Development of renal control of salt and fluid homeostasis during the first year of life

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.

Dosing anticancer drugs in infants: Current approach and recommendations from the Children's Oncology Group's Chemotherapy Standardization Task Force

An analysis of dose modifications for infants in 29 Children's Oncology Group protocols across 10 cancer types revealed 11 sets of criteria defining the infant population using age, weight, body surface area (BSA), or a combination of these parameters and eight dose modification methods. A new method of dosing anticancer drugs in infants was developed based on the rationale that prior modifications were implemented to reduce toxicity, which is not cancer-specific. The new method uses BSA dose banding in dosing tables for infants and children with a BSA <0.6 m² and gradually transitions from body weight based to BSA-based dosing.

Prediction of Human Glomerular Filtration Rate from Preterm Neonates to Adults: Evaluation of Predictive Performance of Several Empirical Models

The objective of this study was to evaluate the predictive performance of several allometric empirical models (body weight dependent, age dependent, fixed exponent 0.75, a data-dependent single exponent, and maturation models) to predict glomerular filtration rate (GFR) in preterm and term neonates, infants, children, and adults without any renal disease. In this analysis, the models were developed from GFR data obtained from inulin clearance (preterm neonates to adults; n = 93) and the predictive performance of these models were evaluated in 335 subjects (preterm neonates to adults). The primary end point was the prediction of GFR from the empirical allometric models and the comparison of the predicted GFR with measured GFR. A prediction error within ±30% was considered acceptable. Overall, the predictive performance of the four models (BDE, ADE, and two maturation models) for the prediction of mean GFR was good across all age groups but the prediction of GFR in individual healthy subjects especially in neonates and infants was erratic and may be clinically unacceptable.

Clinical dehydration and glomerular filtration rate in acute paediatric gastroenteritis

AIM

To evaluate changes in glomerular filtration rate in acute gastroenteritis.

METHODS

The correlation between two clinical diagnostic scales and glomerular filtration rate has been investigated in 113 children with acute gastroenteritis in a paediatric emergency setting.

RESULTS

A significant reduction of GFR was found in 10% children less than, and 5% children higher than, 2 years of age with acute gastroenteritis.

CONCLUSION

The differences observed as for risk of renal hypoperfusion suggests to consider the age of children as an important determinant to consider the dehydration status in acute gastroenteritis.

The efficacy of hypotonic and near-isotonic saline for parenteral fluid therapy given at low maintenance rate in preventing significant change in plasma sodium in post-operative pediatric patients: protocol for a prospective randomized non-blinded study

BACKGROUND

Hyponatremia is the most frequent electrolyte abnormality observed in post-operative pediatric patients receiving intravenous maintenance fluid therapy. If plasma sodium concentration (p-Na+) declines to levels below 125 mmol/L in < 48 h, transient or permanent brain damage may occur. There is an intense debate as to whether the administered volume (full rate vs. restricted rate of infusion) and the composition of solutions used for parenteral maintenance fluid therapy (hypotonic vs. isotonic solutions) contribute to the development of hyponatremia. So far, there is no definitive pediatric data to support a particular choice of parenteral fluid for maintenance therapy in post-surgical patients.

METHODS/DESIGN

Our prospective randomized non-blinded study will be conducted in healthy children and adolescents aged 1 to 14 years who have been operated for acute appendicitis. Patients will be randomized either to intravenous hypotonic (0.23% or 0.40% sodium chloride in glucose, respectively) or near-isotonic (0.81% sodium chloride in glucose) solution given at approximately three-fourths of the average maintenance rate. The main outcome of interest from this study is to evaluate 24 h post-operatively whether differences in p-Na+ between treatment groups are large enough to be of clinical relevance. In addition, water and electrolyte balance as well as regulatory hormones will be measured.

DISCUSSION

This study will provide valuable information on the efficacy of hypotonic and near-isotonic fluid therapy in preventing a significant decrease in p-Na+. Finally, by means of careful electrolyte and water balance and by measuring regulatory hormones our results will also contribute to a better understanding of the physiopathology of post-operative changes in p-Na+ in a population at risk for hyponatremia.

TRIAL REGISTRATION

The protocol for this study is registered with the current controlled trials registry; registry number: ISRCTN43896775.

Fresh goat's milk for infants: myths and realities--a review

Many infants are exclusively fed unmodified goat's milk as a result of cultural beliefs as well as exposure to false online information. Anecdotal reports have described a host of morbidities associated with that practice, including severe electrolyte abnormalities, metabolic acidosis, megaloblastic anemia, allergic reactions including life-threatening anaphylactic shock, hemolytic uremic syndrome, and infections. We describe here an infant who was fed raw goat's milk and sustained intracranial infarctions in the setting of severe azotemia and hypernatremia, and we provide a comprehensive review of the consequences associated with this dangerous practice.

Progression of chronic renal failure in children with dysplastic kidneys

The aim of this study is to describe progression of chronic renal failure (CRF) in children with renal malformations and to study factors influencing this progression. We reviewed retrospectively 176 children with CRF secondary to renal dysplasia, reflux nephropathy or renal obstruction with at least 5 years of follow-up. Serum creatinine was recorded at least every third month, and an estimated glomerular filtration rate (eGFR) was calculated. Number of febrile urinary tract infections (UTI), blood pressure, albuminuria (UaUc), and number of functioning kidneys was also recorded. We found that the development of renal function could be separated into three time periods: (1) During the first years of life, 82% of the children showed early improvement of their kidney function, which lasted until a median age of 3.2 years (median improvement 6.3 ml/year). (2) From the age of 3.2 years until 11.4 years, 52.5% of the studied children showed a stable kidney function, whereas in 47.5%, kidney function immediately started to deteriorate. (3) Around puberty, 42.9% started deterioration in kidney function, whereas 57.1% even after puberty showed a stable function. Patients with UaUc >200 mg/mmol deteriorated faster (-6.5 ml/min per 1.73 m(2) per year compared with -1.5 ml/min per 1.73 m(2) per year) in those with UaUc <50 mg/mmol. Children with more than two febrile UTIs, hypertension or an eGFR at onset of less than 40 ml/min per 1.73 m(2) deteriorated faster than the others. Most children experienced early improvement of kidney function. The further prognosis, early or late deterioration of kidney function or stable function during the whole follow-up, was related to albuminuria, number of febrile UTIs, eGFR at onset of deterioration, hypertension and puberty.

Nutrient requirements for preterm infant formulas

Achieving appropriate growth and nutrient accretion of preterm and low birth weight (LBW) infants is often difficult during hospitalization because of metabolic and gastrointestinal immaturity and other complicating medical conditions. Advances in the care of preterm-LBW infants, including improved nutrition, have reduced mortality rates for these infants from 9.6 to 6.2% from 1983 to 1997. The Food and Drug Administration (FDA) has responsibility for ensuring the safety and nutritional quality of infant formulas based on current scientific knowledge. Consequently, under FDA contract, an ad hoc Expert Panel was convened by the Life Sciences Research Office of the American Society for Nutritional Sciences to make recommendations for the nutrient content of formulas for preterm-LBW infants based on current scientific knowledge and expert opinion. Recommendations were developed from different criteria than that used for recommendations for term infant formula. To ensure nutrient adequacy, the Panel considered intrauterine accretion rate, organ development, factorial estimates of requirements, nutrient interactions and supplemental feeding studies. Consideration was also given to long-term developmental outcome. Some recommendations were based on current use in domestic preterm formula. Included were recommendations for nutrients not required in formula for term infants such as lactose and arginine. Recommendations, examples, and sample calculations were based on a 1000 g preterm infant consuming 120 kcal/kg and 150 mL/d of an 810 kcal/L formula. A summary of recommendations for energy and 45 nutrient components of enteral formulas for preterm-LBW infants are presented. Recommendations for five nutrient:nutrient ratios are also presented. In addition, critical areas for future research on the nutritional requirements specific for preterm-LBW infants are identified.

Medical versus surgical treatment in children with severe bilateral vesicoureteric reflux and bilateral nephropathy: a randomised trial

BACKGROUND

Nephropathy associated with vesicoureteric reflux (VUR) and urinary tract infection can result in end-stage renal failure, hypertension, or both. Whether long-term VUR contributes to these outcomes is unknown. We compared, in a randomised trial, medical with surgical management of children with bilateral severe VUR and bilateral nephropathy.

METHODS

We stratified by age and glomerular filtration rate (GFR) 25 boys and 27 girls aged 1-12 years and randomly assigned them to medical or surgical management. At enrolment and 4 years' follow-up we estimated GFR from the plasma clearance of 51Cr-labelled edetic acid (EDTA), and did intravenous urography. We also did a metastable 99mTc-labelled dimercaptosuccinic acid (DMSA) assay and contrast cystography. The change in GFR at 4 years, expressed as a percentage change between enrolment and 4 years, was available for 26 of 27 patients in the medical and 24 of 25 in the surgical group. We assessed GFR in 48 patients 10 years after enrolment.

FINDINGS

Mean GFR at enrolment was 72.4 mL/min per 1.73 m(2) (SD 24.1) in the medical and 71.7 mL/min per 1.73 m(2) (22.6) in the surgical group. The mean percentage change in GFR at 4 years was 2.4% (SE 4.5) versus 4.7% (5.0) in the medical and surgical groups, respectively. The difference in change in GFR at 4 years between the two groups was not significant (7.1%, 95% CI 6.4% to 20.6%).

INTERPRETATION

Our data do not lend support to the view that the outcome for renal function is improved by surgical correction of VUR in children with bilateral disease.

Values for urinary beta 2-microglobulin and N-acetyl-beta-D-glucosaminidase in normal healthy infants

BACKGROUND

Measuring urinary beta 2 microglobin (B2M) and N-acetyl-beta-D-glucosaminidase (NAG) excretion is widely used as a valuable clinical tool in assessing renal tubular lesions. However, few data are available on normal values for urinary excretion of B2M and NAG in infancy.

METHODS

Urinary B2M and NAG were measured in healthy infants. The logarithmic values of urinary B2M, NAG, B2M/creatinine ratio and NAG/creatinine ratio were distributed almost normally and reference ranges were calculated from the logarithms of the observed values.

RESULTS

The levels of urinary B2M and B2M/creatinine ratio were highest in the 1-month-old group, followed by a decrease during the first 3 months. Urinary B2M excretions in the 3-month-old group showed rather lower levels than those of the 12-month-old and 36-month-old groups. Although urinary NAG excretions were almost constant throughout all groups, urinary NAG/creatinine ratio decreased gradually until 3 years of age.

CONCLUSIONS

We suggest that these reference ranges are of importance in evaluating tubular damage due to a variety of renal diseases in infancy.

Infant salt taste: developmental, methodological, and contextual factors

Two studies investigated the human infant's response to salt during development. In the first study, measures of intake and sucking were obtained from two groups of infants, newborns and 4- to 8-month-olds, in response to brief presentations of two concentrations of salt (0.2 or 0.4 M) and water. For several measures of sucking and for intake, there were significant age and concentration effects. Generally, newborn infants tended to reject saline relative to water more than did 4- to 8-month-old infants. This result, consistent with previously published research, suggests a developmental change in salt acceptability and, probably, sensitivity in the human infant. In the second longitudinal study, the response to salted (0.15 M) versus unsalted formulas was evaluated monthly in infants 2 to 7 months of age. Again, a developmental change was observed: Based on some sucking measures, younger infants appeared to be indifferent to the salted formula relative to the unsalted formula whereas older infants tended to reject the salted formula, presumably because either it was less sweet than the unsalted formulas or because it was novel. These data are consistent with the hypothesis developed from animal model studies that during early human postnatal development, transductive elements sensitive to saltiness mature.

Body electrolytes in bronchopulmonary dysplasia and the effects of diuretic therapy

Body electrolytes and their regulatory hormones were studied in preterm infants who suffered from bronchopulmonary dysplasia under two groups: those who were not treated with diuretics (Group II), and those who were treated with diuretics (Group III). The values were compared with a group of matched healthy controls (Group I). Lower serum Na levels, a need of higher Na intake, and higher urinary Na concentrations and urinary specific gravity were found in Group II infants. FeNa was normal and the urinary flow rate was lower than the controls. These data suggest an inability of these infants to dilute urine. Group III infants who were treated with diuretics showed higher serum Na levels and lower urinary specific gravity than Group II infants. These values, as well as water and Na intake/output ratios, were all similar to the control values. Serum aldosterone level was highest in Group II but did not reach significance. Intracellular K concentration was not different between the groups indicating an optimum total body K balance. A significant negative correlation between serum Na and aldosterone levels was found in Group II infants, which was not noted in the controls. Significant correlations were also found between FeNa and plasma aldosterone level in the BPD groups, unlike the controls. The control group of infants showed significant positive correlation between Na balance and serum Na levels. Our results suggest that inability to dilute urine appropriately might be the reason for the BPD patients to retain body water. Water restriction and diuretic therapy therefore are reasonable therapeutic approaches in such cases.

Renal function in very low birth weight infants: normal maturity reached during early childhood

Development of glomerular and tubular renal function is delayed in preterm infants. To study the pattern of maturation during infancy and childhood, we re-evaluated renal function in 22 very low birth weight infants--in 14 of the infants at 18 months postconceptional age (9 months corrected age) and in the remaining 8 infants at 8 years of age. The glomerular filtration rate remained lower at 9 months corrected age than in term infants of the same postconceptional age: 82 +/- 23 versus 125 +/- 18 ml/min per 1.73 m2 (p < 0.001). At 8 years of age the glomerular filtration rate did not differ from that of healthy control subjects. Effective renal plasma flow, filtration fraction, albumin excretion, maximal concentrating ability, and kidney size determined by ultrasonography were all normal at 8 years of age. We conclude that renal function, which is markedly reduced during the neonatal period in very low birth weight infants, reaches normal maturity by 8 years of age but not by 9 months corrected age.

Partial reversibility of cisplatin nephrotoxicity in children

To evaluate the long-term renal toxicity of cisplatin, 40 children who had been without treatment at least 18 months (range 18 months to 7 years) were observed. In all the children, glomerular filtration rate (GFR) was estimated from the plasma clearance of chromium 51-labeled ethylenediaminetetraacetic acid, both at the end of treatment and at a median follow-up of 2 years 6 months after treatment was stopped (range 18 months to 7 years). In 21 children, serum magnesium level was also measured at follow-up. Median age at diagnosis was 15 months (range 13 days to 13 years 8 months), and median cumulative doses of cisplatin was 500 mg/m2 (range 120 to 1860 mg/m2). In 22 of 24 children with an end-of-treatment GFR of less than 80 ml/min per 1.73 m2, the median improvement in GFR at follow-up was 22 ml/min per 1.73 m2 (range 2 to 56 ml/min per 1.73 m2). Hypomagnesemia was found in 6 of 21 children and was independent of GFR. No significant correlation was found between improvement in renal function and total cisplatin dose, age, gender, tumor type, or associated nephrotoxic medication. We conclude that most children have some recovery from cisplatin glomerular toxicity, especially if damage is not severe, but that hypomagnesemia may persist.

Endocrine control of electrolyte balance during development

The endocrine control of electrolyte balance during development is reviewed. It is suggested that the high urinary sodium excretion observed in premature infants may be secondary to the immaturity of the adrenal gland to adequately increase the secretion of aldosterone (Sulyok et al, 1979b), and to the inability of the distal tubule to respond appropriately to a rise in circulating aldosterone levels (Sulyok et al, 1979a). On the other hand, the elevated plasma aldosterone levels observed in term newborn infants may play an important role in the blunted response of the newborn kidney to saline loading (Sulyok et al, 1979a; Spitzer, 1982). The ability of ANP to induce a natriuresis and to contribute to fluid and electrolyte homeostasis during development has been investigated. It has been found that the immature kidney is less responsive to ANP than later in life (Chevalier et al, 1988; Robillard et al, 1988). On the other hand, it has been suggested that a rise in plasma ANP during the first five days of life may contribute to the physiological weight loss associated with the extracellular volume contraction occurring shortly after birth (Tulassay et al, 1987). The role of glucocorticoids, prostaglandins and the kallikrein-kinin system in regulating electrolyte balance during development is also reviewed.

Early markers of the renal complications of insulin dependent diabetes mellitus

We investigated the associations between albuminuria, metabolic control, glomerular filtration, blood pressure, and platelet function in children with insulin dependent diabetes mellitus. The geometric mean (95% tolerance levels) albumin excretion (expressed as the geometric mean albumin to creatinine ratio on two overnight urine collections (UA/UC], in 60 diabetic children was 0.72 (0.80-6.9) mg/mmol, significantly greater than in 45 normal children (geometric mean 0.41 (0.14-1.17]. Mean (SD) glomerular filtration rate, measured by 51Cr edetic acid clearance during constant infusion, was significantly greater in diabetic children (129 (20) ml/min/1.73 m2) compared with normal controls (109 (13]. Mean (SD) renal length for height standard deviation score was +0.25 (1.1); systolic blood pressure standard deviation score was 0.15 (0.65), and diastolic blood pressure was 0.51 (0.82). Spontaneous platelet aggregation, expressed as percentage fall in platelet count in stirred whole blood after 2 minutes was 17.8 (9.2)% in the diabetic compared with 12.3 (7.9)% in normal children. UA/UC correlated with renal length and of the children with UA/UC above the normal range, 70% also had a glomerular filtration rate above the normal range. There was a weak correlation between UA/UC and glycated haemoglobin (HbA1c). All children with spontaneous platelet aggregation above normal had had diabetes for more than seven years. These cross sectional data define some of the early markers and inter-relationships that may be important in the development of nephropathy.

Renal clearance of theophylline and its major metabolites: age and urine flow dependency in paediatric patients

The renal clearance of theophylline (TH) and its metabolites 1,3-dimethyluric acid (1,3-DMU), 3-methylxanthine (3-MX), and 1-methyluric acid (1-MU) has been studied in 10 children aged 8 months to 14 years. Individual renal clearances were calculated from serum levels and amounts excreted in urine after i.v. administration of the parent drug. The clearance of 1,3-DMU was found to depend both upon urine flow rate and age, which are interrelated. An effect of urinary pH was expected, but was not studied. Consistent age-dependent changes in the relative quantities of metabolites excreted were not observed.

Postnatal development of renal function during the first year of life

Several aspects of renal function vary considerably during the 1st year of life and differ markedly from the equivalent values in the adult. Glomerular filtration rate (GFR) increases little, prior to the time an infant reaches a conceptional age of 34 weeks, the point in renal development from which the absolute GFR (ml/min) increases gradually to mature values when linear growth is completed during adolescence. GFR corrected for body size is not comparable with adult normal values until after 12 months of age; therefore, whether GFR is estimated from Scr or measured by timed urine collection, there is no easily recalled range of normal values for infants. One must know the changes in the renal function of normal infants that take place following birth during the 1st year of life. Despite several attempts to do so, renal function during the 1st year of life cannot be assessed from urine flow rate. A urine flow rate of less than 1 ml/kg per hour may be normal and appropriate and may not be harmful either to preterm or full-term infants with normal GFR. Impaired concentrating ability of the neonatal kidney is probably of no clinical significance in all but the most extreme circumstances and is not a major factor in an infant becoming dehydrated, developing hypernatremia or being at greater risk of acute renal injury. Acid-base status in infants must be interpreted appropriately to know when alkali therapy should be introduced to avoid growth failure secondary to true metabolic acidosis. When plasma renin activity is measured in the infant with renal failure of hypertension, one must compare the result with the normal range of values related to postnatal age of normal infants.

Oral rehydration therapy in neonates and young infants with infectious diarrhoea

The clinical response and changes in water and salt homeostasis during ORT was studied in 15 infants less than 2 months old (range 2-50 days) with acute diarrhoea. Eight patients were neonates and 7 were 1-2 months old. The oral rehydration solution contained 60 mmol sodium per litre. All patients except one were successfully rehydrated. The fluid retention was significantly higher in neonates and young infants than in infants above 3 months of age treated in the same way. One patient in the group of neonates who had a normal sodium level on admission developed hypernatremia with a sodium level of 162 mmol/l 36 hours after the start of ORT. The urinary sodium excretion was lower in the neonates than in the young infants. The results show that neonates and young infants have a lower capacity than older infants to excrete water and salt and therefore run a great risk of developing fluid and salt retention during ORT. The risk is most pronounced in neonates who, due to immaturity of the renal function, are unable to excrete excess fluid and salt.

Oral rehydration therapy in malnourished infants with infectious diarrhoea

The clinical response and changes in water and salt homeostasis was studied for 36 hours during oral rehydration therapy with a rehydration solution containing 60 mmol sodium/l (ORS60) in 14 malnourished 3- to 15-month-old Turkish infants with acute infectious diarrhoea. All patients were successfully rehydrated with this treatment. Sodium was efficiently absorbed from the gut and water balance was rapidly restored. Because of excess fluid retention following the initial rehydration period about 50% of the patients became oedematous. Urine volume and urinary sodium excretion were found to be much lower than in well-nourished patients of the same age with acute diarrhoea who were treated in the same way. In all of the malnourished infants the serum sodium level remained within the normal range during treatment. The results show that malnourished infants retain much more fluid and sodium than infants who are in a normal nutritional state. Excessive retention of water and salt seem to be due to an inability of the kidneys to control sodium and fluid homeostasis while orally administered sodium and fluid are being absorbed from the gut. The results show that ORT is safe and efficient in the treatment of malnourished infants with acute diarrhoea. But since these infants run a high risk of developing a severe retention of fluid and salt, and consequently may develop circulatory failure due to hypervolaemia during oral rehydration therapy, it is important to carefully monitor the volume of fluid that is given.

Modern fluid and electrolyte management of the critically ill premature infant

In this article, the authors introduce the concept of a transitional physiology which governs fluid and electrolyte balance in the immediate postnatal period. The important impact of the extrauterine environment on fluid balance is also discussed. Finally, the pathophysiology of diuresis in RDS, and fluid shifts in the VLBW infant with therapeutic recommendations are presented.

Oral rehydration therapy in infectious diarrhoea. Comparison of rehydration solutions with 60 and 90 mmol sodium per litre

The clinical response and changes in water and salt homeostasis as judged from serum sodium levels, salt and water retention and renal handling of sodium was studied during 36 hours following the start of oral rehydration therapy (ORT) with a solution containing 60 mmol Na/l (ORS60) in 17 well-nourished, moderately dehydrated Turkish infants aged 3 to 15 months who had acute infectious diarrhoea (7 with rotavirus, 3 with enteropathogenic E. coli 0 111: B 84, and one with enteropathogenic E. coli 0 125: B 15, one with salmonella and 5 of unknown etiology. In the successfully treated patients sodium and water balance was normalized within 36 hours. In the cases with hypernatremic dehydration the serum sodium concentration rapidly became normal. The results were compared with those obtained in a previous study of the same type of patients who were rehydrated with a solution containing 90 mmol Na/l (ORS90). Although retention was considered to be satisfactory after ORS60 it was less than after ORS90. The changes in the fractionary urinary sodium excretion and the potassium sodium quotient in the urine indicated a less rapid normalization after ORS60 than after ORS90.

Aldosterone concentrations in dehydrated infants

The mean serum aldosterone concentration of 37 infants with acute gastroenteritis and dehydration was markedly elevated on admission (mean +/- SE 94.3 +/- 12.1 ng/ml) and approximated to normal values (18.2 +/- 3.7 ng/ml) following recovery from the acute disease (t=3.56 p less than 0.005). Serum aldosterone levels were significantly positively correlated with the percent weight loss (r=0.41, p less than 0.05) and with the blood urea nitrogen levels (r=0.55, p less than 0.001). There was no correlation between either serum sodium levels or blood osmolarity and aldosterone concentrations. Serum potassium levels were positively correlated with aldosterone levels (r=0.53, p less than 0.001). These findings indicate that small infants when dehydrated respond appropriately with elevated aldosterone levels. The amount of body fluid depletion and hyperkalemia are the major factors determining the amount of aldosterone response.

Salt and water homeostasis during oral rehydration therapy

Changes in sodium balance and urinary and stool output during orally administered rehydration therapy were studied in 22 well-nourished Turkish infants, aged 2 to 13 months, with acute diarrhea mainly of viral origin. The infants randomly received a rehydration solution containing either 90 mmol Na/L (ORS90) or 40 mmol Na/L (ORS40). Slight transient hypernatremia was noted in a few infants receiving ORS90, and slight transient hyponatremia in a few infants receiving ORS40. In both groups, sodium balance increased most rapidly during the first 12 hours of rehydration, and then more slowly because of increased urinary as well as stool sodium output. Sodium balance was always more positive after ORS90 than after ORS40, but the difference did not change much from 12 to 36 hours after therapy was started. Changes in fractional sodium excretion, urinary K/Na quotient, and urinary aldosterone-creatinine quotient were used as indexes of changes in sodium balance. All values were interpreted to indicate that the sodium deficit on admission was corrected within 12 to 18 hours after ORS90 and, in most cases, after 24 to 36 hours after ORS40. Both groups of infants responded well to orally administered rehydration therapy from the clinical viewpoint.

The role of the kidney in sodium homeostasis during maturation

Evidence is presented that the retention of sodium observed during development is consequent primarily to enhanced tubular reabsorption rather than to low rates of glomerular filtration. The enhanced transport of sodium occurs in nephron segments located beyond the proximal tubule, apparently under the stimulation of the high plasma concentration of aldosterone. This adaptive mechanism may account for the fact that the infant thrives on a rather low intake of sodium, as prevails during the period of breast-feeding. The renin-angiotensin-aldosterone system cannot be fully inhibited even by intravascular volume expansion and this may account for the blunted natriuretic response of the developing animal and human to the acute infusion of saline or albumin solutions. Conversely, the renal sodium loss and the hyponatremia often encountered in premature babies appear to be due to an insufficient rise in aldosterone secretion or to a limited responsiveness of the distal tubule to aldosterone stimulation.

Renal sodium excretory capacity in infants under different dietary conditions

An evaluation of dietary effects on sodium (Na) homeostasis was performed in 28 healthy infants 7--13 weeks of age. Each infant received during one week an ordinary formula where either the Na and/or the protein content was increased twice. The high Na diets induced a significant elevation of the natriuretic response to an oral Na load. The response was most pronounced in those infants receiving a high Na as well as a high protein diet. The diet that was only high in protein resulted in an increased osmotic load to the kidneys but did not affect the Na excretion. The maturation of renal Na excretion thus seems to be accelerated by a high Na intake and further potentiated by a high protein intake. The Na excretory capacity was, even after the period of a high Na diet, well above the level of Na then given.

Correlation between fluid reabsorption and proximal tubule ultrastructure during development of the rat kidney

Parallel functional and ultrastructural studies were performed in maturing rats in order to elucidate factors determining the development of proximal tubular fluid reabsorption. Three groups of hydropenic animals, which were 22 to 24, 28 to 32 and 40 to 45 days old, were studied. Nephron function was evaluated at the single nephron level by micropuncture technique. The ultrastructure of the developing proximal tubules was analysed by morphometric techniques following fixation of single nephrons. Kidney weight, proximal convoluted tubule length and diameter increased during postnatal development. SNGFR increased from 2.98 to 8.57 and to 20.5 nl/min in respective group of rats whereas proximal tubular fluid reabsorption Jv (a) increased from 0.15 to 0.22 and 0.34 micron3.micron-2.s-1. Parallel to the functional development the relative area of lateral and basal cell membrane increased, resulting in a constant relationship between net fluid reabsorption and the lateral and basal cell membrane area during the fourth postnatal week and then only a slight increase in this relation during the further development. The results suggest that net fluid transport during hydropenia is determined by the amount of available lateral and basal cell membranes where the transporting enzyme for sodium is located.

Breast feeding and biological development

The superiority of human milk as compared with milk of other origin for the feeding of newborns, term or preterm, can be analysed in terms of biological development related to digestive, metabolic and excretory functions during foetal and postnatal life. The macro- and micro-anatomical developments of the intestine are complete in the 6th foetal month. The brush border and some of its enzymes (saccharase-isomaltase) exist already from the 6th foetal week, whereas other enzymes (lactase and intracellular transport enzymes) appear much later. The major gastric and pancreatic enzymes, as well as the synthesis of biliary acids, do not reach maturity until after birth. Several metabolic functions, e.g. the synthesis of cystine from methionine, of tyrosine from phenylalanine, and of urea from ammonia, are still limited at the time of birth. The capacity for excretion of sodium, the osmotic urinary load, and hydrogen ions is suboptimal, especially in the prematurely born. All these circumstances imply that human milk, with its protective properties, represents optimal adaptation to the needs of the child in the perinatal period.

Renography in the foetal and newborn lamb

Hippuran renography indicates kidney function as reflected in a substance handled mainly by the tubules. The working conditions of the kidneys undergo a fundamental change at birth with the cessation of placenta circulation, and these organs become responsible for waste elimination. 131I-hippuran renography was performed on foetal and newborn lambs using a gamma camera and a computer. The intervals of the maximum- and half-time renal activity were determined. These decreased by a half from mean foetal value of Tm=7 mi and T12=19 min in 1 to 1.5 days and reached the full-grown level in 2 to 5 weeks. No sudden change occurred as a result of the first breath.

Effect on maturation of kidney function in newborn infants of repeated administration of water and electrolytes

In newborn infants of various ages, the influence of repeated administration of water and electrolytes on renal excretion of urine, sodium, potassium, free and bound hydrogen ions and on urine osmolarity was studied. In 14- and 21-day-old infants the repeated administration of water and electrolytes was followed by diminution of renal excretion of hydrogen ions and potassium, possibly caused by stimulation of hormonal regulation of ion exchange in the kidney. In animal studies performed with a larger water and electrolyte load, stimulation of renal excretion of sodium was caused by the pretreatment.

Effect of arterial blood pressure reduction on renal hemodynamics in the developing lamb

The relationship between pressure and flow in the kidney has been examined in 2-9 and 31-48 day old lambs. Renal blood flow (RBF), determined by the microsphere technique, and glomerular filtration rate (GFR) were first studied under control conditions. The abdominal aorta was then constricted above the renal arteries until the pressure ranged between 60 and 70 mmHg, i.e. just below the normal autoregulatory range, and the hemodynamic recordings were repeated. During control conditions the arterial pressure was lower in the younger (93 mmHg) than in the older lambs (107 mmHg). During aortic constriction total RBF and GFR were reduced. In both age groups GFR was reduced out of proportion to RBF. The sodium excretion fell around 60% in both age groups. The fall in perfusion pressure resulted in a more pronounced blood flow reduction to the outer than to the inner cortical glomerular capillaries. This pressure-induced blood flow redistribution was found in both age groups. The consequences of the pronounced effect of reducing the perfusion pressure to 60-65 mmHg for the young lambs with their basally low arterial blood pressure are discussed.

Fluid and electrolyte metabolism in the newborn infant

This chapter has sought to gather together the background information on systems controlling homoeostasis of salt and water and their clinical derangement. The temptation to adopt an all-embracing approach to the management of these problems is strong but such an approach is difficult to achieve and indeed dangerous. The circumstances of each sick infant are unique and plans for treatment must be individually tailored and flexible, dependent upon clinical and biochemical progress. Future developments in this field are likely to involve further understanding of renal and hormonal control of fluid and electrolyte and it might be expected that as new methods of management emerge they will be accompanied by their own peculiar risks of inducing secondary homoeostatic disturbances. With regard to infant feeding each advance appears to underline the desirability of breast feeding and support current moves toward provision of low solute feeds for those who are artificially fed. Paediatricians should be vocal in their advocation of breast feeding and ensure that the major principles of salt and water handling are understood by all who work with small infants. An extra scoop of powdered milk can be more of a poison than a food.