Will a urodynamic study be necessary for a patient with urinary retention?

Urodynamic Study for Urinary Retention

Urodynamic studies should be performed in patients with urinary retention when invasive or irreversible treatments are being considered, particularly when the cause of retention is unclear after initial assessment or when distinguishing between obstruction and detrusor underactivity is necessary for treatment planning. 1, 2

Initial Assessment Before Considering Urodynamics

• Post-void residual (PVR) measurement: Essential first step using ultrasound (non-invasive) or catheterization

  • PVR >50-100ml suggests significant retention 2
  • A single elevated PVR should not be used alone for diagnosis due to variability 2

• Uroflowmetry: Should be performed when voiding dysfunction is suspected

  • At least 2 flow rates should be obtained (ideally with >150ml voided volume) 1
  • Maximum flow rate (Qmax) is the best single measure of voiding function 1

Indications for Urodynamic Studies in Urinary Retention

Urodynamic studies are indicated when:

1. Planning invasive treatment: Pressure flow studies are recommended before invasive therapy, especially in men with Qmax >10 ml/second 1

2. Distinguishing causes: Pressure flow urodynamic studies are the only method to differentiate between:

   • Detrusor underactivity (weak bladder muscle)
   • Bladder outlet obstruction 1

3. Neurogenic bladder: For patients with neurological conditions affecting bladder function, especially when storage parameters place upper tracts at risk 1

4. Post-surgical evaluation: When assessing patients with urgency incontinence after bladder outlet procedures to evaluate for bladder outlet obstruction 1

5. Complex cases: When the diagnosis remains unclear after initial assessment 2

Types of Urodynamic Testing for Retention

• Pressure flow studies (PFS): Gold standard for diagnosing obstruction

  • Relates detrusor pressure at maximum flow to the maximum flow rate 1
  • If Qmax is <10 ml/second, obstruction is likely and PFS may not be necessary 1

• Multichannel filling cystometry: Evaluates storage phase abnormalities

  • Preferred over single channel cystometrogram which is subject to artifacts 1
  • Assesses for altered compliance, detrusor overactivity, or other abnormalities 1

• Video urodynamics: Combines pressure measurements with imaging

  • Provides additional anatomical and functional information 2

Follow-up Urodynamic Testing

• In patients with impaired storage parameters that place upper tracts at risk, repeat urodynamic studies should be performed at appropriate intervals following treatment 1
• An interval of two years or less is reasonable once pressures have been normalized 1

Clinical Implications of Urodynamic Findings

• Urodynamic findings help predict treatment response and guide therapy selection:

  • Patients with urodynamically proven obstruction have higher re-treatment rates (59%) compared to unobstructed patients (44%) when treated with alpha-blockers 3
  • Patients with detrusor contraction during voiding respond better to alpha-blockers than those with detrusor areflexia 4

• Urodynamic studies can identify patients who may benefit from combination therapy (alpha-blocker plus antimuscarinic) in cases with mixed symptoms 5

Conclusion

Urodynamic studies are not necessary for all patients with urinary retention but are valuable when planning invasive treatment or when the cause of retention remains unclear after initial assessment. They provide objective data to distinguish between obstruction and detrusor underactivity, which is crucial for selecting appropriate treatment and predicting outcomes.