Write a short note on Acute Urinary Retention.

The Concept

Acute urinary retention is the sudden, painful inability to pass urine, with a palpable, tender, distended bladder. It is a common urological emergency, and the pain and acute onset distinguish it from chronic retention (which is painless with a large residual). The commonest cause is bladder outflow obstruction from benign prostatic hyperplasia.

Causes

Besides BPH, causes include a urethral stricture, a blood clot (clot retention), prostatitis or a urinary infection, severe constipation, drugs (anticholinergics, opioids), neurological disease, and the post-operative state. Identifying the precipitant guides definitive management.

Clinical Features & Management

The patient is in acute discomfort with a strong desire to void but cannot, and a tender suprapubic swelling (the distended bladder) is palpable and dull to percussion. Immediate management is to relieve the obstruction by urethral catheterisation (or suprapubic catheterisation if the urethral route fails), which brings prompt relief; the residual volume drained is recorded. The cause is then identified and treated (e.g. An alpha-blocker and later TURP for BPH).

Post-obstructive Diuresis

After decompressing a very full or chronically obstructed bladder, one must watch for post-obstructive diuresis — a large diuresis that can cause dehydration and electrolyte disturbance — with monitoring of urine output and fluid balance. In chronic retention, by contrast, the bladder is grossly distended but painless, and there may already be renal impairment from back-pressure.

Chronic Retention & the High-pressure System

Chronic retention deserves contrast because it is managed differently: it is painless, the bladder is grossly distended, and there may be overflow incontinence. A 'high-pressure' chronic retention causes bilateral hydronephrosis and renal impairment, and relieving it produces a marked post-obstructive diuresis that needs careful fluid and electrolyte monitoring. This is why catheterising a chronically retained bladder is not simply a matter of instant cure but requires attention to renal function and diuresis.

The Bottom Line

Acute urinary retention is a painful emergency (usually from BPH) relieved by immediate catheterisation, after which the cause is treated and post-obstructive diuresis watched for; chronic retention is painless with a large residual and possible renal impairment.

A Note on Catheterisation

Practical management centres on catheterisation: a urethral catheter is passed to relieve the obstruction, but if it fails (as with a tight stricture or a large obstructing prostate) a suprapubic catheter is inserted. The drained residual volume is recorded (a large volume suggests chronic or acute-on-chronic retention), a urine sample is sent, and renal function is checked. This immediate decompression relieves the pain and protects the kidneys while the underlying cause is addressed.

Watch for post-obstructive diuresis after decompression.

• Acute urinary retention = sudden painful inability to void with a palpable, tender, distended bladder; commonest cause BPH.
• Other causes: urethral stricture, clot retention, prostatitis/UTI, constipation, drugs, neurological, post-operative.
• Immediate treatment: urethral (or suprapubic) catheterisation for relief; record residual volume; then treat the cause.
• Watch for post-obstructive diuresis after decompression; chronic retention is painless with a large residual and may cause renal impairment.