What is the most common cause of Acute Kidney Injury (AKI) in critically ill children?

Most Common Cause of AKI in Critically Ill Children

Sepsis is the most common cause of acute kidney injury in critically ill children, followed by cardiac surgery and other critical illnesses requiring intensive care support. 1, 2

Primary Etiologies in Pediatric Critical Care

Sepsis as the Leading Cause

• Sepsis represents the predominant cause of AKI in the pediatric intensive care unit (PICU) setting, with studies demonstrating that sepsis-associated AKI affects a substantial proportion of critically ill children and carries significantly higher mortality rates. 1, 2
• In a recent multicenter study, sepsis-associated AKI occurred in 92% of critically ill children with sepsis, with 59.2% developing stage 3 AKI (the most severe form). 2
• The mortality rate in children with sepsis-associated AKI is substantially elevated compared to those without AKI, with longer PICU stays and worse outcomes. 2

Cardiac Surgery-Related AKI

• AKI complicates 22-36% of cardiac surgical procedures in children, making it the second most common cause in this specific population, with 11.5% developing severe AKI requiring intervention. 3, 4
• Cardiopulmonary bypass (CPB) exposure significantly increases AKI risk through hemodynamic alterations and inflammatory responses. 3
• Post-cardiac surgery AKI can be identified as early as 1 hour after CPB using urinary biomarkers. 3, 4

Other Critical Illness Contexts

• Multi-organ dysfunction syndrome frequently accompanies AKI in critically ill children, with mortality rates reaching 90.3% when multiple organ systems are affected. 1
• Mechanical ventilation requirement is associated with AKI mortality rates of 81.5%, indicating the severity of underlying illness. 1

Incidence and Impact

Overall Burden

• The incidence of AKI in critically ill children ranges from 17.2% to 40.9% depending on the population studied and diagnostic criteria used. 1, 5
• AKI affects approximately one in four critically ill children overall, with even higher rates (one in three) in neonates. 6, 7

Mortality Impact

• Mortality rates increase dramatically with AKI presence: from 58.7% in critically ill children without AKI to 73.4% in those with AKI. 1
• Higher stages of AKI (using pRIFLE or KDIGO criteria) portend progressively worse outcomes and are independently associated with mortality. 6, 5
• Children requiring renal replacement therapy have mortality rates of 71.4%. 1

Risk Stratification

High-Risk Patient Characteristics

• Younger age, particularly infants under one year, face the highest mortality risk when developing AKI in the critical care setting. 1
• Higher Pediatric Risk of Mortality (PRISM) scores at admission correlate with increased AKI risk. 1, 5
• Positive blood cultures, use of nephrotoxic medications (particularly gentamicin), and higher Sequential Organ Failure Assessment (SOFA) scores independently predict severe (stage 3) AKI. 2

Medication-Related Factors

• Nephrotoxic agents, particularly aminoglycosides, significantly increase AKI risk and should be avoided when alternatives exist. 3, 4, 2
• Each additional nephrotoxic medication increases AKI odds by 53%, with three or more nephrotoxins more than doubling the risk. 8

Clinical Context and Diagnostic Approach

Prerenal vs. Intrinsic Causes

While the provided guidelines note that prerenal causes account for >60% of AKI in general populations 8, in critically ill children, the pattern differs substantially—intrinsic kidney injury from sepsis, ischemia, and nephrotoxins predominates rather than simple volume depletion. 1, 2

Diagnostic Considerations

• AKI should be defined and staged using pRIFLE criteria for children over 1 month of age, which accounts for age-appropriate eGFR calculations. 9
• The pRIFLE classification uses either decrease in eGFR, rise in creatinine, or decrease in urine output to stage AKI severity. 9

Important Clinical Pitfalls

• Do not assume prerenal azotemia is the primary cause in critically ill children—sepsis and intrinsic kidney injury are far more common in this population than simple volume depletion. 1, 2
• Fractional excretion of sodium (FENa) has limited utility in critically ill children, particularly those with sepsis or receiving diuretics. 8
• Early recognition is critical, as AKI independently increases mortality and requires prompt intervention to prevent progression and long-term chronic kidney disease. 6, 7