Urinary retention
Bladder scan, catheter, creatinine. Painless retention with a huge volume is chronic high-pressure retention: keep the catheter in.
A 74-year-old man had a hernia repair this morning under spinal anaesthetic. He has not passed urine for 9 hours and is restless with lower abdominal pain. He takes amitriptyline for nerve pain. Bladder scan: 950 mL.
A 70-year-old man in clinic has had poor stream and night-time frequency for years. His creatinine is 2.4 mg/dL (212 µmol/L), and a scan shows 1,400 mL in the bladder with swollen kidneys. He feels no pain.
What's the difference between these two, and what must you watch for after catheterising the second?
- ConfirmBladder scan or palpable bladder. Acute retention is usually painful.
- Catheterise12–14 Fr urethral catheter. Record the residual volume.
- Find the causeProstate, drugs, constipation, pain, anaesthesia, infection, clots, neurological.
- Cauda equinaBack pain with leg symptoms, saddle numbness: urgent MRI.
- Chronic retention with kidney injuryWatch for post-obstructive diuresis: hourly urine output, U&E.
- Men with prostate enlargementStart tamsulosin, trial without catheter after 2–3 days.
- Review medicinesStop anticholinergics and opioids where possible, treat constipation.
- Cauda equina signs
- Failed catheterisation
- Haematuria with clots
- Post-obstructive diuresis with falling BP or electrolyte problems
- Retention with fever (infected obstruction)
- Rising creatinine
- Cauda equina syndrome
- Spinal cord compression
- Clot retention
- Urethral stricture
- Prostate cancer
- Drug cause
- Faecal impaction
| Acute retention | Painful, usually under about 1 L |
| Chronic retention | Painless, often over 1 L, may have kidney injury |
| Catheter | 12–14 Fr |
| Tamsulosin | 400 micrograms once daily |
| Trial without catheter | After 2–3 days of tamsulosin |
| Post-obstructive diuresis | Over 200 mL an hour for 2 hours or more |
| Fluid replacement in diuresis | Part of the losses (about half) orally or IV, per U&E |
Check every dose against a current drug reference and your hospital protocol.
On this page
Causes
| Group | Examples |
|---|---|
| Obstruction | Enlarged prostate, prostate cancer, urethral stricture, clots, stones, constipation, pelvic mass, prolapse |
| Drugs | Anticholinergics, tricyclics, antihistamines, opioids, decongestants, anaesthesia |
| Neurological | Cauda equina, spinal cord compression, MS, diabetic neuropathy, stroke |
| Other | Pain after surgery, UTI, prostatitis, immobility, alcohol |
Acute or chronic?
Acute: catheterise, find trigger
Chronic (high pressure): catheterise, watch diuresis, urology
Cauda equina: urgent MRI
Assessment
- Urinary symptoms before (stream, frequency, nocturia).
- Drugs, recent anaesthesia, alcohol.
- Bowels: constipation.
- Back pain, leg weakness, saddle numbness.
- Examination: palpable bladder, PR (prostate, constipation, anal tone), neurology of the legs, genitals (phimosis, meatal stenosis).
- Women: pelvic mass, prolapse.
Investigations
| Test | Why |
|---|---|
| Bladder scan | Volume |
| U&E | Kidney injury, sodium, potassium |
| Urine dipstick and culture | Infection, blood |
| FBC, CRP | Infection |
| Glucose | Diabetes |
| Ultrasound kidneys | Hydronephrosis in chronic retention |
| PSA | After counselling, not during retention or infection (falsely high) |
| MRI spine | Neurological signs |
Post-obstructive diuresis
After relieving chronic high-pressure retention, the kidneys can pass large volumes of urine.
- Hourly urine output.
- Over 200 mL an hour for 2 hours or more: check U&E, BP, postural BP.
- Replace about half of the losses (orally if well, IV if not).
- Daily weights and U&E until settled.
Trial without catheter (TWOC)
- Start tamsulosin at the time of catheterisation (men).
- Remove the catheter after 2–3 days.
- Check voided volumes and post-void residual by bladder scan.
- Failed TWOC: recatheterise, urology for prostate surgery or long-term catheter.
Treatment
See catheterisation, cauda equina and low urine output.
Common mistakes
- Not recording the residual volume.
- Missing cauda equina in a younger patient with back pain.
- Sending a PSA during retention.
- Forgetting post-obstructive diuresis.
- Leaving the patient on anticholinergics.
- Missing constipation as the cause in the elderly.
Frequently asked questions
How is acute urinary retention treated?
Urethral catheterisation, then treating the cause. Men with prostate enlargement start tamsulosin before a trial without catheter.
What is the difference between acute and chronic retention?
Acute retention is sudden and painful. Chronic retention is painless, often with large volumes, overflow and sometimes kidney injury.
What is post-obstructive diuresis?
A high urine output after relieving chronic retention, which can cause dehydration and electrolyte problems.
Which drugs cause urinary retention?
Anticholinergics, tricyclic antidepressants, antihistamines, opioids and decongestants.
Test yourself
Exam-style questions on this guide, from our two question banks. Choose an answer to see why each option is right or wrong.
1. A 74-year-old man has painless retention with 1600 mL drained and creatinine 2.4 mg/dL (212 µmol/L). What is the plan?
Answer: Keep the catheter, urology. Chronic high-pressure retention with kidney impairment: keep the catheter, monitor hourly urine and electrolytes, urology review.
- Trial without catheter today: Not appropriate.
- Remove the catheter tomorrow: High-pressure chronic retention.
- Restrict fluids: He may diurese heavily.
- Start oxybutynin: Worsens retention.
2. After catheterisation, a man passes 300 mL/hour for 3 hours. What is happening?
Answer: Post-obstructive diuresis. Above 200 mL/hour for 2 hours after relieving retention needs fluid replacement and electrolyte checks.
- Diabetes insipidus: Unlikely in this setting.
- Normal output: This is large.
- Catheter blockage: No, output is high.
- Bladder rupture: No.
3. Which drug is started before a trial without catheter in a man with prostatic enlargement?
Answer: Tamsulosin. Tamsulosin 400 micrograms daily for 2–3 days before the trial improves the chance of success.
- Amitriptyline: Causes retention.
- Codeine: Causes retention.
- Oxybutynin: Anticholinergic; worsens retention.
- Finasteride alone: Too slow for TWOC.
4. A 72-year-old man with BPH has been unable to pass urine for 10 hours and has a tender palpable bladder after taking an over-the-counter cold remedy. What is the immediate management?
Answer: Urethral catheter. Acute urinary retention in men: causes include BPH, constipation, anticholinergics/antihistamines/decongestants, opioids, post-operative, UTI. Catheterise (record residual volume), then start an alpha-blocker (tamsulosin) and attempt trial without catheter after 2–3 days. Watch for post-obstructive diuresis if large volume. Suprapubic catheter if urethral fails or stricture.
- IV fluids and wait 6 hours: Waiting worsens bladder distension.
- Emergency TURP tonight: TURP is not the first emergency step.
- IV furosemide 40 mg: Diuretics make retention worse.
5. A 68-year-old has nocturia, poor stream and hesitancy. The prostate is smoothly enlarged (estimated 60 mL); PSA is consistent with BPH. Which combination reduces both symptoms and progression?
Answer: Tamsulosin + finasteride. BPH lower urinary tract symptoms: alpha-blockers (tamsulosin) relax smooth muscle — rapid symptom relief; 5α-reductase inhibitors (finasteride, dutasteride) shrink large prostates (> 30–40 mL) over 6–12 months, reduce retention and surgery, and halve PSA. Combination for large glands with moderate–severe symptoms. Surgery (TURP, HoLEP) for refractory symptoms, retention, recurrent UTI, stones, haematuria or renal impairment.
- Tamsulosin monotherapy: Tamsulosin alone does not shrink the prostate.
- Oxybutynin monotherapy: Oxybutynin alone risks retention.
- Testosterone replacement: Testosterone worsens BPH.
6. Postganglionic parasympathetic fibres to the lacrimal gland reach it by travelling with branches of which nerve?
Answer: Maxillary nerve. Preganglionic fibres start in the facial nerve (superior salivatory nucleus), travel in the greater petrosal nerve and nerve of the pterygoid canal to the pterygopalatine ganglion. Postganglionic fibres join the maxillary nerve, its zygomatic branch, then the lacrimal nerve (V1) to reach the gland.
- Ophthalmic nerve alone: The lacrimal nerve (V1) carries them for the last part, but they reach it via the maxillary nerve's zygomatic branch first.
- Facial nerve directly: The facial nerve carries the preganglionic fibres, not the postganglionic ones.
- Glossopharyngeal nerve: Supplies the parotid (via the otic ganglion).
- Vagus nerve: Has no supply to the lacrimal gland.
7. During a vagotomy, both vagal trunks are cut at the oesophageal hiatus. Which part of the gut will keep its parasympathetic supply?
Answer: Sigmoid colon. The vagus supplies the gut up to about two-thirds of the way along the transverse colon (midgut territory). The distal colon, sigmoid colon and rectum receive parasympathetic supply from the pelvic splanchnic nerves (S2–S4), which are unaffected by vagotomy.
- Stomach: Directly supplied by the vagal trunks.
- Jejunum: Midgut, supplied by the vagus.
- Transverse colon (proximal two-thirds): Midgut, supplied by the vagus.
- Gallbladder: Supplied by the vagus (hepatic branch).
References and dose sources
- NICE CG97: Lower urinary tract symptoms in men
- NICE CKS: Acute urinary retention
- BAUS
- NICE CKS — acute urinary retention
- Lidocaine (lignocaine) dosing: Drugs.com: Lidocaine dosage (see also our lidocaine (lignocaine) dose page)
- Tamsulosin dosing: Drugs.com: Tamsulosin dosage (see also our tamsulosin dose page)
- Lactulose dosing: Drugs.com: Lactulose dosage (see also our lactulose dose page)
International guidance is linked where it reflects good practice. Where your hospital’s protocol differs, follow your hospital.