Post‑Obstructive Diuresis (POD)
Introduction
Post‑obstructive diuresis (POD) is the polyuric response that can follow relief of urinary tract obstruction. After decompression (usually via urethral or suprapubic catheterisation) the kidneys may excrete large volumes of retained fluid and solutes. The diuresis can begin immediately and may continue for hours to days.
While often self‑limited, POD can be pathologic and cause hypovolaemia, electrolyte disturbances and circulatory collapse. Early recognition, strict monitoring and targeted fluid/electrolyte replacement are the priorities for emergency clinicians (NICE NG148, NICE CG97).
Key pathophysiology
- Chronic obstruction impairs tubular concentrating ability and sodium handling; medullary washout and tubular dysfunction reduce the kidney’s ability to conserve water and solutes.
- On decompression, urine output increases because of:
- “Catch‑up” excretion of retained intravascular and interstitial fluid.
- Osmotic diuresis from retained solutes (urea, sodium).
- Persistent tubular concentrating defect and natriuresis.
- Longer or complete obstruction and pre‑existing renal impairment increase the risk of severe POD.
Who is at higher risk
- Patients with prolonged or high‑grade urinary outflow obstruction (large pre‑drainage bladder volumes).
- Patients with chronic urinary retention, an undrained obstructing stone, or longstanding prostatic outlet obstruction.
- Older, frail patients or those with reduced renal reserve.