Acute kidney injury and fluid balance

Synopsis

Detect paediatric AKI from creatinine change and urine output, distinguish perfusion, intrinsic and obstructive causes, prescribe fluids from repeated weight-based assessment, stop nephrotoxins and escalate complications promptly.

• Paediatric AKI is an abrupt fall in kidney function detected by change from the child's baseline, not by an adult creatinine reference range.
• NICE criteria include creatinine rise of at least 26 micromol/L within 48 hours, at least 50% within 7 days, eGFR fall of at least 25% within 7 days, or urine below 0.5 mL/kg/hour for more than 8 hours.
• Infant creatinine changes rapidly after birth and initially reflects maternal creatinine; neonatal age, gestation, postnatal day and urine output require neonatal interpretation.
• Classify causes as reduced renal perfusion, intrinsic renal injury or post-renal obstruction, while recognising that sepsis and critical illness often combine mechanisms.
• First-line assessment is ABCDE, perfusion, volume status, blood pressure, weight change, measured intake and output, bladder examination and complete medication review.
• First-line tests are serial creatinine, urea and electrolytes, bicarbonate or blood gas, glucose, calcium, phosphate, FBC and urine dipstick for blood, protein, leucocytes, nitrite and glucose.
• Stop or withhold avoidable nephrotoxins and renal-haemodynamic medicines during acute hypovolaemia, including NSAIDs, ACE inhibitors, ARBs and unnecessary aminoglycosides; dose essential medicines to current kidney function.
• For true hypovolaemia, give a cautious isotonic crystalloid bolus under paediatric assessment and reassess pulse, perfusion, pressure, lungs, weight and urine response after each aliquot.
• Do not give repeated fluid boluses to an oedematous, hypertensive or oliguric child without evidence of fluid responsiveness; overload worsens respiratory and renal outcomes.
• Once euvolaemic or overloaded, prescribe daily input from insensible needs plus measured urine and other losses, with adjustments for fever, ventilation, drains and ongoing diarrhoea.
• Loop diuretics do not treat renal injury and are not routine. They may be used for fluid overload while awaiting or during renal replacement therapy if residual urine output exists.
• Kidney replacement therapy is indicated by refractory hyperkalaemia, acidosis, uraemic complications, pulmonary oedema or fluid overload; do not wait for a fixed creatinine threshold.