MRCP2-1177

MRCP2-1177

You are asked to review an 83-year-old woman on the care of the elderly ward as serum sodium results are low. The patient was admitted six hours ago with a diagnosis of community-acquired pneumonia and exacerbation of congestive cardiac failure. She presented with a productive cough, shortness of breath and leg swelling. She has a past medical history of multiple myocardial infarcts five years ago and has subsequently developed heart failure. She also has had osteoarthritis, hypertension and high cholesterol. She takes aspirin, ramipril, furosemide, bisoprolol, omeprazole and atorvastatin. On examination, she has a raised JVP and bilateral crepitations to midzones bilaterally as well as oedema to the sacrum.

Blood tests:
Hb 120 g/l
Platelets 480 * 109/l
WBC 14.2 * 109/l
Na+ 126 mmol/l
K+ 3.5 mmol/l
Urea 6.3 mmol/l
Creatinine 84 µmol/l

Urinary sodium: 16 mmol/l

What is the most likely cause of hyponatraemia?