Makindo Medical Notes

🚨 Obstructive Uropathy = any blockage of urine flow between the renal collecting ducts and the urethral meatus. 👉 Unilateral ureteric obstruction usually causes no detectable change in urine flow or creatinine. 👉 Renal failure develops only when both kidneys are obstructed or in patients with a single functioning kidney.

ℹ️ About

• Obstruction can occur anywhere from collecting ducts → urethral meatus.
• 🖼️ Imaging usually shows dilatation proximal to obstruction (hydronephrosis, hydroureter).
• ⚠️ Chronic obstruction may cause irreversible renal damage.

🧬 Causes

• Renal: Papillary necrosis, staghorn calculus, tumour, clot.
• Ureteric: Stone, extrinsic tumour (e.g. cervical, colorectal), intrinsic tumour, retroperitoneal fibrosis.
• Bladder: Calculi, tumour, clot, neuropathic bladder, retention (e.g. constipation).
• Urethral: Prostatic hypertrophy, prostate cancer, urethral stricture, stone, phimosis.

🩺 Clinical Presentation

• 🔺 AKI: ↑ creatinine, metabolic acidosis, hyperkalaemia.
• Above bladder: Flank pain, fullness.
• Partial bladder outlet obstruction: Hesitancy, weak stream, polyuria, nocturia.
• At/below bladder: Acute retention, painful distended bladder.
• Exam: Palpable bladder, DRE may show enlarged prostate or hard stool.

🔎 Investigations

• 🧪 Bloods: FBC, U&E → AKI, metabolic acidosis, hyperkalaemia.
• 🖥️ Ultrasound: First-line, shows hydronephrosis/hydroureter, identifies obstruction level.
• CT urogram / spiral CT if unclear cause.
• Radionuclide scan (MAG3/DTPA) if function assessment required.
• Bladder scan → postvoid residual >200 mL = abnormal, suggests outlet obstruction.

💡 Post-Obstructive Diuresis: After relief of obstruction, patients may pass very high volumes of urine due to retained sodium/urea and impaired concentrating ability. 👉 Requires close monitoring and IV fluid replacement to prevent hypovolaemia and electrolyte disturbance.

🛠️ Management

• 🚑 Immediate: Catheterisation in retention, monitor urine output.
• 📡 Identify level: Ultrasound ± further imaging to determine site & cause.
• ⚠️ Monitor: Watch for post-obstructive diuresis, correct with fluids and electrolytes.
• 👨‍⚕️ Male BOO: α1-blocker (tamsulosin) or 5α-reductase inhibitor (finasteride). TURP if severe/progressive.
• 🩺 Definitive: Stent insertion, nephrostomy, or surgery depending on cause (e.g. stone removal, tumour resection, fibrosis release).

💡 Exam Pearls:
• Always check for reversible causes (stones, prostate). • Unilateral obstruction = no creatinine rise; bilateral obstruction = AKI. • Post-obstructive diuresis is a common viva question – fluids must match output.