Renal function in sick very low birthweight infants: 1. Glomerular filtration rate

Higher versus lower sodium intake for preterm infants

BACKGROUND

Infants born preterm are at increased risk of early hypernatraemia (above-normal blood sodium levels) and late hyponatraemia (below-normal blood sodium levels). There are concerns that imbalances of sodium intake may impact neonatal morbidities, growth and developmental outcomes.

OBJECTIVES

To determine the effects of higher versus lower sodium supplementation in preterm infants.

SEARCH METHODS

We searched CENTRAL in February 2023; and MEDLINE, Embase and trials registries in March and April 2022. We checked reference lists of included studies and systematic reviews where subject matter related to the intervention or population examined in this review. We compared early (< 7 days following birth), late (≥ 7 days following birth), and early and late sodium supplementation, separately.

SELECTION CRITERIA

We included randomised, quasi-randomised or cluster-randomised controlled trials that compared nutritional supplementation that included higher versus lower sodium supplementation in parenteral or enteral intake, or both. Eligible participants were preterm infants born before 37 weeks' gestational age or with a birth weight less than 2500 grams, or both. We excluded studies that had prespecified differential water intakes between groups.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed eligibility and risk of bias, and extracted data. We used the GRADE approach to assess the certainty of evidence.

MAIN RESULTS

We included nine studies in total. However, we were unable to extract data from one study (20 infants); some studies contributed to more than one comparison. Eight studies (241 infants) were available for quantitative meta-analysis. Four studies (103 infants) compared early higher versus lower sodium intake, and four studies (138 infants) compared late higher versus lower sodium intake. Two studies (103 infants) compared intermediate sodium supplementation (≥ 3 mmol/kg/day to < 5 mmol/kg/day) versus no supplementation, and two studies (52 infants) compared higher sodium supplementation (≥ 5 mmol/kg/day) versus no supplementation. We assessed only two studies (63 infants) as low risk of bias. Early (less than seven days following birth) higher versus lower sodium intake Early higher versus lower sodium intake may not affect mortality (risk ratio (RR) 1.02, 95% confidence interval (CI) 0.38 to 2.72; I2 = 0%; 3 studies, 83 infants; low-certainty evidence). Neurodevelopmental follow-up was not reported. Early higher versus lower sodium intake may lead to a similar incidence of hyponatraemia < 130 mmol/L (RR 0.68, 95% CI 0.40 to 1.13; I2 = 0%; 3 studies, 83 infants; low-certainty evidence) but an increased incidence of hypernatraemia ≥ 150 mmol/L (RR 1.62, 95% CI 1.00 to 2.65; I2 = 0%; 4 studies, 103 infants; risk difference (RD) 0.17, 95% CI 0.01 to 0.34; number needed to treat for an additional harmful outcome 6, 95% CI 3 to 100; low-certainty evidence). Postnatal growth failure was not reported. The evidence is uncertain for an effect on necrotising enterocolitis (RR 4.60, 95% CI 0.23 to 90.84; 1 study, 46 infants; very low-certainty evidence). Chronic lung disease at 36 weeks was not reported. Late (seven days or more following birth) higher versus lower sodium intake Late higher versus lower sodium intake may not affect mortality (RR 0.13, 95% CI 0.01 to 2.20; 1 study, 49 infants; very low-certainty evidence). Neurodevelopmental follow-up was not reported. Late higher versus lower sodium intake may reduce the incidence of hyponatraemia < 130 mmol/L (RR 0.13, 95% CI 0.03 to 0.50; I2 = 0%; 2 studies, 69 infants; RD -0.42, 95% CI -0.59 to -0.24; number needed to treat for an additional beneficial outcome 2, 95% CI 2 to 4; low-certainty evidence). The evidence is uncertain for an effect on hypernatraemia ≥ 150 mmol/L (RR 7.88, 95% CI 0.43 to 144.81; I2 = 0%; 2 studies, 69 infants; very low-certainty evidence). A single small study reported that later higher versus lower sodium intake may reduce the incidence of postnatal growth failure (RR 0.25, 95% CI 0.09 to 0.69; 1 study; 29 infants; low-certainty evidence). The evidence is uncertain for an effect on necrotising enterocolitis (RR 0.07, 95% CI 0.00 to 1.25; 1 study, 49 infants; very low-certainty evidence) and chronic lung disease (RR 2.03, 95% CI 0.80 to 5.20; 1 study, 49 infants; very low-certainty evidence). Early and late (day 1 to 28 after birth) higher versus lower sodium intake for preterm infants Early and late higher versus lower sodium intake may not have an effect on hypernatraemia ≥ 150 mmol/L (RR 2.50, 95% CI 0.63 to 10.00; 1 study, 20 infants; very low-certainty evidence). No other outcomes were reported.

AUTHORS' CONCLUSIONS

Early (< 7 days following birth) higher sodium supplementation may result in an increased incidence of hypernatraemia and may result in a similar incidence of hyponatraemia compared to lower supplementation. We are uncertain if there are any effects on mortality or neonatal morbidity. Growth and longer-term development outcomes were largely unreported in trials of early sodium supplementation. Late (≥ 7 days following birth) higher sodium supplementation may reduce the incidence of hyponatraemia. We are uncertain if late higher intake affects the incidence of hypernatraemia compared to lower supplementation. Late higher sodium intake may reduce postnatal growth failure. We are uncertain if late higher sodium intake affects mortality, other neonatal morbidities or longer-term development. We are uncertain if early and late higher versus lower sodium supplementation affects outcomes.

Population pharmacokinetics and dose optimization of vancomycin in neonates

The pharmacokinetics of vancomycin vary among neonates, and we aimed to conduct population pharmacokinetic analysis to determine the optimal dosage of vancomycin in Korean neonates. From a retrospective chart review, neonates treated with vancomycin from 2008 to 2017 in a neonatal intensive care unit (NICU) were included. Vancomycin concentrations were collected based on therapeutic drug monitoring, and other patient characteristics were gathered through electronic medical records. We applied nonlinear mixed-effect modeling to build the population pharmacokinetic model. One- and two-compartment models with first-order elimination were evaluated as potential structural pharmacokinetic models. Allometric and isometric scaling was applied to standardize pharmacokinetic parameters for clearance and volume of distribution, respectively, using fixed powers (0.75 and 1, respectively, for clearance and volume). The predictive performance of the final model was developed, and dosing strategies were explored using Monte Carlo simulations with AUC_0–24 targets 400–600. The patient cohort included 207 neonates, and 900 vancomycin concentrations were analyzed. Only 37.4% of the analyzed concentrations were within trough concentrations 5–15 µg/mL. A one-compartment model with first-order elimination best described the vancomycin pharmacokinetics in neonates. Postmenstrual age (PMA) and creatinine clearance (CLcr) affected the clearance of vancomycin, and model evaluation confirmed the robustness of the final model. Population pharmacokinetic modeling and dose optimization of vancomycin in Korean neonates showed that vancomycin clearance was related to PMA and CLcr, as well as body weight. A higher dosage regimen than the typical recommendation is suggested.

The dark side of ibuprofen in the treatment of patent ductus arteriosus: could paracetamol be the solution?

INTRODUCTION

Patent ductus arteriosus (PDA) persistence is associated, in prematures, to several complications. The optimal PDA management is still under debate, especially regarding the best therapeutic approach and the time to treat. The available drugs are not exempt from contraindications and side effects; ibuprofen itself, although representing the first-choice therapy, can show nephrotoxicity and other complications. Paracetamol seems a valid alternative to classic nonsteroidal anti-inflammatory Drugs, with a lower toxicity. Areas covered: Through an analysis of the published literature on ibuprofen and paracetamol effects in preterm neonates, this review compares the available treatments for PDA, analyzing the mechanisms underlining ibuprofen-associated nephrotoxicity and the eventual paracetamol-induced hepatic damage, also providing an update of what has been yet demonstrated and a clear description of the still open issues. Expert Opinion: Paracetamol is an acceptable alternative in case of contraindication to ibuprofen; its toxicity, in this setting, is very low. Lower doses may be effective, with even fewer risks. In the future, paracetamol could represent an efficacious first-line therapy, although its safety, optimal dosage, and global impact have to be fully clarified through long-term trials, also in the perspective of an individualized and person-based therapy taking into account the extraordinary individual variability.

Pharmacokinetics of Penicillin G in Preterm and Term Neonates

Group B streptococci are common causative agents of early-onset neonatal sepsis (EOS). Pharmacokinetic (PK) data for penicillin G have been described for extremely preterm neonates but have been poorly described for late-preterm and term neonates. Thus, evidence-based dosing recommendations are lacking. We describe the PK of penicillin G in neonates with a gestational age (GA) of ≥32 weeks and a postnatal age of <72 h. Penicillin G was administered intravenously at a dose of 25,000 or 50,000 IU/kg of body weight every 12 h (q12h). At steady state, PK blood samples were collected prior to and at 5 min, 1 h, 3 h, 8 h, and 12 h after injection. Noncompartmental PK analysis was performed with WinNonlin software. With those data in combination with data from neonates with a GA of ≤28 weeks, we developed a population PK model using NONMEM software and performed probability of target attainment (PTA) simulations. In total, 16 neonates with a GA of ≥32 weeks were included in noncompartmental analysis. The median volume of distribution (V) was 0.50 liters/kg (interquartile range, 0.42 to 0.57 liters/kg), the median clearance (CL) was 0.21 liters/h (interquartile range, 0.16 to 0.29 liters/kg), and the median half-life was 3.6 h (interquartile range, 3.2 to 4.3 h). In the population PK analysis that included 35 neonates, a two-compartment model best described the data. The final parameter estimates were 10.3 liters/70 kg and 29.8 liters/70 kg for V of the central and peripheral compartments, respectively, and 13.2 liters/h/70 kg for CL. Considering the fraction of unbound penicillin G to be 40%, the PTA of an unbound drug concentration that exceeds the MIC for 40% of the dosing interval was >90% for MICs of ≤2 mg/liter with doses of 25,000 IU/kg q12h. In neonates, regardless of GA, the PK parameters of penicillin G were similar. The dose of 25,000 IU/kg q12h is suggested for treatment of group B streptococcal EOS diagnosed within the first 72 h of life. (This study was registered with the EU Clinical Trials Register under EudraCT number 2012-002836-97.).

Assessment of kidney function in preterm infants: lifelong implications

This educational review will highlight the historical and contemporary references that establish a basic understanding of measurements of kidney function in the neonate and its relevance for the life of an individual. Importantly, the differential renal function of preterm infants relative to term infants has become paramount with the increased viability of preterm infants and the realization that kidney function is associated with gestational age. Moreover, neonatal kidney function is primarily associated with absolute renal mass and hemodynamic stability. Neonatal kidney function and its early developmental progression predict lifelong cardiovascular and renal disease risks. Validation of estimation equations of kidney function in this population has provided important reference data for other investigations and a clinical basis for prospective and longitudinal follow-up. Future research should be directed towards a better understanding of surrogate markers of kidney function from infancy through adulthood. Pediatric nephrologists should be aware of the developmental aspects of kidney function including the importance of the congenital nephron endowment and the preservation of kidney function throughout a lifetime. • Nephrogenesis occurs in utero in concert with other organ systems by branching morphogenesis, including the lungs, pancreas, and vascular tree, with over 60 % of nephrons being formed during the last trimester. • Infants born preterm before 36 weeks' gestation are in active nephrogenesis and are at increased risk of having a decreased nephron endowment from prenatal and postnatal genetic and epigenetic hazards that will impact the patient for a lifetime. • Post-natal adaptation of kidney function is directly proportional to the number of perfused nephrons, estimated by total kidney volume (TKV), mean arterial pressure (MAP), and gestational age. • Accurate measurement of glomerular filtration rate (GFR) in infants is problematic due to the unavailability of the gold standard inulin. The traditional use of creatinine to estimate GFR is unreliable in preterm infants due to its tubular reabsorption by immature kidneys and its dependence on muscle mass as an endogenous marker. Alternative endogenous markers to estimate GFR are cystatin C and beta trace protein (BTP). • Long-term follow-up of renal function in those born preterm should be life long and should include assessment of GFR, total kidney volume (TKV) relative to body surface area (BSA), and cardiovascular risks including hypertension and vascular stiffness.

Serum Cystatin C in Pregnancies With Normal and Restricted Fetal Growth

The objective of this study was to investigate circulating levels of cystatin C (an important endogenous marker of renal function) in mothers, fetuses, and neonates from intrauterine growth-restricted (IUGR; characterized by impaired nephrogenesis) and appropriate-for-gestational-age (AGA) pregnancies. Serum cystatin C levels were measured by enzyme immunoassay in 40 parturients and their 20 IUGR (<or=3rd customized centile, due to gestational pathology) and 20 AGA fetuses and neonates on postnatal day 1 (N1) and 4 (N4). Comparatively, creatinine and urea concentrations were determined in the same samples. Fetal cystatin C levels were higher in the AGA than the IUGR group (P = .001). In both groups, maternal cystatin C levels were lower than fetal (P < .001), N1 (P < .001), and N4 (P < .001) levels. Fetal levels were higher than N1 (P < .001) and N4 (P < .001), and N1 levels were higher than N4 (P = .007) ones. In both groups, no correlation existed between maternal and fetal levels, but positive correlations were found between cystatin C, creatinine, and urea levels in maternal and neonatal samples (in all cases, r >or= 0.376 and P <or= .045). Cystatin C levels did not correlate with gestational age and did not differ between males and females. Fetal cystatin C serum levels are lower in the IUGR group, significantly decrease after birth, and do not correlate with maternal levels in both groups. In addition, serum cystatin C levels positively correlate with respective creatinine and urea levels in the perinatal period.

Carboplatin therapeutic monitoring in preterm and full-term neonates

Introduction

Administration of the most appropriate dose of chemotherapy to neonates is particularly challenging and frequently not standardised based on any scientific rationale. We report the clinical utility of carboplatin therapeutic drug monitoring in preterm and full-term neonates within the first month of life.

Methods

Carboplatin therapeutic monitoring was performed to achieve target drug exposures area under the plasma concentration–time curve (AUC values) in nine preterm and full-term neonates diagnosed with retinoblastoma or neuroblastoma treated over an 8 year period. Carboplatin was administered over 3 days with therapeutic drug monitoring utilised to target cumulative AUC values of 5.2–7.8 mg/ml min.

Results

AUC values achieved were within 15% of target values for the individual courses of treatment in all but one patient (12/13 courses of treatment), with dose modifications of up to 215% required to achieve target AUC values, based on initial mg/kg dosing schedules. Carboplatin clearance determined across three consecutive chemotherapy courses in two patients increased from 3.4 to 7.1 ml/min and from 7.2 to 16.5 ml/min, representing increases of 210–230% over several weeks of treatment. Complete remission was observed in 8/9 patients, with no renal toxicity reported and only one patient experiencing ototoxicity.

Conclusion

The study highlights the benefits of utilising therapeutic drug monitoring to achieve target carboplatin AUC values in preterm and full-term neonates treated within the first few weeks of life, particularly in view of marked increases in drug clearance observed over consecutive chemotherapy courses. In the absence of therapeutic drug monitoring, body-weight based dosing is recommended, with dosing guidance provided for both approaches to inform future treatment.

Relationship of maternal creatinine to first neonatal creatinine in infants <30 weeks gestation

OBJECTIVE

To examine the relationship between maternal and neonatal creatinine (Cr) in preterm infants in the context of antenatal and intrapartum maternal and neonatal factors.

STUDY DESIGN

In this 5½-year, single-center, retrospective study, paired maternal and neonatal Cr were compared by t-test. Linear regression for correlated outcomes employing generalized estimating equations was used to examine neonatal Cr as a function of antenatal maternal Cr and potential confounders.

RESULT

A total of 157 neonates of 124 mothers met study criteria. Neonatal Cr values in the first 24 h of life were significantly higher than antenatal maternal values. Linear regression modeling showed that maternal Cr, neonatal lactate, hypoxic-ischemic villous changes on placental pathology and multiple gestation were each significant determinants of the first neonatal Cr.

CONCLUSION

No neonatal Cr was less than its paired maternal value. Maternal Cr, neonatal lactate, hypoxic-ischemic villous changes in the placenta and multiple gestation were each significantly associated with neonatal Cr.

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

Worldwide, approximately 10% of neonates are born preterm. The majority of preterm neonates are born when the kidneys are still developing; therefore, during the early postnatal period renal function is likely reflective of renal immaturity and/or injury. This study evaluated glomerular and tubular function and urinary neutrophil gelatinase-associated lipocalin (NGAL; a marker of renal injury) in preterm neonates during the first month of life. Preterm and term infants were recruited from Monash Newborn (neonatal intensive care unit at Monash Medical Centre) and Jesse McPherson Private Hospital, respectively. Infants were grouped according to gestational age at birth: ≤28 wk (n = 33), 29-31 wk (n = 44), 32-36 wk (n = 32), and term (≥37 wk (n = 22)). Measures of glomerular and tubular function were assessed on postnatal days 3-7, 14, 21, and 28. Glomerular and tubular function was significantly affected by gestational age at birth, as well as by postnatal age. By postnatal day 28, creatinine clearance remained significantly lower among preterm neonates compared with term infants; however, sodium excretion was not significantly different. Pathological proteinuria and high urinary NGAL levels were observed in a number of neonates, which may be indicative of renal injury; however, there was no correlation between the two markers. Findings suggest that neonatal renal function is predominantly influenced by renal maturity, and there was high capacity for postnatal tubular maturation among preterm neonates. There is insufficient evidence to suggest that urinary NGAL is a useful marker of renal injury in the preterm neonate.

Neonatal kidney size and function in preterm infants: what is a true estimate of glomerular filtration rate?

OBJECTIVES

To distinguish between cystatin C (CysC) and creatinine (Cr) as markers of estimated glomerular filtration rate (eGFR) in preterm infants and to correlate eGFR with total kidney volume (TKV) as a surrogate of nephron mass.

STUDY DESIGN

Sixty preterm (<37 weeks' gestational age [GA]) and 40 term infants were enrolled at birth. Serum Cr and CysC levels were assessed during the first week of life. Renal ultrasounds were performed to assess kidney dimensions with calculation of the TKV as a surrogate of nephron mass. Six equations derived from reference inulin, iohexol, and iothalamate clearance studies were used to calculate eGFR. Multiple regression analysis was applied to assess the relative impact of neonatal measures on eGFR, including TKV, GA, and mean arterial pressure (MAP).

RESULTS

Renal lengths correlated with GA and were within the reference values for intrauterine measurements. Estimation equations for glomerular filtration rate (GFR) based on Cr, CysC, and combined CysC + Cr demonstrated that Cr-based equations consistently underestimated GFR, whereas CysC and combined equations were more consistent with referenced inulin clearance studies. Term infants demonstrated significantly better eGFR than preterm infants. TKV, GA, and MAP correlated positively with eGFR, although only MAP and GA remained significant when adjusted for other covariates.

CONCLUSIONS

Primary determinants of eGFR in preterm infants are GA and MAP. The CysC level is a superior biomarker to serum Cr in the assessment of GFR in premature infants.

Factors affecting postnatal changes in serum creatinine in preterm infants with gestational age <32 weeks

OBJECTIVE

The Aim of this study was to investigate maternal and neonatal factors associated with serum creatinine (SeCr) changes in a representative cohort of preterm newborns during their first week of life.

STUDY DESIGN

Retrospective study. All the infants born less than 32 weeks of gestational age (GA) and cared for in our neonatal intensive care unit between January 2001 and December 2005 were eligible for the analysis. Epidemiological data of all mother-infant pairs and neonatal SeCr values were recorded.

RESULT

A total of 652 infants were studied. Multivariate regression analysis showed that the main independent factors associated with high SeCr at day 1 were hypertensive disease of pregnancy (P<0.0001) and advancing hour of life (P<0.0001), with minimal contribution of placental abruption (P<0.05) and higher GA (P<0.05). Lower GA (P<0.0001) and ibuprofen-treated patent ductus arteriosus (PDA; P<0.0001) were the main analyzed factors independently associated with higher SeCr peak (defined as the highest SeCr during the week), with less contribution of respiratory distress syndrome (P<0.01) and early onset infection (P<0.05). In infants with hemodynamically significant PDA (hsPDA) SeCr before ibuprofen administration was higher when compared to GA-matched controls without hsPDA (P< 0.0001).

CONCLUSION

SeCr peak was inversely correlated to GA in preterm infants born less than 32 weeks of GA. Neonatal rather than maternal morbidity affected SeCr peak. In hsPDA, SeCr increase preceded ibuprofen administration.

Human renal function maturation: a quantitative description using weight and postmenstrual age

This study pools published data to describe the increase in glomerular filtration rate (GFR) from very premature neonates to young adults. The data comprises measured GFR (using polyfructose, (51)Cr-EDTA, mannitol or iohexol) from eight studies (n = 923) and involved very premature neonates (22 weeks postmenstrual age) to adulthood (31 years). A nonlinear mixed effects approach (NONMEM) was used to examine the influences of size and maturation on renal function. Size was the primary covariate, and GFR was standardized for a body weight of 70 kg using an allometric power model. Postmenstrual age (PMA) was a better descriptor of maturational changes than postnatal age (PNA). A sigmoid hyperbolic model described the nonlinear relationship between GFR maturation and PMA. Assuming an allometric coefficient of 3/4, the fully mature (adult) GFR is predicted to be 121.2 mL/min per 70 kg [95% confidence interval (CI) 117-125]. Half of the adult value is reached at 47.7 post-menstrual weeks (95%CI 45.1-50.5), with a Hill coefficient of 3.40 (95%CI 3.03-3.80). At 1-year postnatal age, the GFR is predicted to be 90% of the adult GFR. Glomerular filtration rate can be predicted with a consistent relationship from early prematurity to adulthood. We propose that this offers a clinically useful definition of renal function in children and young adults that is independent of the predictable changes associated with age and size.

Perinatal bone turnover in term pregnancies: the influence of intrauterine growth restriction

Intrauterine growth restriction (IUGR) has been associated with low bone mass in infancy and increased risk for osteoporosis development in adult life. We aimed to investigate the effect of IUGR on bone metabolism in mother/infant pairs, by determining circulating biochemical markers of bone turnover in IUGR and appropriate for gestational age (AGA) pregnancies. Circulating markers of bone formation [bone specific alkaline phosphatase (BALP), total alkaline phosphatase (ALP), osteocalcin (OC)] and bone resorption [cross-linked N-telopeptide of type I collagen (NTx)], as well as intact parathormone (PTH), calcium and phosphorus levels were measured in 40 mothers and their 20 IUGR and 20 AGA singleton full-term fetuses and neonates on postnatal days 1 (N1) and 4 (N4). No significant differences in BALP, ALP, OC, NTx, PTH, calcium or phosphorus levels were observed between the AGA and the IUGR groups. In both groups, maternal BALP levels were lower compared to fetal, N1 and N4 levels (p< or =0.005 in all cases). In the AGA group, maternal NTx and OC levels were lower compared to fetal, N1 and N4 levels (p<0.001 in all cases), and fetal NTx levels were lower compared to N1 and N4 ones (p<0.001 and p=0.002, respectively). In the IUGR group, maternal OC levels were lower compared to fetal, N1 and N4 ones (p<0.001 in each case) and fetal OC levels were elevated compared to N1 and N4 ones (p<0.001 and p=0.003, respectively). N4 NTx levels were elevated compared to maternal, fetal and N1 levels (p=0.009, p<0.001 and p=0.002, respectively) and fetal NTx levels were lower compared to N1 and N4 ones (p=0.001 and p<0.001, respectively). Finally, positive correlations were found between maternal NTx and BALP (r=0.332, p=0.037), as well as ALP (r=0.329, p=0.038) levels, and between maternal, fetal, N1, N4 BALP and respective ALP levels (r=0.432, p=0.005, r=0.534, p=0.001, r=0.778, p<0.001, r=0.694, p<0.001, respectively). In conclusion, maternal, fetal and neonatal bone turnover in IUGR cases may not differ from respective bone metabolism in AGA controls. In addition, fetal and neonatal bone remodeling is markedly enhanced and independent of maternal bone turnover in late pregnancy.

Postnatal renal function in preterm newborns: a role of diseases, drugs and therapeutic interventions

Since few data are available about factors affecting renal maturation especially in the lower gestational ages (G.A.), the aim of this work was to study postnatal renal function in a representative population sample of preterm newborns (G.A. <or=36 weeks), admitted to the neonatal intensive care units of seven Italian hospitals, in order to investigate a possible role of drugs, therapeutic interventions and diseases. Data were collected through detailed questionnaires including maternal and neonatal information. To test renal function, serum creatinine and urine output were regularly recorded every 3 days throughout the 1st month of life. A total of 246 subjects were enrolled in the study and divided into four groups according to G.A.: group A, 22-25 weeks; group B, 26-28 weeks; group C, 29-32 weeks; group D, 33-36 weeks. Serum creatinine concentrations at birth were similar in all four groups, while significant differences were evident from the 3rd to the 21st day of life. Within each group, two subpopulations were identified taking into account creatinine values. In subjects with serum creatinine concentrations within the normal range, a physiological decline in creatinine values was observed with increasing postnatal age, and an inverse correlation between creatinine and G.A. was evident from the 3rd day of life to the end of the study period. In neonates with impaired renal function, a marked increase in creatinine values was observed in all neonates from the 3rd day of life, with significant differences among groups on days 7 and 10. Whereas many risk factors were correlated (univariate analysis) with impaired renal function, the multivariate analysis identified only five factors as independent: maternal consumption of nonsteroidal anti-inflammatory drugs (NSAIDs) during pregnancy [odds ratio (OR): 7.38, 95% confidence interval (CI) 3.26-16.7] and intubation at birth (OR: 4.39, 95% CI: 1.2-16.3) were the main risk factors. Respiratory distress syndrome, a low Apgar score and ibuprofen treatment of the neonate were identified as additional risk factors. Our data confirm a multifactorial origin of acute renal impairment in newborns. It is of note that pharmacological treatment with NSAIDs during pregnancy may negatively influence neonatal renal function.

Urinary aquaporin-2 excretion during early human development

This study was undertaken to assess one of the determinants of kidney concentrating capacity, aquaporin-2 (AQP2), in order to understand the physiopathology of water balance in newborn babies. Urinary AQP2 excretion has been shown to be proportional to AQP2 level in the apical plasma membrane of the kidney collecting ducts and has been suggested as a marker of vasopressin (AVP) action. Urinary AQP2 excretion in the early postnatal period and at 3 weeks of age was measured in 123 neonates admitted during a 6-month period to the neonatal intensive care unit of the Children's Hospital of Toulouse, France. Clinical and biochemical data were collected for each child. During the first days after birth, higher urinary AQP2 was observed in boys than in girls (P=0.01) and positively correlated with urinary sodium/potassium (Na/K) ratio (r=0.33, P=0.01). When the babies had reached 3 weeks of age, urinary AQP2 was proportional to the gestational age at birth (r=0.33, P=0.0068) and daily weight gain (r=0.36, P=0.003). It did not correlate with urinary osmolality, which was overall very low in all babies. Urinary AQP2 was decreased in conditions of impaired renal function (r=-0.42, P=0.0005) and acidosis (P=0.03). Prenatal corticosteroid treatment had no significant impact on urinary AQP2 level. Our data show that urinary AQP2 correlates with the overall maturity of tubular function in human neonates. In babies at this early age, urinary AQP2 cannot serve as a direct marker of the renal action of AVP but reflects AQP2 expression level associated with different physiopathological conditions.

Basic principles and practical steps in the management of fluid balance in the newborn

The fluid management of newborn babies can pose many problems. This article discusses the factors that affect fluid balance in the newborn infant, both term and preterm, and the special circumstances of the surgical neonate. The main determinants of management are: (1) an estimation of transepidermal water losses; (2) an awareness of glomerular filtration rate and how this is influenced by age, respiratory distress and medical intervention; and (3) knowledge of tubular function and its maturation and the processes of postnatal adaptation. This knowledge and appropriate monitoring are the mainstay of management of neonatal fluid balance.

Fetal serum concentrations of cystatin C and beta2-microglobulin as predictors of postnatal kidney function

OBJECTIVES

Cystatin C and beta(2)-microglobulin are established serum markers of renal function in children and adults. In contrast to creatinine, diaplacental exchange is minimal. The aim of the study was to establish reference values in fetal serum and to test their efficiency in predicting postnatal kidney function.

STUDY DESIGN

This was a prospective noninterventional study measuring cystatin C and beta(2)-microglobulin by particle-enhanced immunoturbidimetry in excess serum from 129 cordocenteses performed in 84 fetuses. Reference intervals (mean +/- 1.96 SD) were calculated in a subgroup of 54 fetuses without evidence of kidney disease, and these reference values were evaluated in 75 sera from 55 fetuses.

RESULTS

Mean cystatin C was 1.66 +/- 0.202 mg/L (upper limit 2.06), and mean beta(2)-microglobulin was 4.25 +/- 0.734 mg/L. Unlike cystatin C, beta(2)-microglobulin decreased significantly with gestational age so that the upper reference limit was 7.19-0.052 x gestational age in weeks. beta(2)-Microglobulin had higher sensitivity (90.0% vs 63.6%) and cystatin C a higher specificity (91.8% vs. 85.5%) for the prediction of impaired renal function; diagnostic efficiency was equal (87.6% vs. 86.1%). Fetuses with impaired renal function at birth or who were aborted for renal malformations had higher cystatin C concentrations than those in a control group. beta(2)-Microglobulin was increased only in fetuses who were aborted.

CONCLUSION

Fetal serum cystatin C and beta(2)-microglobulin concentrations may be useful predictors of postnatal kidney function.

Plasma creatinine rises dramatically in the first 48 hours of life in preterm infants

OBJECTIVE

Published data show that plasma creatinine falls steadily during the first 28 days of life and that creatinine levels in the neonatal period are higher in more premature infants. However, the best reference data commence on day 2 of life. The objective of this study was to document how plasma creatinine changes in the first 48 hours of life and to examine the reason for the apparently high levels of creatinine in preterm infants, compared with maternal levels.

DESIGN

A prospective observational study on a regional neonatal intensive care unit.

PATIENTS

A total of 42 preterm infants, mean gestational age of 29.4 weeks (range: 23-35), mean birth weight of 1.42 kg (.55-2.77), divided into 4 gestation groups: 23 to 26 weeks (n = 9), 27 to 29 weeks (n = 13), 30 to 32 weeks (n = 12), and 33 to 35 weeks (n = 8).

INTERVENTIONS

Measurement of plasma creatinine and urea concentration in cord blood and in serial samples taken for routine arterial blood gas analysis.

OUTCOME MEASUREMENTS

Changes in creatinine concentration with time and relationship to gestational age, birth weight, and illness severity.

RESULTS

Mean creatinine at birth was 73 micromol/L (95% confidence interval [CI]: 68-79 micromol/L). Plasma creatinine rose significantly over the first 48 hours. Mean peak creatinine in the most preterm infants (23-26 weeks) was 221 micromol/L (CI: 195-247 micromol/L). Peak plasma creatinine was inversely related to gestation (Spearman's coefficient: -.73) and birth weight (Spearman's coefficient: -.76). Significant differences in creatinine concentration were seen among different gestational groups at 24 and 48 hours of life. Peak creatinine correlated with a high Clinical Risk Index for Babies score (Spearman's coefficient:. 64). The fall in creatinine began later in more premature infants. All 38 surviving infants had normal renal function; their mean plasma creatinine at discharge was 52 micromol/L (CI: 46-58 micromol/L).

CONCLUSIONS

Rather than falling steadily from birth, creatinine rises dramatically in the first 48 hours of life, especially in infants of <30 weeks' gestation. Even large rises in creatinine in the first 48 hours may be expected and should not be used in isolation to diagnose renal failure.

Renal processing of glucose in well and sick neonates

AIMS

To determine the extent of renal processing of glucose in sick and well neonates.

METHODS

Glomerular filtration rate (GFR) and the renal processing of glucose, sodium, and water were measured using prolonged inulin infusion in 47 infants of 26-40 weeks of gestation, aged 1-13 days.

RESULTS

GFR rose by 15% after ventilatory support was withdrawn, and was unaffected by clinical instability. Fractional glucose excretion was low in the stable unventilated babies except at very high filtered loads, but rose in one unstable, unventilated baby. It was higher in ventilated babies, and remained high for at least six days after ventilation. For water and sodium, net differences between intake and urine excretion were not affected by ventilation, clinical stability, or glycosuria.

CONCLUSIONS

A combination of a low GFR and a high fluid intake, urine flow, and urine concentrating capacity, makes neonates very unlikely to develop an osmotic diuresis due to glycosuria while they have a blood glucose below 12 mmol/l, despite assertions to the contrary.

Glomerular filtration rate, effective renal plasma flow, blood pressure and pulse rate in the equine neonate during the first 10 days post partum

The aim of this study was to determine glomerular filtration rate (GFR), effective renal plasma flow (RPF) and filtration fraction (FF) values in Pony foals during the first 10 days post partum in order to assess any age-related changes and the reliability of the single injection inulin/p-aminohippurate (PAH) method. Arterial blood pressure and pulse rate were determined in Pony and Thoroughbred (TB) foals during the first 10 days post partum to establish age-related changes, differences between breeds and possible interrelationships with GFR and RPF. Inulin and PAH were injected intravenously (i.v.) in healthy Pony foals (n = 6) on Days 1, 2, 4, 7 and 10 post partum. Blood samples were collected via the contralateral jugular catheter over a 4 h period. Plasma clearances of inulin and PAH showed that GFR and RPF, respectively, remained relatively constant throughout the post natal period, and were similar to values reported for mature horses. The GFR measurements obtained using the inulin method gave clearance values that were significantly higher (P < 0.01) than those of creatinine clearance performed in a separate group of Pony foals (n = 7). Blood pressure and pulse rates were measured using an electronic sphygmomanometer in TB (n = 6) and Pony foals (n = 7) on Days 1, 2, 3, 4, 7 and 10 postpartum. There were no significant differences in these measurements between the breeds, and both cardiovascular parameters increased during the first 3 days post partum. Values remained unchanged for the rest of the study period. Although measurements of GFR, RPF, blood pressure and pulse rates were not determined in the same animals, blood pressure and pulse rates did not appear to correlate with either GFR or RPF in the Pony foals during the post natal period.

Acute renal failure in the newborn: incidence and outcome

OBJECTIVE

To describe an experience from a developing country of newborn renal disease particularly those without advanced neonatal care.

METHODOLOGY

Prospective evaluation from a referral hospital, North-East of Nigeria between 1 July 1990 and 30 June 1994. Babies admitted for any morbidities who were diagnosed as being in acute renal failure (ARF) during the study period (non-oliguric inclusive). Onset of ARF; day on which oliguria or anuria detected, or serum urea first exceeded 10 mmol/L. Urine output quantitated from carefully bagged urine and suprapubic bladder aspiration, and venous blood regularly obtained for serum electrolytes, urea and creatinine. Fractional excretion of sodium (FE(Na)) and renal failure index (RFI) were determined on some babies.

RESULTS

Forty-three neonates (M:F; 3.3:1) with ARF, the majority (27) of whom were out-born, and 14, 26 and three were preterm, full-term and post term, respectively. Encountered incidence was 3.9/1000 live births with a high prevalence rate; 34.5/1000 admissions. A significantly greater incidence was seen in the latter half of study; 10.7 vs 53.7/1000, P < 0.05. Early ARF occurrence (aged; 0-5 days) in 33 (77%) of babies. The aetiology was comprised of perinatal asphyxia, sepsis, obstructive uropathy and miscellaneous in 53.4%, 32.6%, 9.3% and 4.7%, respectively. Twenty-two (51.2%) deaths occurred; however, the exact causes were indeterminable. Fractional excretion of sodium (FE(Na)) and renal failure index (RFI) were of < 1.75% and < or = 2.0, respectively, significantly differentiated sepsis (intrinsic) from perinatal asphyxial (pre-renal) ARF; P < 0.01. No case of persistent renal failure occurred.

CONCLUSION

Our FE(Na) value (although less than reported in previous literature from affluent societies) remained sensitive (along with RFI) in differentiating aetiological group of ARF. Our data and medical management outcome, despite absence of level-III care, support the need for good resuscitation, careful monitoring and constant re-evaluation. The effect of salbutamol on hyperkalaemia is emphasized.

The renal phosphate threshold decreases with increasing postmenstrual age in very low birth weight infants

Our objective was the study of the renal phosphate threshold (TP/GFR) in very low birth weight infants with increasing postmenstrual (pm) age (gestational age plus postnatal age). The case notes of 62 very low birth weight infants were reviewed. Plasma and urine phosphate concentrations (PP, UP) determined on the same day together with the corresponding creatinine concentrations (PCrea, UCrea) built up a data set. Data sets obtained from 29 to 36 wk of pm age were included in the study. UP > or = 1 mmol/L was defined as phosphaturia. TP/GFR = PP - (UP x PCrea/ UCrea). In infants without phosphaturia, maximum PP is a lower limit of TP/GFR and was used as a censored TP/GFR value. We found that in phosphaturic infants, maximum PP (median and range) decreased from 2.8 (1.2-4.6) to 2.0 (1.4-2.7) mmol/L from 29-30 to 35-36 wk of pm age (p < 0.001), and censored TP/GFR (median and 95% confidence interval) decreased from 2.13 (1.95-2.33) to 1.57 (1.31-1.77) mmol/L (p < 0.001). We speculate that the renal phosphate threshold declines with increasing postmenstrual age because tubular reabsorption capacity increases more slowly than GFR.

Regulation of extracellular fluid volume in neonates

This review summarises mechanisms of control of extracellular fluid volume in the neonatal period. 'Normal' body fluid distribution and methods of its measurement are discussed as well as regulatory mechanisms with particular emphasis on hormonal and renal aspects.

Renal function in sick very low birthweight infants: 3. Sodium, potassium, and water excretion

Renal excretion of sodium, water, and potassium was measured on 434 occasions in a sample of 40 infants of 25.5-33 weeks' gestation, birth weight 720-2000 g, between the ages of 0.5 and 36 days. Water excretion varied between 1% and 30% of the glomerular filtration rate, or 15-350 ml/kg/day, and varied widely from day to day in individual infants. Nearly all infants became hyponatraemic before or after the first postnatal week. There were a few instances of hypernatraemia in the first week caused by high insensible water loss. There were high levels of sodium excretion up to 16% of filtered sodium, or 21 mmol/kg/day, in the first two postnatal weeks. Highest levels of sodium excretion were seen in the most immature infants in the first week. In most infants sodium excretion increased either in the first week or later before a subsequent decline. Potassium excretion was often high in the first week, as much as 96% of filtered potassium, or 5 mmol/kg/day, and is associated with early hyperkalaemia.

Renal function in sick very low birthweight infants: 2. Urea and creatinine excretion

Plasma urea and creatinine concentrations and urea and creatinine clearances and excretion were measured in a sample of 40 infants of 25.5-33 weeks' gestation, birth weight 720-2000 g, between the ages of 0.5 and 33 days. Creatinine excretion rate was between 60 and 120 mumol/kg/day in the first five postnatal weeks (mean 90.5) and was independent of sex or growth retardation. This can be used in clinical practice to estimate instantaneous urine flow rate V, if the creatinine concentration is measured in a randomly voided urine sample, from the formula V = 90.5/urine creatinine, with 95% confidence limits +/- 39%. There is a wide range of plasma creatinine at all gestations and ages decreasing from range 75-130 mumol/l in the first two days to 35-80 mumol/l at 3 weeks of age. Plasma urea is a poor indicator of glomerular filtration rate (GFR) in sick preterm infants. GFR (ml/min/kg) can be estimated from plasma creatinine from the formula GFR = 69.2/plasma creatinine but this estimate is imprecise with 95% confidence limits +/- 46%. Urea:creatinine clearance ratio was usually less than 1.0 (range 0.18 to 1.5) and was lower when the urine flow rate was low. Urea excretion was up to 17 mmol/kg/day in the first two weeks, higher in the more immature infants. These high levels were paralleled by a high plasma urea concentration, up to 18 mmol/l. A high plasma urea is not necessarily associated with renal failure or dehydration.

Renal function in sick very low birthweight infants: 4. Glucose excretion

Renal glucose excretion was measured on 239 occasions in a sample of 36 infants of 25.5-33 weeks' gestation, birth weight 720-2000 g, between the ages of 0.5 and 32 days. Glucose was invariably present in urine from the first day. Fractional glucose excretion varied widely from 0.1% to 90% of filtered glucose and glucose excretion rate was up to 15.5 mmol/kg/day and was higher in the most immature infants, especially below 28 weeks' gestation. The highest values were in association with hyperglycaemia between 5 and 15 days but there was no consistent plasma glucose threshold with frequent glucose spillage at normal blood glucose concentrations. There was some correlation with sodium excretion in the first week suggesting that in the absence of hyperglycaemia with a normal filtered glucose load, glucose excretion is caused by proximal tubular immaturity.

A reappraisal of the measurement of glomerular filtration rate in pre-term infants

Thirty-seven single-injection polyfructosan-S (PF-S, Inutest) and 98 continuous-infusion PF-S/creatinine clearance studies were performed in 39 sick very low birth weight infants. The single-injection clearance method for measuring glomerular filtration rate has been shown to be a reliable technique if sampling is continued for 8 h or more and the PF-S (Inutest) assay is sensitive, accurate and precise. The continuous-infusion clearance method is also valid if the infusion is continued for more than 24 h and preceded by a loading dose in the form of a double-rate infusion for 8 h. Creatinine clearance is usually less than PF-S clearance, the mean ratio being 0.91, suggesting that there is some creatinine reabsorption in the renal tubule in sick very low birth weight infants.