Acute Caremiddle twist
An 84-year-old man with prostate cancer and bone metastases is catheterised in the emergency department for painless retention that has built up over several weeks; 1400 mL drains immediately. Six hours later a further 1900 mL has drained, and he has been given 500 mL of sodium chloride 0.9% since arrival. He is very thirsty and light-headed when he sits up. He is afebrile, his heart rate is 76 beats per minute and his blood pressure has fallen from 148/82 to 104/62 mmHg. Capillary glucose is 6.4 mmol/L and corrected calcium 2.30 mmol/L. Which one of the following best explains his urine output and his falling blood pressure?