Acute Urinary Retention

Demographics: Acute urinary retention is a medical emergency. It is relatively common occurring in 7/1000 men. It is more common in men than women, and incidence is higher in men over 70.

Causes:
The most common cause of acute urinary retention is benign prostatic hypertrophy.
Other causes include:
structural changes near the bladder and urethra

in men

• ·      Meatal stenosis
• ·      Penile constricting bands
• ·      Phimosis
• ·      Urethral strictures

In women

• ·      Prolapse
• ·      Urethral strictures

Masses:

• ·      gynaecological masses – malignancy, uterine fibroid, ovarian cyst, retroverted gravid uterus
• ·      Stones – bladder calculi
• ·      Foreign body
• ·      Gastrointestinal, retroperitoneal, and bladder malignancy
• ·      Faecal impactation

Infectious and inflammatory:
In men

• ·      Balantitis
• ·      Prostatitis
• ·      Prostatic abscess

In women

• ·      Acute vulvovaginitis
• ·      Vaginal lichen planus
• ·      Lichen sclerosis
• ·      And vaginal pemphigus

In both

• ·      Bilharzia
• ·      Cystitis
• ·      Herpes simplex virus
• ·      Peri-urethral abscess
• ·      Varicella zoster virus

Drug related

• ·      Anticholinergics
• ·      Opioids and anaesthetics
• ·      Alpha-agonists
• ·      Benzodiazepines
• ·      NSAIDs
• ·      Detrusor relaxants
• ·      Calcium channel blockers
• ·      Antihistamines
• ·      Alcohol

Neurological: (usually causes chronic retention)

• ·      Autonomic or peripheral nerve – neuropathies, polio, guillain-barre etc.
• ·      Brain – Cerebral vascular disease, MS, neoplasm etc.
• ·      Spinal cord – vertebral disc problems, cauda equine, spinal stenosis etc.

Trauma:

• ·      penile trauma, and trauma from labour or other pelvic trauma.

Presentation:

Acute urinary retention tends to present as a gradual onset, tender distended bladder and inability to pass urine. Patient may have had associated symptoms such as fever, sensory changes etc and may have a history of previous episodes of retention or lower urinary tract symptoms.

On examination, the bladder may be palpable above the symphysis pubis and may be dull to percussion. In addition, genitalial examination may show structural abnormalities, or masses. PR exam may be performed to assess anal tone, faecal impactation and prostatic size and character. If neurological cause is suspected, other neurological changes such as sensory loss, change in tone and reflexes or power may be present.

Differential diagnosis:
see causes

Investigations and management
Bedside investigations include a urine analysis to check for infection, haematuria, proteinuria and glucosuria.

Midstream urine – if an infection is suspected, a midstream urine may help confirm this and guide antibiotic use.

Blood test: FBC, Urea and electrolytes, creatinie and eGFR, blood glucose, prostate specific antigen.

Imaging: Ultrasound may show hydronephrosis and any structural abnormalities of the renal tract. It may also show residual urine volume. Ultrasound is also performed to determine if the kidneys have been damaged by prolonged back pressure. This may present as a thinned cortex area.
Further investigations to determine the underlying cause may be performed. This may include a CT scan to identify pelvic or abdominal masses causing urinary retention where this is suspected. A MRI or CT of the brain or MRI of the spine may help determine the cause if neurogenic retention is suspected. Where bladder cancer is suspected, cystoscopy and biopsy may also help with diagnosis.

Acute urinary retention should be treated initially by inserting a Foley catheter to drain and decompress the bladder. Where this is contraindicated, urology input should be sought. If a patient has acute renal injury from the episode they should be monitored for electrolyte imbalances and for fluid management. A patient may have an initial rapid diuresis after having a catheter put in for the first few days. This is due to changes caused by increased back pressure which may persist for a few days. Further management of retention involves treating the cause. Benign prostatic hypertrophy, the most common cause of urinary retention can be treated primarily surgically. Emergency surgery may be performed, or the catheter may be removed to see if the retention persists, and if it does not surgery may be performed on a later date.

Complications and prognosis:

Complications of urinary retention include; urinary tract infections, obstructive acute kidney injury, post obstructive diuresis causing electrolyte imbalances, and haematuria post retention.

There is increased mortality in men with acute urinary retention, which increases with age and comorbidities such as cardiovascular disease, diabetes and chronic pulmonary diseases.

5 alpha reductase inhibitors and alpha blockers may prevent acute urinary retention in men with benign prostatic hypertrophy.

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