Obstructive Uropathy

Post-obstructive diuresis after decompression - Draining a large retained volume sets off prolonged polyuria with heavy salt and water loss, reported in up to half of these patients. It is rarely an issue unless the drained residual is 1,500 mL or more. Defined as more than 200 mL/h for two consecutive hours, or more than 3,000 mL over 24 hours.

Record the drained volume - The immediate residual is the best available predictor of who will diurese. Document anything over 1,000 mL so the ward knows what may be coming.

Do not clamp the catheter - The old teaching was to drain a distended bladder slowly or with intermittent clamping. Current data show immediate, complete drainage on an unrestricted Foley is safe, with no increase in hematuria, vasovagal episodes, hypotension, or post-obstructive diuresis.

What the diuresis costs you - Dehydration, electrolyte derangement, hypotension, hypovolemic shock, and death when it is missed. Urine output every 2 hours at minimum, with sodium, potassium, urea, creatinine, magnesium, and phosphate every 12 hours initially.

Urine specific gravity separates the two types - Below 1.010 the kidneys are not concentrating, which points to pathological salt-wasting diuresis rather than simply offloading retained volume.

Fever changes the case - Fever with obstruction means concomitant UTI and possible septicemia. Send urinalysis and culture, start antibiotics, and treat it as urgent decompression on a septic patient.

Renal function drives the plan - Basic metabolic panel focused on creatinine. Renal function significantly worse than baseline, or significant electrolyte abnormalities, means admission and urgent nephrology rather than same-day discharge.

Bedside ultrasound is the fast answer - It gives bladder volume and the degree of hydronephrosis in a minute and is the least invasive test available. CT abdomen and pelvis when a mass or other intra-abdominal pathology is suspected.

Catheterization can fail - Start with a 16 or 18 Fr Foley; the obstruction itself may defeat it, then a Coudé tip, and suprapubic catheterization or cystostomy when urethral access is not feasible.

Their home medications - Alpha-1 blockers such as tamsulosin and terazosin relax bladder neck and prostatic smooth muscle; finasteride, dutasteride, bicalutamide, and leuprolide shrink the prostate. Orthostasis is the commonly cited concern with alpha-blockers, though several studies have not found significant side effects.

Obstructive uropathy is any hindrance to urine flow — structural or functional — anywhere from the renal pelvis to the urethra. Urine backs up into the collecting system and produces hydronephrosis. Benign prostatic hyperplasia is the most common cause; stones, urethral strictures, phimosis, prostate cancer, retroperitoneal adenopathy, neuropathic bladder dysfunction, and, in neonates, posterior urethral valves account for much of the rest. Presentation is bimodal, clustering in infants and in men over 60.

Rising intratubular pressure plus local ischemia from distension produce obstructive nephropathy: reduced glomerular number, glomerular hyalinization, cortical cysts, and interstitial inflammation, ending in irreversible loss — which is why time to decompression matters. Two things drive perioperative risk: infection behind an obstruction, which turns septic quickly, and post-obstructive diuresis once the obstruction is relieved.