Bladder Outlet Obstruction
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Direct answer
Bladder outlet obstruction in men is most commonly produced by benign prostatic hyperplasia enlarging the transition zone, and presents as obstructive symptoms (hesitancy, weak stream, straining, incomplete emptying, terminal dribbling) with or without irritative symptoms (frequency, urgency, nocturia) from bladder decompensation or trabeculation. Assessment uses the International Prostate Symptom Score, digital rectal examination, uroflowmetry (peak flow under 10-15 mL/s suggests obstruction) and post-void residual, with pressure-flow urodynamics reserved for diagnostic doubt. Treatment escalates from watchful waiting through alpha-blockers and 5-alpha-reductase inhibitors to surgery — transurethral resection of the prostate remains the reference standard, with HoLEP and ThuLEP for larger glands and retention managed by catheterisation followed by a trial without catheter.
What you must remember
- IPSS: seven questions scored 0-35; mild 0-7, moderate 8-19, severe 20-35.
- Uroflowmetry is the simplest objective test: peak flow rate under 15 mL/s is suspicious and under 10 mL/s strongly suggests obstruction, provided the voided volume is adequate (over about 150 mL).
- Medical therapy: alpha-1 blockers (tamsulosin, alfuzosin) act within days and help dynamic obstruction; 5-alpha-reductase inhibitors (finasteride, dutasteride) shrink the gland over 6 months, best for glands over about 30-40 mL, and lower acute retention and surgery risk in the long term.
- Acute retention: firsttwilight management is urethral catheterisation, treat precipitants (constipation, anticholinergics, UTI, post-operative), then a trial without catheter after 1-3 days of an alpha-blocker — success is roughly 40-70 per cent.
- TURP: the gold standard for glands of roughly 30-80 mL; complications include retrograde ejaculation (around 65-75 per cent), urethral stricture or bladder neck stenosis (a few per cent), ureteric injury, and TUR syndrome.
- TUR syndrome: dilutional hyponatraemia from absorption of hypotonic irrigant (glycine 1.5 per cent) through open venous sinuses — bradycardia, hypertension then hypotension, confusion, visual disturbance; treat by stopping surgery, diuretics and hypertonic saline.
- Gland-size options: open simple prostatectomy or HoLEP for glands over about 80-100 mL; transurethral incision of the prostate (TUIP) for small glands in young men wishing to preserve ejaculation.
A typical worked case
A 70-year-old man attends with six months of hesitancy, a stream that has "thinned to a thread", nocturia four times, and now a painful inability to void for eight hours. Step 1: catheterise urethrally, record the residual (900 mL), send urine for culture and exclude the common precipitants — he takes cold remedies containing anticholinergics. Step 2: once comfortable, complete assessment: IPSS 24 (severe), DRE shows a smoothly enlarged 50 g gland with no nodule, PSA checked after counselling (raised PSA here reflects BPH plus retention, not necessarily cancer), uroflowmetry once he voids shows Qmax 7 mL/s with residual 200 mL. Step 3: trial without catheter after 48 hours of tamsulosin; he voids but residuals stay high and symptoms remain severe. Step 4: offer surgery — a 50 g gland suits TURP; discuss retrograde ejaculation (about two-thirds), the small risks of incontinence and transfusion, and bladder recovery (detrusor instability may take months to settle even after perfect surgery).
Where students slip
The most-dropped mark is irritative-versus-obstructive symptom classification: frequency and nocturia are irritative (and shared with cancer, stones and tuberculosis), while hesitancy, straining and poor stream are obstructive. The second is the TUR syndrome question — examiners want the mechanism (absorption of hypotonic glycine irrigant, not blood loss), the timeline (usually within the first hour, related to resection time and open sinuses) and the antidote logic (hypertonic saline with diuresis, and abandoning the procedure). Third, the trap of "retention = immediate TURP": the correct sequence is catheter, precipitant correction, alpha-blocker and TWOC, with elective surgery for failures. Fourth, remember the alternative causes of outlet obstruction in the male — prostate cancer, urethral stricture (check the meatus and urethra before blaming the prostate), bladder neck stenosis and phimosis — and in women, pelvic organ prolapse and Fowler's syndrome in young women with retention. A classic viva closer: "Why does finasteride take months to work?" — because it shrinks the static gland by inducing apoptosis in the transition zone rather than relaxing smooth muscle like the alpha-blocker.
Frequently asked questions
What IPSS range defines severe symptoms?
20-35 out of 35; 0-7 is mild and 8-19 moderate, and the score is paired with a bother score to guide how aggressively to treat.
Which objective test first confirms outflow obstruction?
Uroflowmetry — a peak flow under 10 mL/s with adequate voided volume strongly suggests obstruction; pressure-flow urodynamics definitively separate obstruction from a weak detrusor.
How is acute urinary retention managed initially?
Urethral catheterisation with residual measurement, treatment of precipitants such as infection or constipation, then a trial without catheter after 24-72 hours of an alpha-blocker.
What is TUR syndrome and its management?
Dilutional hyponatraemia from systemic absorption of hypotonic glycine irrigant during transurethral resection — managed by stopping the procedure, fluid restriction with diuresis, hypertonic saline for symptomatic hyponatraemia and oxygen support.
What are the commonest sexual side-effects of TURP?
Retrograde ejaculation in roughly two-thirds of patients and erectile dysfunction in a smaller proportion; these must be explicitly consented before surgery.