Acute Urinary Retention
Acute urinary retention is the painful, sudden inability to void — relieve it immediately by catheterisation, find the cause, start an alpha-blocker, and plan a trial without catheter; never miss high-pressure (high-pressure chronic) retention threatening the kidneys.
The big picture
Retention is failure to empty the bladder. Acute retention is sudden and painful, typically from bladder outlet obstruction (BPH the classic cause), precipitated by constipation, drugs (anticholinergics, sympathomimetics), infection, postoperative factors, or neurological causes. Chronic retention is a large-volume, often painless bladder; when it is high-pressure it transmits back to the kidneys and causes hydronephrosis and renal impairment.
Catheterise and record the residual, find the cause, alpha-block and plan a TWOC — but recognise high-pressure chronic retention (renal impairment/hydronephrosis), which needs sustained drainage and monitoring, not a quick catheter removal.
Red flags
High-pressure chronic retention — sustained drainage and monitoring; do not simply remove the catheter.
Suggests high-pressure retention threatening the kidneys.
Possible cauda equina — urgent neurological assessment.
Diagnostic algorithm
Each step answers one question. Tap to expand.
Treatment ladder
Decompress promptly, treat the cause, optimise the chance of voiding, and tailor catheter strategy to whether retention is acute or high-pressure chronic.
Complications
- Renal impairment (high-pressure retention)
- UTI, bladder over-distension/detrusor damage
- Post-obstructive diuresis after decompression
- Catheter trauma/infection
- Haematuria after rapid decompression (usually self-limiting)
- Identify high-pressure retention and provide sustained drainage
- Monitor and replace post-obstructive diuretic losses
- Treat UTI, manage diuresis, definitive treatment of cause
If treatment fails
If the patient fails to void after TWOC or re-presents, ask: is the outlet obstruction inadequately treated, is the detrusor underactive, or was this high-pressure chronic retention?
Memory hooks
Relieve first (catheter), think second.
Record the residual volume.
Alpha-blocker then TWOC.
Painless + high volume + high creatinine = high-pressure retention.
Watch for post-obstructive diuresis.
Board traps
Painless retention with renal impairment → high-pressure chronic retention, not simple AUR.
Quick catheter removal in high-pressure retention → renal injury risk.
Forgetting post-obstructive diuresis after draining a large-volume bladder.
Clinical cases
A 70-year-old man reports months of nocturnal bedwetting and is found to have a non-tender, hugely distended bladder. Catheterisation drains 1800 mL; creatinine is elevated and ultrasound shows bilateral hydronephrosis.
What is the diagnosis and the key management points?