Renal function and serum aldosterone levels in infants with respiratory distress syndrome

Renal glomerular and tubular function in neonates with perinatal problems

OBJECTIVE

To investigate perinatal risk factors that may be associated with impaired renal function during the first 2 weeks of life.

METHODS

The case notes of 150 neonates of gestational age (GA) 34-36 weeks and 494 of GA > 36 weeks were studied. Clinical risk factors were retrieved, along with indices of renal function: serum creatinine (SeCr), fractional excretion (FE) of sodium (FENa) and potassium (FEK), and the urinary calcium to creatinine ratio (UCa/UCr). Associations were identified by multiple and logistic regression analysis.

RESULTS

In infants with GA > 36 weeks, raised SeCr was related to perinatal stress, odds ratio (OR): 1.9, confidence interval (CI): 1.2-2.9, p < 0.05, and to duration of treatment with aminoglycosides (AGs) (t = 2.4, p < 0.01); FEK was associated with jaundice (t = -3.1, p < 0.01), and FENa with duration of AGs treatment (t = 2.6, p < 0.01). Full-term neonates with both hypoxic-ischemic encephalopathy (HIE) and AGs administration had an 80% increase in OR for impaired SeCr levels. In infants of GA 34-36 weeks, SeCr was related to perinatal stress (OR: 9, CI: 1.3-38, p < 0.05), FEK to jaundice (t = -2.1, p < 0.05), and FENa to duration of AGs administration (t = 2.2, p < 0.05) and antenatal steroid treatment (OR: 0.8, CI: 0.6-0.95, p < 0.05).

CONCLUSION

In neonates, renal impairment, being multifactorial in origin, may be caused by the additive effect of different perinatal factors. The strong negative relationship observed between jaundice and K excretion merits further investigation.

Changes in red cell phosphate metabolism of preterm and fullterm infants with perinatal problems during their first month of life

The effects of perinatal problems on red cell phosphate metabolism were studied in two groups of infants (preterms B and fullterms D) during the first month of life. All infants started milk feeding from day three after birth. The results were compared to those of healthy preterms (A) and fullterms (C), respectively. Comparisons were also made between the preterm and fullterm groups B and D. The preterms with perinatal problems (B) showed a significant delay in catching up with the plasma and red cell inorganic phosphate (Pi) levels of controls (A) throughout the first month of life (p < 0.05). In parallel, the erythrocyte 2,3 diphosphoglycerate (2,3-DPG) concentrations of the sick preterms lagged significantly behind those of controls (p < 0.001); but the ATP levels were comparable between the two groups. The fullterms behaved slightly differently. No significant differences in plasma Pi (Pl Pi) and red cell 2,3-DPG were seen between the sick and healthy neonates during the month of study, while red cell Pi (RBC Pi) and ATP were found to be lower in the sick ones (p < 0.05). The fullterms with perinatal problems (D) had significantly higher Pl Pi (p < 0.05) and RBC Pi (p < 0.01) than preterms with problems (B) from the first week of life and continued in a similar pattern until the end of the month. Red cell 2,3-DPG concentrations were found to be significantly correlated with Pl Pi and RBC Pi in both preterm groups (p < 0.01) and in the sick fullterms (p < 0.001) during the time of the study. In the healthy fullterms 2,3-DPG was found to correlate only with red cell Pi (p < 0.05). Perinatal problems seem to affect Pi metabolism to a different degree in preterm and fullterm neonates in the first month of life.

The urinary activity of angiotensin-converting enzyme in preterm, full-term newborns, and children

The urinary activity of the angiotensin-converting enzyme (U(ACE)) is not yet completely documented in human neonates. We measured the U(ACE) in 36 premature neonates on the 1st day and in the 1st, 2nd, 3rd, and 4th weeks of life, in 22 full-term neonates between the 1st and 2nd days, and in 30 nursing and preschool children between 1 month and 6 years of age. The urinary excretion of sodium (U(Na)/U(Cr)) and the potassium/sodium index (U(K)/U(Na)) were analyzed in the neonates. U(ACE) was greater in premature than in full-term neonates and greater in both than in older children (p<0.001). In the premature neonates, U(ACE) peaked at the 2nd week, the U(Na)/U(Cr) index decreased, and the U(K)/U(Na) index increased between the 1st day and the 2nd week (p<0.001). The U(Na)/U(Cr) index on the 1st day and in the 1st and 2nd weeks was greater in premature than in full-term neonates (p<0.001). There was no significant correlation between the U(ACE) and the U(Na)/U(Cr) index. In conclusion, the U(ACE) profile was shown to be age dependent and related to the postnatal renal development. The increase in U(ACE) activity may reflect the high activity of the neonatal intrarenal renin-angiotensin system (RAS).

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.

Aldosterone cord levels in preterm newborn infants

We measured umbilical cord aldosterone concentrations in 64 premature newborn infants. The median serum aldosterone level was 74.5 ng dl-1 (range 22-280 ng dl-1). Of the studied perinatal factors, only gestational age and birthweight presented a significant influence on the umbilical cord aldosterone levels. Newborn infants with a gestational age of over 34 weeks and a birthweight of over 2000 g had a significantly higher aldosterone cord level than those aged 34 weeks or younger and 2000 g or less in weight.

Short-term outcome of mechanically ventilated infants weighing more than 2499 g at birth: a population based study

Very little data exist describing the neonatal outcome of infants of birthweight 2500 g or more who require mechanical ventilation. Our aim was to collect population-based data on such infants in New South Wales (NSW), and to monitor their neonatal morbidity, mortality to 1 year of age and the associated risk factors. The study group (NICUS infants) comprised all 341 infants weighing > 2499 g who were admitted to the seven neonatal intensive care units in New South Wales and mechanically ventilated for 4 h or more between 1 January and 31 December, 1987. Two groups of infants emerged: those who were preterm and mostly had hyaline membrane disease, and term and post-term infants for whom the most common problem was 'perinatal asphyxia'. The most important factors associated with dying were a birthweight of over 3499 g (OR = 2.6; CI 1.03-6.6) and a 1 min Apgar score < 4 (OR = 4.8; CI 1.4-16.9). Study group mothers were significantly more likely than all NSW mothers to have had a spontaneous abortion in the previous pregnancy (P < 0.01), a pre-existing medical condition or an obstetric complication in this pregnancy, or a Caesarean section for this delivery (P < 0.001). This is the first population-based study of high-risk neonates without congenital anomalies to clearly document the worsening prognosis associated with a birthweight over 3499 g. Further research should be directed towards identifying prenatal and perinatal factors which might minimize the morbidity and mortality in this group of babies.

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: 1. Glomerular filtration rate

A total of 135 measurements of polyfructoside clearance as a measure of glomerular filtration rate (GFR) were made in 39 infants of 25.5-33 weeks' gestation, birth weight 720-2000 g, between the ages of 0.5 and 33 days. GRF was related to postconceptional age and increased exponentially from geometric mean 0.59 ml/min at 26 weeks' postconceptional age to 1.40 ml/min at 33 weeks. GFR in the first week and GFR at later ages were the same for a given postconceptional age. GFR was the same in sick infants with severe ventilatory failure as in less ill infants. There was no evidence that GFR was influenced by nitrogen input. GFR increases postnatally in a preprogrammed way irrespective of other postnatal events. When factored by body weight GFR in the first week increased only little from arithmetic mean 0.70 ml/min/kg at 26 weeks to 0.84 ml/min/kg at 33 weeks, but older infants often had a falsely high GFR per kg when they lost weight in the first week or two after birth or failed to gain weight later.

Hyaline membrane disease and early neonatal aldosterone metabolism in infants of less than 33 weeks gestation

We studied urine excretion of free and conjugated aldosterone by 12 control infants and 14 infants with hyaline membrane disease (HMD) on the first and seventh days after birth. Both groups had a mean gestational age of 29 weeks. Total urine aldosterone excretion (UAE) and percent excreted as conjugate were similar for both groups on both study days, and did not relate to the severity of respiratory failure in infants with HMD. Sodium intake was higher for infants with HMD on both study days (p less than 0.02), but their urine sodium excretion was only significantly (p less than 0.01) higher on day 7. For total UAE values greater than 3 nmol/kg/d, there was no significant difference between estimated sodium-potassium exchange by control (22 +/- 5%, n = 8) and HMD (31 +/- 5%, n = 10) groups. These data suggest that neither the magnitude of excretion of aldosterone in the urine, the ability to conjugate aldosterone nor the degree of relative distal tubular unresponsiveness to aldosterone are related to the severity of pulmonary immaturity in preterm infants.

Mineral balance studies in sick preterm intravenously fed infants during the first week after birth. A guide to fluid therapy

Mineral balance studies were performed in 61 sick preterm infants given parenteral fluids only. Their gestational ages varied from 24 to 35 weeks, and 50 required mechanical ventilation. Two consecutive balance studies were performed; the first from admission to 48 hours in all babies given maintenance fluids of 10% Dextrose, and the second from 48 hours to 7 days in those babies given intravenous feeding (IVN). At the beginning and end of each balance period, the baby was weighed and an arterial blood sample taken for blood gases, electrolyte, urea, creatinine and protein determinations. During the balance period all urine was collected and analysed for electrolyte, urea, and creatinine composition, and all fluid intake was recorded. The balance of a mineral was calculated as the difference between parenteral intake and urine output. Infants requiring IVN were allocated alternatively to regimen X or regimen Y, which had the same calcium content of 9.5 mmol/L, but different phosphate contents, regimen X containing 7.3 mmol/L and regimen Y 11.6 mmol/L. In those infants requiring prolonged IVN, 12-24 hour balance studies were performed at weekly intervals after day 10. 1. Phosphate deficiency developed in infants given regimen X, who had higher urine calcium excretion, lower percentage calcium retention and lower plasma phosphate levels than those given regimen Y. These differences were apparent by day 7 and persisted after day 10. In infants given regimen Y, mean calcium retention from admission to day 7 was 3.9 mmol/kg, and after day 10 was 0.9 mmol/kg/day. 2. In the first 48 hours, urine output and creatinine clearance varied widely and were lower in infants with higher oxygen requirements at 48 hours. Ten babies had severe oliguria with outputs less than 10 mL/kg/day. Creatinine clearance was directly related to gestational age, mean arterial blood pressure, and plasma protein concentrations on admission. After 48 hours, urine output and creatinine clearance increased considerably. 3. In the first 48 hours, metabolic acidosis was produced by increased plasma non-protein metabolisable acid concentrations, which were associated with low creatinine clearances, and were thought to be due to lactic acid accumulation in response to decreased tissue perfusion. At 7 days, metabolic acidosis was of similar severity but was produced by decreased plasma non-metabolisable base concentrations, caused by increased urine loss of net base, and not directly by IVN.(ABSTRACT TRUNCATED AT 400 WORDS)

Surfactant therapy and spontaneous diuresis

The effect of artificial surfactant therapy on renal function and the onset of spontaneous diuresis was prospectively evaluated in 19 infants with hyaline membrane disease in a double-blind, controlled study. Twelve infants were in the surfactant group; seven infants received placebo (0.9% saline solution). There was no difference in the time of onset of spontaneous diuresis (as defined by output greater than or equal to 80% of intake). The glomerular filtration rate, determined by endogenous creatinine clearance, was also similar in the surfactant- and placebo-treated infants during the first 3 days of life. The fractional excretion of sodium was significantly higher in the placebo group at 24 hours and 36 hours. Infants in the placebo group had a higher negative sodium balance than those in the surfactant group. Ventilatory status improved significantly soon after surfactant treatment, as evidenced by improvement in the alveolar/arterial oxygen pressure ratio and by a lower mean airway pressure. These data suggest that ventilatory status can be improved without diuresis; the factors that regulate diuresis are multiple and not fully understood.

Extracellular fluid volume changes in very low birth weight infants during first 2 postnatal months

Serial extracellular volume (ECV) changes were measured in 18 infants of less than 32 weeks gestation. Results were compared with changes in body weight, fluid and sodium intake, urine output, and serum sodium concentration. Mean +/- SD ECV decreased from 550 +/- 116 mL/kg on day 1 to 359 +/- 66 mL/kg on day 14. Thereafter, mean ECV/kg remained between 336 +/- 42 and 349 +/- 54 mL/kg. Clinical hydration and serum sodium concentration usually remained normal during this reduction of stabilization of ECV/kg. Six episodes of hyponatremia occurred at 11 to 31 days of age. Mean ECV/kg was significantly lower in infants with hyponatremia compared with infants of similar age with normal serum sodium concentration (303 +/- 36 mL/kg vs 368 +/- 56 mL/kg, P less than 0.01). Sodium intake in the two groups was similar. We conclude that ECV in the VLBW infant decreases postnatally and is regulated within a range similar to that in older infants, and that postnatal natriuresis in the first 2 weeks of life represents physiologic reduction of the expanded ECV of the fetus. Late hyponatremia may indicate excessive sodium loss and ECV depletion.

Elevated atrial natriuretic factor in neonates with respiratory distress syndrome

Atrial natriuretic factor (ANF) plasma concentrations were measured in 16 healthy term newborn infants and in 18 preterm infants with respiratory distress syndrome during the first 4 postnatal days. Changes in the plasma concentration of ANF were then correlated with postnatal age, severity of respiratory distress, and water and sodium balance. The plasma ANF concentration in healthy term infants increased during the first 2 days of life. Similar values were observed among preterm infants requiring hood oxygen. The plasma ANF concentrations were substantially higher in preterm infants receiving positive pressure ventilation. All infants had negative water and sodium balance during the period of study. No correlation was found, however, between absolute plasma ANF concentrations and urinary flow rate, sodium excretion, or fractional sodium excretion, suggesting that ANF did not exert a dominant role in the excretion of sodium in these infants.

Evaluation of renal function and acute renal failure in the neonate

The diagnosis of renal dysfunction in the neonate can be a challenging problem for the practicing pediatrician. Although there are real differences in renal function between term and preterm infants, overall function is quite adequate in both groups when fluid intake and environmental conditions are carefully controlled. When confronted with an infant with a pathologic decrease in urine output, the clinician must provide adequate fluid resuscitation for the infant with prerenal oliguria without inducing fluid overload in the infant with established, intrinsic renal failure. In addition, the infant with obstruction to urine flow must be distinguished. This requires careful assessment of physical findings and a few key laboratory determinations. Once the diagnosis of renal failure is made, frequent clinical monitoring with anticipation of potential complications is critical. Long-term management of renal failure in infancy and intervention for suspected urinary tract malformation in the fetus have emerged as difficult medical and ethical problems as our technology has advanced.

Role of renin and aldosterone in establishment of electrolyte balance in very low birthweight neonates

Urine sodium, potassium and chloride excretion, plasma renin activity (PRA) and urine aldosterone excretion (UAE) were measured in seven very low birthweight (VLBW) infants during the first 6 weeks after birth. Hyponatraemia was most common, and major changes in urine electrolyte excretion occurred, during the first 2 weeks. These changes in urine electrolyte excretion appeared to relate to improvement in distal tubular function. PRA did not correlate with urine excretion of either aldosterone or electrolytes. However, UAE correlated significantly with fractional sodium-potassium exchange in the distal tubule in a non-linear fashion (P less than 0.001) which suggested a threshold of aldosterone responsiveness between 70 and 100 nmol/24 h per 1.73 m2 UAE. We conclude that in VLBW infants the distal tubule can respond to aldosterone during the first 2-3 weeks, but that the threshold for responsiveness appears to be higher than it is in fullterm infants.

The renal response to acute asphyxia in spontaneously breathing newborn lambs

The effects of acute asphyxia on neonatal renal function were examined in spontaneously breathing newborn lambs. 25 min of asphyxia were induced by addition of a respiratory dead space to reduce PaO2 to 41 +/- 3 mm Hg, pH to 7.03 +/- 0.05 and increase PaCO2 to 68 +/- 5 mm Hg (mean +/- S.E.M.). Glomerular filtration rates did not change significantly during or after asphyxia. Immediately following asphyxia significant (P less than 0.05) increases over the baseline were found in urinary flow rates, fractional sodium excretion, absolute sodium excretion and osmolar clearances. These changes were in part secondary to significant (P less than 0.05) increases in plasma glucose concentrations associated with increases (P less than 0.05) in circulating arterial catecholamine concentrations. The percentage of tubular reabsorption of glucose decreased significantly (P less than 0.05) and urinary glucose excretion increased significantly. Renal blood flow was unchanged. Therefore, asphyxia induced significant hyperglycemia which contributed to the concomitant natriuresis and osmotic diuresis in these newborn lambs.

Development of glomerular filtration rate and excretion of beta 2-microglobulin in neonates during gentamicin treatment

Ten infants of different gestational ages (GA) and postnatal ages (PNA), treated with gentamicin, were compared with 10 control patients of similar GA and PNA to evaluate the possible nephrotoxic effects of this drug. Changes in the glomerular filtration rate (GFR) and the fractional excretion of beta 2-microglobulin in urine (FE beta) were used as indicators of renal dysfunction. In the control infants there was a postnatal increase in the GFR that was higher in full-term than in preterm infants. The FE beta decreased logarithmically as a function of both the GA and the PNA. The GFR was statistically lower in 5/10 and 6/10 of the patients on the first and the last days of gentamicin treatment (GT) respectively. Three weeks after GT, 8/10 had a normal GFR. The FE beta was statistically higher in 4/10 of the patients on their first day of GT and 7/10 on their last day of GT. Three weeks after GT, 9/10 of the patients had a normal FE beta for their postnatal and gestational ages. It is concluded that GT influences filtration and proximal reabsorption in GT infants by decreasing the GFR and increasing the FE beta. However, the observed renal dysfunction seemed to be reversible.

Tubular proteinuria after perinatal hypoxia

Urinary total protein (UTP) and urinary protein pattern have been studied in 23 newborn infants with Apgar scores less than or equal to 3 at one minute or acidosis (pH less than or equal to 7.15) on the first day. On the first and second day UTP excretion was increased in 13 out of 18 patients. At this time the excretion of low molecular weight microproteins (T-4 and T-5) was elevated in 12 patients without increased plasma urea concentration in any case. The increased excretion of the smallest microproteins T-4/T-5 is an early sign of an impaired tubular function.

The diuretic phase of respiratory distress syndrome and its relationship to oxygenation

To determine the relationship between improvement in pulmonary function and diuresis in respiratory distress syndrome, ten consecutive premature infants requiring mechanical ventilation for severe RDS were studied. Every infant had a diuresis (output/intake greater than 80%), which began at 26 to 34 hours of life and which lasted for an additional 64-72 hours. The diuresis preceded significant improvement in AaDo2 and ventilator settings (IMV, PIP, PEEP) by 52 hours. There was a significant decrease in body weight among all study infants during the first four days of life despite an increase in fluid intake. This study suggests a relationship in RDS between improvement in oxygenation and removal of interstitial lung edema.

Sodium balance in very low-birth-weight infants

Sodium balance was studied in 17 consecutively admitted neonates weighing less than 1,200 gm at birth. Infants whose gestation was less than or equal to 30 weeks were sicker and were in markedly negative sodium balance on day 3 (-9.25 mEq/kg day), despite a high sodium intake (7.22 mEq/kg/day). This negative balance was the result of a high fractional sodium excretion and resulted in hyponatremia in six (50%) of the patients. By day 8 these immature infants were in positive sodium balance, although fractional sodium excretion and daily sodium requirements remained high. More mature infants (greater than 30 weeks gestational age) were in positive sodium balance on both days 3 and 8. Creatinine clearance did not differ significantly between groups on either day 3 or 8 but increased within each group during the study period. These data suggest that the daily sodium requirement of immature sick infants may be much higher than was previously suggested.

Renal function in idiopathic respiratory distress syndrome

Renal function was studied in 11 pre-term infants with idiopathic respiratory distress syndrome (IRDS) grade 1 according to Prod'hom's criteria. As a reference 16 healthy pre-term infants were studied. The groups did not differ with regard to mean gestational age (GA) and mean postnatal age (PNA). The studies were prefomred twice, first at a PNA of 33--37 hours and then at 132--148 hours. GFR and CPAH were determined with the single injection technique and the ability to excrete Na+ was determined following an oral Na+ load. GFR was higher in IRDS infants at the first investigation and slightly lower in IRDS infants at the second investigation. The GFR correlated to the lowest recorded PaO2 (r=0.45) in IRDS infants. CPAH was similar in IRDS and controls at the first, and lower in IRDS infants at the second investigation. The urinary Na+ excretion was significantly higher in IRDS infants. Treatment with digitalis was in part responsible for the high urinary Na+ excretion. The IRDS infants had a higher Na+ and glucose intake than the control infants. It is suggested that this higher intake is in part responsible for the relatively high GFR and urinary Na+ excretion in IRDS infants.

Aldosterone and sodium HOMEOSTASIS in preterm infants

A specific mass spectrometric method was used for tetrahydroaldosterone determination in urine of preterm infants (26-34 weeks gestational age) up to 9 weeks of age. Hyponatraemia during the first 2 weeks of life was associated with an excretion of tetrahydroaldosterone (5-50 mug/24 h) comparable with full-term infants. Excretion of tetrahydroaldosterone was significantly elevated in all infants studied during the third week of life (80-350 mug/24 h) and this was associated with establishment of positive sodium balance. The excretion of tetrahydro aldosterone remained high for 2 or 3 weeks. The results are discussed in relation to the development of renal tubules and control mechanism for sodium homeostasis.

Renal function in respiratory distress syndrome

Renal function wa assessed in 20 newborn infants with idiopathic respiratory distress syndrome and compared to that of 10 neonates without respiratory distress or renal disease. Inulin and PAH clearances were markedly depressed in neonates with RDS as compared to controls (5.9 +/- 0.6 vs 9.3 +/- 0.8 ml/min/m2 (p less than 0.01) and 13.5 +/- 2.0 vs 23.2 +/- 1.2 ml/min/m2 ( p less than 0.01), respectively). The impairment of inulin and PAH clearances correlated with the severity of the pulmonary disease. Improvement of the respiratory distress was followed by a progressive rise of inulin and PAH clearances toward normal values. Intravenous administration of hypertonic mannitol in three patients resulted in an immediate increase in urine flow and inulin and PAH clearances. It is concluded that a state of acute, reversible, renal insufficiency can occur in the acute phase of idiopathic respiratory distress syndrome.

Neonatal hyperuricemia

Serum concentrations and urinary excretion of uric acid were measured in ten normal newborn infants and in 13 patients with the idiopathic respiratory distress syndrome. In the normal infants, serum urate increased from a mean value of 6.0 mg/dl in cord blood to 7.0 mg/dl at 24 hours, followed by a decrease to 3.5 mg/dl over the next three days. The infants with IRDS had higher serum urate concentrations during the first three days of life, and the urinary excretion of uric acid over the period of 12 to 36 hours of age was also higher than in the normal infants. In both groups of neonates the correlation of maximal serum urate values with the urinary excretion was positive, which indicates that neonatal hyperuricemia is not due to renal retention but to increased production of uric acid. It is postulated that this overproduction results from increased nucleotide breakdown associated with perinatal hypoxia. Because of high serum and urinary uric acid concentrations, maintenance of adequate hydration and urinary flow as well as alkalinization of urine is recommended.

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.

Amniotic fluid osmolality in pregnancies complicated by diabetes

Amniotic fluid osmolality (AF Osm) was studied in 247 patients whose pregnancies were complicated by maternal diabetes. Significant increases in mean AF Osm accompanied pre-existing fetal as well as subsequent perinatal death. Abnormal increases in AF Osm were associated with a significant increase in risk of perinatal compromise with cumulative morbidity and mortality rates of 54 per cent. These data suggest that serial evaluation of AF Osm enables detection of a "higher risk" group of diabetic pregnancies in which perinatal death is more than doubled.

Plasma renin activity and aldosterone concentration in children

Using semi-micro methods, plasma renin activity (PRA) and plasma aldosterone concentration (PA) were measured concurrently in 79 healthy children aged 1 month to 15 years to establish a reference range. PRA and PA varied inversely with age. Eleven children with renal hypertension had higher PRA and PA than age-matched controls. In contrast, PRA was much greater in 38 saline-depleted children. PA was not uniformly increased in this group and was within the normal range in children with adrenal diseases compared with the high values seen in other salt-wasting states. The findings emphasise the need to relate data from patients to age-matched control values before attempting interpretation and suggest that sodium depletion is a more potent stimulator of renin-aldosterone release than renovascular disease or renal scarring in children. Plasma renin-aldosterone profiles were also valuable in discriminating between renal and adrenal causes of salt loss in childhood.

Angiotensin-I-converting enzyme activity in idiopathic respiratory distress syndrome of the newborn infant and in experimental alveolar hypoxia in mice

Serum angiotensin-I-converting enzyme activity was found to be elevated in infants with idiopathic respiratory distress syndrome when compared with healthy premature infants, normal infants, and acutely ill full-term infants. Serum and lung CE activity has been found to be elevated in mice exposed to hypobaric alveolar hypoxia which also stimulated renal renin production. These findings suggest that alveolar hypoxia stimulates the renin-angiotensin-aldosterone system and this system may be involved in the response to the stress of IRDS.