emptying in term and preterm newborns

The aims of this study were to evaluate the gastric electrical activity and gastric emptying in preterm and term newborns and to assess the development of gastric motility by comparing newborns of different gestational ages. The cutaneous electrogastrography and the ultrasonographic study of the gastric emptying were performed before and after milk formula in three groups of infants: 12 preterm newborns with a gestational age of 28-32 weeks, 11 preterm newborns with a gestational age of 32-36 weeks, and 10 full-term newborns with a gestational age of 36-40 weeks. All recording sessions were performed 1 week after infants had reached full enteral feeding. The percentage of normal slow waves was similar in the three groups but it was not predominant compared to tachygastria in the earliest premature infants (59.3% (12.7-92.3) vs. 29.6% (3.7-78.8); P < 0.05). In addition, a progressive increase in the normal slow wave percentage (59.3% (17.4-87.4), 60.9% (38.1-89.7), 77.8% (66.4-84.8); P < 0.05) was observed as gestation advanced. As regards gastric emptying parameters, the antral area was greater and T(1/2) was longer in the preterm newborns of 28-32 weeks than preterm newborns of 32-36 weeks and full-term newborns (fasting antral area: 0.96 cm2 (0.6-1.5), 0.63 cm2 (0.4-1.2), 0.55 cm2 (0.1-0.9) respectively, P < 0.05; T(1/2): 83.4 min (76.0-108.5), 70 min (57.5-89.5) and 71.8 min (54.9-81.2), respectively P < 0.05). The comparisons of gastric emptying curves made among the three groups showed a reduced antral dilatation in preterm newborns of 28-32 weeks compared to full-term newborns at 30 and 60 min after a meal. In conclusion, although enteral feeding is important for the development process of gastrointestinal motility, gastric electrical activity and gastric emptying show an intrinsic maturation depending on the gestational age.