Renal function in respiratory distress syndrome

When the progresses in neonatology lead to severe congenital nephron deficit: is there a pilot in the NICU?

Advances in the care of neonates to the extreme limits of viability have increased the risk of severe comorbidities in surviving preemies. The respiratory and the neurodevelopmental consequences of premature birth and/or intra-uterine growth retardation have been well described. Because of the usual clinical silence of the kidney, the long-term renal consequences of low birth weight have not been as well studied. A case report illustrates the risk factors associated with low birth weight and prematurity and discusses the pathogenesis of the late consequences of the congenital nephron deficit associated with a low birth weight. Practical recommendations are given for a tight follow-up of these newly born preemies.

Fluid handling and blood flow patterns in neonatal respiratory distress syndrome versus transient tachypnea: a pilot study

Background

Cardiovascular and renal adaptation in neonates with Respiratory Distress Syndrome (RDS) and Transient Tachypnea of the Newborn (TTN) may be different.

Methods

Neonates ≥32 weeks were diagnosed with RDS or TTN based on clinical, radiologic and lung sonographic criteria. Weight loss, feeding, urine output, and sodium levels were recorded for the first 3 days, and serial ultrasounds assessed central and organ Doppler blood flow. A linear mixed model was used to compare the two groups.

Results

Twenty-one neonates were included, 11 with TTN and 10 with RDS. Those with RDS showed less weight loss (− 2.8 +/− 2.7% versus − 5.6 +/− 3.4%), and less enteral feeds (79.2 vs 116 ml/kg/day) than those with TTN, despite similar fluid prescription. We found no difference in urine output, or serum sodium levels. Doppler parameters for any renal or central parameters were similar. However, Anterior Cerebral Artery maximum velocity was lower (p = 0.03), Superior Mesenteric Artery Resistance Index was higher in RDS, compared to TTN (p = 0.02).

Conclusion

In cohort of moderately preterm to term neonates, those with RDS retained more fluid and were fed less on day 3 than those with TTN. While there were no renal or central blood flow differences, there were some cerebral and mesenteric perfusion differences which may account for different pathophysiology and management.

Blood urea in preterm infants on routine parenteral nutrition: A multiple linear regression analysis

BACKGROUND

Blood urea is considered a marker of amino acid utilization in preterm infants on routine parenteral nutrition. However, the association between blood urea and intravenous amino acid intake remains debated.

AIMS

To evaluate the association between blood urea and both nutrition and clinical data, in a large cohort of preterm infants.

METHODS

Consecutively admitted preterm infants with a gestational age of less than 32 weeks and a birth weight lower than 1250 g on routine parenteral nutrition from the first hour of life were studied. Clinical and nutrition data collected hourly during the hospitalization were used in multiple linear regression analysis.

RESULTS

We studied 674 patients and 1863 blood urea determinations. Blood urea concentration was positively associated with blood creatinine concentration, intravenous amino acid intake, patent ductus arteriosus and respiratory distress syndrome, and negatively associated with intravenous non-protein energy intakes, daily weight change, gestational age, being small for gestational age, antenatal steroids therapy and reverse flow in the umbilical artery (p < 0.001; R = 0.7).

CONCLUSIONS

From a nutrition perspective, in our large cohort of small preterm infants blood urea was positively correlated with intravenous amino acid intake and negatively correlated with intravenous non-protein energy intake. This is in line with current knowledge in human physiology and suggest that a reduction of intravenous amino acid intake based on blood urea concentrations was justified.

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.

Effects of acid aspiration-induced acute lung injury on kidney function

Acute lung injury (ALI) in combination with acute kidney injury carries a mortality approaching 80% in the intensive care unit. Recently, attention has focused on the interaction of the lung and kidney in the setting of ALI and mechanical ventilation (MV). Small animal models of ALI and MV have demonstrated changes in inflammatory mediators, water channels, apoptosis, and function in the kidney early in the course of injury. The purpose of this investigation was to test the hypothesis that ALI and injurious MV cause early, measurable changes in kidney structure and function in a canine HCl aspiration model of ALI when hemodynamics and arterial blood gas tensions are carefully controlled. Intratracheal HCl induced profound ALI as demonstrated by increased shunt fraction and airway pressures compared with sham injury. Sham-injured animals had similar mean arterial pressure and arterial Pco(2) and HCO(3) levels compared with injured animals. Measurements of renal function including renal blood flow, urine flow, serum creatinine, glomerular filtration rate, urine albumin-to-creatinine ratio, and kidney histology scores were not different between groups. With maintenance of hemodynamic parameters and alveolar ventilation, ALI and injurious MV do not alter kidney structure and function early in the course of injury in this acid aspiration canine model. Kidney injury in large animal models may be more similar to humans and may differ from results seen in small animal models.

Mechanical ventilation and acute renal failure

OBJECTIVE

To review the current literature on possible mechanisms by which mechanical ventilation may initiate or aggravate acute renal failure.

DATA SOURCE

A Medline database and references from identified articles were used to perform a literature search relating to mechanical ventilation and acute renal failure.

DATA SYNTHESIS

Acute renal failure may be initiated or aggravated by mechanical ventilation through three different mechanisms. First, strategies such as permissive hypercapnia or permissive hypoxemia may compromise renal blood flow. Second, through effects on cardiac output, mechanical ventilation affects systemic and renal hemodynamics. Third, mechanical ventilation may cause biotrauma-a pulmonary inflammatory reaction that may generate systemic release of inflammatory mediators. The harmful effects of mechanical ventilation may become more significant when a comorbidity is present. In these situations, it is more difficult to maintain normal gas exchange, and moderate arterial hypoxemia and hypercapnia are often accepted. Renal blood flow is compromised due to a decreased cardiac output as a consequence of high intrathoracic pressures. Furthermore, the effects of biotrauma are not limited to the lungs but may lead to a systemic inflammatory reaction.

CONCLUSIONS

The development of acute renal failure during mechanical ventilation likely represents a multifactorial process that may become more important in the presence of comorbidities. Development of optimal interventional strategies requires an understanding of physiologic principles and greater insight into the precise molecular and cellular mechanisms that may also play a role.

Renal effects of adenosine A1-receptor blockade with 8-cyclopentyl-1,3-dipropylxanthine in hypoxemic newborn rabbits

The key role of intrarenal adenosine in mediating the hypoxemic acute renal insufficiency in newborn rabbits has been well demonstrated using the nonspecific adenosine antagonist theophylline. The present study was designed to define the role of adenosine A1 receptors during systemic hypoxemia by using the specific A1-receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX). Renal function parameters were assessed in 31 anesthetized and mechanically ventilated newborn rabbits. In normoxia, DPCPX infusion induced a significant increase in diuresis (+44%) and GFR (+19%), despite a significant decrease in renal blood flow (RBF) (-22%) and an increase in renal vascular resistance (RVR) (+37%). In hypoxemic conditions, diuresis (-19%), GFR (-26%), and RBF (-35%) were decreased, whereas RVR increased (+33%). DPCPX administration hindered the hypoxemia-induced decrease in GFR and diuresis. However, RBF was still significantly decreased (-27%), whereas RVR increased (+22%). In all groups, the filtration fraction increased significantly. The overall results support the hypothesis that, in physiologic conditions, intrarenal adenosine plays a key role in regulating glomerular filtration in the neonatal period through preferential A1-mediated afferent vasoconstriction. During a hypoxemic stress, the A1-specific antagonist DPCPX only partially prevented the hypoxemia-induced changes, as illustrated by the elevated RVR and drop in RBF. These findings imply that the contribution of intrarenal adenosine to the acute adverse effects of hypoxemia might not be solely mediated via the A1 receptor.

Complementary effects of adenosine and angiotensin II in hypoxemia-induced renal dysfunction in the rabbit

The acute renal effects of hypoxemia and the ability of the co-administration of an angiotensin converting enzyme inhibitor (perindoprilat) and an adenosine receptor antagonist (theophylline) to prevent these effects were assessed in anesthetized and mechanically-ventilated rabbits. Renal blood flow (RBF) and glomerular filtration rate (GFR) were determined by the clearances of para-aminohippuric acid and inulin, respectively. Each animal acted as its own control. In 8 untreated rabbits, hypoxemia induced a significant drop in mean blood pressure (-12 +/- 2%), GFR (-16 +/- 3%) and RBF (-12 +/- 3%) with a concomitant increase in renal vascular resistance (RVR) (+ 18 +/- 5%), without changes in filtration fraction (FF) (-4 +/- 2%). These results suggest the occurrence of both pre- and postglomerular vasoconstriction during the hypoxemic stress. In 7 rabbits pretreated with intravenous perindoprilat (20 microg/kg), the hypoxemia-induced changes in RBF and RVR were prevented. FF decreased significantly (-18 +/- 2%), while the drop in GFR was partially blunted. These results could be explained by the inhibition of the angiotensin-mediated efferent vasoconstriction by perindoprilat. In 7 additional rabbits, co-administration of perindoprilat and theophylline (1 mg/kg) completely prevented the hypoxemia-induced changes in RBF (+ 11 +/- 3%) and GFR (+ 2 +/- 3%), while RVR decreased significantly (-14 +/- 3%). Since adenosine and angiotensin II were both shown to participate, at least in part, in the renal changes induced by hypoxemia, the beneficial effects of perindoprilat and theophylline in this model could be mediated by complementary actions of angiotensin II and adenosine on the renal vasculature.

Randomised trial of fluid restriction in ventilated very low birthweight infants

BACKGROUND

Fluid restriction has been reported to improve survival of infants without chronic lung disease (CLD), but it remains unknown whether it reduces CLD in a population at high risk of CLD routinely exposed to antenatal steroids and postnatal surfactant without increasing other adverse outcomes.

AIM

To investigate the impact of fluid restriction on the outcome of ventilated, very low birthweight infants.

STUDY DESIGN

A randomised trial of two fluid input levels in the perinatal period was performed. A total of 168 ventilated infants (median gestational age 27 weeks (range 23-33)) were randomly assigned to receive standard volumes of fluid (60 ml/kg on day 1 progressing to 150 ml/kg on day 7) or be restricted to about 80% of standard input.

RESULTS

Similar proportions of infants on the two regimens had CLD beyond 28 days (56% v 51%) and 36 weeks post conceptional age (26% v 25%), survived without oxygen dependency at 28 days (31% v 27%) and 36 weeks post conceptional age (58% v 52%), and developed acute renal failure. There were no statistically significant differences between other outcomes, except that fewer of the restricted group (19% v 43%) required postnatal steroids (p < 0.01). In the trial population overall, duration of oxygen dependency related significantly to the colloid (p < 0.01), but not crystalloid, input level; after adjustment for specified covariates, the hazard ratio was 1.07 (95% confidence interval 1.02 to 1.13).

CONCLUSIONS

In ventilated, very low birthweight infants, fluid restriction in the perinatal period neither reduces CLD nor increases other adverse outcomes. Colloid infusion, however, is associated with increased duration of oxygen dependency.

Effect of severe normocapnic hypoxia on renal function in growth-restricted newborn piglets

To examine the effects of intrauterine growth restriction and acute severe oxygen deprivation on renal blood flow (RBF), renovascular resistance (RVR), and renal excretory functions in newborns, studies were conducted on 1-day-old anesthetized piglets divided into groups of normal weight (NW, n = 14) and intrauterine growth-restricted (IUGR, n = 14) animals. Physiological parameters, RBF, RVR, and urinary flow, were similar in NW and IUGR piglets, but glomerular filtration rate (GFR) and filtration fraction were significantly less in IUGR animals (P < 0.05). An induced 1-h severe hypoxia (arterial PO(2) = 19 +/- 4 mmHg) resulted in, for both groups, a pronounced metabolic acidosis, strongly reduced RBF, and increased fractional sodium excretion (FSE; P < 0.05) with a less-pronounced increase of RVR and arterial catecolamines in IUGR piglets. Of significance was a smaller decrease in RBF for IUGR piglets (P < 0.05). Early recovery showed a transient period of diuresis with increased osmotic clearance and elevated FSE in both groups (P < 0.05). However, GFR and renal O(2) delivery remained reduced in NW piglets (P < 0.05). We conclude that, in newborn IUGR piglets, RBF is maintained, although GFR is compromised. Severe hypoxemia induces similar alterations of renal excretion in newborn piglets. However, the less-pronounced RBF reduction during hypoxemia indicates an improved adaptation of newborn IUGR piglets on periods of severely disturbed oxygenation. Furthermore, newborn piglets reestablish the ability for urine concentration and adequate sodium reabsorption early after reoxygenation so that a sustained acute renal failure was prevented.

Failure of the loop diuretic torasemide to improve renal function of hypoxemic vasomotor nephropathy in the newborn rabbit

The use of diuretic therapy in vasomotor nephropathy is a controversial topic. It is generally agreed that diuretics in this situation enhance urinary output, reduce the degree of volume expansion, and improve cardiac and especially the compromised lung function. It is less clear whether diuretic therapy improves kidney function. The present study evaluates the effects of intravenous torasemide on renal function in 25 anesthetized ventilated hypoxemic newborn New Zealand White rabbits with vasomotor nephropathy. This well-established animal model mimics the renal physiology of the human newborn and, in particular, that of the premature infant. Three groups of hypoxemic rabbits were studied. The animals of group 1 (n = 8) received no diuretic therapy (hypoxemic control), and those of group 2 (n = 9) were given a single intravenous dose of torasemide (1 mg/kg) in a curative fashion 2 h after hypoxemia was induced. In the third group of animals (n = 8), torasemide was given preventively; a bolus intravenous dose of torasemide (0.2 mg/kg) was given before the induction of hypoxemia and sustained by the addition of 0.2 mg x kg(-1) x h(-1) of the drug to the continuous intravenous infusion given throughout the entire 3-h hypoxemic period. Hypoxemia alone (group 1) caused acute renal insufficiency with a significant fall in mean arterial blood pressure, GFR, and renal blood flow; the renal vascular resistance increased, and the filtration fraction was unchanged. The curative dose of torasemide (group 2) induced a significant diuresis and natriuresis with minimal augmentation of urinary potassium excretion, converting mildly oliguric to nonoliguric acute renal insufficiency. In this group of animals, torasemide did not improve the glomerular dysfunction. The preventive dose of torasemide (group 3) even somewhat worsened the already impaired renal functions without further increasing the diuretic effect of the drug. We conclude that in hypoxemic newborn animals with renal dysfunction, torasemide is an effective potassium-sparing diuretic that unfortunately does not improve renal blood flow and GFR. The failure of torasemide to attenuate the glomerular dysfunction of hypoxemic vasomotor nephropathy in the newborn rabbit is disturbing. These data certainly caution against the overzealous use of loop diuretics in hypoxemic oliguric neonates.

The pharmacokinetics of theophylline in premature neonates during the first few days after birth

The aims of the study were to estimate the pharmacokinetic parameters, clearance rate (CL), and volume of distribution (V) of theophylline in premature neonates during the first few days after birth, and to identify factors contributing to interindividual variability. The authors obtained 263 serum concentrations from 105 apneic premature neonates receiving intravenous (IV) theophylline. Mean (SD) birth weight and postnatal ages were 1.3 (0.3) kg and 1.1 (0.3) days, respectively. The data were analyzed using the nonlinear mixed effects model (NONMEM). A one-compartment model with first order elimination was used. The final models were: CL (L/h) = 0.006 * WGT 0.75 * P, V (L) = 0.63 * WGT, WGT = weight (kg) P = 1.47 with oxygen support and 1.0 without oxygen support. The CL in the study population was low, resulting in long half-lives. After inclusion of the above covariates, as well as interoccasion variability, the interindividual variability in CL was 56% and in V was 47%. Interoccasion variability in CL and V was 34% and 35% respectively. Theophylline pharmacokinetics are variable in the premature neonate during the first week of life, and this high variability makes it difficult to predict drug concentrations with the same degree of accuracy as in other populations.

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.

Antibiotics in neonatal infections: a review

The bacteria most commonly responsible for early-onset (materno-fetal) infections in neonates are group B streptococci, enterococci, Enterobacteriaceae and Listeria monocytogenes. Coagulase-negative staphylococci, particularly Staphylococcus epidermidis, are the main pathogens in late-onset (nosocomial) infections, especially in high-risk patients such as those with very low birthweight, umbilical or central venous catheters or undergoing prolonged ventilation. The primary objective of the paediatrician is to identity all potential cases of bacterial disease quickly and begin antibacterial treatment immediately after the appropriate cultures have been obtained. Combination therapy is recommended for initial empirical treatment in the neonate. In early-onset infections, an effective first-line empirical therapy is ampicillin plus an aminoglycoside (duration of treatment 10 days). An alternative is ampicillin plus a third-generation cephalosporin such as cefotaxime, a combination particularly useful in neonatal meningitis (mean duration of treatment 14 to 21 days), in patients at risk of nephrotoxicity and/or when therapeutic monitoring of aminoglycosides is not possible. Another potential substitute for the aminoglycoside is aztreonam. Triple combination therapy (such as amoxicillin plus cefotaxime and an aminoglycoside) could also be used for the first 2 to 3 days of life, followed by dual therapy after the microbiological results. In late-onset infections the combination oxacillin plus an aminoglycoside is widely recommended. However, vancomycin plus ceftazidime (+/- an aminoglycoside for the first 2 to 3 days) may be a better choice. Teicoplanin may be a substitute for vancomycin. However, the initial approach should always be modified by knowledge of the local bacterial epidemiology. After the microbiological results, treatment should be switched to narrower spectrum agents if a specific organism has been identified, and should be discontinued if cultures are negative and the neonate is in good clinical condition. Penicillins and third-generation cephalosporins are generally well tolerated in neonates. There is controversy regarding whether therapeutic drug monitoring of aminoglycosides will decrease toxicity (particularly renal damage) in neonates, and on the efficacy and safety of a single daily dose versus multiple daily doses of these drugs. Toxic effects caused by vancomycin are uncommon, but debate still exists over the need for therapeutic drug monitoring of this agent. When antibacterials are used in neonates, accurate determination of dosage is required, particularly for compounds with a low therapeutic index and in patients with renal failure. Very low birthweight infants are also particularly prone to antibacterial-induced toxicity.

Spot urine samples for evaluating solute excretion in the first week of life

AIM

To evaluate whether the urinary creatinine concentration is a reliable reference value to standardise urinary solute excretion in a spot urine sample during the first week of life.

METHODS

Spontaneously voided urine specimens were obtained in 48 healthy, full term neonates, aged 1 to 6 days (median 2.4) and in 168 healthy older children with a median age of 1.5 years (range 1 month to 3 years). In 62% of the children two urine samples were available with an interval of 2 to 4 (neonates) and 7 days (older children).

RESULTS

In neonates both the urinary creatinine concentration and the urinary creatinine:osmolality ratios were significantly higher than in the older children, and were spread over a wider range. During the first postnatal week of life the mean urinary creatinine and urinary creatinine: osmolality ratio values in the first urine samples were also significantly higher than in the second samples. In children aged between 1 month and 3 years of age, these data were remarkably stable without any significant changes between repeat urine samples.

CONCLUSIONS

The urinary creatinine concentration during the first days of life is high and variable, even when corrected for urinary osmolality. This is the opposite of what is found in older children and adults. Urinary creatinine and the urinary creatinine:osmolality ratio, therefore, cannot be used to standardise the urinary excretion of solutes in the first week of life.

Protective effect of perindoprilat in the hypoxemia-induced renal dysfunction in the newborn rabbit

The renal effects of acute hypoxemia and the ability of perindoprilat, a potent angiotensin-converting enzyme inhibitor, to prevent these effects were assessed in 31 anesthetized and mechanically ventilated newborn (5 to 8 d of age) rabbits. Renal blood flow (RBF) and GFR were determined by the clearances of para-aminohippuric acid and inulin, respectively. Each animal acted as its own control. In eight normoxemic rabbits (group 1), the i.v. infusion of saline did not change renal and hemodynamic functions. In eight additional rabbits, acute hypoxemia (PaO2= 40 mm Hg) induced a significant decrease in mean blood pressure (-8+/-2%), RBF (-36+/-3%), and GFR (-31+/-3%) and an increase in renal vascular resistance (+50+/-12%). A third group of newborn animals (n=7) was used to determine the renal effects of perindoprilat administration (20 microg/kg) under normoxemic conditions. RBF significantly increased (+15+/-2%) and renal vascular resistance significantly decreased (-15+/-3%), whereas GFR, mean blood pressure, and filtration fraction did not change significantly. In group 4 (n=7), perindoprilat infusion completely prevented the hypoxemia-induced alterations in GFR and renal vascular resistance and partially prevented the fall in RBF. These results demonstrate that angiotensin II modulates the renal immature microcirculation and that inhibition of its formation effectively prevents the hypoxemia-induced decrease in GFR.

[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.

Role of nitric oxide in the hypoxemia-induced renal dysfunction of the newborn rabbit

The current study was performed in 30 anesthetized and mechanically ventilated newborn rabbits to investigate the role of the endothelium-derived relaxing factor nitric oxide (NO) in the renal vasoconstriction observed during hypoxemia. Renal blood flow (RBF) and GFR were determined by the clearance of p-aminohippuric acid and inulin, respectively. In nine newborn rabbits (group 1), acute hypoxemia induced a significant decrease in RBF (-17 +/- 7%) and GFR (-11 +/- 6%). A second group of nine animals was used to determine the role of NO in regulating renal hemodynamics of the immature kidney in physiologic conditions. N omega-Nitro-L-arginine methyl ester (L-NAME), a NO synthesis inhibitor, significantly increased the renal vascular resistance by 31 +/- 9% and decreased RBF and GFR (-20 +/- 6% and -13 +/- 5%, respectively). Acute hypoxemia was induced in 12 additional newborn rabbits during L-NAME infusion (group 3) to define the role of NO in the renal vasoconstriction observed during hypoxemia. The changes in renal hemodynamics were greater in this group than in those induced by hypoxemia alone. The present results suggest that: 1) endogenous NO has a crucial role in maintaining basal renal perfusion, 2) the activity of NO synthase is maintained during acute hypoxemia, and 3) NO could blunt the effects of acute hypoxemia in the immature newborn rabbit kidney.

Comparison of 5-hydroxyindole-acetic acid and para-amino hippurate clearances in newborn rabbits

Recent study indicates that endogenous 5-hydroxyindole-acetic acid (5-HIAA) clearance can be used as an alternative procedure to para-amino hippurate (PAH) clearance for the estimation of renal plasma flow in human patients. In view of the limitations of PAH clearance measurements in newborn infants we made an attempt to validate the technique of measuring renal blood flow with 5-HIAA quantitatively against PAH clearance. Thirty-four simultaneous determinations of PAH and 5-HIAA clearances were performed in 14 newborn rabbits. 5-HIAA concentrations in plasma and urine were measured by using HPLC coupled with electrochemical detection (Beckman). Renal blood flow was found to range between 0.60 and 6.90 ml/min/kg (mean: 3.39 ml/min/kg) for 5-HIAA and from 0.93 to 6.61 ml/min/kg (mean: 3.68 ml/min/kg) for PAH clearances. There was a significant positive correlation between the values obtained by the two techniques (r = 0.84, P < 0.001). When 5-HIAA clearance was analyzed as a function of plasma 5-HIAA level only a weak, but statistically significant correlation could be detected (r = 0.33, P < 0.05). Plasma 5-HIAA measurement alone, therefore, does not reflect renal blood flow in newborn rabbits. It is concluded that endogenous 5-HIAA clearance might serve as a reliable estimate of renal blood flow in the neonate under different physiologic and pathologic conditions.

Effects of theophylline on renal insufficiency in neonates with respiratory distress syndrome

We report here 6 cases of critically ill newborn infants with both RDS and acute renal insufficiency, unresponsive to conventional treatment (furosemide, dopamine). Theophylline, an adenosine antagonist, has been shown to prevent hypoxemia-induced renal insufficiency in rabbits and our patients thus received compassionately a low-dose of theophylline (1 mg . kg-1 i.v.). Urinary water excretion and creatinine clearances increased significantly in 5 out of 6 neonates, thus suggesting a beneficial role of theophylline in neonatal prerenal failure.

Vasopressin, atrial natriuretic factor and renal water homeostasis in premature newborn infants with respiratory distress syndrome

Arginine vasopressin (AVP), human atrial natriuretic peptide (hANP), and body fluid and electrolyte balance were examined during the first five days of life in eleven premature infants (birthweight 1610 +/- 240 g, gestation 30 +/- 1 weeks) receiving mechanical ventilation for respiratory distress syndrome (RDS). Plasma hANP and urine AVP concentrations were determined by radioimmunoassay on the first, third and fifth days. Arginine vasopressin urine levels remained constantly elevated during the study period (mean +/- SD 13.5 +/- 7.8 day 1, 12.0 +/- 9.9 day 3, 13.2 +/- 5.1 ng/l day 5, p = n.s.), while plasma hANP was significantly increased on the third day (626 +/- 495 vs. 298 +/- 240 pg/ml on day 1, p < .05). Urine sodium concentration, urine osmolality and osmolality and osmolar clearance were elevated significantly as well on day 3, p < .05, and correlated to hANP levels. Body weight decreased during the study by 8.2% on the third day and by 11.3% of birthweight on the fifth day. A significant increase in creatinine clearance occurred after the third day (p < .01), while free water clearance remained essentially the same during the first five days of life. We speculate that an increase in plasma hANP concentration on day 3 of life results in a natriuresis and osmolar diuresis without correlations or temporal relationships to hypervasopressinemia of the premature neonate with RDS.

Protection from hypoxemic renal dysfunction by verapamil and manganese in the rabbit

The ability of calcium channel blockers to prevent and/or to reverse the hypoxemia-induced renal dysfunction was studied in anesthetized and mechanically-ventilated rabbits. Renal blood flow (RBF) and glomerular filtration rate (GFR) were determined by para-aminohippuric acid and inulin clearance, respectively. Each animal was considered as its own control. In 9 rabbits (group 1), verapamil infusion, 1 microgram.kg-1.min-1, did not change basal renal hemodynamics. In a second group (n = 9), hypoxemia induced marked significant decreases in GFR, RBF and urine flow rate (-22 +/- 5%, -18 +/- 6% and -34 +/- 7% respectively). The administration of verapamil partially reversed the hypoxemia-induced renal dysfunction. Likewise, hypoxemia did not induce any change in renal function in verapamil pretreated rabbits (n = 8). This study shows that verapamil is able to prevent and to partially reverse the adverse effects of hypoxemia on renal hemodynamics. The intrarenal infusion of manganese chloride, another calcium channel blocker, was also effective in blunting the hypoxemia-induced changes in the left infused kidney, but not in the contralateral kidney. The overall results demonstrate that a significant protection from hypoxemic renal dysfunction can be achieved by inhibitors of calcium ion transport.

Renal impairment in very low birthweight infants following antenatal indomethacin administration

Three cases of neonatal renal insufficiency in very low birthweight (VLBW) infants following repeated antenatal administration of indomethacin to prevent premature labor are reported. Three pregnant women received indomethacin (total doses of 150-850 mg) for 3-14 days from admission until delivery. The gestational ages and birthweights of the infants ranged from 24 to 28 weeks and 612 to 1432 g, respectively. Oliguria, early onset of hyperkalemia and prolonged renal dysfunction occurred after birth. Renal failure did not improve in one infant. Despite the efficacy of indomethacin for tocolysis in premature labor, VLBW infants born after repeated maternal administration near the time of delivery may have developed impairment of the premature kidney.

Clinical pharmacokinetics of amikacin in hypoxic premature foals

The pharmacokinetics of amikacin, administered iv at 7 mg/kg, every 8 h, were evaluated over the first 48 h of hospitalisation in 7 critically ill hypoxic premature foals and compared with those in 8 full-term nonhypoxic critically ill neonatal foals. The pharmacokinetic data were used to calculate dosage schedules that would maintain the plasma amikacin concentrations in individual foals within a target range of > or = 15 micrograms/ml but < 30 micrograms/ml for peak values and < or = 3 micrograms/ml for trough values. The results indicated a statistically significant increase in the amikacin serum half-life (5.39 +/- 3.46 h) and smaller elimination rate constant (0.17 +/- 0.09 h-1) in premature foals. The pharmacokinetic derangements required increasing the dose to 8.5-10.5 mg/kg bwt in 6 of 7 premature foals and an increase in the dosage interval to 12-24 h in all 7 foals. Overall, the total dosage of amikacin was decreased in the hypoxic, premature foals so that target peaks and troughs could be maintained. Our findings suggest that prematurity and hypoxia are variables related to a prolonged serum half-life of amikacin in hypoxic, premature foals. Although there was no evidence of amikacin-induced nephrotoxicity in any of these foals, daily monitoring and tailoring of the dose schedule to the individual foal are strongly advised.

Effects of hypoxia and azotaemia on the pharmacokinetics of amikacin in neonatal foals

The effects of hypoxia and azotaemia on the pharmacokinetics of amikacin were evaluated in 20 full-term neonatal critically ill foals which required 24-h supportive care, antibiotics and dextrose-supplemented polyionic fluids given intravenously, nasal insufflation with oxygen and nutritional supplementation. There was no association between sepsis score or survival and pharmacokinetic parameters. Concurrent hypoxia and azotaemia were associated with significantly decreased clearance and increased peak and trough serum concentrations of amikacin; however, peaks or troughs did not exceed toxic values. Derangements in serum peak, trough and clearance values, which were present on admission, persisted over the 6-day duration of this study. Daily monitoring of serum amikacin concentration revealed a tendency to underdose (particularly in foals receiving aggressive fluid therapy), which necessitated increasing the dose/kg body weight (9-12 mg/kg) and increasing the dose interval (10-12 h) in 40% (8/20) of the cases, so that blood concentrations of amikacin could be maintained within the target range of 3-15 micrograms/ml. Amikacin-induced nephrotoxicity was not indicated by conventional laboratory testing, nor was it strongly suspected after examination of post mortem lesions.

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.

Salbutamol infusion to treat neonatal hyperkalaemia

Salbutamol infusion, 4 micrograms/kg in 5 ml of water infused for 20 minutes, was given to treat hyperkalaemia (potassium level > 6.0 mmol/l) in 10 critically ill preterm infants (median gestational age 26 weeks). Seven infants had acute renal failure, two had persistent metabolic acidosis without renal failure and the remaining infant had a combination of acute renal failure and persistent metabolic acidosis. No infant developed a tachycardia or became hyperglycaemic in response to the infusion. Seven of the 10 infants ultimately died but this was at a mean of 9 days following the infusion and as a consequence of complications due to their extreme prematurity or major congenital abnormality. In response to the infusion the potassium level fell in 7 infants with acute renal failure by a median of 1.1 mmol/l (range 0.7-1.8) at one hour but in the three infants with a persistent metabolic acidosis, the potassium level continued to rise. We conclude that salbutamol infusion achieves, without side-effects, at least a temporary reduction in hyperkalaemia in preterm infants with renal failure, but not metabolic acidosis. Its effect is of sufficient duration to allow ample time for definitive therapy to be instituted and thus may be a useful alternative for infants in whom the possible hypoglycaemic side-effects of glucose and insulin should be avoided.

Vasoactive factors in the immature kidney

The newborn infant is in a state of renal insufficiency with a glomerular filtration rate (GFR) as low as 20 ml/min per 1.73 m2 at term, and 10 ml/min per 1.73 m2 at 28 weeks of gestation. While the immature "insufficient" kidney can cope with most of the normal demands, its reserve is limited, and often overwhelmed by commonly occurring neonatal stresses. Various vasoactive systems such as the renin-angiotensin system, intrarenal adenosine, the prostaglandins and the atrial natriuretic peptide, are hyperactive in the neonatal period. Some of these systems appear crucial for the maintenance of GFR. Overstimulation of both angiotensin II and adenosine by an hypoxaemic stress can further impair the GFR, eventually leading to established renal failure. Inhibition of angiotensin II formation by the administration of angiotensin converting enzyme inhibitors can, on the other hand, also lead to renal failure. Prevention of these renal risks requires a precise knowledge of the newborn kidney physiology, physiopathology and pharmacology.

Special needs of the newborn infant in fluid therapy

The preterm baby, although less able to tolerate high fluid and solute loads, has a remarkable ability to adapt to a rather broad range of environmental challenges, and thus renal function in the preterm infant should no longer be considered impaired. Lower rather than higher fluid administration is the current trend in neonatal care because it is safer and more physiologic. Although changes in body weight over time provide a good indicator of water balance, determination of plasma and urine electrolytes and tonicity are also essential in the monitoring of fluid therapy in preterm infants.

The influence of postnatal respiratory adaptation on sodium handling in preterm neonates

The relationship between sodium handling and alveolar-arterial oxygen gradient (AaDO2) was studied in 26 preterm babies requiring ventilation from birth. The difference between sodium intake and urinary sodium excretion was determined in sequential, four hourly periods throughout the course of the respiratory illness. Sodium retention changed from positive (mean 1.42 mmol kg-1 day-1) during the phase of deteriorating respiratory function to negative (mean - 1.99 mmol kg-1 day-1) during improving respiratory function. This difference is highly significant (P less than 0.001). A temporal relationship is also shown, in the form of individual time plots of AaDO2 and sodium retention for each baby; changes in sodium handling parallel changes in AaDO2. The diuresis that accompanies improving respiratory function is characterised as a natriuresis, with free water clearance remaining unchanged before and after the point of improvement. We suggest that a primary change in sodium handling, triggered by postnatal respiratory adaptation, may initiate the contraction in extracellular fluid volume that characterises early postnatal existence.

Pharmacokinetics of amikacin in critically ill neonatal foals treated for presumed or confirmed sepsis

Fourteen foals less than four days of age were treated with the aminoglycoside, amikacin sulphate, and either penicillin or ampicillin for septicaemia, pneumonia, and/or failure of passive immunoglobulin transfer. Serum amikacin concentrations were determined at three times during an 8 or 12 h dosing interval. A 7.0 mg/kg bodyweight dose of amikacin every 8 h was appropriate. Prematurity did not influence mortality. All seven premature foals survived, whereas four of the seven full term foals died. Uraemia in three foals was caused by urinary bladder rupture; amikacin-induced nephrotoxicity was not recognised by clinical chemistries (elevations in serum creatinine or blood urea nitrogen concentrations) or post-mortem findings.

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)

Fetal renal failure associated with intrauterine growth retardation

Four preterm infants with severe intrauterine growth retardation had renal failure from birth. The amount of asphyxia associated with the birth process did not fully explain the renal failure. Before delivery all for fetuses had severe oligohydramnios and an empty urinary bladder. These observations strengthen the view that severe intrauterine growth retardation may be accompanied by oligohydramnios caused by fetal renal failure.

Treatment of renal failure in neonates

Thirty neonates with acute renal failure were studied, 27 of whom died (90%) including nine of 12 treated by peritoneal dialysis. Three main aetiological groups were identified. Septicaemia was a principal cause of late onset acute renal failure, with an incidence equal to that of serious perinatal disorders. It is recommended that tolazoline should be used with caution in the treatment of hyperkalaemia as it may have a role in the aetiology of acute renal failure, the incidence of which is increasing.

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.

Theophylline prevents the hypoxemia-induced renal hemodynamic changes in rabbits

The acute renal effects of hypoxemia and the ability of theophylline to prevent these effects were assessed in anesthetized and mechanically-ventilated newborn and adult rabbits. Renal blood flow (RBF) and glomerular filtration rate (GFR) were determined by the clearance of para-aminohippuric acid and inulin, respectively. Each animal acted as his own control. In 14 newborn rabbits (group 1), hypoxemia was significantly associated with a fall in GFR (-22 +/- 6%) and filtration fraction (-17 +/- 3%) and with an increase in renal vascular resistance (+13 +/- 6%). Hypoxemia also induced a significant decline in GFR (-27 +/- 6%) and RBF (-29 +/- 6%) in 7 adult rabbits (group 3). Intravenous theophylline (0.5 mg/kg) completely prevented the hypoxemia-induced changes in GFR, filtration fraction (FF) and renal vascular resistance (RVR) in 8 newborn rabbits (group 2). An intravenous dose of 2.4 mg theophylline given after the induction of hypoxemia partially reversed the drop in GFR in adult rabbits (group 3). Separate renal functions were studied in 8 additional adult rabbits (group 4). Low-dose theophylline (27 micrograms/min) infused intra-arterially in the left kidney partially prevented the hypoxemia-induced decline in urine flow rate, GFR, RBF, FF as well as the increase in renal vascular resistance. The beneficial effects of theophylline could be mediated by its adenosine antagonistic properties.

Magnesium therapy in premature neonates with apnea neonatorum

Apnea, bradycardia, and neuromuscular hyperirritability have been associated with magnesium (Mg) deficiency in young human infants and weanling animals. This is a retrospective review of a clinical experience of Mg therapy among 200 premature neonates who showed physical and clinical chemical changes compatible with Mg deficiency. The 200 infants all had idiopathic apnea neonatorum, and 93% also had the respiratory distress syndrome (RDS). This review was conducted to learn whether Mg therapy was associated with a significant reduction in apnea. The author suggested that the dose of Mg be 0.4 mEq/kg body weight/day, as 50% MgSO4.7H2O intramuscularly (IM) for 5 days; or as 1.0 mEq/kg/day, as 10% MgCl2.6H2O by mouth for 2 or more weeks, with appropriate monitoring of plasma Mg values in all infants. Sixty-one infants received a minimum of 5 days of Mg by either route (mean, 11.4 +/- 0.9, Group A); five received 3-4 doses IM (mean, 3.6 +/- 0.2, Group B); and 134 received 0-2 doses IM (0.5 +/- 0.1, Group C). Group A infants Mg-treated before Day 20 showed earlier cessation of apnea and bradycardia than those treated after Day 20. In Group A patients, 7 dose-days [corrected] of Mg therapy was associated with continuation of apnea; 14 dose-days [corrected], with cessation of apnea. Compared with Group A, Group C continued to develop apnea (P less than .003) and bradycardia (P less than 0.03) over longer periods of time. Group A infants showed no record of death or of hospital readmission for recurrent apnea, while 32 of 134 Group C infants had one or both of those unfavorable outcomes (P less than 0.001), with four of the five deaths in Group C (NS) as the sudden infant death syndrome (SIDS). In conclusion, Mg was associated with a reduction of apnea in this population. Emphasis was placed on the need to closely observe infants receiving supplementary Mg, with monitoring of plasma Mg levels.

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.

Hyperkalaemia, cardiac arrhythmias, and cerebral lesions in high risk neonates

The case notes of 20 infants with hyperkalaemia (defined as two successive serum potassium measurements of greater than 7.5 mmol/l) were reviewed. The incidence of hyperkalaemia was also looked at in an unselected population of 200 low birthweight infants. The mean gestational age of the 20 affected infants was 29 weeks and the mean birth weight 1235 g. The incidence of hyperkalemia in the cohort of 200 infants weighing less than 1500 g at birth was 3.5%. Hyperkalaemia was associated with a high incidence of cardiac arrhythmia (60%), impaired renal function (50%), and changes on cerebral ultrasonography (88%). Hyperkalaemia responds slowly to conventional treatment with dextrose, insulin, and exchange resins. There is a close temporal relation in some infants between hyperkalaemia and cardiac arrhythmias and periventricular leukomalacia, suggesting a causal association.

Acute oliguria in preterm infants with hyaline membrane disease: interaction of dopamine and furosemide

Ten premature infants with hyaline membrane disease and with acute oliguria were treated with furosemide or furosemide and dopamine. Furosemide alone did not increase diuresis. Furosemide when combined with dopamine, however, caused significant increases in urine output, sodium excretion, fractional sodium excretion and creatinine clearance. These data suggest that the increase in the sodium excretion was due not only to a reduction in the tubular sodium reabsorption but also to an increase in the glomerular filtration rate. Since in premature neonates the creatinine clearance is not a very precise index of the glomerular filtration rate, the extent of contribution of the increase in the glomerular filtration rate to the enhanced sodium excretion cannot be determined. Despite the increase in the sodium excretion, the serum sodium concentration did not fall significantly. We conclude that the combined treatment with dopamine and furosemide is useful for treating furosemide-resistant, severe functional renal failure in preterm infants with hyaline membrane disease.

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.

Renal response to frusemide in preterm infants with respiratory distress syndrome during the first three postnatal days

The renal effects of frusemide treatment in infants with respiratory distress syndrome shortly after birth and during the first three postnatal days were evaluated. Eighty five infants were randomly assigned to two groups. Forty two received three doses of intravenous frusemide (1 mg/kg) starting at age, mean (SD) 7.5 (4.1) hours and given at approximately 24 hour intervals. Forty three control infants were treated similarly but were not given frusemide. The groups were comparable in birthweight, gestational age, and Apgar score and in pulmonary status, blood gases, serum electrolytes, and postnatal age. Infants who received frusemide had significantly higher fractional excretion of sodium and chloride at 12 to 24, 24 to 48, and 48 to 72 hours, and higher calcium excretion at 24 to 48 and 48 to 72 hours after entry into the study than control infants. The study group had a significantly higher urine output and greater weight loss than the control group at 48 to 72 hours after entry into the study. There was no significant difference between groups in serum sodium, potassium, and calcium and in fractional excretion of potassium and the glomerular filtration rate. Infants with an Apgar score of more than 3 had higher urine output and had a better diuretic response to frusemide than those with a lower score. The results suggest that perinatal hypoxia may play an important role in renal function and in diuretic response to frusemide shortly after birth and early in the postnatal life of infants with respiratory distress syndrome.

Alimentary absorption of gentamicin in preterm infants

Fifty-two preterm neonates receiving oral gentamicin from birth, as prophylaxis against necrotizing enterocolitis (NEC), had serum gentamicin levels measured on the second day of life (52 infants) and on the seventh to tenth days (43 infants). The serum gentamicin concentrations on the second day were 0.5 microgram/ml or less in 21 percent, 0.6 to 1.0 microgram/ml in 15 percent, 1.1 to 2 micrograms/ml in 34 percent, 2.1 to 5 micrograms/ml in 25 percent, and 5 to 7.1 micrograms/ml in 4 percent of the infants. Paired serum gentamicin levels were significantly lower (p less than 0.001) on the seventh to tenth day as compared to the second day. We conclude that preterm infants in the first few days of life absorb orally administered gentamicin. Concomitant use of systemic gentamicin under such circumstances may potentially lead to toxic serum gentamicin concentration.

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.