Current Pediatric Reviews - Volume 10, Issue 2, 2014

Survival of critically ill neonates in the intensive care unit has improved over the past decades reflecting improvements in obstetric, delivery room and neonatal intensive care, however, morbidity remains significant. Acute kidney injury is a common occurrence in these neonates and despite improved understanding of the pathophysiology and management of acute kidney injury in full term and preterm infants, the mortality remains as high as 61%. Furthermore, there is growing evidence that despite recovery from the acute injury, these infants are at risk for developing hypertension and chronic kidney disease later in life. Emphasis on improving our capability to detect renal insult and injury early, before renal failure occurs, and identification of novel therapeutic agents to prevent and treat acute kidney injury may impact mortality and morbidity. This review focuses on our current knowledge of acute kidney injury in the newborn, approaches to investigating and managing this complication and what future trends in this field may bring.

Genetic disorders of the kidney include cystic diseases, metabolic diseases and immune glomerulonephritis. Cystic diseases include autosomal dominant and recessive polycystic kidney disease (ADPKD, ARPKD, respectively). Neonates with enlarged, cystic kidneys should be evaluated for PKD. Patients with ADPKD have cysts and renal enlargement. Most patients present with hypertension, hematuria or flank pain; the most common extrarenal manifestation is polycystic liver disease. Oligohydramnios, bilaterally enlarged kidneys and decreased urine are featured in utero in ARPKD. Medullary sponge kidney is uncommon and features nephrocalcinosis, recurrent calcium stones and a history of polyuria/nocturia and/or urinary tract infections. Alport syndrome (AS) is an inherited disease of the glomerular basement membrane that is usually inherited as an X-linked dominant trait. Most patients with AS present in the first two decades of life with persistent microscopic or gross hematuria. Later, proteinuria is seen and its presence portends disease progression. Other findings may include sensorineural hearing loss and ocular abnormalities. There are various inherited tubulopathies, including Bartter syndrome, a group of renal tubular disorders that consist of two phenotypes with four genotypes. Patients usually present early in life with salt wasting, hypokalemia and metabolic alkalosis. Other features, depending on genotype, may include polyhydramnios and premature birth. Gitelman syndrome is also a salt-losing tubulopathy characterized by hypokalemic alkalosis. The majority of patients with Gitelman syndrome present during adolescence or early adulthood.

Neonatal renal vein thrombosis (RVT) is associated with potentially serious morbidities. Almost 80% of cases of RVT present within the first postnatal month. The most common risk factors for RVT are birth asphyxia/ in utero fetal distress, being the infant of a diabetic mother, volume contraction and coagulation abnormalities. Thrombus formation may be initiated by vascular injury, diminished vascular flow, increased blood viscosity, hyperosmolality or underlying thrombophilia. The classic triad of RVT includes gross hematuria, flank mass (unilateral or bilateral enlargement of kidneys) and thrombocytopenia. Laboratory tests may reveal hematuria, proteinuria, polycythemia, hemolytic anemia, thrombocytopenia and possibly acute kidney injury. The etiology for a hypercoagulable state should be investigated. Renal ultrasound with Doppler may show increased size of the affected kidney, increased echogenicity and loss of corticomedullary differentiation. Renal venography remains the gold standard for the diagnosis of RVT. Other causes of renal enlargement must be considered. Supportive treatment includes correction of fluid and electrolyte disturbances and treatment of infection and underlying pathophysiologic abnormalities. Use of unfractionated heparin (UFH) or low molecular weight heparin (LMWH) should be considered if there is evidence of disseminated intravascular coagulation. Conventional anticoagulants may attenuate hypercoagulability and decrease the risk for thrombus progression and embolism. Surgery is rarely indicated unless there is bilateral involvement with involvement of the IVC. RVT carries the risk of hypertension and chronic kidney disease.

Renal development begins in-utero and continues throughout childhood. Almost one-third of all developmental anomalies include structural or functional abnormalities of the urinary tract. There are three main phases of in-utero renal development: Pronephros, Mesonephros and Metanephros. Within three weeks of gestation, paired pronephri appear. A series of tubules called nephrotomes fuse with the pronephric duct. The pronephros elongates and induces the nearby mesoderm, forming the mesonephric (Woffian) duct. The metanephros is the precursor of the mature kidney that originates from the ureteric bud and the metanephric mesoderm (blastema) by 5 weeks of gestation. The interaction between these two components is a reciprocal process, resulting in the formation of a mature kidney. The ureteric bud forms the major and minor calyces, and the collecting tubules while the metanephrogenic blastema develops into the renal tubules and glomeruli. In humans, all of the nephrons are formed by 32 to 36 weeks of gestation. Simultaneously, the lower urinary tract develops from the vesico urethral canal, ureteric bud and mesonephric duct. In utero, ureters deliver urine from the kidney to the bladder, thereby creating amniotic fluid. Transcription factors, extracellular matrix glycoproteins, signaling molecules and receptors are the key players in normal renal development. Many medications (e.g., aminoglycosides, cyclooxygenase inhibitors, substances that affect the renin-angiotensin aldosterone system) also impact renal development by altering the expression of growth factors, matrix regulators or receptors. Thus, tight regulation and coordinated processes are crucial for normal renal development.

Tubular development continues after birth in full and pre-term infants. As the survival of premature infants increases, serious imbalances in water and electrolytes in this group have become more prevalent. A diminished ability of the immature kidney to reabsorb water and respond to mineralocorticoids, a high excretion of filtered sodium, perinatal complications affecting tubular function, and the use of medications such as diuretics, indomethacin and amphotericin B, are common factors leading to sodium and potassium imbalances in this age group. Appropriate diagnosis and treatment should be guided by a careful assessment of volume status, urine electrolytes and osmolality.

The upper urinary tract forms as a consequence of the reciprocal inductive signals between the metanephric mesenchyme and ureteric bud. A clue to the timing of events leading to an abnormality of the upper urinary tract can be the presence also of associated anomalies of internal genitalia since separation of these systems occurs at about the 10th week of gestation. Prenatal sonography has facilitated the detection of urological abnormalities presenting with hydronephrosis. Hydronephrosis suggests obstruction, but by itself cannot be equated with it. Instead, further radiographic imaging is required to delineate anatomy and function. Now, moreover, non-surgical management of CAKUT should be considered whenever possible. Despite the widespread use of prenatal screening sonography that usually identifies the majority of congenital anomalies of the urinary tract, many children still present with febrile urinary tract infection (UTI). Regardless of the etiology for the presentation, the goal of management is preservation of renal function through mitigation of the risk for recurrent UTI and/or obstruction. In the past many children underwent surgical repair aimed at normalization of the appearance of the urinary tract. Today, management has evolved such that in most cases surgical reconstruction is performed only after a period of observation - with or without urinary prophylaxis. The opinions presented in this section are not espoused by all pediatric urologists but represent instead the practice that has evolved at Children’s National Medical Center (Washington DC) based significantly on information obtained by nuclear renography, in addition to sonography and contrast cystography.

Disorders of calcium and phosphorus homeostasis present both acute and chronic clinical consequences for newborns. The etiologies responsible range from iatrogenic, idiopathic, and inherited metabolic abnormalities. Maintenance of physiologically normal serum calcium and phosphorus requires complex interactions between the kidneys, gastrointestinal tract, and bone. Calciotropic hormones such as vitamin D and parathyroid hormone, as well as hormones controlling phosphorus homeostasis, such as fibroblast growth factor-23 (FGF-23), are essential in controlling these interactions. In newborns, calcium and phosphorus balance must necessarily be positive in order to provide the requisite building blocks for growth and maturation. Renal tubular handling of these minerals is a key control point in regulating the overall body balance in calcium and phosphorus. Adaptive changes in renal calcium and phosphorus reabsorption in newborns explain how a net positive total body balance of these minerals is achieved. Monogenetic disorders leading to abnormal renal handling of calcium and/or phosphorus have immediate clinical consequences in terms of complications associated with high or low levels of these minerals. Perhaps more importantly, chronic abnormalities of calcium and/or phosphorus, without treatment, may have serious consequences for growth and development of the growing skeleton. This article serves to review calcium and phosphorus regulation in the human body, describe differences in handling of these minerals by the newborn, and review the conditions, both acquired and congenital, that may present with abnormalities in calcium and/or phosphorus in the newborn period.

At birth, GFR and tubular function of neonates is compromised as compared to older children and adults. These functions are even less developed in premature infants. These facts have a direct bearing on drug dosing, fluid and electrolyte administration, and maintenance of acid-base balance in neonates. Although many detailed methods of assessing renal functions have been provided in this article, laboratory and radiologic studies available in most healthcare facilities are often sufficient to provide a clinically relevant data in most patients, including neonates.

Nonalcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease in children and adolescents in the United States. It is strongly associated with childhood obesity, insulin resistance and metabolic syndrome. Although some children with NAFLD may remain asymptomatic, progression to nonalcoholic steatohepatitis (NASH), and to advanced stages of fibrosis and cirrhosis is well recognized. Unfortunately, despite the increase in awareness of this disease, there are still no reliable non-invasive diagnostic tests and liver biopsy remains the gold standard for the diagnosis of NASH and staging of fibrosis. In addition, there are no approved pharmacological treatments currently. Lifestyle modification remains the cornerstone of treatment. Team based multidisciplinary approach involving hepatologists, endocrinologists, exercise physiologist, dieticians, and cardiologists may lead to better outcomes. Recently, the American Association for the Study of Liver Diseases (AASLD) and European Society for Pediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) committees have made recommendations for the diagnosis and management of NAFLD in pediatric patients. This review focuses on current literature on epidemiology, natural history, pathogenesis along with summarizing the recent guidelines on diagnosis and treatment of pediatric NAFLD.

Surfactant replacement therapy is now the standard of care for infants with respiratory distress syndrome. As the understanding of surfactant structure and function has evolved, surfactant-associated proteins are now understood to be essential components of pulmonary surfactant. Their structural and functional diversity detail the complexity of their contributions to normal pulmonary physiology, and deficiency states result in significant pathology. Engineering synthetic surfactant protein constructs has been a major research focus for replacement therapies. This review highlights what is known about surfactant proteins and how this knowledge is pivotal for future advancements in treating respiratory distress syndrome as well as other pulmonary diseases characterized by surfactant deficiency or inactivation.