Assessment of renal functional maturation and injury in preterm neonates during the first month of life

Postnatal renal tubule development: roles of tubular flow and flux

PURPOSE OF REVIEW

Postnatal renal tubule development is critical to adult kidney function. Several postnatal changes regulate the differentiation and proliferation of renal tubular cells. Here, we review the literature and our efforts on thick ascending limb (TAL) development in Bartter syndrome (BS).

RECENT FINDINGS

Glomerular filtrate quickly increases after birth, imposing fluid shear stress and circumferential stretch on immature renal tubules. Recent studies showed that kidney organoids under flow (superfusion) have better development of tubular structures and the expression of cilia and solute transporters. These effects are likely mediated by mechanosensors, such as cilia and the piezo1 channel. Improved renal oxygenation and sodium pump-dependent active transport can stimulate mitochondrial respiration and biogenesis. The functional coupling between transport and mitochondria ensures ATP supply for energy-demanding reactions in tubular cells, including cell cycle progression and proliferation. We recently discovered that postnatal renal medulla maturation and TAL elongation are impaired in Clc-k2-deficient BS mice. Primary cultured Clc-k2-deficient TAL cells have G1-S transition and proliferation delay. These developmental defects could be part of the early pathogenesis of BS and worsen the phenotype.

SUMMARY

Understanding how tubular flow and transepithelial ion fluxes regulate renal tubule development may improve the treatment of congenital renal tubulopathies.

Actual electrolyte intake during the first week of life and morbidity in very-low-birthweight infants

AIM

To describe sodium and potassium intake, their sources and plasma concentrations, and the association between intake and morbidity in very-low-birthweight (VLBW, <1500 g) infants during the first week of life.

METHODS

This retrospective cohort study comprised 951 VLBW infants born at <32 weeks. Infants were divided into three groups according to gestational age: 23-26 (n = 275), 27-29 (n = 433) and 30-31 (n = 243) weeks. Data on fluid management and laboratory findings were acquired from an electronic patient information system.

RESULTS

The median sodium intake was highest in the 23-26 week group, peaking at 6.4 mmol/kg/day. A significant proportion of sodium derived from intravascular flushes; it reached 27% on day 1 in the 23-26 week group. High cumulative sodium intake in the first postnatal week was associated with weight gain from birth to day 8 in the 23-26 week group. High intake of sodium associated with an increased risk of surgically ligated patent ductus arteriosus (PDA), bronchopulmonary dysplasia and intraventricular haemorrhage, whereas low intake of potassium associated with an increased risk of PDA.

CONCLUSION

Sodium intake in the most premature infants exceeded recommendations during the first postnatal week. Saline flushes accounted for a significant proportion of the sodium load.

Insulin-like growth factor-1 effects on kidney development in preterm piglets

BACKGROUND

Preterm birth disrupts fetal kidney development, potentially leading to postnatal acute kidney injury. Preterm infants are deficient in insulin-like growth factor 1 (IGF-1), a growth factor that stimulates organ development. By utilizing a preterm pig model, this study investigated whether IGF-1 supplementation enhances preterm kidney maturation.

METHODS

Cesarean-delivered preterm pigs were treated systemically IGF-1 or vehicle control for 5, 9 or 19 days after birth. Blood, urine, and kidney tissue were collected for biochemical, histological and gene expression analyses. Age-matched term-born pigs were sacrificed at similar postnatal ages and served as the reference group.

RESULTS

Compared with term pigs, preterm pigs exhibited impaired kidney maturation, as indicated by analyses of renal morphology, histopathology, and inflammatory and injury markers. Supplementation with IGF-1 reduced signs of kidney immaturity, particularly in the first week of life, as indicated by improved morphology, upregulated expression of key developmental genes, reduced severity and incidence of microscopic lesions, and decreased levels of inflammatory and injury markers. No association was seen between the symptoms of necrotizing enterocolitis and kidney defects.

CONCLUSION

Preterm birth in pigs impairs kidney maturation and exogenous IGF-1 treatment partially reverses this impairment. Early IGF-1 supplementation could support the development of preterm kidneys.

IMPACT

Preterm birth may disrupt kidney development in newborns, potentially leading to morphological changes, injury, and inflammation. Preterm pigs have previously been used as models for preterm infants, but not for kidney development. IGF-1 supplementation promotes kidney maturation and alleviates renal impairments in the first week of life in preterm pigs. IGF-1 may hold potential as a supportive therapy for preterm infants sensitive to acute kidney injury.

Early-life exposure to ambient air pollutants and kidney function in adolescents: a cohort study based on the 'Children of 1997' Hong Kong birth cohort

OBJECTIVES

Air pollution is increasingly linked to impaired kidney function in adults. However, little is known about how early-life exposure to air pollutants affects kidney function in adolescents.

STUDY DESIGN

Cohort study.

METHODS

We leveraged data from the 'Children of 1997' Hong Kong population-representative birth cohort (N = 8327). Residential exposure to average ambient levels of four air pollutants, including inhalable particle (PM10), sulfur dioxide (SO2), nitrogen dioxide (NO2), and nitrogen monoxide (NO), during in utero, infancy, and childhood periods was estimated using the inverse distance weighting. Kidney function was assessed using estimated glomerular filtration rate (eGFR) calculated from age-adjusted equations for adolescents. Generalized linear regression was used to examine the association of air pollutant exposure in each period with kidney function at 17.6 years. Two-pollutant models tested the robustness of the association.

RESULTS

Of the 3350 participants included, 51.4% were boys. Exposure to PM10 was associated with poorer kidney function. Each interquartile range increment in PM10 was inversely associated with eGFR (β: -2.933, 95% confidence interval -4.677 to -1.189) in utero, -2.362 (-3.992 to -0.732) infancy, -2.708 (-4.370 to -1.047) childhood, and -2.828 (-4.409 to -1.247) overall. Exposure to PM10 and SO2in utero had a stronger inverse association with kidney function in males. The associations were robust to PM10 exposure in two-pollutant models.

CONCLUSIONS

Our findings suggest that early-life exposure to ambient PM10 and SO2 is associated with reduced kidney function in adolescents, especially exposure in utero.

Time to regain birthweight and association with neurodevelopmental outcomes among extremely preterm newborns

OBJECTIVE

Determine association between time to regain birthweight and 2-year neurodevelopment among extremely preterm (EP) newborns.

STUDY DESIGN

Secondary analysis of the Preterm Erythropoietin Neuroprotection Trial evaluating time to regain birthweight, time from birth to weight nadir, time from nadir to regain birthweight, and cumulative weight loss with 2-year corrected Bayley Scales of Infant and Toddler Development 3rd edition.

RESULTS

Among n = 654 EP neonates, those with shorter nadir-to-regain had lower cognitive scores (≤1 day versus ≥8 days: -5.0 points, [CI -9.5, -0.6]) and lower motor scores (≤1 day versus ≥8 days: -4.6 points [CI -9.2, -0.03]) in adjusted stepwise forward regression modeling. Increasingly cumulative weight loss was associated with lower cognitive scores (≤-50 percent-days: -5.6, [CI -9.4, -1.8]), motor scores (≤-50 percent-days: -4.2, [CI -8.2, -0.2]); and language scores (≤-50 percent-days: -6.0, [CI -10.1, -1.9]).

CONCLUSION

Faster nadir-to-regain and excessive cumulative weight loss are associated with adverse 2-year neurodevelopmental outcomes.

TRIAL REGISTRATION

PENUT Trial Registration: NCT01378273. https://clinicaltrials.gov/ct2/show/NCT01378273 .

CLINICAL TRIAL REGISTRATION

This study is a post-hoc secondary analysis of pre-existing data from the PENUT Trial (NCT #01378273).

Prolonged renal function impairment in infants born during the peri-viable period: A retrospective longitudinal cohort study

BACKGROUND

The number of infants born during the peri-viable period who survive has been increasing.

AIM

To clarify renal function in infants from the time of birth during the peri-viable period until their due date.

STUDY DESIGN

This retrospective cohort study was conducted at a single center.

SUBJECTS

We reviewed the data of infants born at ≤28 weeks of gestation between 2018 and 2022 at our hospital. The infants were divided into the following groups: born at 22-24 weeks vs. 25-28 weeks (appropriate-for-gestational age [AGA] infants), and AGA infants vs. small-for-gestational age (SGA) infants (born at 22-28 weeks).

OUTCOME MEASURES

We compared the perinatal data and renal function of the infants from birth until their due date.

RESULTS

Eighty-one infants were included. Their serum creatinine, fractional excretion of sodium, and urine glucose levels were high or positive soon after birth but gradually improved. The urine albumin level was significantly higher among AGA infants born at 22-24 weeks, even at term equivalent age, than among those born at 25-28 weeks.

CONCLUSIONS

Persistent renal insufficiency was observed even around the term equivalent age in peri-viable infants. Follow-up data collected after the neonatal period should be investigated in these infants.

Ongoing exposure to endocrine disrupting phthalates and alternative plasticizers in neonatal intensive care unit patients

Due to endocrine disrupting effects, di-(2-ethylhexyl) phthalate (DEHP), a plasticizer used to soften plastic medical devices, was restricted in the EU Medical Devices Regulation (EU MDR 2017/745) and gradually replaced by alternative plasticizers. Neonates hospitalized in the neonatal intensive care unit (NICU) are vulnerable to toxic effects of plasticizers. From June 2020 to August 2022, urine samples (n = 1070) were repeatedly collected from premature neonates (n = 132, 4-10 samples per patient) born at <31 weeks gestational age and/or <1500 g birth weight in the Antwerp University Hospital, Belgium. Term control neonates (n = 21, 1 sample per patient) were included from the maternity ward. Phthalate and alternative plasticizers' metabolites were analyzed using liquid-chromatography coupled to tandem mass spectrometry. Phthalate metabolites were detected in almost all urine samples. Metabolites of alternative plasticizers, di-(2-ethylhexyl)-adipate (DEHA), di-(2-ethylhexyl)-terephthalate (DEHT) and cyclohexane-1,2-dicarboxylic-di-isononyl-ester (DINCH), had detection frequencies ranging 30-95 %. Urinary phthalate metabolite concentrations were significantly higher in premature compared to control neonates (p = 0.023). NICU exposure to respiratory support devices and blood products showed increased phthalate metabolite concentrations (p < 0.001). Phthalate exposure increased from birth until four weeks postnatally. The estimated phthalate intake exceeded animal-derived no-effect-levels (DNEL) in 10 % of samples, with maximum values reaching 24 times the DNEL. 29 % of premature neonates had at least once an estimated phthalate intake above the DNEL. Preterm neonates are still exposed to phthalates during NICU stay, despite the EU Medical Devices Regulation. NICU exposure to alternative plasticizers is increasing, though currently not regulated, with insufficient knowledge on their hazard profile.

Early postnatal nutrition and renal consequences in preterm infants

Perinatal nutritional factors may lead to decreased nephron endowment, decreased kidney function, and long-term development of chronic kidney disease and non-communicable diseases. At the same time, optimal postnatal nutrition and catch-up growth are associated with better neurodevelopmental outcomes in preterm infants. Therefore, nutritional management of preterm infants is a major challenge for neonatologists. In this context, the Section of Nutrition, Gastroenterology and Metabolism reviewed the current knowledge on nutritional issues related to kidney function. This narrative review discusses the clinical impact of early postnatal nutrition on long-term kidney function. In preterm infants, data are largely lacking to determine the extent to which early nutrition contributes to nephrogenesis and nephron endowment. However, some nutritional principles may help clinicians better protect the developing kidney in preterm infants. IMPACT: Clinical data show that preterm infants are an emerging population at high risk for chronic kidney disease. Both undernutrition and overnutrition can alter long-term kidney function. In preterm infants, data are largely lacking to determine the extent to which early postnatal nutrition contributes to nephrogenesis, nephron endowment and increased risk for chronic kidney disease. Some nutritional principles may help clinicians better protect the developing kidney in preterm infants: avoiding extrauterine growth restriction; providing adequate protein and caloric intakes; limiting exposure to high and prolonged hyperglycaemia; avoiding micronutrient deficiencies and maintaining acid-base and electrolyte balance.

Somatic growth outcomes in response to an individualized neonatal sodium supplementation protocol

Objective

Evaluate the impact of a sodium (Na) supplementation protocol based upon urine Na concentration on growth parameters and morbidities.

Study Design

Retrospective cohort study of infants 260/7-336/7 weeks gestational age (GA) cared for before (2012-15, n = 225) and after (2016-20, n = 157) implementation of the protocol. Within- and between-group changes over time were assessed using repeated measures generalized linear models.

Results

For infants 260/7-296/7 weeks GA, utilization of the protocol was associated with increased mean body weight z-score at 8-weeks postnatal age, increased mean head circumference z-score at 16-weeks postnatal age, and decreased time on mechanical ventilation (all p < 0.02). No impact on growth was identified for infants 30-336/7 weeks GA. Incidences of hypertension, hypernatremia, bronchopulmonary dysplasia, and culture positive sepsis were unaffected by the protocol.

Conclusion

Protocolized Na supplementation results in improved growth and reduced time on invasive mechanical ventilation in extremely preterm infants without increasing incidence of morbidities.

Early-life sodium deprivation programs long-term changes in ingestive behaviors and energy expenditure in C57BL/6J mice

Postnatal growth failure remains a significant problem for infants born prematurely, despite aggressive efforts to improve perinatal nutrition. Though often dysregulated in early life when children are born preterm, sodium (Na) homeostasis is vital to achieve optimal growth. We hypothesize that insufficient Na supply in this critical period contributes to growth restriction and programmed risks for cardiometabolic disease in later adulthood. Thus, we sought to ascertain the effects of prolonged versus early-life Na depletion on weight gain, body composition, food and water intake behaviors, and energy expenditure in C57BL/6J mice. In one study, mice were provided a low (0.04%)- or normal/high (0.30%)-Na diet between 3 and 18 wk of age. Na-restricted mice demonstrated delayed growth and elevated basal metabolic rate. In a second study, mice were provided 0.04% or 0.30% Na diet between 3 and 6 wk of age and then returned to standard (0.15%)-Na diet through the end of the study. Na-restricted mice exhibited growth delays that quickly caught up on return to standard diet. Between 6 and 18 wk of age, previously restricted mice exhibited sustained, programmed changes in feeding behaviors, reductions in total food intake, and increases in water intake and aerobic energy expenditure while maintaining normal body composition. Although having no effect in control mice, administration of the ganglionic blocker hexamethonium abolished the programmed increase in basal metabolic rate in previously restricted mice. Together these data indicate that early-life Na restriction can cause programmed changes in ingestive behaviors, autonomic function, and energy expenditure that persist well into adulthood.

Hair as an alternative matrix to assess exposure of premature neonates to phthalate and alternative plasticizers in the neonatal intensive care unit

Due to adverse health effects, di-(2-ethylhexyl) phthalate (DEHP), a plasticizer used to soften plastic medical devices (PMDs), was restricted, and gradually replaced by alternative plasticizers (APs). Up to this date, urine was the sole matrix studied for plasticizer exposure in neonates hospitalized in the neonatal intensive care unit (NICU), a population highly vulnerable to toxic effects of plasticizers. The primary aim of this study was to assess simultaneous measurement of phthalate and AP metabolites in neonatal scalp hair. In addition, we aimed to use this matrix to investigate exposure of premature neonates to plasticizers during their stay in the NICU. Hair samples in this study were collected from premature neonates and their mothers included in a prospective birth cohort study in a tertiary NICU at the Antwerp University Hospital (UZA), Belgium. Samples from premature neonates (n = 45) and their mothers (n = 107) as well as from control neonates (n = 24) and mothers (n = 29) were analyzed using liquid-chromatography coupled to tandem mass spectrometry. This is the first study reporting metabolites of phthalate and alternative plasticizers in neonatal hair samples as biomarkers for exposure to these plasticizers. Results showed that hair sampled from premature neonates after a NICU stay contained significantly higher metabolite concentrations of both phthalates (DEHP, DiBP, and DnBP; 9.0-2500, 9.3-2200, and 24.7-5300 ng/g), and alternative plasticizers (DEHA, DEHT, and TOTM; 38.8-3400, 127.5-5700, and 10.8-8700 ng/g) - when compared to healthy control neonates. Besides, DEHP and DEHT metabolite concentrations were significantly higher than in hair sampled from adult populations. In addition, prolonged NICU exposure to non-invasive respiratory support devices and gastric tubes was correlated with increased concentrations in hair samples, indicating accumulation of plasticizers in this alternative matrix. In conclusion, our data indicate that preterm neonates are still highly exposed to phthalate and alternative plasticizers during NICU stay, despite the EU Medical Devices Regulation.

Preceding risks and mortality outcomes of different neonatal acute kidney injury in preterm infants

BACKGROUND

The aim of the study was to examine preceding risks and mortality outcomes of oliguric and non-oliguric acute kidney injury (AKI) in very preterm infants.

METHODS

Infants born ≤30 weeks' gestation were included. AKI was diagnosed based on neonatal Kidney Disease: Improving Global Outcomes criteria and was classified as oliguric and non-oliguric according to the urine-output criteria. We used modified Poisson and Cox proportional-hazards models for statistical comparisons.

RESULTS

Of 865 enrolled infants (gestational age 27.2 ± 2.2 weeks and birth weight 983 ± 288 gm), 204 (23.6%) developed AKI. Before AKI, the oliguric AKI group had significantly higher prevalence of small-for-gestational age (p = 0.008), lower 5-min Apgar score (p = 0.009) and acidosis (p = 0.009) on admission, and hypotension (p = 0.008) and sepsis (p = 0.001) during admission than the non-oliguric AKI group. Oliguric (adjusted risk ratio 3.58, 95% CI 2.33-5.51; adjusted hazard ratio 4.93, 95% CI 3.14-7.72) instead of non-oliguric AKI had significantly higher mortality risks than no AKI. Oliguric AKI showed significantly higher mortality risks than non-oliguric AKI, irrespective of serum creatinine and severity of AKI.

CONCLUSIONS

Categorizing AKI as oliguric and non-oliguric was crucial because of the distinct preceding risks and mortality outcomes of these two types of AKI in very preterm neonates.

IMPACT

The differences of the underlying risks and prognosis between oliguric and non-oliguric AKI in very preterm infants remain unclear. We found that oliguric AKI, but not non-oliguric AKI, carries higher mortality risks than infants without AKI. Oliguric AKI possessed higher mortality risks than non-oliguric AKI, irrespective of concomitant serum creatinine elevation and severe AKI. Oliguric AKI is more associated with prenatal small-for-the-gestational age and perinatal and postnatal adverse events, while non-oliguric AKI is associated with nephrotoxins exposures. Our finding highlighted the importance of oliguric AKI and is helpful in developing future protocol in neonatal critical care.

Time to Regain Birthweight and Association with Neurodevelopmental Outcomes among Extremely Preterm Newborns

Objective

Determine association between time to regain birthweight and 2-year neurodevelopment among extremely preterm (EP) newborns.

Study Design

Secondary analysis of the Preterm Erythropoietin Neuroprotection Trial evaluating time to regain birthweight, time from birth to weight nadir, time from nadir to regain birthweight, and cumulative weight loss with 2-year corrected Bayley Scales of Infant and Toddler Development 3rd edition.

Results

Among n = 654 EP neonates, those with shorter nadir-to-regain had lower cognitive scores (2-4 days versus ≥ 8 days: -3.5, [CI -7.0, 0.0]; ≤1 day versus ≥ 8 days: -5.0, [CI -10.2, 0.0]) in fully adjusted stepwise forward regression modeling. Increasingly cumulative weight loss was associated with lower cognitive scores (-50 to <-23 percent-days: -4.0, [95% CI -7.6, -0.4]) and language scores (≤-50 percent-days: -5.7, [CI -9.8, -1.6]; -50 to <-23 percent-days: -6.1, [CI -10.2, -2.0]).

Conclusion

Faster nadir-to-regain and prolonged, severe weight loss are associated with adverse 2-year neurodevelopmental outcomes.

Trial registration

PENUT Trial Registration: NCT01378273. https://clinicaltrials.gov/ct2/show/NCT01378273.

Early Fluid and Nutritional Management of Extremely Preterm Newborns During the Fetal-To-Neonatal Transition

During the fetal-to-neonatal transitional period, extremely preterm newborns undergo significant intrabody fluid shifts and resulting weight loss due to increased insensible fluid losses due to immature skin, kidneys, among other factors. These ongoing physiologic changes make fluid and nutritional management complex in the neonatal-to-fetal transitional time period for extremely premature newborns. However, limited literature exists to guide optimal practices for providers caring for this population. Here, we review the evidence on optimal fluid and nutritional management during the fetal-to-neonatal transition of extremely preterm newborns.

Sodium and Growth in Preterm Infants: A Review

Aim

This article is intended to review the relationship between sodium homeostasis and growth, outline reasons why preterm infants may become sodium deficient, and share data from our group and others regarding the potential benefits of dietary sodium supplementation.

Background

Despite tremendous efforts over the past 20 years to optimize neonatal nutrition, postnatal growth failure in preterm infants remains a significant problem. Compelling associations have been identified between in-hospital growth failure and cardiometabolic and neurodevelopmental disorders, heightening the need to further identify the optimal nutritional needs of preterm infants.

Results

The impact of sodium deficiency may have on somatic growth is poorly studied and reported upon within the human literature. In contrast, animal studies dating back almost 100 years highlight the nutritional importance of dietary sodium. Sodium homeostasis during early postnatal life is understudied and underappreciated by neonatologists.

Conclusion

Insufficient sodium intake during early life is likely a critical yet underappreciated contributor to growth failure. Total body sodium depletion may be an important risk factor driving complications of premature birth.

Clinical significance

Increased awareness of sodium homeostasis in preterm infants may improve outcomes in this population. Sodium intake recommendations are provided based on the interpretation of currently available literature.

Exposure of preterm neonates receiving total parenteral nutrition to phthalates and its impact on neurodevelopment at the age of 2 months

This prospective study assessed the exposure to phthalates of preterm neonates who received total parenteral nutrition (TPN) during their stay in the neonatal intensive care unit (NICU) and the risk of neurodevelopment delays at the age of 2 months. Our study recruited 33 preterm neonates who required TPN upon NICU admission. Urine samples for analyzing phthalate metabolites were obtained at admission and then daily until the last day of receiving TPN. Phthalates in the daily TPN received by the preterm neonates were analyzed. The neurodevelopment of the neonates was assessed using the Ages and Stages Questionnaire Edition 3 (ASQ-3). Diethyl phthalate and butyl benzyl phthalate were found in all TPN samples, while 27% and 83% contained dibutyl phthalate and di-(2-ethylhexyl) phthalate (DEHP), respectively. Yet, the daily dose of each phthalate that our preterm neonates received from TPN was much lower than the recommended tolerable limit. Urinary levels of monobenzyl phthalate and four metabolites of DEHP [i.e., mono-(2-ethylhexyl) phthalate (MEHP), mono-(2-ethyl-5-hydroxyhexyl) phthalate, mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP), and mono-(2-ethyl-5-carboxypentyl) phthalate (MECPP)] and the sum of four DEHP metabolites (∑₄DEHP) increased significantly in preterm neonates before discharge. However, these levels were not correlated with their phthalate parent compounds in TPN, suggesting other sources of exposure in the NICU. At 2 months, we found that urinary levels of mono-iso-butyl phthalate (MiBP), MECPP, MEHP, and ∑₄DEHP were inversely related to fine motor skills. After adjusting for head circumference, the inverse relationships remained significant, suggesting direct effects from phthalates. Given the extreme vulnerability of our population, it is critical to minimize exposure to phthalates during their NICU stay.

The impact of intrauterine growth restriction and prematurity on nephron endowment

In humans born at term, maximal nephron number is reached by the time nephrogenesis is completed - at approximately 36 weeks' gestation. The number of nephrons does not increase further and subsequently remains stable until loss occurs through ageing or disease. Nephron endowment is key to the functional capacity of the kidney and its resilience to disease; hence, any processes that impair kidney development in the developing fetus can have lifelong adverse consequences for renal health and, consequently, for quality and length of life. The timing of nephrogenesis underlies the vulnerability of developing human kidneys to adverse early life exposures. Indeed, exposure of the developing fetus to a suboptimal intrauterine environment during gestation - resulting in intrauterine growth restriction (IUGR) - and/or preterm birth can impede kidney development and lead to reduced nephron endowment. Furthermore, emerging research suggests that IUGR and/or preterm birth is associated with an elevated risk of chronic kidney disease in later life. The available data highlight the important role of early life development in the aetiology of kidney disease and emphasize the need to develop strategies to optimize nephron endowment in IUGR and preterm infants.

Urine podocyte mRNA loss in preterm infants and related perinatal risk factors

BACKGROUND

Preterm birth has been identified as a risk factor for development of long-term chronic kidney disease. Podocyte loss has been reported to contribute to this process in preterm animal models. However, details about podocyte loss in preterm infants and related perinatal risk factors have not been well clarified.

METHODS

Forty full-term infants and 106 preterm infants were enrolled. Urine samples were collected from full-term infants within 4-7 days of birth and preterm infants at 37-40 weeks of corrected age. Levels of urine podocin mRNA, urine protein (UP), and urine microalbumin (UMA) were measured, and the relationship between these markers was evaluated. Clinical information in these infants was collected, and potential correlates that may lead to increased podocyte loss during the perinatal period were identified using linear regression analysis.

RESULTS

Urine podocyte loss indicated by the urine podocin mRNA to creatinine ratio (UpodCR) was higher in preterm infants than in full-term infants. UpodCR was correlated with the levels of UP and UMA. Multiple linear regression analysis also showed that lower gestational age (GA) at birth and small for gestational age (SGA) were high risk factors for urine podocyte loss.

CONCLUSIONS

Increasing urine podocyte loss was identified in preterm infants. Moreover, perinatal factors were associated with podocyte loss and may be a potential direction for comprehensive research and intervention in this field. A higher resolution version of the Graphical abstract is available as Supplementary information.

The cumulative risk assessment of phthalates exposure in preterm neonates

Phthalates are widely used plasticizers in various consumer products and medical devices, with some reporting as having estrogenic and anti-androgenic endocrine-disrupting effects. Premature neonates may be exposed to high levels of specific phthalates during hospitalization in the neonatal intensive care unit (NICU) because of reliance on multiple medical procedures that pose a possible health risk. The present study utilized seven urinary phthalate metabolites of dibutyl phthalate isomers [(di-n-butyl phthalate (DnBP) and diisobutyl phthalate (DiBP)], butylbenzyl phthalate (BBzP), and di(2-ethylhexyl) phthalate (DEHP) that had been previously measured in 33 preterm neonates sampled at hospital admission (N = 23) and daily during their NICU stay (N = 260). We aimed to perform: (1) cumulative risk assessment (CRA) using the volume and creatinine-adjusted models; (2) examine the temporal variability of CRA from repeated measures and (3) estimate the risk of cumulative exposure to phthalates based on their anti-androgenic and/or estrogenic properties. We multiplied the relative activity of individual phthalates exhibiting estrogenic or anti-androgenic effects by daily intake. For each preterm neonate, CRA was assessed based on the hazard index (HI) metric [the sum of hazard quotients] based on three reference doses for anti-androgenicity: the tolerable daily intake (TDI) from the European Food Safety Authority, the reference dose (RfD-AA) published in 2010 and newly revised published in 2020 (NRfD-AA). The metabolites of BBzP and DEHP were 2-23 fold higher in preterm neonates during their NICU stay. Median HIs increased in the order of HI_NRfDAA > HI_RfDAA > HI_TDI. In the creatinine-based model, 87% (92%), 87% (96%), and 100% (100%) of preterm neonates at admission (during NICU stay) showed HI_TDI, HI_RfD-AA, and HI_NRfD-AA exceeding 1, respectively with DEHP the most prevalent. The temporal reproducibility of HI (based on three reference doses) during preterm neonate stay in the NICU was high, with intra-class correlation coefficients ranging between 0.77 and 0.97, suggesting persistent exposure to phthalates. The four phthalates that preterm neonates were exposed to in the NICU exhibited estrogenic binding and anti-androgenic effects with median values (creatinine-based) of 98.7 and 56.9 μg/kg body weight/day, respectively. This was especially true for DEHP. The results indicate that preterm neonates in this NICU setting are probably at high risk of cumulative phthalate exposure with anti-androgenic properties that may have long-term adverse reproductive and developmental effects.

Urinary protein to creatinine ratio during the first month of life in very preterm infants-a prospective cohort study (PROTIPREMA)

BACKGROUND

Preterm infants have physiological proteinuria and values of urine protein to creatinine ratio (UPr/Cr) are higher compared to full-term infants during the first week of life. Few investigations explored the changes of proteinuria in very preterm infants (VPI, ≤ 31 weeks of gestation) older than a week, and it is unclear whether high and persistent proteinuria is associated with kidney injury in this population. This study aimed to (1) observe the changes of UPr/Cr during the first month of life in VPI and (2) describe clinical and biological variables associated with the changes of UPr/Cr.

METHODS

Spot urine samples for UPr/Cr were collected on the first day of life (DOL1) and then on DOL2-3, DOL5-6, second week of life (WOL2), WOL3, and WOL4 in VPI cared for in a third-level NICU. We tested the relationship of UPr/Cr with perinatal variables and diseases.

RESULTS

A total of 1140 urine samples were obtained for 190 infants. UPr/Cr values (mg/mmol) (median with interquartile) at DOL1, DOL2, DOL3, WOL2, WOL3, and WOL4 were, respectively, 191 (114-399), 226 (152-319), 225 (156-350), 282 (200-488), 308 (188-576), and 325 (175-664). At the multivariate analysis, lower gestational age (GA) and increasing postnatal age were the only variables significantly associated with higher UPr/Cr values (p < 0.001). There was wide intra- and interindividual variability in UPr/Cr, especially in infants with higher GA and clinical stability.

CONCLUSIONS

In VPI, UPr/Cr is higher at lower GA and increases with advancing postnatal age. High persistent proteinuria is not associated with clinical and biological variables reflecting kidney injury during the first month of life. A higher resolution version of the Graphical abstract is available as Supplementary information.

Enteral Nutrition in Preterm Infants (2022): A Position Paper From the ESPGHAN Committee on Nutrition and Invited Experts

OBJECTIVES

To review the current literature and develop consensus conclusions and recommendations on nutrient intakes and nutritional practice in preterm infants with birthweight <1800 g.

METHODS

The European Society of Pediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) Committee of Nutrition (CoN) led a process that included CoN members and invited experts. Invited experts with specific expertise were chosen to represent as broad a geographical spread as possible. A list of topics was developed, and individual leads were assigned to topics along with other members, who reviewed the current literature. A single face-to-face meeting was held in February 2020. Provisional conclusions and recommendations were developed between 2020 and 2021, and these were voted on electronically by all members of the working group between 2021 and 2022. Where >90% consensus was not achieved, online discussion meetings were held, along with further voting until agreement was reached.

RESULTS

In general, there is a lack of strong evidence for most nutrients and topics. The summary paper is supported by additional supplementary digital content that provide a fuller explanation of the literature and relevant physiology: introduction and overview; human milk reference data; intakes of water, protein, energy, lipid, carbohydrate, electrolytes, minerals, trace elements, water soluble vitamins, and fat soluble vitamins; feeding mode including mineral enteral feeding, feed advancement, management of gastric residuals, gastric tube placement and bolus or continuous feeding; growth; breastmilk buccal colostrum, donor human milk, and risks of cytomegalovirus infection; hydrolyzed protein and osmolality; supplemental bionutrients; and use of breastmilk fortifier.

CONCLUSIONS

We provide updated ESPGHAN CoN consensus-based conclusions and recommendations on nutrient intakes and nutritional management for preterm infants.

Neonatal exposure to phthalate and alternative plasticizers via parenteral nutrition

Di-(2-ethylhexyl) phthalate (DEHP), a plasticizer used to soften plastic medical devices (PMDs), was restricted in PMDs due to adverse health effects, being gradually replaced by alternative plasticizers (APs). Parenteral nutrition (PN), essential in the care for premature neonates in the neonatal intensive care unit, is stored in plastic storage bags and administered intravenously through plastic infusion circuits. We investigated to which extent PN contributes to current phthalate and AP exposure in premature neonates. First, we showed that DEHP and several APs are present in relevant amounts in PMDs used for neonatal PN administration. Secondly, ex vivo experiments mimicking clinical PN administration showed that lipid emulsions contained significant concentrations of DEHP and several APs (ATBC, TOTM, DEHT & DEHA), while hardly any plasticizers were detected in non-lipid solutions. ATBC leached from infusion circuits, while lipid emulsions were the major source for DEHP, TOTM, DEHT, and DEHA. PN administration resulted in estimated daily exposures of 13.9 µg/kg/d DEHP and 95.7 µg/kg/d ATBC in premature neonates, below their respective reference doses. Our data indicate that premature neonates requiring PN are still exposed to DEHP, as well as to a range of APs, making it a target for reduction of harmful plasticizer exposure.

Early detection of acute kidney injury in preterm newborns with perinatal asphyxia using serum cystatin

Introduction:The diagnosis of acute kidney injury (AKI) in preterm newborns with perinatal asphyxia based on increased serum creatinine (sCr) value and oliguria/anuria is usually delayed. The Aim of this paper is to evaluate serum cystatin C as an early predictor of AKI. Materials and methods:The study included 42 preterm newborns (24-37 weeks) with perinatal asphyxia (Apgar score (AS) ≤ 3 at 5 minutes of life or blood pH on admission ≤ 7.00). The sCr and sCysC levels were measured on the 1st, 3rd, and 7th day of life. According to KDIGO criteria, the newborns were classified into groups, and sCr and sCys-C values were compared. Results:The mean gestational age was 29.9 ± 3.0 weeks. AKI was diagnosed in 62.8 % of patients. Of these patients, 81.5% belonged to AKI 1 group, and 18.5 % to AKI 2 group.No newborns had the criteria for AKI 3. On day 7 the mean sCr values were significantly higher in AKI (65.4± 21.8) compared with the non-AKI group (168.4±38.2) (p<0.001), but not on day 1 and 3 (p = 0.322, 0.012, respectively). The sCys-C values were significantly higher in the AKI group on day 3 ( AKI vs. non-AKI group, 0.69 ±0.22 vs. 1.22 ±0.20; p <0.001) and day 7 (AKI vs. non-AKI group, 0.62 ±0.41 vs. 1.68 ±0.20; p <0.001). The sCys-C was also an earlier marker of a more severe stage of AKI than sCr. Conclusion:The sCys-C was elevated earlier than sCr, making it a valuable diagnostic tool for AKI in preterm newborns.

Anakinra Pilot - a clinical trial to demonstrate safety, feasibility and pharmacokinetics of interleukin 1 receptor antagonist in preterm infants

BACKGROUND

Bronchopulmonary dysplasia (BPD), its complication pulmonary hypertension (BPD-PH) and preterm brain and gut injury lead to significant morbidity and mortality in infants born extremely prematurely. There is extensive evidence that the pro-inflammatory cytokine interleukin 1 (IL-1) plays a key role in the pathophysiology of these illnesses. Two decades of clinical use in paediatric and adult medicine have established an excellent safety and efficacy record for IL-1 blockade with IL-1 receptor antagonist (IL-1Ra, medication name anakinra). Building on robust pre-clinical evidence, the Anakinra Pilot trial aims to demonstrate safety and feasibility of administering anakinra to preterm infants, and to establish pharmacokinetics in this population. Its ultimate goal is to facilitate large studies that will test whether anakinra can ameliorate early-life inflammation, thus alleviating multiple complications of prematurity.

METHODS AND ANALYSIS

Anakinra Pilot is an investigator-initiated, single arm, safety and feasibility dose-escalation trial in extremely preterm infants born between 24 weeks 0 days (240) and 276 weeks of gestational age (GA). Enrolled infants will receive anakinra intravenously over the first 21 days after birth, starting in the first 24 h after birth. In the first phase, dosing is 1 mg/kg every 48 h, and dosage will increase to 1.5 mg/kg every 24 h in the second phase. Initial anakinra dosing was determined through population pharmacokinetic model simulations. During the study, there will be a interim analysis to confirm predictions before undertaking dose assessment. Anakinra therapy will be considered safe if the frequency of adverse outcomes/events does not exceed that expected in infants born at 240-276 weeks GA.

CLINICAL TRIAL REGISTRATION

https://clinicaltrials.gov/, identifier NCT05280340.

Acute kidney injury in pediatrics: an overview focusing on pathophysiology

Acute kidney injury (AKI) is defined as an abrupt decline in glomerular filtration rate, with increased serum creatinine and nitrogenous waste products due to several possible etiologies. Incidence in the pediatric population is estimated to be 3.9 per 1,000 hospitalizations, and prevalence among children admitted to intensive care units is 26.9%. Despite being a condition with important incidence and morbimortality, further evidence on pathophysiology and management among the pediatric population is still lacking. This narrative review aimed to summarize and discuss current data on AKI pathophysiology in the pediatric population, considering all the physiological particularities of this age range and common etiologies. Additionally, we reported current diagnostic tools, novel biomarkers, and newly proposed medications that have been studied with the aim of early diagnosis and appropriate treatment of AKI in the future.

Prenatal and early childhood critical windows for the association of nephrotoxic metal and metalloid mixtures with kidney function

INTRODUCTION

As renal development and maturation processes begin in utero and continue through early childhood, sensitive developmental periods arise during which metal exposures can program subclinical nephrotoxicity that manifests later in life. We used novel dentine biomarkers of established nephrotoxicants including arsenic (As), cadmium (Cd), lead (Pb), chromium (Cr), and lithium (Li), and their mixtures, to identify critical windows of exposure-associated kidney function alterations in preadolescents.

METHODS

Participants included 353 children in the Programming Research in Obesity Growth, Environment and Social Stressors (PROGRESS) longitudinal birth cohort study based in Mexico City. Estimated glomerular filtration rate (eGFR) was assessed in 8-12 year old children using serum cystatin C measures. Pre- and postnatal metal(loid) concentrations were assessed in weekly increments by analyzing deciduous teeth with laser ablation-inductively coupled plasma-mass spectrometry. We used reverse distributed lag models (rDLMs) and lagged Weighted Quantile Sum (L-WQS) regression to examine time-varying associations between weekly perinatal metal(loid) exposure or metal(loid) mixtures and preadolescent eGFR while adjusting for age, sex, BMI z-score, SES and prenatal tobacco smoke exposure.

RESULTS

We identified a critical window of susceptibility to Pb exposure, in the late 3rd trimester (5 weeks prior to birth) during which higher Pb exposure was associated with children's increased eGFR. When all elements were assessed as a mixture, we identified late 2nd/early 3rd trimester (weeks 8-17 of gestation) as a window of vulnerability associated with decreased eGFR, with Li and Cr contributing the greatest weights to the association. When stratified by sex, we observed stronger effects among boys than girls.

CONCLUSIONS

Using tooth-matrix biomarkers, we identified discrete developmental exposure windows wherein Pb and metal(loid) mixtures were associated with altered preadolescent kidney function.

Maturation of Glomerular Filtration Rate in Term-Born Neonates: An Individual Participant Data Meta-Analysis

Background: The evidence from individual studies to support the maturational pattern of glomerular filtration rate (GFR) in healthy term-born neonates is inconclusive. We performed an individual participant data (IPD) meta-analysis of reported measured GFR (mGFR) data aimed to establish neonatal GFR reference values. Furthermore, we aimed to optimise neonatal creatinine-based GFR estimations Methods: We identified studies reporting mGFR measured by exogenous markers or creatinine clearance (CrCL) in healthy term-born neonates. The relationship between postnatal age and clearance was investigated using cubic splines with generalized additive linear mixed models. From our reference values, we estimated an updated coefficient for the Schwartz equation (eGFR(ml/min/1.73m²)=(k*height (cm))/serum creatinine(mg/dl)). Results: Forty-eight out of 1521 screened articles reported mGFR in healthy term-born neonates, and 978 mGFR values from 881 neonates were analysed. IPD were available for 367 neonates and the other 514 neonates were represented by 41 aggregated data points as means/medians per group. GFR doubled in the first five days after birth from 19.6 (95%CI 14.7;24.6) ml/min/1.73m² to 40.6 (95%CI 36.7;44.5) ml/min/1.73m², then more gradually increased to 59.4 (95%CI 45.9;72.9) ml/min/1.73m² by four weeks of age. A coefficient of 0.31 to estimate GFR best fitted the data. Conclusions: These reference values for healthy term-born neonates show a biphasic increase in GFR with the largest increase between days 1 and 5. Together with the re-examined Schwartz equation, this can help identify altered GFR in term-born neonates. To enable widespread implementation of our proposed eGFR equation, validation in a large cohort of neonates is required.

Critical windows of perinatal particulate matter (PM2.5) exposure and preadolescent kidney function

Air pollution exposure, especially particulate matter ≤2.5 μm in diameter (PM2.5), is associated with poorer kidney function in adults and children. Perinatal exposure may occur during susceptible periods of nephron development. We used distributed lag nonlinear models (DLNMs) to examine time-varying associations between early life daily PM2.5 exposure (periconceptional through age 8 years) and kidney parameters in preadolescent children aged 8-10 years. Participants included 427 mother-child dyads enrolled in the PROGRESS birth cohort study based in Mexico City. Daily PM2.5 exposure was estimated at each participant's residence using a validated satellite-based spatio-temporal model. Kidney function parameters included estimated glomerular filtration rate (eGFR), serum cystatin C, and blood urea nitrogen (BUN). Models were adjusted for child's age, sex and body mass index (BMI) z-score, as well as maternal education, indoor smoking report and seasonality (prenatal models were additionally adjusted for average first year of life PM2.5 exposure). We also tested for sex-specific effects. Average perinatal PM2.5 was 22.7 μg/m3 and ranged 16.4-29.3 μg/m3. Early pregnancy PM2.5 exposures were associated with higher eGFR in preadolescence. Specifically, we found that PM2.5 exposure between weeks 1-18 of gestation was associated with increased preadolescent eGFR, whereas exposure in the first 14 months of life after birth were associated with decreased eGFR. Specifically, a 5 μg/m3 increase in PM2.5 during the detected prenatal window was associated with a cumulative increase in eGFR of 4.44 mL/min/1.732 (95%CI: 1.37, 7.52), and during the postnatal window we report a cumulative eGFR decrease of -10.36 mL/min/1.732 (95%CI: -17.68, -3.04). We identified perinatal windows of susceptibility to PM2.5 exposure with preadolescent kidney function parameters. Follow-up investigating PM2.5 exposure with peripubertal kidney function trajectories and risk of kidney disease in adulthood will be critical.

Fluid management considerations in extremely preterm infants born at 22-24 weeks of gestation

Emerging data regarding the encouraging outcomes of extremely preterm infants from centers taking active approaches to the care of these infants have prompted dialogue regarding optimal medical management. Among the multitude of decisions providers make in caring for extremely premature infants is the prescribing of parenteral fluids. Surprisingly, there are limited data to guide evidenced-based approaches to fluid and electrolyte management in this population. Immaturity of renal function and skin barriers contribute to the impaired capacity of the preterm infant to maintain salt and water homeostasis. This perspective paper highlights developmental physiological properties of the kidney and skin, which the provider needs to understand to provide parenteral fluid therapy. Additionally, we provide recommendations for initial fluid and electrolyte management of the preterm infant based on novel data as well as the published literature.

Index for the appropriate vancomycin dosing in premature neonates and infants

BACKGROUND

In neonates, vancomycin (VCM) is used to treat Gram-positive bacterial infections. However, VCM blood concentrations are affected by gestational age, bodyweight (BW), and renal function. The initial VCM dose adjustment can therefore be difficult, and few reports have evaluated this issue. In this study, we investigated the factors determining the appropriate VCM dosing schedule in neonates, especially premature infants.

METHODS

The VCM dosage and trough concentrations were retrospectively investigated from the initial treatment to maintenance therapy in neonatal intensive care unit patients who underwent therapeutic drug monitoring. We examined the average single-administration VCM dosage during maintenance therapy. We then compared the actual VCM dose with that calculated using an index comprising six items that influence the VCM daily dose (postnatal age, gestational age, BW, serum creatinine level, urine output, and lactate level).

RESULTS

Twenty premature infants were included. The average BW of patients at the initial VCM administration was 975 g. During maintenance therapy, the average VCM dose was 8.4 mg/kg, and the median trough concentration was 12.4 μg/mL. When we applied the six-item index, 18 of 20 patients (90%) had concordant results between the actual VCM dosing schedule and the VCM calculated using the index.

CONCLUSIONS

The average VCM dose and six-item index can facilitate the transition from the initial VCM dose to an appropriate dose in many cases and contribute to early treatment in low-birthweight infants with more variable BW, distribution volumes, and renal function. In conclusion, our six-item index may help standardize VCM administration in premature infants.

Neonatal Proteinuria in Calves-A Quantitative Approach

Simple Summary

A newborn’s survival depends on the quick adaptation of the organism to new environmental conditions. Newborn calves show high somatic maturity compared to, for example, human newborns, but their body functions with a lower efficiency than that of adult cattle. Adaptation processes concern all organs, including the kidneys, which are not morphologically mature after birth. The ongoing morphological changes imply functional alterations in the kidneys. There is an increase in blood flow through the kidneys and the glomerular filtration rate, as well as an increase in the efficiency of resorption processes of primary urine components into the blood, including proteins. Protein is present in trace amounts in the urine of healthy adults of various species. It can occur in larger amounts in the urine of sick animals, as well as in certain physiological states, e.g., in newborns. The presence of protein in the urine of newborns in the quantity exceeding 300 mg/24 h/m² is called neonatal proteinuria. The causes of proteinuria in healthy newborns have not been clearly elucidated. Many studies have focused on proteinuria in newborns and sick children and sick animals, especially dogs and cats. The present study was the first to quantify the hypothesis of the occurrence of proteinuria in healthy calves in the first week of life and to assess its intensity and dynamics, based on the analysis of changes in total protein excretion in the urine and its fractions differing in molecular weight (albumin, low molecular weight proteins (LMW) and high molecular weight proteins (HMW)). It should be noted that the analysis of excreted protein fractions is a sensitive diagnostic indicator of the type of kidney disease, e.g., increased HMW protein excretion may indicate damage to the renal glomeruli, and loss of LMW proteins may indicate renal tubular disease.

Abstract

Urine testing is a convenient, non-invasive method of obtaining information about body functions. Depending on the intended purpose, urine testing may be qualitative and/or quantitative. Urine analysis can also include proteins. There are no data in the literature on the occurrence of proteinuria in healthy neonatal calves. The present study was the first that aimed to quantify the hypothesis of proteinuria occurrence in these animals in the first week of life, to assess its intensity and dynamics and to understand the underlying causes of proteinuria in healthy calves. The research was carried out on 15 healthy calves in the first seven days of life. Calves were catheterized to determine minute diuresis. Total protein concentration was determined in blood plasma and urine. Urine proteins were separated by electrophoresis (SDSPAGE) and their concentration and percentage were determined by densitometry using an image archiving and analysis software. The separated proteins were divided into three groups according to molecular weight for albumin, LMW and HMW proteins. The results were standardized per 1 m² of body surface area and statistically analyzed. Neonatal proteinuria was demonstrated in healthy calves, mainly resulting from the high concentration of LMW proteins in the urine. Their percentages decreased significantly from 84.46% on the first day of calves’ life to 64.02% on day 7. At the same time, a statistically significant increase was observed in the proportion of albumin and high molecular weight proteins in urine total protein. Albumin percentage increased from 9.54% (on day 1) to almost 20% (on day 7), while the proportion of HMW proteins increased from 6.68% to 18.13%, respectively. The concentration of total protein in the urine of newborn calves amounted to 14.64 g/L and decreased statistically significantly during the first 72 h of postnatal life, stabilizing at the level of 3–4 g/L. The mean value of total protein excretion in the first week of life was 4.81 mg/min/m² (i.e., 6.93 g/24 h/m²). The analysis of protein concentration in the urine and its excretion, as well as changes in urinary excretion of the tested protein fractions, indicated that neonatal proteinuria in healthy neonatal calves was tubular (i.e., main reason is the reduced absorption of proteins in nephrons). In addition, research showed that there was a rapid improvement in resorptive mechanisms in tubular cells. It should be assumed that the filtration barrier in the kidneys of these animals after birth is morphologically prepared to retain high molecular weight proteins. It seems that the increased permeability of the filtration barrier in the glomeruli does not necessarily indicate the immaturity of the kidneys, but may indicate the kidneys’ adaptation to excess protein removal from the body during feeding with high-protein food (colostrum), with an open intestinal barrier enabling protein absorption from the gastrointestinal tract to the blood.

Maturational changes in sodium metabolism in periviable infants

BACKGROUND

Sodium depletion results in impaired somatic growth. The sodium requirements of extremely preterm (periviable) infants early in life are not known. We therefore investigated sodium homeostasis in this population over the first 10 weeks following birth.

METHODS

This was a longitudinal, observational study of sodium intake and urine sodium excretion in a convenience cohort of 23 infants born at 22 0/7-23 6/7-week gestation.

RESULTS

Sodium intake ranged from 5.2 ± 0.4 to a maximum of 7.9 ± 0.5 mEq/kg/day at 2 and 8 weeks of postnatal age, respectively, while urinary sodium loss was 7.7 ± 1.0 mEq/kg/day and 6.9 ± 0.7 mEq/kg/day at these time points. Sodium balance (sodium intake - urine sodium output) was first positive at 6 weeks of age, though a positive sodium balance exceeding 1.4 mEq/kg/day (i.e., a balance associated with weight gain of 30 g/day) was not observed until 10 weeks.

CONCLUSIONS

Infants born at 22-23-week gestational age have a prolonged period of high urinary losses of sodium and negative sodium balance. Sodium intakes greater than those currently recommended by the American Academy of Pediatrics are needed to achieve a significant positive sodium balance in this population.

Birthweight and the Prevalence, Progression, and Incidence of CKD in a Multideterminant Model in a High-Risk Australian Aboriginal Community

INTRODUCTION

We have previously showed that albuminuria was associated with low birthweight in young adults in a remote Australian Aboriginal community that has high rates of kidney disease. Here we describe the association of birthweight with incidence and progression of kidney disease over time.

METHODS

Among 695 members of an Aboriginal community with recorded birthweights, urine albumin creatinine ratio (ACR) and estimated glomerular filtration rate (eGFR) were measured at ages 5 to 40 years, and follow-up values were measured or imputed again a median of 11.6 years later. Prevalence of markers on each occasion and change over time were evaluated in the context of birthweights and other potentially significant factors.

RESULTS

On the second screen, ACR was inversely and significantly correlated with birthweight and eGFR was directly correlated with birthweight. Increases in ACR and in proportions of persons who developed new-onset (incident) albuminuria between screens were higher in those of lower birthweights (<2.5 kg). Proportions of persons who lost ≥20% of their baseline eGFR were higher in the lower birthweight groups. Lower birthweights also amplified elevations of ACR associated with other risk factors, specifically higher body mass indexes (BMIs) and a prior history of poststreptococcal glomerulonephritis (PSGN). At both screens, progressively higher levels of ACR beyond the mid-microalbuminuria range were correlated with lower levels of eGFR.

CONCLUSIONS

Lower birthweight contributes to an excess of kidney disease and its progression in this population. Because an excess of low birthweight and episodes of PSGN are eminently preventable, substantial containment of kidney disease is feasible.

Nephrotoxicity in Neonates

Acute kidney injury (AKI) is classified based on prerenal, intrinsic, and postrenal causes. In the newborn, AKI can occur after an insult during the prenatal, perinatal, or postnatal period. AKI is usually an underrecognized condition and its true incidence is unknown. AKI may result from the administration of a number of different nephrotoxic medications, which are often used concurrently in critically ill neonates, exponentially increasing the risk of renal injury. Drug toxicity may also compromise the formation and development of nephrons, and this is particularly important in preterm infants, who have incomplete nephrogenesis. Little is known about the pharmacokinetics and pharmacodynamics of different medications used in neonates, especially for the most immature infant, and the use of most medications in this population is off label. Strategies to prevent AKI include the avoidance of hypotension, hypovolemia, fluid imbalances, hypoxia, and sepsis as well as judicious use of nephrotoxic medications. Treatment strategies aim to maintain fluids and electrolytic and acid-base homeostasis, along with an adequate nutritional status. Neonates are especially prone to long-term sequelae of AKI and benefit from long-term follow-up. This review summarizes the most relevant aspects of nephrotoxicity in neonates and describes the prevention, treatment, and follow-up of AKI in neonates.

The progression of serum cystatin C concentrations within the first month of life after preterm birth-a worldwide systematic review

Multiple single-center studies have examined the progression of kidney function biomarkers such as serum cystatin C (Cys C) in the first 30 days of life (DOL) after preterm birth, but from different ethnicities and in different gestational ages (GA), without a functional summary available. We performed a systematic literature review within PubMed, Google Scholar, and Scopus, with additional use of the snowballing method to find studies including data on serum Cys C concentrations in the first 30 DOL. We identified 15 papers that met criteria, published from 2000 to 2019, from 10 countries across 4 continents, in 1468 babies born preterm. Cys C was superior to creatinine in 11/13 studies, and equal in 2/13. For infants born at 24-28 weeks GA, the DOL1 Cys C concentrations ranged from 1.44 to 1.90 mg/L, from 1.20 to 1.77 on DOL3, and from 1.36 to 2.02 between DOL 4 and 30. For infants born at 29-33 weeks GA, the DOL1 Cys C values ranged from 1.41 to 1.96 mg/L, from 1.28 to 1.70 on DOL3, and 1.51 to 1.87 between DOL 4 and 30. For preterm infants born after 34 weeks GA, the DOL1 Cys C values ranged from 1.22 to 1.96 mg/L, from 1.24 to 1.85 on DOL3, and 1.22 to 1.82 between DOL 4 and 30. This systematic review provides generalizable worldwide reference data on Cys C that could be used to estimate progression or resolution of abnormal kidney function in the first months after preterm birth, stratified by GA.

Population Model of Serum Creatinine as Time-Dependent Covariate in Neonates

Serum creatinine (sCr) is a commonly measured biomarker to estimate glomerular filtration rate (GFR) and therefore widely used as a covariate in population pharmacokinetic models of renally excreted drugs. In neonates, sCr dynamically changes during the first few weeks after birth. Missing covariates are a common problem in pharmacokinetic modeling of neonates due to the limited availability of blood sampling in number and volume. The objective of this work is to develop a parsimonious population model describing time courses of sCr in neonates with the intent to be incorporated into pharmacokinetic models of various drugs where sCr values are sparse or missing. The data for model development consisted of sCr measurements in 1080 newborns with a gestational age of 24-42 weeks. The model is based on a pharmacokinetic model of sCr that involves GFR, backflow of creatinine from the renal tubules, and urinary flow. Gestational age is the only covariate explaining between-subject variability of sCr. The model adequately describes distinct features of the sCr time course such as a peak and decline to a plateau. For a neonate with a GA of 35 weeks, the typical value of sCr at birth was 0.584 mg/dL, the peak (0.794 mg/dL) occurred 2.3 days after birth, to reach a plateau of 0.255 mg/dL approximately after 24.7 days. Model simulations reveal that in neonates with a similar postnatal age, sCr decreases with increasing GA. In summary, our model is designed to be a part of full random effects pharmacokinetic models where sCr is a significant covariate.

Urine NMR Metabolomics Profile of Preterm Infants With Necrotizing Enterocolitis Over the First Two Months of Life: A Pilot Longitudinal Case-Control Study

Objective: To investigate changes in the urine metabolome of very low birth weight preterm newborns with necrotizing enterocolitis (NEC) and feed intolerance, we conducted a longitudinal study over the first 2 months of life. The metabolome of NEC newborns was compared with two control groups that did not develop NEC: the first one included preterm babies with feed intolerance, while the second one preterm babies with good feed tolerance.

Methods: Newborns developing NEC within the 3 weeks of life were identified as early onset NEC, while the remaining as late onset NEC. Case-control matching was done according to the gestational age (±1 week), birth weight (± 200 g), and postnatal age. A total of 96 urine samples were collected and analyzed. In newborns with NEC, samples were collected before, during and after the diagnosis over the first 2 months of life, while in controls samples were collected as close as possible to the postnatal age of newborns with NEC. Proton nuclear magnetic resonance (¹H NMR) spectroscopy was used for metabolomic analysis. Data were analyzed by univariate and multivariate statistical analysis.

Results: In all the preterm newborns, urine levels of betaine, glycine, succinate, and citrate positively correlated with postnatal age. Suberate and lactate correlated with postnatal age in preterms with NEC and in controls with food intolerance, while N,N-dimethylglycine (N,N-DMG) correlated only in controls with good digestive tolerance. Preterm controls with feed intolerance showed a progressive significant decrease of N-methylnicotinamide and carnitine. Lactate, betaine, myo-inositol, urea, creatinine, and N,N-dimethylglycine discriminated late-onset NEC from controls with good feed tolerance.

Conclusion: Our findings are discussed in terms of contributions from nutritional and clinical managements of patients and gut microbiota.

Distribution of proteinuria- and albuminuria-to-creatinine ratios in preterm newborns

BACKGROUND

Urine protein assessment is important when glomerular disease or injury is suspected. Normal values of proteinuria already published for preterm newborns suffer from limitation, with small cohorts of patients. This prospective study was conducted to update the urine total protein- and albumin-to-creatinine ratio values.

METHODS

Urine samples were collected from 231 preterm newborns within the first 48 h (D0-1) and/or between 72-120 h of life (D3-4). Total protein, albumin, and creatinine were measured, their distribution and upper-limit values determined.

RESULTS

At D0-1 and D3-4, respectively, the median for the total protein-to-creatinine ratio were 80 and 107 mg/mmol (upper-limit values 223 and 289 mg/mmol) in the whole studied population, 149 and 214 mg/mmol in children born before 29 weeks of gestational age, 108 and 130 mg/mmol in those born between 29 and 33 weeks, and 61 and 93 mg/mmol in those born after 33 weeks. For the albumin-to-creatinine ratio, the median were 12 and 17 mg/mmol (upper-limit values 65 and 62 mg/mmol) in the whole studied population, 22 and 50 mg/mmol in children born before 29 weeks, 21 mg/mmol in those born between 29 and 33 weeks, and 8 and 12 mg/mmol in those born after 33 weeks. The use of nephrotoxic drugs and mechanical ventilation seems to influence proteinuria and albuminuria values.

CONCLUSIONS

We report distribution of proteinuria- and albuminuria-to-creatinine in preterm newborns, including the upper-limit values. These values should be taken into account in the detection and diagnosis of glomerular disease and/or injury in daily clinical practice. Graphical abstract.

Fluid Balance in the Critically Ill Child Section: "How Bad Is Fluid in Neonates?"

Fluid overload (FO) in neonates is understudied, and its management requires nuanced care and an understanding of the complexity of neonatal fluid dynamics. Recent studies suggest neonates are susceptible to developing FO, and neonatal fluid balance is impacted by multiple factors including functional renal immaturity in the newborn period, physiologic postnatal diuresis and weight loss, and pathologies that require fluid administration. FO also has a deleterious impact on other organ systems, particularly the lung, and appears to impact survival. However, assessing fluid balance in the postnatal period can be challenging, particularly in extremely low birth weight infants (ELBWs), given the confounding role of maternal serum creatinine (Scr), physiologic weight changes, insensible losses that can be difficult to quantify, and difficulty in obtaining accurate intake and output measurements given mixed diaper output. Although significant FO may be an indication for kidney replacement therapy (KRT) in older children and adults, KRT may not be technically feasible in the smallest infants and much remains to be learned about optimal KRT utilization in neonates. This article, though not a meta-analysis or systematic review, presents a comprehensive review of the current evidence describing the effects of FO on outcomes in neonates and highlights areas where additional research is needed.

How should we assess renal function in neonates and infants?

AIM

Review of current knowledge on assessing renal function in term and preterm neonates.

METHODS

Literature review and analysis of own data.

RESULTS

Prematurity, genetic, environmental and maternal factors may alter peak nephron endowment and life-long renal function. Nephrogenesis continues until 34-36 weeks of gestation, but it is altered with premature delivery. Variability of nephron endowment has a substantial impact on the clearance of renally excreted drugs. Postnatally, glomerular function rate (GFR) increases daily, doubles by two weeks, and slowly reaches full maturity at 18 months of age. Ideally, renal function biomarkers should be expressed as age-independent z-scores, and evidence suggests indexing these values to post-conceptual age rather than chronological age. Newborn and maternal serum creatinine correlate tightly for more than 72 hours after delivery, rendering this biomarker unsuitable for the assessment of neonatal renal function. Cystatin C does not cross the placenta and may be the preferred biomarker in the neonate. Here, we provide preliminary data on the natural evolution of the cystatin C eGFR in infancy.

CONCLUSION

Cystatin C may be superior for GFR estimation in neonates, but the best approach to drug dosing of renally excreted drugs remains to be established.

Urinary Cystatin-C, a marker to assess and monitor neonatal kidney maturation and function: validation in twins

BACKGROUND

Nephrogenesis is a complex process of nephron formation and maturation that can be compromised by preterm delivery and intrauterine growth restriction. This study aimed to evaluate and compare urinary Cys-C levels with renal volume in a cohort of preterm and term twins, adequate for gestational age or intrauterine growth restricted, to investigate their values in different conditions of nephrogenesis.

METHODS

The study was performed on twins at 30-40 days of postnatal corrected age: renal volumes were measured by 3D ultrasound technology and urine samples were analyzed for Cystatin-C. A follow-up was performed by Cystatin-C.

RESULTS

Renal volumes in preterm and intrauterine growth-restricted twins showed values significantly lower than those observed in term twins and were inversely correlated to urinary Cystatin-C levels. During the follow-up, intrauterine growth-restricted twins showed amplified levels of urinary Cystatin-C; in contrast, invariable or decreased levels were observed in adequate for gestational age twins.

CONCLUSIONS

Urinary Cystatin-C, evaluated when intrauterine/extrauterine nephrogenesis could be considered completed, concurrently with renal volume assessment can improve the identification of neonates with initial kidney impairment. Its potential value as a useful marker in monitoring physiological/pathological renal conditions could be considered, mainly for neonates at elevated risk of developing long-term renal diseases.

IMPACT

Urinary Cys-C levels are inversely correlated to renal volumes and reflect nephrogenesis conditions. No data in literature are reported regarding: (a) the concurrent assessment of renal volumes and urinary levels of Cystatin-C in preterm and term twins with different conditions of gestational life, i.e., AGA and IUGR and (b) the follow-up of IUGR and preterm neonates using the urinary Cys-C determination. The variations of urinary Cys-C levels, observed in the follow-up of preterm and/or IUGR neonates, support the usefulness of monitoring those neonates with altered nephrogenesis, who are later at risk for renal impairment and for long-term renal diseases.

A physiological approach to fluid and electrolyte management of the preterm infant: Review

Despite the fact that hundreds of thousands of preterm infants receive parenteral fluids each year, study of optimal fluid and electrolyte management in this population is limited. Compared to older children and adults, preterm infants have an impaired capacity to regulate water and electrolyte balance. Appropriate fluid and electrolyte management is critical for optimal care of low birth weight or sick infants, as fluid overload and electrolyte abnormalities pose significant morbidity. This review highlights basic physiological principles which need to be applied when prescribing parenteral fluids and builds upon published literature to outline a rational approach to initial fluid and electrolyte management of the preterm infant.

Urine biomarkers for monitoring acute kidney injury in premature infants

Background

Premature infants are at high risk for acute kidney injury (AKI). Serum creatinine (Cr) has limitations for evaluating kidney function in premature infants. We evaluated whether urine biomarkers could be used to monitor AKI in premature infants.

Methods

A prospective cohort study was conducted among infants born at < 37 weeks. Urine biomarkers and serum Cr were measured on postnatal days 1, 3, 5, 7, 10, and 14. Infants were divided into 3 groups according to gestational age (GA); < 28, 28 to < 32 and 32 to < 37 weeks.

Results

AKI occurred in 17 of 83 (20.5%) recruited infants at a median age of 7 (interquartile range 5–10) days. While the most common cause of AKI was hemodynamically significant patent ductus arteriosus (53.8%) in infants of GA < 28 weeks, necrotizing enterocolitis was the leading cause (50.0%) in infants of GA 28 to < 32 weeks. Urinary levels of neutrophil-gelatinase-associated lipocalin/Cr were higher and epidermal growth factor/Cr were lower in AKI group before the onset of AKI in infants of GA < 28 weeks. In infants of GA 28 to < 32 weeks, urinary interleukin-8/Cr levels were higher in AKI group at approximately the time of AKI onset.

Conclusion

Several urine biomarkers were significantly different between AKI and no AKI groups, and some had changed before the onset of AKI. These groups were distinct according to causative factors of AKI and GA. Urine biomarkers could be useful for monitoring the development of AKI in premature infants.

Pediatric Renal Ontogeny and Applications in Drug Development

The clinical applications of renal ontogeny mainly include renal function evaluation and optimal dosing of renally eliminated drugs in pediatric patients, which rely on pharmacometric models and/or bedside estimated glomerular filtration rate equations. However, these applications in drug development are based on an understanding of renal function development, especially when considering premature infants, and the renal biomarkers that can be used for renal function assessment. This review provides a general overview on (1) renal function development, (2) the biomarkers that are used to assess renal function, and (3) the practical application of this knowledge to drug dosing for renally eliminated drugs during pediatric development. While pharmacometric approaches for estimating renal function during development have improved considerably, the number of drug development programs that have studied premature infants is small and suggests that caution should be taken in estimating doses for renally eliminated drugs during periods of rapid change in renal function.

What Inotrope and Why?

Primary function of cardiovascular system is to meet body's metabolic demands. The aim of inotrope therapy is to minimise adverse impact of cardiovascular compromise. Current use of inotropes is primarily guided by the pathophysiology of cardiovascular compromise and anticipated actions of inotropes. Lack of significant reduction in morbidity and mortality associated with cardiovascular compromise despite inotrope use, highlights major gaps in our understanding of circulatory targets, thresholds and choices of inotrope therapy. Thus far, prevention of cardiovascular compromise remains the most effective strategy to optimize outcomes. Studies of alternative design are needed for further advancement in cardiovascular therapy in neonates.

Creatinine filtration kinetics in critically Ill neonates

BACKGROUND

Creatinine values are unreliable within the first weeks of life; however, creatinine is used most commonly to assess kidney function. Controversy remains surrounding the time required for neonates to clear maternal creatinine.

METHODS

Eligible infants had multiple creatinine lab values and were admitted to the neonatal intensive care unit (NICU). A mathematical model was fit to the lab data to estimate the filtration onset delay, creatinine filtration half-life, and steady-state creatinine concentration for each subject. Infants were grouped by gestational age (GA) [(1) 22-27, (2) >27-32, (3) >32-37, and (4) >37-42 weeks].

RESULTS

A total of 4808 neonates with a mean GA of 34.4 ± 5 weeks and birth weight of 2.34 ± 1.1 kg were enrolled. Median (95% confidence interval) filtration onset delay for Group 1 was 4.3 (3.71, 4.89) days and was significantly different than all other groups (p < 0.001). Creatinine filtration half-life of Groups 1, 2, and 3 were significantly different from each other (p < 0.001). There was no difference in steady-state creatinine concentration among the groups.

CONCLUSIONS

We quantified the observed kidney behavior in a large NICU population as a function of day of life and GA using creatinine lab results. These results can be used to interpret individual creatinine labs for infants to detect those most at risk for acute kidney injury.

IMPACT

One of the largest cohorts of premature infants to describe the evolution of kidney development and function over their entire hospitalization. New concept introduced of the kidney filtration onset delay, the time needed for the kidney to begin clearance of creatinine, and that it can be used as an early indicator of kidney function. The smallest premature infants from 22 to 27 weeks gestation took the longest time to begin and complete maternal creatinine clearance. Clinicians can easily compare the creatinine level of their patient to the normative curves to improve understanding of kidney function at the bedside.

Shaping of the nephron - a complex, vulnerable, and poorly explored backdrop for noxae impairing nephrogenesis in the fetal human kidney

Background

The impairment of nephrogenesis is caused by noxae, all of which are significantly different in molecular composition. These can cause an early termination of nephron development in preterm and low birth weight babies resulting in oligonephropathy. For the fetal human kidney, there was no negative effect reported on the early stages of nephron anlage such as the niche, pretubular aggregate, renal vesicle, or comma-shaped body. In contrast, pathological alterations were identified on subsequently developing S-shaped bodies and glomeruli. While the atypical glomeruli were closely analyzed, the S-shaped bodies and the pre-stages received little attention even though passing the process of nephron shaping. Since micrographs and an explanation about this substantial developmental period were missing, the shaping of the nephron in the fetal human kidney during the phase of late gestation was recorded from a microanatomical point of view.

Results

The nephron shaping starts with the primitive renal vesicle, which is still part of the pretubular aggregate at this point. Then, during extension of the renal vesicle, a complex separation is observed. The medial part of its distal pole is fixed on the collecting duct ampulla, while the lateral part remains connected with the pretubular aggregate via a progenitor cell strand. A final separation occurs, when the extended renal vesicle develops into the comma-shaped body. Henceforth, internal epithelial folding generates the tubule and glomerulus anlagen. Arising clefts at the medial and lateral aspect indicate an asymmetrical expansion of the S-shaped body. This leads to development of the glomerulus at the proximal pole, whereas in the center and at the distal pole, it results in elongation of the tubule segments.

Conclusions

The present investigation deals with the shaping of the nephron in the fetal human kidney. In this important developmental phase, the positioning, orientation, and folding of the nephron occur. The demonstration of previously unknown morphological details supports the search for traces left by the impairment of nephrogenesis, enables to refine the assessment in molecular pathology, and provides input for the design of therapeutic concepts prolonging nephrogenesis.

Renal Function Profiles in Preterm Neonates With Birth Asphyxia Within the First 24 H of Life

The characteristics of early renal function in preterm neonates of different gestational ages (GAs) with birth asphyxia (BA) remain unclear. Kidneys are sensitive to oxygen deprivation, and renal insufficiency may occur within 24 h of BA. We aimed to elucidate the renal function profiles within the first 24 h after the development of BA among vulnerable preterm neonates of different GAs. The medical records of 128 preterm neonates born to mothers with normal renal function were retrospectively analyzed. Data regarding the serum creatinine (SCr) and urea nitrogen (BUN) levels in venous blood, estimated creatinine clearance (eCCI) within the first hours after birth, and urinary output (UOP) in the first 24 h after birth were compared between the preterm with BA population and GA-matched population without BA (n = 64 and n = 64, respectively). Significantly higher SCr levels and lower eCCI were observed in mid-late preterm neonates with BA than in preterm neonates without BA (84.05 versus [vs.] 64.20 μmol/L, z = 4.41, p < 0.001; 15.02 vs. 21.30 mL/min/1.73 m², z = 3.57, p < 0.001, respectively). Very preterm neonates showed a higher UOP (2.01 vs. 1.66 mL/kg/h, z = 2.01, p = 0.045) after the development of BA than before. In preterm neonates with BA, the incidence of SCr > 133 μmol/L, CCI < 16 mL/min/1.73 m² and UOP < 1.0 ml/kg/h, was 10.94%, 62.50%, and 20.31%, respectively. Within 24 h after birth, BA was associated with eCCI < 16 mL/min/1.73 m² (p = 0.016, odds ratio = 2.83, 95% confidence interval: 1.210-6.613) in preterm neonates. Different renal function profiles were observed in preterm neonates of different GAs within the first 24 h of life after the development of BA. Candidate therapies based on different renal function statuses will bring these vulnerable patient populations of different GAs closer to receiving precision medicine.