Acute kidney injury: Viva

Branch 1: Definition and staging

The candidate should recognise that this girl has acute kidney injury by the KDIGO criteria. The creatinine has risen to 3.0 times the baseline of 55 micromoles per litre, which places her in stage 3 on the creatinine criterion alone, and the oliguria adds to the staging. A strong candidate states the KDIGO definition precisely: a rise in serum creatinine of 0.3 mg per dL or more within 48 hours, or to 1.5 times baseline or more within seven days, or a urine output below 0.5 mL per kg per hour for six hours. The staging is by the magnitude of the change, and stage 3, which this girl has, is a creatinine of 3.0 times baseline or more, or a rise to 4.0 mg per dL or more, or the initiation of renal replacement therapy, or in a patient under 18 years an estimated GFR below 35 mL per min per 1.73 m2. [1]

If the examiner presses on the paediatric pRIFLE classification, the candidate should describe the modification by Akcan-Arikan and colleagues that uses the estimated creatinine clearance: risk is a 25 percent reduction, injury is a 50 percent reduction, and failure is a 75 percent reduction or an estimated clearance below 35 mL per min per 1.73 m2. The candidate should note that the pRIFLE is validated for critically ill children and complements the KDIGO definition in the intensive care setting, and that the PODIUM consensus and the ADQI 26 report endorse KDIGO as the primary definition in children. [1]

Branch 2: The staged management of hyperkalaemia

If asked about the immediate management, the candidate should treat the hyperkalaemia with ECG changes as an emergency. The first medication is intravenous calcium gluconate at 0.5 mL per kg of the 10 percent solution over 5 to 10 minutes with cardiac monitoring, for myocardial membrane stabilisation, because the peaked T waves signal an immediate risk of cardiac arrest. The candidate should state that calcium does not lower the potassium and must be followed immediately by the agents that shift potassium into the cells, including insulin with glucose, nebulised salbutamol, and sodium bicarbonate. The third step is the removal of potassium with resins or dialysis, and the potassium is rechecked after each intervention because the effect is transient. [2]

A strong candidate places the hyperkalaemia treatment in the context of the whole resuscitation. The airway and breathing are stabilised, the intravenous access is established, and the volume status is assessed. If the child is hypovolaemic or in shock, an isotonic crystalloid bolus of 10 to 20 mL per kg is given with reassessment, and the candidate should cite the PRoMPT BOLUS trial finding of no difference between balanced crystalloids and 0.9 percent saline in children with septic shock. The candidate should be cautious with further boluses once the shock has resolved, because the fluid overload itself worsens the outcome in a child with AKI. [3]

Branch 3: The decision for renal replacement therapy

If the examiner moves to the renal replacement therapy decision, the candidate should state the indications clearly: refractory hyperkalaemia unresponsive to the staged medical therapy, severe metabolic acidosis unresponsive to bicarbonate, fluid overload causing pulmonary oedema unresponsive to diuretics, and uraemic complications such as encephalopathy, pericarditis, and a bleeding diathesis. This girl, with a potassium of 6.9 mmol per litre and ECG changes, may need dialysis if she does not respond to the staged therapy promptly, and the candidate should involve the nephrologist and the intensivist early and establish the vascular access. [2]

The candidate should describe the modality choice. Continuous kidney replacement therapy is preferred for the haemodynamically unstable child because it provides a slow, steady clearance that does not provoke the blood pressure swings of intermittent dialysis. Intermittent haemodialysis is used for the stable older child and for toxin removal. Peritoneal dialysis is used for the small infant and in resource-limited settings. The candidate should cite the KDIGO summary recommendation of continuous therapy for the haemodynamically unstable patient and note that the modality does not clearly change the survival, so the choice is made on practical grounds. [2]