Hypokalaemia and hyperkalaemia — formative SAQs

SAQ 1 (10)

A 7-year-old boy with acute kidney injury secondary to post-infectious glomerulonephritis is noted to have a serum potassium of 7.2 mmol/L. The cardiac monitor shows bradycardia with a widened QRS and tall peaked T waves. He is drowsy but maintains his airway. ^[2][3]

1. Define hyperkalaemia and explain why this child requires immediate treatment, citing the ECG findings. (2) ^[2][4]
2. Give the emergency management in the first 30 minutes, naming each drug, dose, route, and its specific purpose, including the monitoring required. (6) ^[2][7]
3. Outline the definitive steps once he is stabilised, including the role of dialysis, and state two safety pitfalls in this management. (2) ^[1][8]

Model answer

Definition and urgency. Hyperkalaemia is a serum potassium above 5.5 mmol/L, and this child's level of 7.2 mmol/L is severe and immediately dangerous. The ECG shows bradycardia, a widened QRS and tall peaked (tented) T waves — advanced hyperkalaemic cardiotoxicity that can progress within minutes to a sine wave and asystole. The ECG, not the number alone, mandates emergency treatment now; a repeat result should not delay therapy. ^[2][4]

Emergency management (first 30 minutes). First, stabilise the myocardium with intravenous 10 percent calcium gluconate 0.5 mL/kg (maximum about 10 mL) given slowly over 5 minutes with continuous cardiac monitoring; this raises the membrane threshold and restores conduction within minutes but does not lower potassium. Second, shift potassium into cells: give nebulised salbutamol 5 mg (he is over 25 kg only if heavier than 25 kg — at a typical 7-year-old weight use 2.5 mg if under 25 kg) together with intravenous insulin 0.1 unit/kg and glucose 0.5 g/kg (for example 5 mL/kg of 10 percent dextrose), which begins to lower potassium within 15 minutes. Third, attach cardiac monitoring and a reliable intravenous line, check blood glucose every 15 to 30 minutes for at least two hours to detect insulin-induced hypoglycaemia, and repeat the potassium at 30 to 60 minutes. ^[2][7]

Definitive steps and pitfalls. Once stabilised, remove potassium from the body: in a child with acute kidney injury and a refractory or recurring level, the definitive removal is dialysis. Identify and treat the precipitant (the post-infectious glomerulonephritis and any potassium-raising drugs), and restrict potassium intake. Two pitfalls: (1) iatrogenic hypoglycaemia after insulin-dextrose occurs in roughly 10 to 20 percent of treatments and can be severe, prevented only by generous glucose and relentless monitoring; (2) cation-exchange resins are too slow for emergency use and must not be relied on as sole therapy. ^[1][8]