Acute Urinary Retention

Acute urinary retention (AUR) requires immediate catheterisation. Bladder scan >300–400ml confirms the diagnosis. Cauda equina syndrome must be excluded as an emergency. An alpha-blocker (tamsulosin) started at catheterisation improves trial without…

TWOC Protocol / BUA Guidelines

The pathway

1 · Bladder scan

>300ml on bladder scan in symptomatic patient confirms AUR
>400ml is unequivocal
Document residual volume precisely — relevant for post-obstructive diuresis risk
Ultrasound also assesses for bilateral hydronephrosis (upper tract obstruction)

2 · Exclude cauda equina emergency

Ask about bilateral leg weakness
Saddle anaesthesia (numbness around perineum, inner thighs, genitals)
Bowel dysfunction (loss of anal tone or bowel control)
If present → emergency MRI spine and neurosurgical/spinal referral immediately

3 · Urethral catheterisation

12–14Fr urethral catheter for uncomplicated AUR
18Fr (three-way) if haematuria or clot retention
Use 2% lidocaine gel (instill, wait 3–5 minutes before passing catheter)
Measure and document residual volume
If urethral catheterisation fails → suprapubic catheter (urology or trained clinician)

4 · Post-catheterisation monitoring

Residual volume >1L: monitor for post-obstructive diuresis (UO >200ml/hr)
Haematuria ex vacuo: frank haematuria after decompression of chronically distended bladder — usually self-limiting, reassure, irrigate if clots
Monitor U&E: AKI common with chronic retention

5 · Start tamsulosin

Tamsulosin 400mcg OD from day of catheterisation
Alpha-1 blocker: reduces urethral and prostatic smooth muscle tone
Improves TWOC success rate by ~50% vs placebo
Warn about postural hypotension — especially in elderly

6 · Trial without catheter (TWOC)

TWOC at 48h–2 weeks (hospital protocol dependent)
Successful TWOC: patient voids >200ml with residual <150ml
Can be performed in community TWOC clinic
Failed TWOC criteria: refer to urology for TURP or urodynamics
Document voided volume + post-void residual (bladder scan)

7 · Urology referral

All failed TWOCs
Bilateral hydronephrosis on USS
AKI secondary to obstruction
Recurrent AUR
Suspected malignancy (DRE findings, elevated PSA)
Start finasteride if large prostate and long-term alpha-blocker therapy planned

Drugs

Drug	Dose	Route	Notes
Tamsulosin	400mcg OD	PO	Start on day of catheterisation. Improves TWOC success. Warn about postural hypotension.
Lidocaine gel 2%	11ml (standard syringe)	Intraurethral	Instil and wait 3–5 minutes before passing catheter. Anaesthesia and lubrication.
Morphine	5mg	IV/IM	If severe pain associated with AUR — uncommon but can occur.
Finasteride	5mg OD	PO	Long-term — for large prostate. Takes 6 months to achieve maximum effect. Not for acute management.

When to escalate

Cauda equina syndrome (saddle anaesthesia/bilateral leg weakness/bowel dysfunction) — emergency MRI spine,Bilateral hydronephrosis on USS — urology referral for upper tract decompression,Post-obstructive diuresis (UO >200ml/hr for ≥2 hours) — monitor electrolytes, risk of hypovolaemia,Failed urethral catheterisation — suprapubic catheter insertion by trained clinician,Recurrent AUR or failed TWOC — urology referral for TURP/urodynamics

Reference: British Urology Association (BUA) / EAU Guidelines on Male LUTS and BPH 2023

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