17th February 2025

A 69-year-old gentleman with a background of hypertension and schizophrenia is admitted with a community-acquired pneumonia.

A 69-year-old gentleman with a background of hypertension and schizophrenia is admitted with a community-acquired pneumonia. His hypertension and schizophrenia are well controlled in the community on ramipril and olanzapine. On the ward, during his 4th day of admission, he develops confusion and agitation. His investigations are as follows. 

Haemoglobin 145 (130 – 180)

White cell count 17 (4 -11)

Platelets 195 (150 – 450)

Sodium: 124 (135 – 145)

Potassium: 4.6 (3.5 – 5.5)

Creatinine kinase: 250 (22 – 198)

Serum osmolality: 269 (275 – 295)

Urine sodium: 38 (< 20)

Urine osmolality: 750 (50 – 1200)

What is the likely cause of his confusion?

Select the SINGLE most appropriate option from the list below. Select ONE option only.