Acute Urinary Retention (AUR) Causes

Mnemonic - MOND - medications, obstruction, neurologic, distention
Obstruction = Most Common Cause.  The urethra and urethral meatus simply cannot empty the urine from the bladder due to some more proximal narrowing/stricture/compression.

• This can be mechanical or secondary to a mass.  BPH may be the cause of AUR in up to 53% of men.  Medications such as anticholinergics may also play a role in outflow obstruction.

Neurological Dysfunction

• Diabetes
• Spinal Cord Injury/Spinal Cord Compression
• CVA

Medications

• Anticholinergics:  Decrease detrusor muscle contractility (these are used for urge incontinence!).  Remember that many drugs have anticholinergic properties and these effects are additive.  Geriatric patients are increasingly sensitive to the properties of these drugs.
• Sympathomimetics like pseudoephedrine.

Overdistention

• This may be secondary to obstruction
• Lack of a foley in anesthetized patients with an epidural/spinal.

These factors often combine to result in acute urinary retention, a preventable cause of renal failure.

• Example:  an elderly woman with diabetes on an antihistamine, nasal decongestant, oxybutin, and other miscellaneous medications with anticholinergic properties.  
• Example:  a man with chronic BPH who takes decongestants for his URI symptom

References:

Barrisford, Glen W, Steele, Graeme S.  "Acute Urinary Retention."  July 8, 2011.  http://www.uptodate.com.ezproxylocal.library.nova.edu/contents/acute-urinary-retention?source=related_link#H4  Accessed on January 6,  2012