Acute Kidney Injury (Renal Failure) in Children

Topic Name Introduction Etiology Pathophysiology Clinical Presentation Diagnosis Management Prognosis Prevention

Introduction to Acute Kidney Injury in Children

Acute Kidney Injury (AKI), previously known as acute renal failure, is a sudden decrease in kidney function resulting in the inability to maintain fluid, electrolyte, and acid-base homeostasis. In pediatric populations, AKI is a significant cause of morbidity and mortality, particularly in critically ill children.

Key points:

• AKI in children is defined as an abrupt decrease in kidney function, manifesting as a reduction in glomerular filtration rate (GFR).
• The incidence of AKI in hospitalized children ranges from 5% to 35%, with higher rates in intensive care settings.
• Early recognition and management are crucial for improving outcomes and preventing long-term renal complications.
• The etiology and management of AKI in children can differ significantly from adults due to developmental differences and underlying causes.

Etiology of Acute Kidney Injury in Children

The causes of AKI in children can be categorized into three main groups:

1. Prerenal AKI (55-60% of cases):
   • Dehydration (most common cause in children)
   • Sepsis
   • Cardiac failure
   • Hepatorenal syndrome
2. Intrinsic Renal AKI (35-40% of cases):
   • Acute tubular necrosis (ATN)
   • Glomerulonephritis
   • Hemolytic uremic syndrome (HUS)
   • Interstitial nephritis
   • Tumor lysis syndrome
3. Postrenal AKI (5-10% of cases):
   • Urinary tract obstruction
   • Posterior urethral valves
   • Neurogenic bladder

Age-specific considerations:

• Neonates: Perinatal asphyxia, sepsis, congenital abnormalities
• Infants: Dehydration, sepsis, congenital heart disease
• Older children: Post-infectious glomerulonephritis, HUS, nephrotic syndrome

Pathophysiology of Acute Kidney Injury in Children

The pathophysiology of AKI involves complex mechanisms that lead to a rapid decline in renal function:

1. Altered Renal Hemodynamics:
   • Decreased renal blood flow leads to reduced glomerular filtration rate (GFR)
   • Activation of the renin-angiotensin-aldosterone system (RAAS) and sympathetic nervous system
2. Tubular Injury:
   • Ischemia or toxins cause direct damage to tubular epithelial cells
   • Loss of brush border, cell swelling, and apoptosis or necrosis
3. Inflammation and Oxidative Stress:
   • Release of pro-inflammatory cytokines and chemokines
   • Infiltration of inflammatory cells into the kidney
   • Generation of reactive oxygen species (ROS)
4. Microvascular Dysfunction:
   • Endothelial injury and dysfunction
   • Disruption of normal microvascular blood flow
5. Metabolic Alterations:
   • Impaired acid-base balance
   • Electrolyte disturbances (hyperkalemia, hyponatremia)
   • Uremia and accumulation of toxic metabolites

These pathophysiological changes result in a rapid decline in GFR, leading to the clinical manifestations of AKI. The severity and duration of the insult determine the extent of kidney damage and the potential for recovery.

Clinical Presentation of Acute Kidney Injury in Children

The clinical presentation of AKI in children can vary widely depending on the underlying cause, severity, and rate of onset. Common signs and symptoms include:

• General symptoms:
  • Fatigue and weakness
  • Decreased urine output (oliguria or anuria)
  • Edema (particularly facial and peripheral)
  • Nausea and vomiting
• Cardiovascular:
  • Hypertension
  • Tachycardia
  • Signs of fluid overload (in severe cases)
• Respiratory:
  • Tachypnea
  • Dyspnea (in cases of fluid overload)
• Neurological:
  • Altered mental status
  • Seizures (in severe cases or with electrolyte imbalances)
• Gastrointestinal:
  • Abdominal pain
  • Decreased appetite

Key clinical features by age group:

• Neonates: Poor feeding, lethargy, jaundice
• Infants: Irritability, poor weight gain, vomiting
• Older children: Headache, fatigue, decreased urine output

It's important to note that some children, especially in the early stages of AKI, may be asymptomatic, and the condition may only be detected through laboratory investigations.

Diagnosis of Acute Kidney Injury in Children

Diagnosis of AKI in children involves a combination of clinical assessment, laboratory tests, and imaging studies:

1. Clinical Assessment:
   • Detailed history and physical examination
   • Evaluation of fluid status and urine output
2. Laboratory Tests:
   • Serum creatinine and blood urea nitrogen (BUN)
   • Electrolytes (sodium, potassium, calcium, phosphate)
   • Complete blood count (CBC)
   • Urinalysis and urine microscopy
   • Urine output measurement
3. Diagnostic Criteria:

   The Kidney Disease: Improving Global Outcomes (KDIGO) criteria for pediatric AKI:

   • Increase in serum creatinine by ≥0.3 mg/dL within 48 hours; or
   • Increase in serum creatinine to ≥1.5 times baseline, which is known or presumed to have occurred within the prior 7 days; or
   • Urine volume <0.5 mL/kg/h for 6 hours
4. Imaging Studies:
   • Renal ultrasound: To assess kidney size, echogenicity, and detect obstruction
   • Doppler studies: To evaluate renal blood flow
   • CT or MRI: In specific cases to further evaluate structural abnormalities
5. Additional Tests (as indicated):
   • Complement levels (C3, C4)
   • Antinuclear antibodies (ANA)
   • Anti-streptolysin O (ASO) titers
   • Renal biopsy (in select cases)

Differential Diagnosis:

• Chronic kidney disease
• Urinary tract infection
• Nephrotic syndrome
• Hemolytic uremic syndrome
• Congenital renal anomalies

Early and accurate diagnosis is crucial for appropriate management and improved outcomes in pediatric AKI.

Management of Acute Kidney Injury in Children

The management of AKI in children focuses on addressing the underlying cause, supporting kidney function, and preventing complications. The approach includes:

1. Supportive Care:
   • Fluid and electrolyte management
   • Nutritional support
   • Blood pressure control
2. Specific Interventions:
   • Treatment of underlying cause (e.g., antibiotics for sepsis)
   • Correction of electrolyte imbalances
   • Management of acidosis
3. Pharmacological Management:
   • Diuretics (in cases of fluid overload)
   • Antihypertensive medications (if needed)
   • Avoid nephrotoxic medications
4. Renal Replacement Therapy (RRT):

   Indications for RRT in pediatric AKI:

   • Severe fluid overload unresponsive to diuretics
   • Refractory electrolyte abnormalities
   • Severe metabolic acidosis
   • Uremic complications

   RRT modalities:

   • Peritoneal dialysis
   • Intermittent hemodialysis
   • Continuous renal replacement therapy (CRRT)
5. Monitoring and Follow-up:
   • Regular assessment of fluid status
   • Daily weight measurements
   • Frequent monitoring of electrolytes and renal function
   • Continuous assessment for complications

Special Considerations in Pediatric AKI Management:

• Medication dosing adjustments based on renal function
• Attention to growth and development
• Psychological support for the child and family
• Long-term follow-up to monitor for chronic kidney disease

The management of AKI in children requires a multidisciplinary approach involving pediatric nephrologists, intensivists, and other specialists as needed.

Prognosis of Acute Kidney Injury in Children

The prognosis of AKI in children varies depending on the underlying cause, severity, and management. Key points include:

• Short-term Outcomes:
  • Mortality rates range from 3-5% in general pediatric populations to 10-30% in critically ill children
  • Complete recovery of renal function occurs in 40-70% of cases
  • Partial recovery or progression to chronic kidney disease (CKD) in 30-60% of cases
• Long-term Outcomes:
  • Risk of developing CKD: 10-20% within 1-3 years post-AKI
  • Increased risk of hypertension and proteinuria
  • Potential impact on growth and development
• Prognostic Factors:
  • Severity and duration of AKI
  • Underlying cause (better prognosis for prerenal causes)
  • Presence of multi-organ dysfunction
  • Need for renal replacement therapy
  • Age (younger children may have better outcomes)
• Follow-up and Monitoring:
  • Regular assessment of renal function (at least annually)
  • Monitoring of blood pressure and proteinuria
  • Evaluation of growth and development
  • Early intervention for emerging complications

Potential Long-term Complications:

• Chronic kidney disease
• Hypertension
• Proteinuria
• Cardiovascular complications
• Growth impairment
• Neurocognitive deficits

It's important to note that even children who appear to have fully recovered from AKI may be at increased risk for long-term renal and cardiovascular complications. Therefore, long-term follow-up is essential for all children who have experienced AKI, regardless of the apparent severity or resolution of the initial episode.

Prevention of Acute Kidney Injury in Children

Prevention of AKI in children involves a multifaceted approach focusing on risk reduction and early intervention:

1. Risk Assessment:
   • Identify high-risk patients (e.g., critically ill, post-surgical, or those with underlying renal conditions)
   • Regular monitoring of renal function in at-risk children
2. Maintaining Adequate Renal Perfusion:
   • Ensure proper hydration
   • Maintain appropriate blood pressure
   • Optimize cardiac output in critically ill children
3. Medication Management:
   • Avoid or minimize use of nephrotoxic drugs when possible
   • Adjust medication dosages based on renal function
   • Monitor drug levels for medications with narrow therapeutic indices
4. Infection Prevention:
   • Implement proper infection control measures
   • Prompt treatment of infections to prevent sepsis-induced AKI
5. Contrast-Induced AKI Prevention:
   • Use contrast-sparing imaging techniques when possible
   • Ensure adequate hydration before and after contrast administration
   • Consider N-acetylcysteine in high-risk patients (though evidence is mixed)
6. Nutritional Support:
   • Maintain adequate nutrition to support renal function and overall health
   • Monitor and supplement electrolytes as needed
7. Education and Awareness:
   • Train healthcare providers in early recognition and management of AKI
   • Educate families of at-risk children about signs and symptoms of AKI

Special Considerations in Pediatric AKI Prevention:

• Age-specific risk factors (e.g., congenital anomalies in neonates)
• Tailored fluid management based on age and underlying conditions
• Vigilant monitoring in children with chronic illnesses predisposing to AKI

Implementing these preventive strategies can significantly reduce the incidence and severity of AKI in pediatric populations, leading to improved outcomes and reduced long-term complications.

Acute Kidney Injury (Renal Failure) in Children

1. What is the definition of Acute Kidney Injury (AKI) in children? Abrupt decrease in kidney function leading to accumulation of waste products and fluid imbalance
2. What are the three main categories of AKI causes? Prerenal, intrinsic renal, and postrenal
3. What is the most common cause of AKI in hospitalized children? Prerenal azotemia due to volume depletion
4. How is AKI staged using the pRIFLE criteria? Risk, Injury, Failure, Loss, and End-stage renal disease
5. What percentage increase in serum creatinine defines the "Risk" stage in pRIFLE criteria? 50% increase
6. What is the most common cause of intrinsic AKI in children? Acute tubular necrosis (ATN)
7. Which electrolyte abnormality is most concerning in severe AKI? Hyperkalemia
8. What is the most common cause of postrenal AKI in children? Posterior urethral valves in boys
9. How does the fractional excretion of sodium (FENa) help in diagnosing AKI? FENa <1% suggests prerenal AKI; >2% suggests intrinsic renal AKI
10. What imaging study is typically first-line in evaluating AKI? Renal ultrasound
11. What is the role of urinalysis in AKI evaluation? Helps differentiate between prerenal, intrinsic, and postrenal causes
12. How does AKI affect drug dosing? May require dose adjustment or avoidance of nephrotoxic drugs
13. What is the primary goal of fluid management in AKI? Maintain euvolemia and avoid fluid overload
14. When is renal replacement therapy indicated in pediatric AKI? Severe electrolyte imbalances, fluid overload, uremia, or intoxications
15. What is the preferred method of renal replacement therapy in infants with AKI? Peritoneal dialysis
16. How does continuous renal replacement therapy (CRRT) differ from intermittent hemodialysis? CRRT provides continuous, gentler fluid and solute removal
17. What is the role of diuretics in AKI management? May help manage fluid overload but does not improve renal recovery
18. How does AKI affect nutrition requirements in children? May require protein restriction and increased caloric intake
19. What is hepatorenal syndrome? Functional renal failure in patients with advanced liver disease
20. How does rhabdomyolysis cause AKI? Release of myoglobin leads to tubular injury and obstruction
21. What is the role of renal biopsy in AKI? May be indicated in cases of unclear etiology or suspected glomerulonephritis
22. How does tumor lysis syndrome cause AKI? Release of intracellular contents leads to hyperuricemia and crystal-induced nephropathy
23. What is the prognosis for children who recover from AKI? Generally good, but 10-20% may develop chronic kidney disease
24. How does sepsis-induced AKI differ from other forms of AKI? Often multifactorial, involving inflammation and microvascular dysfunction
25. What is contrast-induced nephropathy? AKI caused by the use of iodinated contrast media in radiological procedures
26. How can contrast-induced nephropathy be prevented? Adequate hydration before and after contrast administration
27. What is the role of N-acetylcysteine in preventing contrast-induced nephropathy? Controversial, may have some protective effect but not consistently proven
28. How does cardiac surgery contribute to AKI in children? Through mechanisms such as ischemia-reperfusion injury and inflammatory responses
29. What is the significance of urine output in monitoring AKI? Oliguria or anuria may indicate worsening kidney function
30. How does AKI affect drug metabolism? May lead to drug accumulation and increased risk of toxicity
31. What is the role of novel biomarkers like NGAL in AKI diagnosis? May allow earlier detection of AKI compared to serum creatinine

Further Reading

• Acute Kidney Injury in Children: Clinical Features, Etiology, Evaluation, and Diagnosis - Pediatric Clinics of North America
• Management of Acute Kidney Injury in Children: A Guide for Pediatricians - Pediatric Research
• Acute Kidney Injury in Children - New England Journal of Medicine
• KDIGO Clinical Practice Guideline for Acute Kidney Injury - Kidney International Supplements
• Long-term Outcomes Following Acute Kidney Injury in Children - American Journal of Kidney Diseases