What causes decreased urine output and leg swelling in the elderly?

The main causes of oliguria and bilateral foot swelling in the elderly include: (1) Renal insufficiency: glomerular lesions lead to decreased glomerular filtration rate, resulting in reduced urine output and sodium-water retention, which causes dependent edema; (2) Cardiopulmonary insufficiency: commonly seen in patients with acute or chronic heart failure or cor pulmonale, impaired systemic and pulmonary circulation leads to fluid leakage into dependent areas, causing bilateral lower limb edema; (3) Benign prostatic hyperplasia (BPH): elderly men with BPH may experience frequent urination, reduced urine output, and increased residual urine, which can also lead to bilateral foot swelling. Symptoms often improve once urinary obstruction is relieved.