Casey M. Glass
EPIDEMIOLOGY
The most common cause of acute urinary retention is benign prostatic hypertrophy. There are a number of other causes of acute urinary retention (Table 56-1) some of which are gender specific (Table 56-2).
Acute urinary retention is more common in men and is associated with advancing age.
Precipitated urinary retention referes to retention associated with other causes including recent surgery, medical illness, or drug effect (commonly anticholin-ergics, antihistamines, anaesthesia agents, cold medications, and α-sympathomimetics).
Acute urinary retention associated with benign pro-static hypertrophy alone is considered spontaneous urinary retention and is associated with a greater risk of recurrence comapred to precipitated retention (15% vs 9%) and need for surgical intervention (75% vs 26%).
TABLE 56-1 Causes of Acute Urinary Retention
TABLE 56-2 Gender-Specific Causes of Acute Urinary Obstruction
PATHOPHYSIOLOGY
Acute urinary retention may be secondary to physical obstruction to urine flow or as a result of decreased neurologic control of bladder emptying.
Sympathetic innervation of the bladder originates from the T10-L2 levels of the spinal cord. Somatic innervation is via the pudendal nerve (S2–4).
Progressive obstruction leads to bladder dilation and decreased stream intensity as well as increased frequency of voiding.
CLINICAL FEATURES
Patients with urinary retention complain of lower abdominal pain and the sensation of needing to void. Chronic retention may present with pain and a history of frequent incomplete voiding (overflow incontinence).
The history should be directed at identifying the cause of precipitated urinary retention. A history of hematuria may be related to bladder or renal calculi, urinary tract neoplasm, or infection. Patients should be asked about new medications or recent surgical procedures. A comprehensive urologic history including known anatomic abnormalities and recent surgical interventions is vital.
Prostate examination is necessary to assess for size, consistency, and the possibility of prostatitis. An enlarged, hard, nodular prostate is concerning for malignancy.
Women with urinary retention should have a pelvic examination to assess for pelvic masses or pelvic inflammatory disease.
A comprehensive neurologic examination is necessary to exclude a neurogenic cause. The examination should include assessment of rectal tone and perineal sensation.
DIAGNOSIS AND DIFFERENTIAL
Bedside ultrasound is recommended as an intitial noninvasive test to assess for urinary retention (Fig. 56-1).
When ultrasound is not available, placement of a ure-thral Foley catheter is both diagnostic and therapeutic.
Urinary volumes greater than 75 to 150 cc are consistent with retention.
Urinalysis is necessary to determine the presence or absence of infection.
CBC is recommended for patients with massive hematuria, suspected infection, and hematologic diseases.
Serum chemistries are recommended to asses for renal dysfunction.
FIG. 56-1. Transverse and sagittal views of the urinary bladder. The prostate is visualized as a medium echogenicity structure posterior and caudal to the bladder. Anterior-posterior, cradio-caudal, and transverse measurements of the bladder are obtained for calculation of the bladder volume. (Reproduced with permission from Casey Glass, MD.)
EMERGENCY DEPARTMENT CARE AND DISPOSITION
The primary treatment of acute urinary retention is placement of a urethral or suprapubic catheter to allow for bladder drainage.
Urologist consultation may be necessary if initial attempts at placement of a catheter are unsuccessful.
Urologist consultation is recommended as the initial intervention when there is a history of a recent urologic procedure or after a traumatic Foley placement attempt with concern for creation of a false passage.
Chronic obstruction is a risk factor for postobstruc-tive diuresis and renal failure. Patients with chronic obstruction should be observed for 4 hours. Persistent diuresis greater than 200 cc an hour is abnormal. Patients with significant diuresis should be started on IV rehydration. Renal function should be checked regularly.
Patients with significant hematuria need admission for conintued irrigation as blood clots commonly cause obstruction of the Foley catheter.
Patients with significant comorbid illness as a cause of their obstruction (eg, cystitis, prostatitis), significant postobstructive diuresis, or abnormal measures of renal function need admission for additional treatment and monitoring.
Antibiotics are not indicated unless a specific source of infection is noted.
Men with spontaneous urinary retention can be started on an α-adrenergic blocker (tamsulosin, 0.4 milligram PO daily). They should be warned about the possibility of hypotension related to α-adrenergic blocker use.
All patients dischared home should be set up with a leg bag for Foley catheter drainage and be instructed in how to care for the catheter and empty the bag.
Urologist follow up in 4 to 7 days is recommended for discharged patients.
Patients with precipitated urinary retention may have a trial of voiding in the ED if the precipitating cause is resolved. The bladder is drained and the catheter removed. The patient is observed for a period of time and allowed to attempt to void. Ultrasound can be used to confirm a minimal post-void residual.
Occasionally medications are needed to manage pain from bladder spasms which are often secondary to irritation from the Foley catheter. The anticholinergic oxybutinin can be tried at a dose of 2.5 milligrams 3 times a day. Consistent with its class, this medication can itself cause urinary retention.
For further reading in Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 7th ed., see Chapter 95, “Acute Urinary Retention,” by David Hung-Tsang Yen and Chen-Hsen Lee.