Post-operative Acute Urinary Retention

Michael J. Borrie, BSc, MB, ChB, FRCPC, Chair, Division of Geriatric Medicine, University of Western Ontario, London, ON.

Acute urinary retention (AUR) occurs predominantly in men and the incidence increases with age. The most common cause of urinary retention is benign prostatic hypertrophy (BPH). For men in their 40s who have no or mild obstructive symptoms (American Urologic Association Symptom Score 7 or less), the incidence of acute urinary retention is 2.6/1000 person years and 3.0/1000 person years in people with moderate to severe symptoms. In contrast, men in their 70's with mild to moderate symptoms have an incidence of AUR of 9.3/1000 person years and this rises to 34.7/1000 person years in those with moderate to severe symptoms.¹ Over five years, the risk of AUR for men in their 70s is 10% and for men in their 80s it is almost 30%.¹ These findings are based on a cohort of over 2,000 men 40-79, followed over four years and is one of the few longitudinal epidemiologic studies in the area.

Definition
Acute urinary retention has been defined as painful inability to void with a urine volume on catheterization of less than 800 ml.^2,3 Chronic retention has been defined as the presence of the post-void residual urine volume greater than 500 mls (estimated on bladder ultrasound scan) with or without upper tract dilatation on ultrasound and/or uremia occurring in a patient who is still able to void spontaneously. Acute on chronic retention has been defined as painful inability to void with a urine volume on catheterization of greater than 800 mls.

Implications
The clinical implications of AUR are significant. First, men who are admitted to hospital for immediate surgery after acute urinary retention are at higher risk of developing perioperative complications than are those sent home for delayed surgery.⁴ Second, acute urinary retention can affect glomerular filtration and the ability of renal tubular function to reabsorb protein. Fifteen patients whose renal function was still affected six months after the episode of acute urinary retention were re-evaluated at 18 months. The lowered creatinine clearance and elevated alpha-1 microglobulin excretion had increased in prevalence from 57% to 79% and 71% to 100%, respectively.⁵ Third, post-operative urinary retention increases the length and cost of acute hospital stay.⁶ These implications highlight the urgency of identifying and treating acute urinary retention as soon as possible.

Post-operative Urinary Retention
There are three processes that contribute to the occurrence of acute urinary retention.⁷ These are:

1. a resistance to the flow of urine, either structural (such as BPH or a urethral stricture) or functional (such as failure of the sphincter to relax (dyssynergia) or constipation);
2. alteration in sensory or motor innervation to the bladder;
3. overdistension of the detrusor muscle.

Overfilling of the bladder can occur during surgery and general anesthetic.^1,8 Some reports also suggest that narcotics given perioperatively or post-operatively may contribute to urinary retention.^9,10 However, in a study by Boulis, there was no correlation between the incidence of post-operative urinary retention and post-operative narcotic use.⁶

Post-operative urinary retention following prostatectomy occurred in 9.2% of men who had presented with acute retention as compared to 2.3% in those who had obstructive symptoms only.⁴ A retrospective review of 379 men reported 12% failure to void after transurethral resection of the prostate (TURP) on the initial trial without a catheter.³ A Canadian study of 50 men, mean age 69.5 years, who presented with acute urinary retention, found that 38% had residual urine >100 mls post-op and were begun on intermittent catheterization. At three months, 10% were unable