Abstract
A 62-year-old man with no major comorbidities became acutely hyponatraemic on the second postoperative day following a routine carotid endarterectomy. He developed a headache, became hypertensive and confused, and then had a seizure and required intubation and admission to the intensive care unit. A CT angiogram of his head and carotid arteries was normal, as was a subsequent MRI head. His serum and urine osmolality were low. He was treated by fluid restriction and his hyponatraemia resolved over 3 days. On discontinuation of sedation the patient woke up appropriately. The cause of his hyponatraemia was initially a mystery but when questioned by the medical team he admitted that he drank about 5 litres of water in the afternoon on the second postoperative day. At this point the diagnosis of dilutional hypervolaemic hyponatraemia secondary to water intoxication could be made.