Urodynamic evaluation in SCI  

Cystometry (Cystometrogram, CMG)

  • Concept:
    • Measurement of intravesical pressure during the course of bladder filling and voiding
  • Technique:
    • Standard cystometry:
      • Using a dual lumen catheter, measuring Pves (intravesical pressure)
      • Rectal catheter to measure Pabd (abdominal pressure)
      • Pdet (detrusor pressure) is a virtual value obtained by subtraction of Pabd from Pabd
    • Dr McGuire’s technique: [McGuire 1996]
      • Using a triple lumen catheter, measuring Pves and Pure
  • Types of cystometry
    • Filling cystometry: 3 segments (
      • Initial pressure rise:
        • Normal: <10cmH2O
        • Viscoelastic component of the bladder wall induced by filling
      • Stable tonus limb: reflects bladder compliance
      • Increase in tonus: rise in bladder pressure
    • Voiding cystometry: detrusor contraction
  • Measurement parameters and interpretation [Abrams 2002]

    • Filling cystometry
      • Detrusor function
        • Normal detrusor function
        • Detrusor overactivity
          • Phasic detrusor overactivity
            • Any contraction during storage phase is abnormal
            • Minimal criteria of contraction: >5cmH2O
          • Terminal detrusor overactivity
          • Detrusor overactivity incontinence
      • Bladder compliance (normal, decreased, increased) (
      • Bladder sensation
        • Normal bladder sensation
          • First sensation of bladder filling
          • First desire to void
          • Strong desire to void
        • Increased bladder sensation
        • Reduced bladder sensation
        • Absent bladder sensation
        • Non-specific bladder sensation: abdominal fullness or vegetative symptoms
        • Bladder pain
  • Bladder capacity: normal in adult =300-500ml
  • Urethral function
    • Normal urethral closure mechanism
    • Incompetent urethral closure mechanism
    • Urodynamic stress incontinence
  • Filling cystometry
    • Detrusor function
      • Normal detrusor function
      • Abnormal dertusor activity
      • Detrusor underactivity
      • Acontractile detrusor
    • Urethral function
      • Normal urethral function
      • Abnormal urethral function
        • DSD
        • Dysfunctional voiding
        • Non-relaxing urethral sphincter obstruction
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    Sphincter Electromyography (EMG)

    • Concept:
      • Recording of the bioelectric activity generated in the striated sphincter
      • Synchronous cystometrogram and sphincter EMG is essential in most SCI/D patients (to detect DSD)
    • Technique:
      • Surface EMG
      • Skin patch electrode
      • Self-adhesive EKG electrode positioned on perineal skin overlying the striated sphincter
      • Most commonly used
      • Easier to place and more comfortable
      • Artifacts: incl. improper grounding, record activity from other adjacent muscles such as levator ani (difficulty in precise localization of the origin of the electromyographic activity)
      • Other types of electrode: Anal plug electrode, vaginal sponge electrodes or catheter mounted ring electrodes
      • Coaxial Needle EMG
      • More accurate placement, more accurate recordings
      • Only select motor units at the needle tip are sampled
    • Interpretation of the striated sphincter activity
      • Synergic, dyssynergic, bradykinetic, impaired voluntary control, fixed tone
    • Clinical significance:
      • In SCI disease, the detection of DSD is very important.
      • EMG can provide sufficient information for DSD.
      • Fluoroscopic monitoring on the urethra can offer an easier and more accurate way to identify DSD.
      • Applied to measure bulbocavernosus reflex latency [Dmochowski 1995]
    • Other comments:
      • There is no reliable way to evaluate smooth sphincter function with EMG. To assess smooth sphincter, fluoroscopic monitoring of the proximal sphincter is needed. Also VLPP measurement technique is needed.
    • Also refer to here

    Urethral Pressure Profile (UPP)

    • Concept: measuring the intraurethral pressure either at rest or during voiding
    • Types of measurement
      • Static UPP
        • Concept:
          • intraluminal pressure along the length of the urethra with the bladder at rest
          • Urethral catheter with side holes is slowly withdrawn from the urethra while being perfused with liquid
          • maximal urtethral pressure obtained during UPP study almost always is at the level of the external sphincter [Watanabe 1996]
        • current practice is based on the Brown and Wickham’s method [Brown 1969]
        • Technique:
          • The most common method is the perfusion technique
          • Performed by slowly withdrawing the urethral port of the catheter through the urethra [Watanabe 1996]
        • Measured parameter:
          • MUCP (maximal difference between the urethral pressure and Pves
        • Clinical significance:
          • Not a functional test but a static study
          • provides no physiologic information on urethral function during voiding [Watanabe 1996]
          • MUCP lacks both sensitivity and specificity in its ability to classify incontinence [McGuire 1995]
          • diagnostic value is limited [Rink 1984]
      • Dynamic or stress UPP
        • Introduced by Asmussen and Ulmsten in 1976 [Asmussen 1976]
        • Technique:
          • Bladder pressure measurement can be made simultaneous with urethral pressure
          • Measuring catheter is withdrawn very slowly through the urethra with the patient coughing at regular interval
        • Measured parameters: pressure transmission ratio (PTR)
        • Clinical significance
          • Decreased conduction of increased abdominal pressure is associated with urodynamic stress urinary incontinence
          • Is rarely used now
      • Voiding UPP (micturitional UPP)
        • Technique
          • The same manner as a static UPP
          • Only the patient voids while the catheter is being withdrawn
          • During voiding, bladder pressure and urethral pressure should be same (isobaric)
        • Measured parameter
          • If there is any obstruction the pressure difference occurs between the distal and proximal to the obstruction point
        • Clinical significance
          • Is used to diagnose bladder outlet obstruction, correlate well with pressure-flow study results
          • Difficult to perform
          • Many distortion artifact, prone not to be accurate

    Detrusor Leak Point Pressure

    • Definition: the lowest bladder pressure (in the absence of a detrusor contraction) at which leakage occurs across the urethra [McGuire 1996]
    • Concept [McGuire 1996]
      • bladder outlet resistance is the main determinant of detrusor pressure
    • History
      • In 1981, McGuire introduced DLPP is clinical reality. McGuire’s group found that in myelodysplastic patients, those with DLPP> 40 cm H2 O were at significantly higher risk for upper tract deterioration than those with DLPPs < 40 cm H2 O [McGuire 1981]
      • More information: -> link to the Increased intravesial pressure
    • Technique [McGuire 1996]
      • Measure in conjunction of the fluoroscopy
      • While filling the bladder at 60ml/min, measuring Pdet (without increasing abdominal pressure)
      • Urethral meatus is observed for leakage
      • Study ends when Pdet=40cmH2O
    • Clinical meaning in SCI/D
      • a reflection of the urethral resistance to the bladder as an expulsive force
      • a measure of the storage pressures in the bladder
      • outlet resistance from fixed external sphincters
      • Not useful to determine whether or not obstruction exists in non-neurogenic situations
      • Not useful to characterize bladder contractility
      • A high leak point pressure if untreated will result in the bladder response. This response occurs in any obstructive uropathy condition but is exaggerated in neurogenic conditions.
    • Clinical interpretation
      • If the outlet resistance is high, a higher bladder pressure will be needed to overcome this resistance. If the LPP detrusor approaches 40 to 50cmH2O, storage function will deteriorate and average bladder pressures will stay nearly at the LPP-det. This sustained pressure of 40cmH2O will result in cessation of ureteral urine transport columnation of urine in the ureter, reflux, and direct transmission of Pdet to the renal papillae. This is the mechanism of renal damage and failure in these conditions.

    Valsalva Leak Point Pressure (VLPP)

    • Definition: the lowest total bladder pressure at which urinary leakage occurs during progressive increases in intra-abdominal pressure by Valsalva's maneuver
    • Concept [McGuire 1996]
      • Ability of urethra to resist Pabd (= resistance of urethra to the bladder)
      • Interaction between bladder pressure and outlet resistance
      • Normally the Pves component is quite small, and the major force measured is Pabd.
      • A normal urethra will not leak.
      • Similar concept: abdominal LPP or cough LPP
    • History
      • In 1993, McGuire proposed the VLPP to identify ISD [McGuire 1993]
    • Technique [McGuire 1996]
      • Performed during cystometry with a 10Fr three-lumen catheter
      • Bladder is filled slowly at 60ml/min to about 200ml
      • The patient is tilted upright
      • Patients are asked to do a progressive valsalva maneuver until the patient leaks
      • If no leakage occurs, repetitive coughing
    • Clinical meaning in SCI/D
      • Low VLPP has ISD. ISD refers to a urethra which is not mobile but nevertheless leaks with an increase in abdominal pressure. If the proximal urethra has poor or absent function the leak point pressure will be low.
      • In general the abdominal pressure which induces leakage is proportional to the strength of the continence mechanism. Thus a bad urethra will leak at low pressure, and a less bad urethra at a higher pressure. A normal urethra will not leak at any abdominal pressure. A destroyed urethra, after catheter drainage for a long time will leak at 0 to 5 cmH2O.
    • Clinical interpretation
      • In patients with stress incontinence, VLPP appears to be a good index of sphincteric function [Wan 1993]
        • VLPP<60cmH2O: type III stress urinary incontinence (ISD) [McGuire 1993]
        • VLPP>90cmH2O: type II stress urinary incontinence [McGuire 1993]
      • Strong correlation between the subjective degree of urinary incontinence and VLPP [Nitti 1995.]
      • Poor correlation between VLPP and maximum urethral closure pressure [McGuire 1993; Bump 1993]
  • Other comments
  • VLPP vary with patient position, with catheter size, bladder volume, subjective effort and with detrusor pressure changes.
  • A low compliance bladder combines the effect of Pves with Pabd and recorded VLPP do not accurately reflect the closing strength of the urethra vis a vis Pabd as an expulsive force.
  • Video (fluoroscopic) urodynamic evaluation

    • Separate Studies:
      • Simple radiography alone:
        • Providing anatomical information of the pathologic state of the SCI/D (VUR, hydronephrosis, bladder trabeculation, etc).
        • Difficult to detect DSD
      • Simple urodynamic study alone:
        • Commonly being consisted of cystometry and sphincter EMG
        • Providing functional information on the pressure of the bladder and urethra. However, it can be misinterpreted because of artifactual errors exist.
    • Videourodynamic study:
      • Concept
        • Combination of the conventional urodynamic study (cystometry and sphincter EMG) and a simultaneous image monitoring
        • Also called as fluoroscopic urodynamic study (FUDS) since fluoroscopic visualization is most commonly applied for the image monitoring.
        • Essential for investigation of complex urinary incontinence such as in SCI/D.
      • Advantages
        • Allows us to get the anatomical information (bladder, urethra, or upper tract if VUR is present) as well as functional information at the same time:
          • Bladder configuration during filling and emptying
            • Diverticulum
            • Contracted bladder
            • Bladder behavior during filling
            • Bladder behavior during emptying
          • Urethra: Accurate in detecting leakage of urine or sphincter (proximal and distal) behavior
            • Loss of proximal sphincter (ISD): contrast medium will be seen in the proximal urethra in the absence of a bladder contraction [VIDEO]
            • DSD: closed distal sphincter region during voiding phase or uninhibited detrusor contraction
            • DLPP and VLPP: detection of leakage is facilitated by fluoroscopic monitoring
          • Upper urinary tract: VUR indicating upper urinary tract damage
        • Therefore, very useful in identifying significant risk factors to the upper tract, for example, DSD, VUR, leak point pressure, areflexic voiding and etc.
      • Disadvantages:
        • Cost of the equipment
        • Expertise required to perform the test and to interpret the results in a reliable and reproducible manner.
    • Special situations when video-urodynamic study is reliably helpful in SCI/D [McGuire 1996]
      • During a simple cystometry, undetected leakage per urethra or VUR can occur, both of which detrusor compliance appear better than it really is (misinterpretation of actual bladder compliance). [McGuire 1996]
      • Dysfunction of sphincter and bladder may coexist, videourodynamic study offer a very reliable method of determining their individual functional status when that cannot be achieved with simple urodynamic test. [McGuire 1996]
      • Video-urodynamic study can offer additional information in differenciation of coexisting bladder outlet obstruction in SCI/D.
      • For case study, please refer here
    • Dr McGuire’s video-urodynamic technique: [McGuire 1996] (Video clips: PVA V323 FUDS procedure.mpg)
      • Using a triple lumen catheter, measuring Pves and Pure under the fluoroscopic visualization

    Indication and Timing of Urodynamic Study in SCI/D

    • First urodynamic study:
      • Mandatory
      • Timing:
        • Immediately after recovery from spinal shock
        • Providing the most useful information regarding bladder dysfunction
      • Purpose: to identify risk factors to the upper tract and planning future managements
    • Subsequent urodynamic study:
      • Indications:
        • Whenever symptoms evolves
        • Before the new surgical treatment will be planned
        • Confirmation of the effect of treatment
    • Long-term surveillance
      • Interval: At 18 months to 2 years most upper motor neuron lesions are fully evolved and bladder function if within acceptable parameters for pressure, and capacity will stay that way. Periodic evaluation at intervals of 2 to 5 years is acceptable. Lower motor neuron leasions are slower to evolve, and Q 6 months evaluation for 3 years is safer.
      • The objective is to determine that bladder storage activity occurs within acceptable pressure limits.
    • Also refer to this this (link to the Tx-6-2) Long-term Management Program)

     

    Key Points of This Section
    • There are instances where simple cystometry will suffice but only when there are no symptoms, and no incontinence and all the operator needs to know is at the max volume seen by this bladder are pressures safe.
    • The most important variable is bladder compliance. A normal bladder fills to capacity with little pressure increase. Abnormal compliance exists when detrusor pressures rise with filling.
    • Detrusor contractility will occur at the same volume repeatedly in these cases if present. Thus the diagnosis of DSD, reflux, altered morphology (trabeculation, etc) is straightforward with video urodynamic techniques.
    • Conditions which will give rise to poor compliance are also identifiable early and one can correct these: i.e., DSD, or detrusor areflexia with high fixed outlet resistance.
    • It is important to note that the detrusor leak point pressure and the abdominal leak point pressure measure completely different things.
    • Detrusor leak point pressures are a simple way to follow patients after sphincterotomy in quads where total sphincterotmy is the only acceptable procedure. The LPP detrusor with the condom catheter on should be less than 20 and preferably less than 10cmH2O.
    • He most complete is video urodynamics as it allows the operator to measure bladder and urethral pressure, observe bladder and urethral morphology, detect reflux, reflex voiding, DSD, incontinence, and leak point pressures.
    • Finally there are times when incontinence continues despite control of Pdet. In that case assessment of the urethral sphincter is essential. This is best done with video urodynamics and leak point pressure testing.

    References

    • Abrams P, Cardozo L, Fall M, Griffiths D, Rosier P, Ulmsten U, van Kerrebroeck P, Victor A, Wein A; Standardisation Sub-committee of the International Continence Society. The standardisation of terminology of lower urinary tract function: report from the Standardisation Sub-committee of the International Continence Society. Neurourol Urodyn. 2002;21(2):167-78.
    • Asmussen M, Ulmsten U. Simultaneous urethro-cystometry with a new technique. Scand J Urol Nephrol. 1976;10(1):7-11.
    • Brown M, Wickham JE. The urethral pressure profile. Br J Urol. 1969 Apr;41(2):211-7.
    • Dmochowski, R. R., Ganabathi, K., Zimmern, P. E. and Leach, G. E.: Coaxial needle electromyography (EMG) as an adjunct to clinical neurourologic testing. J. Urol., part 2, 153: 335A, abstract 428, 1995.
    • McGuire EJ, Cespedes RD, Cross CA, O'Connell HE. Videourodynamic studies. Urol Clin North Am. 1996 May;23(2):309-21.
    • McGuire EJ, Cespedes RD, O'Connell HE. Leak-point pressures. Urol Clin North Am. 1996 May;23(2):253-62.
    • McGuire EJ, Woodside JR, Borden TA, Weiss RM. Prognostic value of urodynamic testing in myelodysplastic patients. 1981. J Urol. 2002 Feb;167(2 Pt 2):1049-53.
    • McGuire EJ. Urodynamic evaluation of stress incontinence. Urol Clin North Am. 1995 Aug;22(3):551-5.
    • Wan J, McGuire EJ, Bloom DA, Ritchey ML. Stress leak point pressure: a diagnostic tool for incontinent children.J Urol. 1993 Aug;150(2 Pt 2):700-2.
    • Watanabe T, Rivas DA, Chancellor MB. Urodynamics of spinal cord injury. Urol Clin North Am. 1996 Aug;23(3):459-73.

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