Urinary retention

• Acute urinary retention is a sudden and painful inability to pass urine and is always an emergency.

• Bladder scans help rapidly diagnose the condition, and a volume of > 400ml is compatible with the diagnosis.

• Patients often note that they have been trying to pass urine for a few hours but cannot pass more than a few drops. They’ll be seen pacing around trying to get comfortable, and are often quite distressed.
  
  

  
  

Image 1 - Distended bladder

Aetiology:

1. Mechanical - Constipation (via mechanical compression on the urethra), calculi in the bladder or urethra and foreign bodies

2. Men - BPH, Prostate cancer, urethral strictures, phimosis and paraphimosis

3. Women - prolapses, pelvic masses, gravid uterus

4. Infective - UTI

5. Medication-related - Anaesthesia, anticholinergics, Alpha agonists, antidepressants

6. Pain

7. Constipation

8. Neurological causes - Cauda equina

Examination:

Distended, palpable bladder with suprapubic tenderness.

DRE - Assess the prostate size and feel for any irregularities, as well as any faecal impaction causing retention. Assess anal tone and perianal sensation.

PV exam - Any prolapses or palpable pelvic masses.
Lower limb neurological examination, if indicated.

Management:

1. Routine blood tests (there is no indication for PSA in this context, as it will be raised secondary to retention).

2. Catheterise with a long-term catheter.

A 14 or 16Fr catheter in men

A 12 or 14Fr catheter in women.

Send a urine sample for dipstick and a M/C/S

3. Monitor the urine output and watch for diuresis if the residual urine volume post-catheterisation is >1000ml (diuresis is defined as a urine output of >200ml for 2 or more consecutive hours).

4. In uncomplicated cases, a TWOC can be arranged at the local urology intervention centre with 72 hours of tamsulosin cover (3 doses). However, some centres prefer a delayed approach with a TWOC in a week, which is sensible.

5. Start treatment for manageable causes of retention, such as antibiotics if suspecting a UTI or tamsulosin and finasteride if BPH was the likely cause of retention.

6. In women, an ultrasound TATV is useful to exclude pelvic pathology

Pitfalls:

1. Nothing's draining - Incorrect catheter placement, anuric patients and false positive bladder scans can cause this.
   Anuric patients - there is no urine in the bladder. In this case, the cause of anuria must be sought, and rehydration commenced. A review by the renal team is recommended.

2. Decompression haematuria - a common phenomenon where urine turns red or dark brown as a result of decompression of the kidneys once back pressure is relieved. This is transient, and patients should be reassured.

Chronic retention often has volumes >800ml, and patients may surprisingly not have much discomfort with these volumes of urine.

It is important to differentiate high-pressure chronic retention (altered renal function with hydronephrosis) and low-pressure chronic retention (minimal derangement and normal kidneys on imaging), as the former warrants a long-term catheter until the cause is managed. A history of nocturnal enuresis is a red flag symptom for high-pressure retention.

If blood tests are deranged and you suspect high-pressure chronic retention, arrange for an ultrasound scan KUB, correct diuresis at the rate of 50% of the hourly urine output with 0.9% sodium chloride, get daily body weights, lying and standing blood pressures and daily blood tests monitoring renal function and electrolytes.

Images:
Image 1 - Used under the Creative Commons licence - Frivadossi, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons