Renal function in idiopathic 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.

[Hydroelectrolytic requirements during the first week of life in premature infants weighing less than 1000 g. Physiopathology and recommendations]

Fluid and electrolyte maintenance in very low birth weight infants during the first week of life must be adapted to their physiological characteristics and to pathological events. Insensible water losses are elevated and may reach 100 mL/kg/24 h depending upon many factors, such as type of incubator, phototherapy, presence of respiratory distress syndrome, changes in transepidermal water losses and renal water and electrolyte regulation (prediuretic, diuretic and postdiuretic phases); there is also a major risk of hypernatremia and hyperkaliema. In cases of insufficient fluid intake the main complication is dehydration with hypernatremia. Excessive fluid intake results in increased incidence of bronchopulmonary dysplasia, patent ductus arteriosus and necrotizing enterocolitis. Hypernatremia is a major risk factor of intracranial hemorrhage. A careful management of water and electrolyte requirements is therefore mandatory in very low birth weight infants. Guidelines on daily maintenance and management are presented.

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)

Glomerular filtration rate in the preterm infant: the relation to gestational and postnatal age

In 41 preterm neonates with a gestational age (GA) varying from 27 to 36 weeks, glomerular filtration rate (GFR) was measured by means of the continuous inulin infusion technique. The reliability of the technique was confirmed. During postnatal development GFR was found to increase in two ways: firstly, an increase with advancing gestational age, associated with the increase in body weight (BW) [GFR (ml/min) = 0.15 X GA-3.20, r = 0.48, P = 0.0048]; secondly, a postnatal increase, being independent from increment in BW. An increase in GFR (ml/min.kg) from 0.88 +/- 0.23 to 1.18 +/- 0.28 was observed between day 4 and day 11 postnatally (P less than 0.008). This latter increase is probably associated with changes in renal haemodynamics. No significant influence of artificial ventilation on GFR could be demonstrated in preterm neonates.

A controlled study of the nephrotoxicity of mezlocillin and gentamicin plus ampicillin in the neonate

The nephrotoxicity of the aminoglycoside gentamicin was evaluated in an open, controlled study of newborn infants randomly allocated to receive either combination drug therapy with gentamicin and ampicillin or single drug therapy with mezlocillin for treatment of presumed neonatal sepsis. There were no significant differences in initial clinical characteristics between the groups. Neonates receiving gentamicin, in contrast to those receiving mezlocillin, had significant nephrotoxicity manifested by a smaller postnatal fall in mean serum creatinine concentration (-9%, P NS vs -21%, P less than 0.005, respectively) and a diminished postnatal rise in mean creatinine clearance (+ 21%, P NS vs + 51%, P less than 0.01, respectively). In neonates with a fall in creatinine clearance, the mean decline was significantly greater in those receiving gentamicin (44% vs 20%, P less than 0.01). There was no relationship between the incidence of gentamicin nephrotoxicity and either peak or trough gentamicin levels. For treatment of presumed neonatal sepsis, gentamicin proved more nephrotoxic than mezlocillin.

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.

Glomerular tubular balance in preterm and fullterm infants

The development of glomerular and tubular function was studied in preterm and fullterm infants of varying gestational and postnatal age. The results indicate that glomerular functional development precedes tubular functional development until the 34th postmenstrual week. After the 34th week the tubular transport capacity seems to be more vulnerable than the glomerular filtration rate in states of disease. The release of a postulated renal vasoconstriction could account for the rapid changes in renal function after birth. The purpose of such a vasoconstriction could be to protect the tubules from an overload.

Postnatal control of water and electrolyte homeostasis in pre-term and full-term infants

A review is given of the progress which has been made during the last decade within the field of renal control of water and sodium homeostasis in newborn infants of varying gestational age. Both preterm and full-term infants have a low capacity for rapid excretion of a salt load. The natriuretic response improves gradually up to the age of 15 months. The capacity to excrete a load of sodium bicarbonate is higher than to excrete a load of sodium chloride. Under basal conditions preterm infants of a gestational age below 35 weeks have a higher renal sodium excretion than full-term infants. They also appear to be unable to retain sodium when in negative balance. The capacity to concentrate the urine is low in newborn infants, the maximal osmolality being only slightly above that of plasma. The concentrating capacity increases relatively fast during the first 4-6 postnatal weeks in full-term as well as in pre-term infants but does not reach the adult level until the second year. Water loaded newborn infants are able to excrete a urine with a osmolality as low as 30-50 mOsm per kg. In full-term infants free water clearance per unit filtered water is higher than in adults. Water-loaded pre-term infants with a gestational age of more than 30 weeks also have a supernormal diluting capacity.

Role for glucagon as a mineralocorticoid antagonist during the fetal-perinatal period

The progressive decrease in total body water (TBW) and sodium during the fetal-perinatal period; the normally noted 5-10 per cent largely water weight loss noted in term infants during the first 3-4 days postnatally; and, the even greater TBW and sodium losses incurred by premature infants during the initial post-natal week may, in part, be secondary to a glucagon-mediated, renal distal tubular hyporesponsiveness to aldosterone.

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 excretion in relation to sodium intake and aldosterone excretion in newborn pre-term and full-term infants

The importance of aldosterone for the control of salt balance has been examined in pre-term infants (gestational age 28--34 weeks) and in full-term infants. The post-natal age has varied from 2--21 days. Eight-hour urinary specimens have been analysed with regard to sodium, potassium and aldosterone. The daily sodium intake has been recorded following determination of milk intake and analyses of sodium in breast milk. Due to variations of sodium content of breast milk, the daily sodium intake in pre-term infants was lower than in full-term infants during the first 10 days of life. The sodium excretion was significantly higher in pre-term infants than in full-term infants during the first six days of life. During the first week of life the sodium balance is negative in pre-term infants and positive in full-term infants. Aldosterone excretion is high during the first week of life and increases further from the 2nd to the 3rd week of life in both pre-term and full-term infants. The correlation between aldosterone excretion and urinary potassium/sodium quotient is 0.87 in full-term infants, 0.57 in pre-term infants aged 13--20 days and does not exist in pre-term infants aged 2--10 days. It is suggested that the high sodium excretion in newborn pre-term infants can in part be explained by an unresponsiveness to aldosterone at this developmental stage.

Beta-2-microglobulin, an indicator of renal tubular maturation and dysfunction in the newborn

The urinary excretion and proximal tubular reabsorption of beta-2-microglobulin was studied in 17 healthy newborn infants in relation to gestational and post-natal age. The effect of IRDS and non-conjugated hyperbilirubinemia on the tubular reabsorption of the protein was evaluated in 10 IRDS infants and 14 infants with non-conjugated hyperbilirubinemia. The urinary excretion of beta-2-microglobulin was determined under standardized conditions. When GFR was determined, the single injection clearance method was used. The filtered load of beta-2-microglobulin was found to increase with increasing gestational age. This was due to a rise in plasma beta-2-microglobulin concentration as well as to a rise in the GFR. Although the smallest filtered load was recorded in infants with a mean GA of 32.4 weeks, these infants had a lower fractional reabsorption of the protein (88%) than infants with a mean GA of 35.0 weeks or more (98%). In infants with a GA of 35 weeks or more a glomerulo-tubular balance for beta-2-microglobulin apparently was established. In these infants the filtered load of beta-2-microglobulin increased rapidly during the first days of life. This was paralleled by an increase in the reabsorptive capacity for the protein. In infants with IRDS and in infants with non-conjugated hyperbilirubinemia the fractional reabsorption of beta-2-microglobulin was lower than in control infants of a corresponding gestational and postnatal age. This indicates, that in the neonatal period, the proximal tubular transporting capacity is more vulnerable than the glomerular filtration rate in states of hypoxia and hyperbilirubinemia.

Renal function in infants with hyperbilirubinemia

A total of 45 infants were studied on the fourth or fifth day of life: 13 term and 10 pre-term infants with serum bilirubin levels ranging between 257 and 390 mumol/l were compared with 12 term and 10 pre-term infants with serum bilirubin levels below 195 mumol/l. The groups did not differ with regard to mean gestational age or mean post-natal age. GFR and CPAH were determined with the single injection clearance method and ability to excrete Na+ was determined following an oral loading of sodium chloride. GFR was lower in infants with hyperbilirubinemia and correlated negatively to the highest recorded serum bilirubin value. CPAH was similar in hyperbilirubinemic infants and controls. The urinary sodium excretion was significantly higher in infants with hyperbilirubinemia.