Abnormal renal function in the newborn infant

Oligohydramnios: antepartum fetal urine production and intrapartum fetal distress

Animal and human studies suggest that fetal oliguria is a normal physiologic response to hypoxemia. To assess the clinical significance of this observation, we studied (before their admission) 51 fetuses of women whose pregnancies were complicated by oligohydramnios at greater than or equal to 38 weeks' gestation. We found that the mean hourly fetal urine production decreased significantly in relation to the severity of subsequent intrapartum fetal compromise. The mean antepartum rate was 95 ml/hr in the 21 fetuses with a normal intrapartum heart rate pattern; this fell to 59 ml/hr in the 18 fetuses who had an abnormal intrapartum heart rate pattern but who responded to intrauterine resuscitation. The rate was 33 ml/hr in the 12 fetuses who were delivered by cesarean section as a result of fetal distress. These findings suggest that oligohydramnios associated with fetal oliguria may be used to identify those fetuses who have less intrinsic or uteroplacental reserve than do those of women with oligohydramnios who have a higher rate of fetal urine production.

Doppler ultrasound studies in renal arteries of normal newborn babies

The renal arteries of 89 healthy full-term infants were examined using duplex Doppler ultrasonography to establish a normal range for renal blood flow velocity in the first 3 days of life. In the first 24 h a wide range of renal blood flow velocities was noted with a statistically significant decrease in Pourcelot's index over the next 2 days.

Beta 2-microglobulin clearance in neonates: index of tubular maturation

Serum and urinary beta 2-microglobulin (beta 2M) were studied by enzyme immunoassay in 28 normal neonates at day 1 and day 4 of life in relation to gestational age (GA) and postnatal age (PNA). The infants were grouped according to GA; 10 with GA ranging from 32 to 35 weeks (mean 33.5 weeks) and 18 with GA ranging from 36 to 41 weeks (mean 38.3 weeks). Serum beta 2M varied directly with both GA and PNA. When values for serum beta 2M were related to conceptional age (CA), a significant positive correlation was present for all the infants studied (r = 0.68, P less than 0.01). Fractional excretion of beta 2M (FE beta 2M) decreased as a function of both GA and PNA. When a comparison of FE beta 2M was made in infants of all CA, a significant inverse correlation was noted for infants with CA less than or equal to 35 weeks (r = -0.89, P less than 0.001). The fall in FE beta 2M reached a plateau by 36 weeks. The highest FE beta 2M (33%) was observed in infants of 32 weeks CA who had the lowest filtered beta 2M (F beta 2M). No statistically significant relationship between changes in FE beta 2M and fractional urine flow rate was observed within each of the CA categories (infants less than or equal to 35 weeks, r = 0.21, P = 0.28; infants greater than or equal to 36 weeks, r = 0.25, P = 0.18).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Intrapartum hypoxia: the association between neurological assessment of damage and abnormal excretion of ATP metabolites

A series of 29 newborn infants had been studied after intrapartum hypoxia defined as meconium aspiration, an Apgar score of less than or equal to 6 at 5 min or a peripheral blood pH of 7.2 or less after resuscitation. Two independent sets of techniques were used; one concerned with the critical system in hypoxic damage, the central nervous system, the other assessing the central biochemical events in hypoxia. Both sets of data were assembled, then graded separately and only then combined. In this way detailed neurological assessment has been combined with measurement of urinary excretion of the ATP metabolites, hypoxanthine and xanthine. The essential metabolic consequence of hypoxia is a reduction in the synthesis of the energy currency of cells, ATP. This is associated with an outflow of ATP metabolites from cells. The extent of neurological damage was related to the magnitude of the hypoxanthine and xanthine excretion; neither were closely related to the initial blood pH. Infants who were normal neurologically had normal oxypurine excretion. Infants with neurological abnormalities for less than 48 h had lower excretion than those who were abnormal for more than 48 h. The duration of abnormal oxypurine excretion after an acute episode of hypoxia was studied in two infants with respiratory distress and in two other infants with apnoeic attacks. Severe hypoxia was followed by abnormal oxypurine excretion for at least 40 h after an acute episode. It is justifiable to suggest that abnormalities of oxypurine excretion should indicate intrapartum hypoxia in newborn infants. This excretion should also quantify the metabolic damage.

Plasma creatinine in the first month of life

The creatinine-kinetics method of analysis was used to study the changes, during the first month of life, in plasma creatinine levels in 34 newborn infants receiving no treatment with drugs. Plasma creatinine values during the first 5 days of life ranged from 188 to 17 mumol/l. After day 5 plasma levels were fairly stable throughout the first month, with a mean value of 35 +/- 2 (range 12-62) mumol/l. Twenty-two infants receiving treatment with gentamicin-ampicillin-cloxacillin were also studied. Seven of them had raised plasma creatinine concentrations after day 5, well beyond the range of concentrations found for infants receiving no drugs. Plasma creatinine, measured by the kinetic method, appears to provide a useful index of renal function in the neonatal period.

Developmental aspects of the renal response to hypoxemia in the lamb fetus

The effects of fetal hypoxemia on renal hemodynamics and renal function were studied in two groups of chronically catheterized young (< 120 days of gestation) and near-term lamb fetuses (> 130 days). Fetal hypoxemia produced, in both groups, a significantly decrease in renal blood flow (RBF) and a significant increase in the filtration fraction. However, the glomerular filtration rate (GFR) did not change significantly suggesting that the renal vasoconstriction associated with fetal hypoxemia was more important at the efferent than at the afferent arteriolar level. In the group of near-term fetuses, the decrease in RBF correlated closely with changes in plasma renin activity (PRA) (r = 0.77). No changes in PRA were observed during hypoxemia in the group of young fetuses. After hypoxemia, reactive hyperemia associated with a significant increase in urinary prostaglandin excretion (PGE and PGF2 alpha) was observed in near-term fetuses but not in young fetuses. It also was demonstrated that fetal hypoxemia produced a significant increase in fetal plasma concentrations of vasopressin associated with an antidiuresis in all but one near-term fetus and in 50% of the young fetuses, suggesting that the ability of the fetal kidney to reabsorb free water is more developed in near-term fetuses. Finally, fetal hypoxemia had no effect on mean arterial pressure and heart rate in young fetuses; however, in near-term fetuses, a significant increase in blood pressure and a decrease in heart rate were observed. In summary, it appears that the response of the fetal kidney to hypoxemia depends on the degree of fetal maturation.