Maturation of Intestinal Oxygenation: A Review of Mechanisms and Clinical Implications for Preterm Neonates

Feeding Outcomes in Preterm Neonates with Antenatal Abnormal Umbilical Artery Doppler Profile: A Retrospective Cohort Study

Neonates with absent-or-reversed umbilical artery end-diastolic flow (AREDF) are at an increased risk of feeding problems. In this retrospective study, authors evaluated the incidence of feed intolerance in 213 preterm neonates (January 2017-May 2022) with AREDF. The median (IQR) gestation and birth weight were 32 (30, 33) wk and 1120 (840, 1425) g, respectively. Of 213 neonates, 103 (48.4%; 95% CI 41.5%, 55.3%) neonates developed feed intolerance. Twelve of 213 neonates developed any stage necrotizing enterocolitis (NEC) (5.6%; 95% CI 2.9%, 9.6%) at a median age of 10 d. On multivariate regression, gestation was the only independent predictor of feed intolerance (OR 1.48; 95% CI 1.28, 1.70; for every 1 wk decrease below 36 wk). Almost 50% of preterm neonates with AREDF develop feed intolerance. Alternative feeding strategies warrant exploration to optimise nutrition in these neonates.

Neonatal somatic oxygenation and perfusion assessment using near-infrared spectroscopy : Part of the series on near-infrared spectroscopy by the European Society of Paediatric Research Special Interest Group "Near-Infrared Spectroscopy"

In this narrative review, we summarize the current knowledge and applications of somatic near-infrared spectroscopy (NIRS), with a focus on intestinal, renal, limb, and multi-site applications in neonates. Assessing somatic oxygenation at various body locations in neonates may aid in the understanding of underlying pathophysiology of organ injury. Considering cerebral autoregulation may be active to protect the brain during systemic circulatory failure, peripheral somatic oxygenation may potentially provide an early indication of neonatal cardiovascular failure and ultimate hypoxemic injury to vital organs including the brain. Certain intestinal oxygenation patterns appear to be associated with the onset and course of necrotizing enterocolitis, whereas impaired renal oxygenation may indicate the onset of acute kidney injury after various types of hypoxic events. Peripheral muscle oxygenation measured at a limb may be particularly effective in the early prediction of shock in neonates. Using multi-site NIRS may complement current approaches and clinical investigations to alert for neonatal tissue hypoxemia, and potentially even guide management. However, somatic NIRS has its inherent limitations in regard to accuracy. Interpretation of organ-specific values can also be challenging. Last, currently there are limited prospective intervention studies, and clinical benefits need to be examined further, after the clarification of critical threshold-values. IMPACT: The assessment of somatic oxygenation using NIRS may contribute to the prediction of specific diseases in hemodynamically challenged neonates. Furthermore, it may give early warning signs for impending cardiovascular failure, and impaired cerebral circulation and oxygenation. We present a comprehensive overview of the literature on applications of NIRS to various somatic areas, with a focus on its potential clinical applicability, including future research directions. This paper will enable prospective standardized studies, and multicenter collaboration to obtain statistical power, likely to advance the field.

Impact of hyperoxia on the gut during critical illnesses

Molecular oxygen is typically delivered to patients via oxygen inhalation or extracorporeal membrane oxygenation (ECMO), potentially resulting in systemic hyperoxia from liberal oxygen inhalation or localized hyperoxia in the lower body from peripheral venoarterial (VA) ECMO. Consequently, this exposes the gastrointestinal tract to excessive oxygen levels. Hyperoxia can trigger organ damage due to the overproduction of reactive oxygen species and is associated with increased mortality. The gut and gut microbiome play pivotal roles in critical illnesses and even small variations in oxygen levels can have a dramatic influence on the physiology and ecology of gut microbes. Here, we reviewed the emerging preclinical evidence which highlights how excessive inhaled oxygen can provoke diffuse villous damage, barrier dysfunction in the gut, and gut dysbiosis. The hallmark of this dysbiosis includes the expansion of oxygen-tolerant pathogens (e.g., Enterobacteriaceae) and the depletion of beneficial oxygen-intolerant microbes (e.g., Muribaculaceae). Furthermore, we discussed potential impact of oxygen on the gut in various underlying critical illnesses involving inspiratory oxygen and peripheral VA-ECMO. Currently, the available findings in this area are somewhat controversial, and a consensus has not yet to be reached. It appears that targeting near-physiological oxygenation levels may offer a means to avoid hyperoxia-induced gut injury and hypoxia-induced mesenteric ischemia. However, the optimal oxygenation target may vary depending on special clinical conditions, including acute hypoxia in adults and neonates, as well as particular patients undergoing gastrointestinal surgery or VA-ECMO support. Last, we outlined the current challenges and the need for future studies in this area. Insights into this vital ongoing research can assist clinicians in optimizing oxygenation for critically ill patients.

Gene expression in the intestine of newborn piglets after hypoxia-reoxygenation

BACKGROUND

In preterm infants, intestinal hypoxia may partly contribute to the pathophysiology of necrotizing enterocolitis through changes in gene expression. Splanchnic hypoxia can be detected with monitoring of regional splanchnic oxygen saturation (rsSO2). Using a piglet model of asphyxia, we aimed to correlate changes in rsSO2 to gene expression.

METHODS

Forty-two newborn piglets were randomized to control or intervention groups. Intervention groups were subjected to hypoxia until they were acidotic and hypotensive. Next, they were reoxygenated for 30 min according to randomization, i.e., 21% O2, 100% O2, or 100% O2 for 3 min followed by 21% O2, and observed for 9 h. We continuously measured rsSO2 and calculated mean rsSO2 and variability of rsSO2 (rsCoVar = SD/mean). Samples of terminal ileum were analyzed for mRNA expression of selected genes related to inflammation, erythropoiesis, fatty acid metabolism, and apoptosis.

RESULTS

The expression of selected genes was not significantly different between control and intervention groups. No associations between mean rsSO2 and gene expression were observed. However, lower rsCoVar was associated with the upregulation of apoptotic genes and the downregulation of inflammatory genes (P < 0.05).

CONCLUSION

Our study suggests that hypoxia and reoxygenation cause reduced vascular adaptability, which seems to be associated with the upregulation of apoptosis and downregulation of inflammation.

IMPACT

Our results provide important insight into the (patho)physiological significance of changes in the variability of rsSO2. Our findings may advance future research and clinical practice regarding resuscitation strategies of preterm infants.

Clinical usefulness of splanchnic oxygenation in predicting necrotizing enterocolitis in extremely preterm infants: a cohort study

BACKGROUND

Impaired intestinal microcirculation seems to play an important role in the pathogenesis of necrotizing enterocolitis (NEC). A previous study showed that a SrSO2 < 30% is associated with an increased risk of developing of NEC. We aimed to determine the clinical usefulness of the cut off < 30% for SrSO2 in predicting NEC in extremely preterm neonates.

METHODS

This is a combined cohort observational study. We added a second cohort from another university hospital to the previous cohort of extremely preterm infants. SrSO2 was measured for 1-2 h at days 2-6 after birth. To determine clinical usefulness we assessed sensitivity, specificity, positive and negative predictive values for mean SrSO2 < 30. Odds ratio to develop NEC was assessed with generalized linear model analysis, adjusting for center.

RESULTS

We included 86 extremely preterm infants, median gestational age 26.3 weeks (range 23.0-27.9). Seventeen infants developed NEC. A mean SrSO2 < 30% was found in 70.5% of infants who developed NEC compared to 33.3% of those who did not (p = 0.01). Positive and negative predictive values were 0.33 CI (0.24-0.44) and 0.90 CI (0.83-0.96), respectively. The odds of developing NEC were 4.5 (95% CI 1.4-14.3) times higher in infants with SrSO2 < 30% compared to those with SrSO2 ≥ 30%.

CONCLUSIONS

A mean SrSO2 cut off ≥ 30% in extremely preterm infants between days 2-6 after birth may be useful in identifying infants who will not develop NEC.

The role of intestinal alkaline phosphatase in the development of necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a devastating neonatal disease that affects neonates worldwide and often leads to high morbidity and mortality rates. Despite extensive research, the cause of NEC remains unclear, and current treatment options are limited. An important novel finding is the potential role of intestinal Alkaline Phosphatase (IAP) in both pathogenesis and treatment of NEC. IAP can play a vital role in detoxifying liposaccharides (LPS), a key mediator of many pathological processes, thereby reducing the inflammatory response associated with NEC. Furthermore, IAP can help prevent dysbiosis, improve intestinal perfusion, and promote autophagy. In this comprehensive review, we present evidence of the possible connection between IAP and the LPS/Toll-like receptor 4 (TLR4) pathway, impaired gut immunity, and dysbiosis in the preterm gut. Based on these findings, the administration of exogenous IAP might provide promising preventive and therapeutic avenues for the management of NEC.

Evaluation of the Hypotensive Preterm Infant: Evidence-Based Practice at the Bedside?

Choosing the appropriate management approach for the preterm infant with low blood pressure during the transition period generally involved intervening when the blood pressure drifted below a certain threshold. It is now clear that this approach is too simplistic and does not address the underlying physiology. In this chapter, we explore the many monitoring tools available for evaluation of the hypotensive preterm and assess the evidence base supporting or refuting their use. The key challenge relates to incorporating these outputs with the clinical status of the patient and choosing the appropriate management strategy.

The effect of drip versus intermittent feeding on splanchnic oxygenation in preterm infants with intrauterine growth restriction: a prospective randomized trial

The main purpose of this study was to evaluate the impact of drip versus intermittent feeding on splanchnic oxygenation in preterm infants with intrauterine growth restriction. The second objective was to assess the relationship between fetal splanchnic circulation parameters and splanchnic oxygenation during the first week of life. A single-center, prospective, randomized study with 51 fetuses/infants was conducted. Fetal Doppler measurements including umbilical artery, middle cerebral artery, and superior mesenteric artery (SMA) were recorded in IUGR fetuses. After preterm delivery, the infants were randomly assigned to one of two feeding modalities: drip (3-h continuous) or intermittent (bolus in 10 min). Continuous regional splanchnic saturation (rSO₂S) monitoring was carried out during the first week of life, simultaneously with continuous oxygen arterial saturation (SaO₂) monitoring, and the infants' fractional oxygen extractions (FOE) were calculated. These parameters were evaluated as means on a daily basis for the first week of life, as well as pre-prandial and post-prandial measurements on the seventh day. Fetal Doppler flow velocimetry disturbances were present in 72.5% of the study cohort. The drip (26 infants) and intermittent (25 infants) groups were similar in demographic and clinical characteristics, as well as the prevalence of feeding intolerance and necrotizing enterocolitis. During the first week of life, there was no difference in daily mean rSO₂S and FOE values between the drip and intermittent groups, whereas unfed infants had mostly lower rSO₂S values. Pre-prandial and post-prandial rSO₂S values remained stable in both groups. Also, no association was detected between fetal splanchnic circulation parameters and neonatal splanchnic oxygenation. RSO₂S values were strongly correlated to gestational age and birth weight. During the whole week, except for the first 2 days, infants with umbilical catheters had significantly lower rSO₂S values than infants without.  Conclusion: Our data suggest that the key factor in splanchnic oxygenation is feeding, not the feeding modality. In addition, the umbilical vein catheter had a negative impact on splanchnic oxygenation.  Clinical Trial Registration: The Effect of Neonatal Feeding Modalities on Splanchnic Oxygenation, NCT05513495,  https://clinicaltrials.gov/ct2/results cond=&term=NCT05513495&cntry=TR&state=&city=&dist= . Retrospectively registered, date of registration: August 2022. What is Known: • It is known that preterm infants with IUGR are at increased risk of hypoxic-ischemic intestinal damage and impaired splanchnic oxygenation. What is New: • The key factor in splanchnic oxygenation of preterm infants with IUGR is feeding, not the feeding modality (drip or intermittent). • In addition, the umbilical vein catheter had a negative impact on splanchnic oxygenation.

Molecular Mechanisms of Hyperoxia-Induced Neonatal Intestinal Injury

Oxygen therapy is important for newborns. However, hyperoxia can cause intestinal inflammation and injury. Hyperoxia-induced oxidative stress is mediated by multiple molecular factors and leads to intestinal damage. Histological changes include ileal mucosal thickness, intestinal barrier damage, and fewer Paneth cells, goblet cells, and villi, effects which decrease the protection from pathogens and increase the risk of necrotizing enterocolitis (NEC). It also causes vascular changes with microbiota influence. Hyperoxia-induced intestinal injuries are influenced by several molecular factors, including excessive nitric oxide, the nuclear factor-κB (NF-κB) pathway, reactive oxygen species, toll-like receptor-4, CXC motif ligand-1, and interleukin-6. Nuclear factor erythroid 2-related factor 2 (Nrf2) pathways and some antioxidant cytokines or molecules including interleukin-17D, n-acetylcysteine, arginyl-glutamine, deoxyribonucleic acid, cathelicidin, and health microbiota play a role in preventing cell apoptosis and tissue inflammation from oxidative stress. NF-κB and Nrf2 pathways are essential to maintain the balance of oxidative stress and antioxidants and prevent cell apoptosis and tissue inflammation. Intestinal inflammation can lead to intestinal damage and death of the intestinal tissue, such as in NEC. This review focuses on histologic changes and molecular pathways of hyperoxia-induced intestinal injuries to establish a framework for potential interventions.

A Multiscale Spatiotemporal Model Including a Switch from Aerobic to Anaerobic Metabolism Reproduces Succession in the Early Infant Gut Microbiota

The human intestinal microbiota starts to form immediately after birth and is important for the health of the host. During the first days, facultatively anaerobic bacterial species generally dominate, such as Enterobacteriaceae. These are succeeded by strictly anaerobic species, particularly Bifidobacterium species. An early transition to Bifidobacterium species is associated with health benefits; for example, Bifidobacterium species repress growth of pathogenic competitors and modulate the immune response. Succession to Bifidobacterium is thought to be due to consumption of intracolonic oxygen present in newborns by facultative anaerobes, including Enterobacteriaceae. To study if oxygen depletion suffices for the transition to Bifidobacterium species, here we introduced a multiscale mathematical model that considers metabolism, spatial bacterial population dynamics, and cross-feeding. Using publicly available metabolic network data from the AGORA collection, the model simulates ab initio the competition of strictly and facultatively anaerobic species in a gut-like environment under the influence of lactose and oxygen. The model predicts that individual differences in intracolonic oxygen in newborn infants can explain the observed individual variation in succession to anaerobic species, in particular Bifidobacterium species. Bifidobacterium species became dominant in the model by their use of the bifid shunt, which allows Bifidobacterium to switch to suboptimal yield metabolism with fast growth at high lactose concentrations, as predicted here using flux balance analysis. The computational model thus allows us to test the internal plausibility of hypotheses for bacterial colonization and succession in the infant colon. IMPORTANCE The composition of the infant microbiota has a great impact on infant health, but its controlling factors are still incompletely understood. The frequently dominant anaerobic Bifidobacterium species benefit health, e.g., they can keep harmful competitors under control and modulate the intestinal immune response. Controlling factors could include nutritional composition and intestinal mucus composition, as well as environmental factors, such as antibiotics. We introduce a modeling framework of a metabolically realistic intestinal microbial ecology in which hypothetical scenarios can be tested and compared. We present simulations that suggest that greater levels of intraintestinal oxygenation more strongly delay the dominance of Bifidobacterium species, explaining the observed variety of microbial composition and demonstrating the use of the model for hypothesis generation. The framework allowed us to test a variety of controlling factors, including intestinal mixing and transit time. Future versions will also include detailed modeling of oligosaccharide and mucin metabolism.

Splanchnic oxygen saturation during reoxygenation with 21% or 100% O2 in newborn piglets

BACKGROUND

Increasing evidence recognizes the harm of excess oxygen to lungs, eyes, and brain of preterm infants, but not yet to the intestine. We assessed changes in splanchnic oxygenation during reoxygenation with 21% compared to 100% O₂ in a newborn piglet model of perinatal asphyxia.

METHODS

We randomized 25 piglets to control or intervention. Intervention groups underwent global hypoxia until acidosis and hypotension occurred. Piglets were reoxygenated for 30 min with 21% or 100% O₂ and observed for 9 h. We continuously measured regional splanchnic oxygen saturation (r_sSO₂) using near-infrared spectroscopy (NIRS). We calculated mean r_sSO₂ and r_sCoVar (as SD/mean). We measured PaO₂ and SaO₂, sampled from the right carotid artery.

RESULTS

Reoxygenation after global hypoxia restored r_sSO₂. Reoxygenation with 100% O₂ increased r_sSO₂ to values significantly higher than baseline. In intervention groups, r_sCoVar decreased during observation compared to baseline. We found a correlation between r_sSO₂ and PaO₂ (r = 0.420, P < 0.001) and between r_sSO₂ and SaO₂ (r = 0.648, P < 0.001) in pooled data from the entire experiment.

CONCLUSION

Reoxygenation after global hypoxia improves splanchnic oxygenation, but is associated with reduced variability of r_sSO₂. Reoxygenation with 100% O₂ exposes the intestine to hyperoxia. Splanchnic NIRS is able to detect intestinal hypoxia and hyperoxia.

IMPACT

Splanchnic oxygenation improves during reoxygenation after global hypoxia, though reoxygenation with 100% O₂ exposes the intestine to hyperoxia. Decreased variability of splanchnic oxygenation several hours after hypoxia and reoxygenation seems to be independent of the resuscitation strategy, and may indicate intestinal injury. Splanchnic NIRS monitoring was able to detect intestinal hypoxia and exposure to hyperoxia, as evidenced by a strong correlation between splanchnic oxygenation and arterial oxygen content.

Disrupted establishment of anaerobe and facultative anaerobe balance in preterm infants with extrauterine growth restriction

BACKGROUND

Extrauterine growth restriction (EUGR) in preterm birth infants could have long-term adverse impacts on health. Less is known about the gut microbiota regarding its establishment in early life and its role in long-term growth in preterm birth infants.

METHODS

A prospective, longitudinal observational study was conducted with 67 preterm infants in a level III neonatal intensive care unit. Clinical information was obtained from medical records, and fecal samples were collected weekly during hospitalization and processed for 16S rRNA gene sequencing.

RESULTS

The bacterial profiles from the weekly sampling of preterm infants demonstrated that the early-life gut microbiota was clustered into the following four stages in chronological order: stage 1: 0-4 days, stage 2: 1-2 weeks, stage 3: 3-7 weeks, and stage 4: 8-10 weeks. The development of gut microbiota showed latency at stage 4 in EUGR infants compared with that in non-EUGR infants, which resulted from their consistently high level of facultative anaerobes, including Enterobacteriaceae and Staphylococcus, and lack of obligate anaerobes, including Clostridium and Veillonella. In the 2-year follow-up, infants with a high level of obligate anaerobes-to-facultative anaerobes ratio at stage 4 had a lower risk of long-term growth restriction at the margin of statistical significance.

CONCLUSION

The results of this study indicate that the development of gut microbiota in the early life of EUGR infants is delayed compared with that of non-EUGR infants. The obligate-to-facultative anaerobes ratio could be an indicator of the maturity of gut microbiota development and associated with the risk of long-term growth restriction in preterm infants.