Hyperkalaemia on the surgical ward

A 56 year old woman was admitted with an infected stump wound at the site of a below the knee amputation. Her medical history included type 2 diabetes, diabetic foot ulcer, and painful peripheral neuropathy. Her regular drugs were metformin, amitriptyline, lansoprazole, Humulin I and Novorapid SC insulin, aspirin, paracetamol, morphine sulfate, gabapentin, and carbamazepine. In hospital, she was also prescribed dalteparin 5000 units subcutaneously once daily, intravenous benzylpenicillin, and flucloxacillin.

Before admission, serum potassium was 4.6-4.8 mmol/L (reference range 3.6-5.0). During admission, she had persistent hyperkalaemia peaking at 6.2 mmol/L and received repeated doses of insulin-dextrose and salbutamol over three days. Renal function was stable throughout (creatinine 60-85 μmol/L (60-120), estimate glomerular filtration rate >60 mL/min/1.73 m²). She was mildly acidotic (bicarbonate 18-20 mmol/L (22-30)) and serum lactate was 1.9 mmol/L (0.6-2.4). A paired sample of serum and urine showed serum: potassium 5.7 mmol/L, osmolality 312 mOsm (280-296); urine: sodium 69 mmol/L, potassium 18 mmol/L, osmolality 370 mOsm.