What is the purpose and procedure of cystometry in evaluating urinary tract symptoms?

Cystometry: Purpose and Procedure in Evaluating Urinary Tract Symptoms

Cystometry is an essential urodynamic study that measures bladder function by assessing the pressure-volume relationship during bladder filling and emptying, providing critical diagnostic information for patients with complex lower urinary tract symptoms that cannot be diagnosed through basic evaluation alone.

Purpose of Cystometry

Cystometry serves several key purposes in urological evaluation:

• Differentiates between types of urinary incontinence - Distinguishes between stress and urge incontinence by detecting uninhibited detrusor contractions 1
• Evaluates bladder storage function - Assesses bladder capacity, compliance, and sensation during filling
• Identifies detrusor overactivity - Detects abnormal involuntary bladder contractions
• Evaluates bladder emptying - Identifies detrusor underactivity or bladder outlet obstruction
• Guides treatment decisions - Helps determine appropriate therapeutic interventions for complex urinary symptoms

When Cystometry Should Be Performed

According to guidelines, cystometry is not recommended for routine initial evaluation of urinary symptoms but should be reserved for specific clinical scenarios:

• Diagnostic uncertainty after initial evaluation of overactive bladder symptoms 2
• Mixed incontinence where the predominant type is unclear 2
• Obstructive voiding symptoms with elevated post-void residual 2
• Suspected neurogenic lower urinary tract dysfunction 2
• Recurrent complicated UTIs with suspected anatomical or functional abnormalities 2
• Prior to invasive or irreversible treatments for urinary symptoms 2
• Change in signs/symptoms in moderate or high-risk neurogenic lower urinary tract dysfunction patients 2

Procedure of Cystometry

The cystometry procedure typically involves:

1. Patient preparation:

   • Empty bladder completely before the test
   • Position patient (usually supine or seated)
   • Explain procedure and expected sensations

2. Catheterization:

   • Insert a small catheter into the bladder to measure intravesical pressure
   • May place a second catheter in the rectum/vagina to measure abdominal pressure
   • Catheter placement is critical - conventional placement in bladder apex can physically inhibit bladder wall movement 3

3. Filling phase:

   • Sterile fluid (water or saline) is instilled into the bladder at a controlled rate
   • Patient reports sensations (first sensation, first desire to void, strong desire, urgency)
   • Bladder pressure is continuously monitored
   • Sensations may differ based on underlying condition - patients with detrusor overactivity typically report perineal/vaginal sensations, while stress incontinence patients report suprapubic sensations 4

4. Provocation maneuvers:

   • Coughing, position changes, running water to provoke symptoms
   • Observe for uninhibited detrusor contractions

5. Voiding phase:

   • Patient voids while pressure measurements continue
   • Assesses detrusor contractility and outlet resistance

Types of Cystometry

• Simple cystometry: Measures intravesical pressure only
• Multichannel cystometry: Measures both intravesical and abdominal pressures to calculate true detrusor pressure
• Video urodynamics: Combines cystometry with fluoroscopic imaging
• Ambulatory urodynamics: Extended monitoring in more natural conditions

Clinical Significance and Interpretation

• Detrusor overactivity: Involuntary detrusor contractions during filling phase
• Detrusor underactivity: Reduced strength/duration of detrusor contraction during voiding
• Bladder compliance: Relationship between volume change and pressure change
• Bladder sensation: Normal, increased, reduced, or absent

Limitations and Risks

• Risk of urinary tract infection: Post-procedure infection rates of 21-27% have been reported, with elderly and males with high residual volumes being more susceptible 5
• Invasive procedure: Can cause discomfort and anxiety
• Artificial environment: May not replicate natural filling and voiding conditions
• Poor correlation with symptoms: Some studies show poor correlation between cystometry findings and lower urinary tract symptoms 6
• Treatment outcomes: One study found similar treatment outcomes in patients with symptoms of overactive bladder regardless of whether cystometry confirmed detrusor instability 6

Special Considerations

• Neurogenic patients: May require regular cystometry to monitor for changes in bladder function that could lead to upper tract damage 2
• Post-surgical evaluation: Useful in evaluating recurrent symptoms after incontinence surgery
• Pediatric patients: Modified techniques and interpretation required
• Frail elderly: Consider risks versus benefits carefully due to higher infection risk 5

Cystometry remains a valuable diagnostic tool when used appropriately for complex urinary symptoms that cannot be diagnosed through basic evaluation, but should not be performed routinely due to its invasive nature and potential complications.