Unit
- Kidney development: Nephrogenesis completes by 36 weeks gestation, resulting in each kidney containing approximately one million nephrons. Premature infants have fewer nephrons, increasing vulnerability to acute kidney injury and long-term hypertension. Understanding this developmental timeline is essential for assessing renal function in neonates and young children.
- Glomerular filtration rate: GFR in newborns starts low (about 20 mL/min per 1.73 m2) and matures to adult levels by age two. Clinicians use age-adjusted formulas (e.g., Bedside Schwartz equation) to estimate GFR in children, avoiding adult-based calculations that overestimate function.
- Tubular function: The neonatal kidney has limited concentrating and diluting ability, making infants prone to dehydration and electrolyte imbalances. Tubular reabsorption of sodium and glucose matures gradually, requiring careful monitoring of fluid and electrolyte therapy in hospitalized children.
- Renal blood flow: At birth, renal blood flow is low (about 20% of cardiac output) and doubles to adult proportions (25%) by early childhood. Autoregulation mechanisms develop postnatally, but premature kidneys are more sensitive to hypoperfusion and nephrotoxic agents.
- Acid-base regulation: The immature kidney has reduced ability to excrete acid and generate bicarbonate, explaining the lower serum bicarbonate levels in healthy newborns. This physiologic state places infants at higher risk for metabolic acidosis during illness.
- Endocrine functions: The pediatric kidney produces erythropoietin and activates vitamin D, roles that are compromised in chronic kidney disease. Children with CKD often require recombinant erythropoietin and active vitamin D analogs to prevent anemia and renal osteodystrophy.
- Urine output patterns: Normal urine output varies by age: neonates produce 1-3 mL/kg/hour, while older children average 0.5-1 mL/kg/hour. Oliguria is defined as less than 1 mL/kg/hour in infants and less than 0.5 mL/kg/hour in older children, and requires prompt evaluation.
- Bladder and urethra: The bladder capacity increases from about 30 mL at birth to 350 mL in adolescence. Voiding control develops between ages two and four; persistent incontinence beyond age five warrants urologic assessment. Urethral length and diameter differences between sexes affect catheterization practices.
- Renal imaging in children: Ultrasound is the first-line imaging modality for pediatric kidneys, providing assessment of size, echogenicity, and structural anomalies without radiation. Voiding cystourethrography is used for suspected vesicoureteral reflux, while DMSA scans evaluate renal scarring. Nuclear medicine studies help assess differential renal function in obstructive uropathy.
- Hematuria and proteinuria: Hematuria in children may be transient (e.g., post-streptococcal glomerulonephritis) or persistent (e.g., IgA nephropathy). Orthostatic proteinuria is common in adolescents and benign, whereas persistent proteinuria warrants evaluation for glomerular disease. Spot urine protein-to-creatinine ratio is a convenient screening tool compared to 24-hour collection.
- Hypertension in children: Pediatric hypertension is defined by age, sex, and height percentile. Primary hypertension is increasingly recognized in older children due to obesity. Secondary causes (renal parenchymal disease, renovascular abnormalities) are more common in younger children. Ambulatory blood pressure monitoring aids diagnosis and management of white-coat hypertension.
Scope of Practice
Role: Pediatric Nephrology Nurse Coordinator
Within scope:
- Educating families on normal kidney function and expected developmental changes
- Assisting with collection of timed urine samples and documentation of intake/output
- Reinforcing provider instructions regarding fluid and electrolyte management
- Coordinating referrals to pediatric urology for structural abnormalities
Outside scope:
- Interpreting renal biopsy results or adjusting dialysis prescriptions
- Diagnosing congenital anomalies of the kidney and urinary tract without imaging confirmation
- Prescribing diuretics or antihypertensives without a provider order
- Performing ultrasound or other diagnostic procedures
Quick Revision
- Nephrogenesis is complete by 36 weeks gestation; preterm infants have reduced nephron mass.
- GFR matures over the first two years; use the Bedside Schwartz equation for children.
- Neonatal kidneys have limited concentrating ability and acid-base regulation.
- Urine output norms vary by age; oliguria requires prompt evaluation.