Urinary Retention

Technique ranks the risk - POUR risk is greatest with spinal, then epidural, then general. Neuraxial blocks interrupt the afferent and efferent limbs of the micturition reflex arc at the cord. General anesthetics relax bladder smooth muscle, reduce detrusor contractility, and measurably increase bladder capacity while interfering with autonomic detrusor regulation.

Opioids hit the bladder from both ends - They blunt the sensation of distension by inhibiting bladder parasympathetics and simultaneously raise bladder neck tone through sympathetic overstimulation, creating functional outlet obstruction. POUR rates track directly with the amount of systemic opioid given postoperatively — a real argument for the opioid-sparing multimodal plan.

Identify the high-risk patient preoperatively - Male sex nearly doubles risk; age over 50 raises it 2.4-fold. Named comorbidities include renal failure, diabetes (especially with complications), psychiatric illness including depression, and untreated or undertreated BPH. Use the International Prostate Symptom Score (IPSS) — urgency, frequency, and nocturia scoring high predicts POUR. Knee, hip, and colon procedures carry the greatest surgical risk.

Alpha-blockers are the prophylaxis that works - Patients already on an alpha-blocker are more than 60% less likely to develop POUR, and prophylactic dosing benefits the highest-risk group. Tamsulosin takes up to 72 hours to reach maximal effect, so starting it the morning of surgery is too late.

Intraoperative levers - Operating time over 2 hours predicts POUR, and in total joint patients risk climbs about 25% per additional 15 minutes in the room. Large intraoperative IV fluid volumes raise the rate when no catheter is placed, from stretching an undrained bladder over a long case.

Get them up early - Early ambulation dropped POUR rates from 52% to 19% in one series. Slow time to ambulation is a modifiable postoperative risk factor.

Don't trust symptoms in PACU - More than 60% of outpatient surgical patients with over 600 mL in the bladder had no subjective symptoms at all, and sedation masks the rest. Use a bladder scanner or ultrasound — treat it as an extension of the exam. On percussion, dullness just below the umbilicus is roughly 500 mL and dullness above the umbilicus can mean 1000 mL, but the physical exam overestimates volume. Most patients should not go more than 6 to 7 hours without passing urine.

Drain completely - Immediate, complete drainage with an unrestricted Foley is safe; the old practice of intermittent clamping to prevent hematuria, vasovagal response, and hypotension is not supported. Start an alpha-blocker such as tamsulosin if the patient isn't already on one, and plan a trial without catheter at 1 to 3 days. There is no role for clamp-and-release "bladder training" before removal.

Post-obstructive diuresis - The complication to anticipate when you drain a large volume. It is uncommon unless the residual is 1,500 mL or more, and is defined as urine output of at least 200 mL for two consecutive hours after decompression, or more than 3,000 mL over 24 hours. Untreated it causes dehydration, electrolyte derangement, hypotension, and hypovolemic shock.

Replace fluid deliberately, not one-for-one - Use normal saline limited to no more than 75% of the prior 1 to 2 hours of urine output, so you don't drive further diuresis. Monitor urine output at least every 2 hours and check sodium, potassium, urea, creatinine, magnesium, and phosphate every 12 hours initially. A random urine sodium above 40 mEq/L suggests renal tubular injury and progression to pathologic diuresis; a urine specific gravity below 1.010 means the kidneys are not concentrating.

Who fails the voiding trial - Age over 70, severe pre-existing voiding symptoms, spinal surgery, hydronephrosis, and a bladder volume over 1,000 mL at catheter insertion. Anticholinergic medications are on the risk list too — factor them into your intraoperative drug choices in the patient who already has voiding symptoms.

Urinary retention is the inability to void voluntarily, confirmed by an elevated post-void residual. Normal micturition depends on two systems working in sequence. Filling is sympathetic — thoracolumbar outflow (T10 to L2) via the hypogastric nerves inhibits the detrusor and tightens the bladder base, neck, and urethra. Emptying is parasympathetic — pelvic nerves (S2 to S4) contract the detrusor and relax urethral smooth muscle while the pudendal nerve relaxes the external sphincter under voluntary control.

Anything that interrupts that loop causes retention. In men the leading cause is benign prostatic hyperplasia (BPH); acute retention in women is rare. Perioperatively, anesthetic technique, opioids, surgical pain, and dissection near the pelvic plexus each attack a different point in the pathway, and postoperative urinary retention (POUR) is reported in 5% to 70% of cases.