What is the definition of Acute Kidney Injury (AKI) in pediatric patients?

Definition of Acute Kidney Injury (AKI) in Pediatric Patients

The pediatric-modified RIFLE (pRIFLE) criteria are the standard for defining AKI in children over 1 month of age, which stages AKI based on decreases in estimated GFR (eGFR), rises in serum creatinine, or decreases in urine output. 1

pRIFLE Classification System

The pRIFLE system classifies pediatric AKI into three stages:

• Risk (Stage 1):

  • eGFR decrease by ≥25% or
  • 50-99% rise in creatinine from baseline within 7 days or
  • Urine output <0.5 ml/kg/h for more than 8 hours 1

• Injury (Stage 2):

  • eGFR decrease by ≥50% or
  • 100-199% rise in creatinine from baseline within 7 days or
  • Urine output <0.5 ml/kg/h for more than 16 hours 1

• Failure (Stage 3):

  • eGFR decrease by 75% or
  • eGFR <35 ml/min per 1.73 m² or
  • ≥200% rise in creatinine from baseline within 7 days or
  • Urine output <0.3 ml/kg/h for 24 hours or anuria for 12 hours 1

Important Considerations in Pediatric AKI Definition

Baseline Kidney Function

• If no prior creatinine is available within the previous 3 months, baseline kidney function can be imputed by assuming a normal GFR of 100 ml/min/1.73 m² and using the patient's height 1, 2
• This imputation is justified because the likelihood of a child who develops AKI having undiagnosed CKD is very low compared to adults 1

eGFR Calculation

• The revised "Bedside Schwartz equation" is recommended for calculating eGFR in children:
  • GFR (ml/min per 1.73 m²) = 0.413 × (height in cm) ÷ (creatinine in mg/dl) 1
  • Or GFR (ml/min per 1.73 m²) = 36.5 × (height in cm) ÷ (creatinine in mmol/l) 1

Special Considerations

• Small changes in serum creatinine may represent relatively large changes in actual GFR in pediatric patients 1, 2
• The pRIFLE definition has not been validated for neonates (under 1 month of age) and further research is needed before it can be recommended for this population 1
• Using eGFR with the original Schwartz formula results in a higher prevalence of AKI diagnosis compared to using changes in creatinine alone in pediatric inpatients 1

KDIGO vs. pRIFLE

• The Kidney Disease: Improving Global Outcomes (KDIGO) guidelines refer to pRIFLE for defining AKI in children 1, 2
• KDIGO criteria include:
  • Rise of ≥26 μmol/l (0.3 mg/dl) within 48 hours or
  • 50-99% rise in creatinine from baseline within 7 days 1
• There are important differences between KDIGO and pRIFLE criteria that require further validation before full adoption of KDIGO criteria into pediatric practice 2

Clinical Significance

• AKI occurs in at least 5% of all non-critically ill hospitalized children without known CKD 3
• In pediatric intensive care units, the prevalence of AKI is estimated to be 26.9% 4
• Studies show correlation between increasingly severe AKI and adverse outcomes 1
• Early detection is crucial as AKI can progress to acute kidney disease (AKD) and chronic kidney disease (CKD) 5

Practical Implications

• Accurate height measurement is necessary to calculate eGFR using the Schwartz formula, which can be challenging in sick, ventilated patients 1
• Using serum creatinine alone (without eGFR) has been validated in pediatric intensive care unit populations 1
• Enzymatic assays for creatinine measurement are preferred for pediatric populations due to the low creatinine values encountered in children 1

Understanding and applying the appropriate AKI definition in pediatric patients is essential for early detection, proper management, and improved outcomes in this vulnerable population.