Preparing for Urodynamic Study: Clinician, Patient, and Facility

Once the decision has been made to perform UDS on a particular patient, it is important to consider what information is expected from the test. The simple fact that a patient has symptoms or a disorder that may affect the lower urinary tract is not sufficient to start the UDS evaluation. A list of problems or questions that should be solved or answered by UDS should be made before any testing is performed. All patients are not alike, so each urodynamic evaluation may be different depending on the information needed to answer the questions relevant to a particular patient. We follow three important rules before starting the UDS evaluation (Nitti and Combs, 1998):

By following these simple rules, one can maximize the chance of obtaining useful information from a study. If a particular question is not answered, the study can be repeated in the same session. Most people who do urodynamics regularly would concur that a urodynamic test is not always perfect in answering all important questions, but by defining the information needed before starting the study, “unanswered questions” can be kept to a minimum. As mentioned earlier, one of the most important parts of UDS is its proper performance with careful attention to technical details so that accurate interpretation is possible. It is beyond the scope of this chapter to describe the proper performance of UDS in detail; however, the reader is referred to Schafer and colleagues (2002) for good urodynamic practices and Abrams and colleagues (2002) for terminology. The International Continence Society (ICS) has now defined the term “urodynamic observations” to denote those observations that occur during and are measured by the UDS test itself. In order to be consistent, it is recommended that all clinicians performing and interpreting UDS use the current ICS terminology (Abrams et al, 2002). A list of common UDS terms is provided in Table 62–1.

Table 62–1 Terminology for Common Urodynamic Terms and Observations According to the International Continence Society Standardization Subcommittee

Ideally a room of suitable size should be dedicated to urodynamics (Nitti and Combs, 1998). This area does not have to be exclusively for urodynamics, but when a study is being performed, there should not be distractions from people walking into and out of the area for other reasons. A quiet, private area is the best. It is difficult enough to recreate a natural environment during testing without outside distractions. The room should be large enough to allow for the patient to lie down to have catheters placed and also to be able to stand and sit on a commode as needed. Many patients undergoing urodynamic testing will have neurologic problems that limit mobility and will require assistance with positioning. This includes patients in wheelchairs. This must be considered when determining the size of the room. Centers that perform video-urodynamics (VUDS) will require a larger area to allow for x-ray equipment.

The importance of a well-trained, attentive, and supportive staff involved with the UDS study cannot be overemphasized. With that said, in general, UDS is well tolerated. However, patients should be properly prepared and told why the test is being done, how the results may affect treatment, and what to expect during the actual UDS test. Scarpero and colleagues (2005) used a questionnaire-based study to assess patient expectations of anxiety, pain, embarrassment, and apprehension before UDS and compared it with the patient’s actual experience. They found that UDS was associated with minimal to moderate degrees of anxiety, discomfort, and embarrassment. After testing, most respondents (>90% per question) thought that the test was the same or better than expected and had an expected or less than expected level of pain and embarrassment. This did not vary between the sexes, but a higher number of younger individuals found that the test experience was worse than expected, whereas a higher number of older individuals found that it was better than expected. Therefore younger patients may require more reassurance and attention in preparation for the procedure.

Many patients undergoing urodynamic testing will have been placed on medications that affect bladder function (e.g., antimuscarinics). For such patients the clinician should decide in advance what information is desired and whether or not the study should be done on or off medication. For example, if the goal of the study is to determine the therapeutic effect of a medication, obviously the UDS should be done with the patient on a regular dosing schedule for that medication. On the other hand, if medication was started empirically to treat symptoms and the goal of the urodynamic test is to uncover the etiology of those symptoms, then consideration can be given to discontinuing the medication before testing because this may give the highest yield.

Urodynamic Systems

Various urodynamic systems are available today. They range in price from several thousand dollars to more than 100,000 dollars depending on their complexity and the features they contain. Most high-end systems are computer-based digital systems that allow for easy data storage and postprocessing of the study. In addition, they allow for hardware and software upgrades as needed. It is beyond the scope of this chapter to describe in detail the options available for UDS systems. However, it is recommended that, when choosing a system, one must consider the patient population and spectrum of diseases frequently encountered, space, convenience of operation (if a factor), and the need for data storage and processing. In addition, it is recommended that a multichannel system in which channels are available to measure vesical pressure, abdominal pressure (and subtracted detrusor pressure), and flow rate is used. Some clinicians may also desire channels for electromyography and urethral pressure measurement. The UDS system and software market is constantly changing, so what is state-of-the-art today may seem “outdated” tomorrow. However, despite all the advances, the clinician performing the study remains the most important constant in data collection and interpretation. For the most realistic assessment, the infusant should be a liquid (e.g., normal saline or radiographic contrast) that will most approximate urine. The use of gas such as carbon dioxide is no longer recommended. Many advanced urodynamic centers now perform VUDS. Adding this capability is expensive but allows one to perform the most comprehensive study possible. There are certain clinical settings in which VUDS is the test of choice (see later). In addition to the necessary urodynamic hardware and software, a fluoroscopy unit and room of adequate size are required. Obviously, this is not practical or necessary in every setting. Video-urodynamic studies also require a greater time commitment on the part of the clinician to ensure accurate data collection.

Signal Transmission and Transducers

Transducers are the hardware that allows pressure in the patient to be measured and transferred to the UDS system. External strain-gauge transducers located “between” the patient and the urodynamic machine have been popular for years. Pressurized tubing (to avoid dampening or dissipation of the pressure) extends from the pressure transducer to the catheters placed in the patient. An electronic cable or “wireless transmission” brings the signal from the transducer to the urodynamic machine. Traditionally a water-filled system in which the entire system from transducer to patient is filled with water has been used. Since this system depends on the transmission of pressure through fluid (water), it is crucial that there are no air bubbles in the transducer or tubing. The pressurized tubing transmission lines should be lucent to allow for easy recognition of air in the line. The transducers are usually set at the level of the patient’s bladder (symphysis pubis) at the start of the study. This is important because if the patient changes position during the test (e.g., standing to sitting), the height of the transducer can be adjusted so that it remains at the level of the bladder.

More recently, air-charged catheters have become popular for pressure measurement (T-Doc, Wenonah, NJ). This catheter uses a miniature, air-filled balloon placed circumferentially around a polyethylene catheter. External forces on the balloon of the catheter are transmitted to the air-filled catheter lumen and communicated to an external semiconductor transducer. The technology of the balloon system allows circumferential measurement readings. The catheters are disposable and single use. Air-charged catheters have several practical advantages over fluid-filled pressure lines because there is no fluid connection between the patient and the urodynamic equipment—just air. This means there is no hydrostatic pressure effect to account for so that there is no need to position anything at the level of the symphysis pubis and there is no need to flush the system through to exclude air (essential when using a fluid-filled system). Also, there are no artifactual fluctuations in pressure produced when the patients move. It must also be remembered that many UDS nomograms and other “standards of measurement” were determined using fluid-filled systems. Although there is comparative evidence for the use of air-charged catheters to measure urethral pressure (Pollak et al, 2004), no studies have shown definitively that air-charged catheters provide an acceptable alternative to fluid-filled lines for measuring intravesical and intra-abdominal pressure in UDS. Thus it is recommended that investigators planning to use air-charged catheters for intravesical and intra-abdominal pressure monitoring check for themselves that they have an equivalent performance to their current system for measuring pressure (Hosker et al, 2009).

Finally a microtip or fiberoptic system can be used to process pressure transmission. Here the transducer is contained within the catheter. This in turn is connected directly into the urodynamic machine via a cable. These catheters are quite expensive but reusable. They must be sterilized before each use.

Uroflowmeters

Urine flow rate or uroflow can be determined by a number of different types of devices or uroflowmeters. Modern uroflowmeters use weight, electrical capacitance, or a rotating disc to determine urinary flow rates. The two most common techniques used today are the weight transducer or load cell method and the rotating disc method. With the load cell the voided “weight” is measured and is then differentiated with respect to time to determine the flow rate. In the rotating disc method the urine stream is directed onto a rotating disc, and the power necessary to keep a disc rotating at a constant rate is measured. This power is proportional to the flow rate. The electronic dipstick flowmeter measures the electrical capacitance of a dipstick mounted in a collecting chamber. The output of the signal is proportional to the accumulated volume, and the volumetric flow rate is determined by differentiation. Each of these methods has advantages and disadvantages. The weight transducer method is simple, reliable, and accurate regardless of the site of stream impact but requires that the density of urine must be set. The rotating disc method is also reliable and accurate, and it provides a direct measurement without need for differentiation of volume with respect to time. Electronic flowmeters provide a range of electronically read flow parameters with graphical depiction of the uroflow and have sufficient precision for clinical use with error rates of 1% to 8% in voided volume and 4% to 15% in flow rate (Susset, 1983). Variations in specific gravity of the fluid voided (infusant when doing UDS studies) can affect the calculated flow rate. Most systems allow for calibrations for various fluids such as radiographic contract.

Electromyography

Muscle depolarization must be detected by an electrode placed in or near the muscle. Several different methods are available to do this including surface electrodes and needle electrodes (the two most common methods), as well as anal plug or urethral catheter–mounted electrodes (O’Donnell, 1998). Surface electrodes are self-adhesive skin patch electrodes that are applied over the skin of the anal sphincter. Except in some neurologic diseases, the external anal sphincter EMG will be the same as the external urethral sphincter EMG. Surface electrodes have a significant advantage compared with the needle electrode regarding patient convenience and comfort. However, the surface electrodes provide an inferior signal source and must be precisely placed to provide an adequate signal source. Most clinicians feel that the concentric needle electrode is the superior technique for obtaining a signal source of EMG activity of the striated external sphincter muscles. Compared with the surface electrode, placement of the needle electrode has the disadvantage of being uncomfortable for the patient, especially if more than one attempt at placement of the electrode is required to obtain an adequate signal. Also, the needle electrode is easily dislodged and may require replacement during the study. Patients typically have a low tolerance for replacement of the needle electrode during urodynamic studies. The performance of an EMG and the selection of the type of electrode to be used depend on the UDS question to be answered.

Normal Filling and Storage

Normally, the bladder should store urine at low pressure and not contract involuntarily. Once capacity is reached or voluntary voiding is desired, intravesical pressure will increase (voluntary detrusor contraction). In actuality this is preceded by a relaxation of the external sphincter. A normalized adult CMG is shown in Figure 62–3. Normally detrusor pressure should remain near zero during the entire filling cycle until voluntary voiding is initiated. That means baseline pressure stays constant (and low) and there are no involuntary contractions.

Figure 62–3 Normal, idealized adult cystometrogram with low pressure storage until the patient is given the command to void and the voiding phase starts. Note that the baseline bladder pressure is near zero (compliant) and there are no involuntary contractions.

As mentioned previously, the simultaneous measurement of Pabd, usually by a rectal or vaginal catheter, and Pves during urodynamics provides a means of calculating the true Pdet. The ability to calculate subtracted Pdet allows one to distinguish between a true rise in detrusor pressure (either via a contraction or loss of compliance) and the effect of increased abdominal pressure (e.g., straining, Valsalva). This is especially important when rises in detrusor pressure are small or when they are accompanied by changes in abdominal pressure.

Abnormalities of Bladder Filling—Detrusor Overactivity and Impaired Compliance

During filling, involuntary detrusor contractions (IDCs) can occur. These are often associated with urgency and even urgency incontinence. Detrusor overactivity (DO) is a urodynamic observation characterized by IDCs during the filling phase, which may be spontaneous or provoked (Fig. 62–4). DO may be further characterized as neurogenic DO, which means it is associated with a relevant neurologic condition (e.g., spinal cord injury, multiple sclerosis) or idiopathic DO, which means there is “no defined cause” (non-neurogenic) (Abrams et al, 2002). The term idiopathic is a bit of a misnomer in that the cause of DO in a non-neurogenic patient may be readily apparent (e.g., bladder outlet obstruction, inflammatory process) or may be truly “unknown.” Thus from a practical standpoint, the terms neurogenic and non-neurogenic DO make sense but do not fit the ICS definitions. (It should be noted that the term neurogenic DO replaced the term detrusor hyperreflexia, and the term idiopathic DO replaced the term detrusor instability in previous ICS terminology). Neurogenic and idiopathic DO may look identical on CMG. These terms are strictly defined by the patient’s neurologic status and not the CMG appearance of the IDCs.

Figure 62–4 Detrusor overactivity. In this tracing there are two involuntary detrusor contractions (arrows). There is a rise in Pves with no associated rise in Pabd, and therefore the subtracted Pdet looks identical to the Pves.

The presence of DO during UDS must be interpreted in the context of the patient’s symptoms and condition. Ideally, a patient’s symptoms should be reproduced during UDS, so we would expect DO to be accompanied by urgency or urgency incontinence, although it can occur and be significant without being symptomatic, particularly in neurogenic DO. However, DO can also be “test induced” or clinically insignificant. It has been reported in 14% to 18% of healthy asymptomatic volunteers undergoing UDS (van Waalwijk van Doorn et al, 1992; Robertson, 1999; Wyndaele et al, 2002). This is even more dramatic in ambulatory UDS studies where DO has been found in up to 69% of asymptomatic females (van Waalwijk van Doorn, et al, 1996). Conversely, failure to demonstrate DO on UDS does not rule out its existence. It is well known that up to 50% of women with urgency incontinence do not demonstrate DO on UDS. However, the ability to suppress DO during UDS test may in and of itself be significant. For example, Osman (2003) showed that patients with mixed incontinence and a normal CMG (no DO) not only had excellent cure rates for stress incontinence but also had an 87% cure rate for urgency incontinence (compared with only 43% cure for urgency incontinence for women randomized to receive antimuscarinic medication instead of stress incontinence surgery).

It is important that the person performing the UDS study be absolutely sure that the contraction is indeed involuntary. Sometimes a patient may become confused during the study and actually void as soon as the desire is felt. The volume at which contractions occur and the pressure of the contractions should be recorded. It is often worthwhile to repeat the CMG at a slower filling rate if the patient experiences uncharacteristic symptoms associated with DO. If the patient experiences incontinence during an involuntary contraction (DO incontinence), this should be noted.

In addition to the presence of DO, its characteristics can be noted. DO can be observed as a single event or as multiple IDCs. It can be phasic (continuous), sporadic, or terminal (occurring at the end of filling near capacity). It can also be suppressed or nonabortable and may lead to leakage or precipitant micturition. Classifying DO in such a way can be valuable in certain circumstances. For example, overactivity bladder symptoms associated with obstruction have been shown to have a higher likelihood of resolving with intervention (e.g., transurethral resection of the prostate [TURP]) when DO occurs as a single terminal IDC rather than continuous or sporadic IDCs (Kageyama et al, 2000).

The viscoelastic properties of the bladder, on the basis of its composition of smooth muscle, collagen, and elastin, normally produce a highly compliant structure. Therefore as the bladder fills there is little change in pressure (see normalized CMG Fig. 62–3). Compliance is the relationship between change in bladder volume and change in detrusor pressure (Δ volume/Δ pressure) and is measured in mL/cm H₂O. The ICS recommends two standard points, the Pdet at the start of bladder filling (usually zero) and the Pdet at cystometric capacity or before the start of any detrusor contraction that results in significant leakage (Abrams et al, 2002). Both points are measured excluding any detrusor contractions. It is difficult to define what “normal compliance” is in terms of mL/cm H₂O. Several authors have shown that mean values for compliance in healthy subjects range from 46 to 124 mL/cm H₂O (Sorensen et al, 1988; van Waalwijk van Doorn et al, 1992; Hosker, 2004). However, there is great variation. For example, van Waalwijk van Doorn and colleagues (1992) showed a variation of compliance from 11 to 150 mL/cm H₂O (mean 46) in 17 healthy subjects. Some of the variation in “normal” is likely due to the fact that compliance per se is dependent on bladder capacity. Furthermore, various definitions of impaired compliance have been used (e.g., between 10 and 20 mL/cm H₂O); however, there is no consistent definition based on mL/cm H₂O. Stohrer and colleagues (1999) suggest that a value of less than 20 mL/cm H₂O is consistent with impaired compliance and implies a poorly accommodating bladder. However, examples in which this may not be the case can be cited (e.g., small cystometric capacity). Therefore in practical terms, absolute pressure is probably more useful than a “compliance number” or value. For example, it has been shown that storage greater than 40 cm H₂O is associated with harmful effects on the upper tracts (McGuire et al, 1981) (Fig. 62–5). Also, depending on the clinical scenario, a particular compliance in terms of mL/cm H₂O can mean different things (Fig. 62–6). As a general rule, prolonged storage at high pressures can lead to upper tract deterioration. Elevated storage pressures and impaired compliance should be interpreted in the context of the clinical scenario. It appears that conventional cystometry may provoke filling pressures higher than natural filling in some cases. Robertson (1999) showed that for six patients with neuropathic bladder and severely impaired compliance on conventional cystometry, compliance was actually normal on ambulatory monitoring with natural filling.

Figure 62–5 Impaired compliance. Note the rise in Pves (and Pdet) with bladder filling. The Pdet at the end of filling is approximately 45 cm H₂O, which is a potentially dangerous situation. In this case the bladder was filled to a volume of 300 mL, so the compliance is 6.67 mL/cm H₂O. The arrow is the point at which incontinence was demonstrated, which is the detrusor leak point pressure (DLPP).

Figure 62–6 A problem with measuring compliance. Shown are two theoretical cystometrograms. The one on the left demonstrates impaired compliance with a constant rise in Pdet throughout filling. At 400 mL the Pdet is 50 cm H₂O (8 mL/cm H₂O), a dangerous situation. There is significant storage time where the det is greater than 40 cm H₂O. The CMG on the right could represent a small-capacity bladder with DO and precipitant micturition. At a volume of only 40 mL, an IDC occurs. The Pdet just before this was only 5 cm H₂O. The calculated compliance would be 6 mL/cm H₂O, the same as the one on the left. Yet the CMG on the right does not demonstrate a dangerous situation, just a highly symptomatic (incontinent) patient.

Impaired compliance is seen in a variety of neurologic conditions (spinal cord injury/lesion, spina bifida) and usually results from increased outlet resistance (e.g., detrusor-external sphincter dyssynergia [DESD]) or decentralization in the case of lower motor neuron lesions. It can also result from long-term bladder outlet obstruction (e.g., BPH) (Leng and McGuire, 2003) or structural changes like radiation cystitis or tuberculosis.

The measurement of compliance can be affected by a number of factors. Sometimes an increase in Pdet during cystometry is seen as a result of rapid filling (filling during cystometry is almost always faster than physiologic filling). This is more of an accommodation problem rather than a true decrease in compliance. When Pdet is seen to be rising, filling may be stopped or reduced to see if the effect is real. An IDC, particularly if it is of sustained and low amplitude, can be confused with impaired compliance. If filling is stopped and the pressure returns to baseline, then the compliance is not impaired. Finally, a number of “pop-off” mechanisms can make compliance seem better than it actually is. Vesicoureteral reflux and bladder diverticulum are two examples. With reflux, pressure is actually transferred to the refluxing renal unit and may be harmful. The author has seen instances where the upper tract holds more urine than the bladder. VUDS (see later) is useful in these cases. Because a bladder diverticulum is actually part of the bladder, it may provide a protective effect for the upper tracts. Finally, an incompetent outlet may be a pop-off mechanism. This may only become apparent when outlet resistance is increased, which can be done during cystometry by occluding the outlet but may not be seen until the outlet resistance is surgically increased (e.g., with an artificial urinary sphincter or sling procedure).

Leak Point Pressures

Two distinct types of leak point pressures can be measured in the incontinent patient: abdominal leak point pressure (ALPP) and detrusor leak point pressure (DLPP). The two are independent of each other and conceptually measure completely different things.

ALPP is a measure of sphincteric strength or the ability of the sphincter to resist changes in abdominal pressure (McGuire et al, 1993). ALPP is defined as the intravesical pressure at which urine leakage occurs due to increased abdominal pressure in the absence of a detrusor contraction (Abrams et al, 2002). This measure of intrinsic urethral function is applicable to patients with stress incontinence. An ALPP can only be demonstrated in a patient with stress urinary incontinence (SUI). Conceptually, the lower the ALPP, the weaker the sphincter. There is no normal ALPP because patients without stress incontinence will not leak any physiologic abdominal pressure. ALPP should be measured as the total abdominal pressure required to cause leakage, not the change in pressure (McGuire et al, 1993). Therefore if ALPP is measured in the standing position, it should include the baseline Pabd (or Pves), which is usually about 20 to 40 cm H₂O. Classically, the reading is taken from the Pves channel as long as there is no involuntary contraction (Fig. 62–7). In cases where patients do not leak with a urethral catheter in place, the ALPP can be measured from the abdominal pressure channel either rectally or vaginally (Stohrer et al, 1999). The original description of ALPP was done at an arbitrary bladder volume of 150 milliliters; however, in some cases it is necessary to fill the bladder more. The volume at which ALPP is determined should be noted as some investigators have found that it decreases at higher volumes (Faerber and Vashi, 1998). As a general rule, one should start testing at 150 mL and then every 50 mL thereafter until SUI is demonstrated. If there is no SUI demonstrated at capacity, the urethral catheter is removed and ALPP is measured via the rectal catheter (provided there is no increase in Pdet from DO or impaired compliance).

Figure 62–7 Abdominal leak point pressure measurement. After progressive Valsalva maneuvers, leakage is demonstrated on the last one at 109 cm H₂O (arrow). There is no rise in Pdet.

Attempts have been made to quantify intrinsic sphincter deficiency (ISD) in women using ALPP. In 1993 McGuire and colleagues measured ALPP in 125 women with SUI. When the ALPP was less than 60 cm H₂O, all patients had high-grade incontinence with 81% having continuous leakage and 75% having a fixed urethra (no urethral hypermobility). When ALPP was between 61 and 89 cm H₂O, 80% had pronounced urethral hypermobility and moderate to high-grade incontinence. When ALPP was greater than 90 cm H₂O, patients had lesser grades of incontinence and minimal to gross urethral hypermobility. The inferences are that:

Current technology does not permit a method to distinguish between ISD in the face of urethral hypermobility in women. Therefore although these ALPP values are often used as guidelines, they should be interpreted with caution. For example, if there is no urethral hypermobility, SUI must be caused by ISD, regardless of the ALPP. Furthermore, Fleischmann and colleagues (2003) found that urethral hypermobility was equally common in women with lower versus higher ALPP. ISD and urethral hypermobility may coexist, and they do not define discrete classes of patients with stress urinary incontinence. Thus an isolated measure of ALPP without considering other factors such as cystometry and urethral mobility is of limited utility in predicting success for commonly performed female SUI procedures (Hosker et al, 2009).

The term ALPP has been used interchangeably with “Valsalva” leak point pressure (VLPP); however, this is not entirely correct. An ALPP can be measured during UDS testing by a voluntary Valsalva maneuver (VLPP) or by a cough (cough leak point pressure or CLPP). In the same person, VLPP tends to be significantly lower than CLPP. Therefore exact terminology and methods should be used when describing an ALPP. ALPP can also be influenced by the presence or the size of a urethral catheter (Bump et al, 1995; Huckabay et al, 2005; Türker et al, 2010). It has been shown in women with SUI that the larger the catheter, the lower the ALPP. ALPP can also be measured without a urethral catheter by assessing the abdominal pressure via a rectal (or vaginal) catheter. It has been shown that 15% of women with SUI (Türker et al, 2010) and 35% of men with postprostatectomy SUI (Huckabay et al, 2005) will demonstrate an ALPP only with the urethral catheter removed.

The second type of leak point pressure is the detrusor leak point pressure (DLPP), which is a measure of detrusor pressure in patients with decreased bladder compliance. It is defined as the lowest detrusor pressure at which urine leakage occurs in the absence of either a detrusor contraction or increased abdominal pressure (Abrams et al, 2002) (see Fig. 62–5). The higher the urethral resistance, the higher the DLPP. One can imagine that in a poorly compliant bladder, if outlet resistance is low, incontinence will occur at a relatively low or “safe” pressure. However, if outlet resistance is high, the pressure in the bladder will continue to increase as the bladder fills. There is potentially less incontinence, but eventually the pressure is transmitted to the upper tracts (Fig. 62–8).

Related posts:

Definitive Therapy for Localized Prostate Cancer: An Overview Tuberculosis and Other Opportunistic Infections of the Genitourinary System Surgical Procedures for Sphincteric Incontinence in the Male: The Artificial Genitourinary Sphincter and Perineal Sling Procedures Prosthetic Surgery for Erectile Dysfunction Neuropathic Dysfunction of the Lower Urinary Tract Ectopic Ureter, Ureterocele, and Ureteral Anomalies

Stay updated, free articles. Join our Telegram channel

Join