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A 73-year-old man with malnutrition was transferred to the emergency department with hypothermia, severe dehydration, hypotension, diarrhoea and acute renal dysfunction. He had a medical history of mild hypertension and chronic kidney disease. Further evaluation revealed hypernatremia with a serum sodium level of 163 mmol/L. He was treated with lactated lactate solution and his serum sodium level dropped to 143 mmol/L after 36 hours. Five days...