Postoperative Urinary Retention

Postoperative urinary retention (POUR) is inability to void after surgery despite a full bladder. The usual operational definition is bladder volume over 400 to 600 mL on scan or catheterisation, or no void within 6 to 8 hours of surgery or catheter removal.

Epidemiology. Reported rates range from about 4% to 25% overall, depending on definition and surgery. Rates are highest after anorectal surgery, hernia repair, hip and knee arthroplasty, pelvic surgery and spinal surgery.

Risk factors. Male sex with prostatic enlargement, age over 60 years, neuraxial anaesthesia (especially long acting local anaesthetic or intrathecal opioid), intraoperative fluid over 750 mL to 1 L, operations over 2 hours, opioids, anticholinergics, alpha agonists, diabetes, neurological disease and previous retention.

Complications. Bladder overdistension injury with detrusor damage, urinary infection, post-renal acute kidney injury and hydronephrosis.

Pathophysiology.

Anaesthetic block of sacral parasympathetic outflow (S2 to S4) and opioid effect on detrusor and sphincter reduce detrusor contraction.

Pain and surgical stress raise sympathetic sphincter tone. Pelvic surgery can injure autonomic nerves. Overdistension causes ischaemic detrusor injury that prolongs retention.

Suprapubic discomfort, urgency, restlessness or agitation (sometimes the only sign in sedated or older patients), tachycardia and hypertension. A palpable or dull suprapubic mass, overflow dribbling, or small frequent voids with high residual volume.

Red flags.

• Back pain, perineal numbness, leg weakness or sphincter loss after neuraxial block (epidural haematoma or abscess, cauda equina).
• Anuria with a catheter in place.
• Haematuria or clots.
• Fever, loin pain or rising creatinine.
• Retention after pelvic surgery with suspected ureteric or bladder injury.

Bladder ultrasound scan is the first test. Catheterise if volume is over 600 mL, or over 400 mL with symptoms. Send urinalysis and culture, and check urea, creatinine and electrolytes if retention is large or prolonged. Measure post-void residual after catheter removal. Image the spine urgently if neurological signs are present.

Differential diagnosis.

• Oliguria from hypovolaemia or acute kidney injury.
• Blocked catheter.
• Ureteric or bladder injury and urinary leak.
• Neurogenic bladder.
• Urethral stricture or clot retention.
• Spinal haematoma or abscess.

Prevention. Avoid fluid excess, minimise opioids and anticholinergics, favour short acting spinal agents in ambulatory surgery, mobilise early, and allow patients to void in a normal position. Consider tamsulosin prophylaxis in men at risk.

Catheterisation. Use intermittent catheterisation if the first volume is under 1 L and the cause is reversible. Leave an indwelling catheter for 24 to 48 hours if the volume is 1 L or more, if retention recurs, or if intermittent catheterisation is not feasible (up to 3 to 7 days after very large volumes). Then assess voiding after removal.

Tamsulosin.

• Tamsulosin: 0.4 mg orally once daily, 30 minutes after the same meal each day, started 1 to 2 days before catheter removal and continued for about 3 to 7 days or up to 4 weeks in persistent cases; maximum 0.8 mg daily; monitor for postural hypotension and dizziness; no adjustment for creatinine clearance over 10 mL/min; avoid in severe hepatic impairment; inform surgeons of tamsulosin use before cataract surgery.

Monitoring. Time and volume of each void, post-void residual by scan, creatinine, and signs of infection.

Referral and escalation. Refer to urology after two failed voiding assessments, for haematuria or clots, after pelvic surgery with suspected injury, or when a suprapubic catheter is needed. Urgent spinal MRI and neurosurgical review if neuraxial complications are suspected.