Kidney replacement therapy and dialysis in children: SAQ

This boy has severe acute kidney injury complicating septic shock, and he meets several of the AEIOU criteria for urgent kidney replacement therapy: refractory hyperkalaemia with electrocardiogram changes, severe metabolic acidosis, and fluid overload with pulmonary oedema. Critically, he is haemodynamically unstable on two vasopressors, which dictates the modality of choice. ^[1]

Question 1 (10 marks)

Outline the kidney replacement therapy you would choose for this child, your immediate medical management while it is being prepared, and the principles of its prescription. ^[1]

This boy is in septic shock on high-dose dual vasopressors, so he cannot tolerate the rapid fluid and solute shifts of intermittent haemodialysis, which would precipitate circulatory collapse. The correct modality is continuous renal replacement therapy, the slow continuous blood circuit run at the bedside that removes fluid and solute gently over hours to days and tolerates low blood pressure. He needs a central venous access line, favouring the right internal jugular vein, and I would avoid a subclavian line because it stenoses the veins needed for a future fistula. ^[1]

While the circuit is being prepared I would treat the hyperkalaemia immediately as a bridge to definitive removal. Ten percent calcium gluconate at 0.5 mL per kg slow intravenously (maximum 20 mL) stabilises the myocardium and reduces the risk of arrhythmia from the peaked T waves. Insulin with dextrose, nebulised or intravenous salbutamol, and sodium bicarbonate for the acidosis shift potassium into cells. I would also review his vasopressors and ventilation to optimise renal perfusion, recognising that these measures are bridges, not solutions, and that definitive clearance by dialysis must follow. ^[3]

The prescription of continuous renal replacement therapy targets an effluent dose of 25 to 35 mL per kg per hour, balancing adequate clearance against the need to minimise filter clotting and protect his circulating volume. Anticoagulation is usually with heparin, but if he has a bleeding risk or coagulopathy from his sepsis I would use regional citrate anticoagulation, monitoring the ionised calcium and the total to ionised calcium ratio to avoid citrate accumulation, which is a particular risk in liver dysfunction. Fluid removal would be set to bring him gently back toward his dry weight over the next 24 to 48 hours, guided by his haemodynamics and oxygenation rather than a fixed target. ^[1]