Urodynamics
Gunnar Lose
Niels Klarskov
Introduction
Urodynamics (UDS) comprise all the measurements that assess the function and dysfunction of the lower urinary tract (LUT) by any appropriate method.1 Consequently, UDS can be subdivided into the following:
Invasive UDS, which are tests that involves insertion of one or more catheters or any other transducer into the bladder and/or other body cavities, or the insertion of probes or needles, for example, for electromyography (EMG) recording.1
Noninvasive UDS are those tests performed without insertion of catheters, needles, or probes into the bladder and/or other body cavities, for example, micturition diary, uroflowmetry, or postvoid residual (PVR) measurement by ultrasonography.1
UDS testing provides an objective description of LUT function and dysfunction in terms of qualitative and quantitative variables during: (1) bladder filling and storage and (2) bladder emptying.
Urodynamic investigations and terms are standardized.1,2 The International Urogynecological Association (IUGA)/International Continence Society (ICS) terminology report highlights the need to base diagnoses for female pelvic floor dysfunction on the correlation between a woman’s symptoms, signs (Table 12.1), and any relevant diagnostic test including UDS.2
UDS tests have gradually been developed and implemented clinically since the 1950s. The mantra has been, “If urodynamics is not very useful clinically, it is not important to understand how the LUT functions in order to treat it” (Derek Griffiths).
The rational for the development and use of UDS testing stems from consistent clinical findings showing a weak correlation between symptoms and the underlying dysfunction documented by UDS. Furthermore, it has turned out that only a minor fraction (about onethird) of women urodynamically tested before surgery for stress urinary incontinence (SUI) can be classified as “uncomplicated” SUI. It has been reported that up to 40% of uncomplicated SUI women will have their symptomatic diagnosis changed versus 75% of those classified as complicated after invasive UDS.3 Thus, even in women with symptomatic pure SUI, invasive UDS may unveil detrusor overactivity (DO) and/or unsuspected voiding dysfunction (VD). Consequently, a history of pure SUI yields a positive predictive value and a negative predictive value of the order 70% in predicting only urodynamic SUI.4 Hence, a normal invasive UDS does not exclude the diagnosis of SUI.
Between 2009 and 2017, several retrospective and prospective studies and one small randomized controlled trial have demonstrated that UDS can guide appropriate decision-making in female SUI. However, it has not been possible, so far, to establish robust evidence regarding the clinical value of UDS before stress incontinence surgery.5 Three recent randomized controlled trials (VUSIS-I/II and VALUE study)6,7,8 have unfortunately had major conceptual flaws first and foremost breach in the principle of good urodynamic practice (GUP) but also in the choice of UDS, quality, expertise, lack of clear definition of urodynamic entities, and lack of relationship between the result of the urodynamic question and the treatment strategy. The VALUE study (referred to as “high-quality evidence”) has obtained “landmark” status, although the study does not follow the principles of GUP by asking a urodynamic question before the investigation and most remarkably the result of the UDS testing had little or no weight in the decision regarding treatment approach (in both the invasive UDS group and the office group, 93% had the same treatment namely a midurethral sling). If you do not use the result of a test, you cannot evaluate its usability!
However, altogether, accumulative evidence indicates that UDS can reduce the dangers of empiric management in female LUTs.5
GOOD URODYNAMIC PRACTICE
GUP was defined by the ICS in 2002.9 GUP comprises three main elements:
A clear indication for and appropriate selection of relevant test measurements and procedures
Precise measurement with data quality control and complete documentation
Accurate analysis and critical reporting of results
TABLE 12.1 Examples of Lower Urinary Tract Diagnoses | ||||||||||||||||
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The aim of clinical UDS is to reproduce the patient’s symptoms while making precise measurements in order to identify the underlying causes for the symptoms and to quantify the related pathophysiologic processes. By doing so, it should be possible to establish objectively the presence of a dysfunction and understand its clinical implication.
Thus, we may either confirm a diagnosis and/or give a new specifically urodynamic diagnosis that might alter diagnosis or treatment. For example, symptomatic SUI may turn out to be caused by DO or the general diagnosis (urodynamic SUI) may be correct, but additional urodynamic findings (DO, bladder outflow obstruction [BOO], or detrusor underactivity [DU]) mandate therapeutic considerations.
Thus, GUP implies a urodynamic “question” followed by an “answer,” and treatment guided accordingly.
In 2017, an updated ICS GUP 2016 version was published which provides evidence-based specific recommendations for routine clinical urodynamic testing and includes expert consensus where evidence is lacking. This rapport has newly or more precisely defined more than 30 terms and provides standards for practice, quality control, interpretation, and reporting of UDS.1
The reporting of UDS in medical journals may be unclear and ambiguous. For example, in some papers, UDS means invasive UDS. In other papers “homemade” definitions are used. UDS should be reported in a clear meaningful way, which implies clear definition of the urodynamic tests used, following the principles of GUP and sticking to IUGA/ICS standardization and terminology.10
INDICATION FOR URODYNAMICS
Basic assessment of women with urinary incontinence or VDs aims to identify patients with complicated symptomatology and findings (signs). ICS (working group) suggests, as a minimum, all ICS standard urodynamic test data, that is, (1) a clinical history (should include valid symptom[s] and bother score[s] and medication list), (2) relevant clinical examination, (3) (3-day) bladder diary (rule out polyuria >20 mL/kg/24 h), and (4) representative uroflowmetry with PVR.1 Clinical examination may also include a cough stress test (detect leakage = sign) and pad testing (quantification of leakage).
The indication of invasive UDS in terms of transurethral cystometry and pressure-flow study (PFS) is still a matter of debate. According to the ICS, “standard urodynamic protocol”1 cystometry and pressure flow is routinely recommended. However, the indication depends on the urodynamic question. The gain is dubious in uncomplicated women with predominantly SUI and a normal uroflowmetry and PVR.
The indication for invasive UDS, however, is strong, especially before surgery in the following:
“Complicated” patients (e.g., recurrent incontinence after surgery, voiding symptoms, or previous pelvic surgery)
Urgency predominant mixed urinary incontinence
Unclear type of urinary incontinence
Abnormal uroflowmetry (decreased maximum flow rate and/or abnormal flow curve configuration) and/or increased PVR
The challenge is when choosing UDS to find an appropriate balance between reducing the danger of empiric management and the drawbacks of especially invasive UDS.
Although UDS generally is well tolerated, there are drawbacks. UDS testing is time-consuming and costly, and it may evoke discomfort and anxiety. Invasive tests may be painful, and catheterization of the bladder carries a small risk of introducing infection (<5%). There are other issues such as technically challenging, burdensome, prone to methodologic errors (artefacts), and the issue of reimbursement.
An explanatory leaflet about UDS may be helpful for both patients and the staff.
Patients with Pelvic Organ Prolapse
Noninvasive UDS may show signs on voiding difficulties in terms of decreased flow rate or abnormal flow curve and/or increased PVR especially in women with a large pelvic organ prolapse (POP).
The risk of de novo urinary incontinence after POP surgery is in average about 15%.11 A variety of preoperative tests have been tried to uncover occult SUI, but no reliable test has been identified so far. Conversely, women with combined SUI and POP may have their incontinence improved or cured after POP surgery. Currently, however, there is no consensus about the role of UDS before POP surgery, but it is important that patients undergoing POP surgery is informed of the risk of de novo incontinence.
TABLE 12.2 Urodynamic Examinations Divided into Invasive and Noninvasive and Filling versus Emptying Phase Tests | |||||||||||||||||||||||
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Urodynamic Examinations
The LUT has two opposite functions: (1) bladder filling and storage where the bladder pressure is low while the bladder distends and the urethral pressure is relatively high and (2) bladder emptying where the urethral pressure drops to a pressure close to zero followed by a detrusor pressure increase. Urodynamic tests can be divided into those that evaluate the LUT in the filling phase and in the emptying phase. A filling phase test cannot uncover pathology during bladder emptying and vice versa. For example, a high urethral pressure measured during storage is not indicative of bladder outlet obstruction. The urodynamic tests can be divided into a 2 × 2 table based on if it is a filling or emptying phase test and if it is an invasive or noninvasive test (Table 12.2).
NONINVASIVE TEST OF BLADDER FILLING
Bladder Diary
The woman measures and notes the time and amount of voided volume and fluid intake. The bladder diary often includes the incontinence episodes and degree of incontinence, urgency episodes, pad usage, and activities during or immediately preceding the leakages. The ideal duration of the bladder diary has not yet been established. A short duration increases patient compliance, although the more days recorded, the better the spectrum or variation is recorded. A diary should at least cover 24 hours, but 2 to 3 days will generally provide more useful clinical data. A 7-day bladder diary might be used in clinical studies. The bladder diary should be representative for the patients daily living and the woman should perform her normal daily activities during the registration period. Table 12.3 shows the information which can be obtained from a bladder diary.
The bladder diary is mandatory as initial assessment of patients with LUT syndrome. Unfavorable amount and timing of fluid intake can be disclosed, and the diary may be therapeutic as it provides insight into behavior and can be used to monitor the treatment during follow-up.
Polyuria should be addressed before further UDS. Figure 12.1 shows an example of a bladder diary.
Pad Test
The pad test is a diagnostic method for detection and quantification of urine leak based on weight gain in absorbable pads. The pads are weighted before and after the test, and the weight gain is the results of the test. The tests can be divided into office-based and home-based tests.
The office-based tests are short tests from 20 minutes to 2 hours. The bladder volume, fluid intake, and physical
activity can be standardized during the test. The homebased tests are conducted under circumstances as close as possible to the woman’s standard daily life with normal activities often combined with a bladder diary. The test typically lasts 24 hours, but tests up to 72 hours have been tried; however, the longer test only increases the sensitivity slightly but decreases the patient compliance.
activity can be standardized during the test. The homebased tests are conducted under circumstances as close as possible to the woman’s standard daily life with normal activities often combined with a bladder diary. The test typically lasts 24 hours, but tests up to 72 hours have been tried; however, the longer test only increases the sensitivity slightly but decreases the patient compliance.
TABLE 12.3 Information Obtained with a Bladder Diary and the Definitions of the Entities | ||||||||||||||||||||||||
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 FIGURE 12.1 A bladder diary from a woman with nocturia and nocturnal enuresis. Nocturnal urine volume is 200 + 250 + 300 + 100 (from the pad) = 850 mL, which is 45% of the 24-hour urine production; thus, the woman has nocturnal polyuria. The woman drinks 800 mL in the evening and 100 mL during the night which explains the nocturnal polyuria. The woman had fluid restriction during the evening which cured her symptoms. |
 FIGURE 12.2 A schematic representation of urine flow over time. (From Haylen BT, de Ridder D, Freeman RM, et al. An International Urogynecological Association [IUGA]/International Continence Society [ICS] joint report on the terminology for female pelvic floor dysfunction. Int Urogynecol J 2010;21[1]:5-26, with permission.) |
The pad test cannot be used to diagnose the type of incontinence and the reproducibility is generally low. The home-based test has higher sensitivity in detecting urinary incontinence compared to the office-based test.
A small group of women have the unusual complain of incontinence unassociated with symptom of stress or urgency incontinence. The leakage is not associated with urgency or increased abdominal pressure and is often described as continuously leaking despite that the woman often only uses few panty liners per day. Incontinence cannot be demonstrated objectively at stress test or during a cystometry. In these cases, vaginal discharge or sweat might be suspected rather than urinary incontinence. Urinary incontinence can be verified or refuted by coloring the urine during the pad test. The urine can be colored bright yellow by an oral intake of a high dose of vitamin B2 (riboflavin).
 FIGURE 12.3 Liverpool Nomogram for maximum urine flow rate in women. (From Haylen BT, Yang V, Logan V. Uroflowmetry: Its current clinical utility for women. Int Urogynecol J Pelvic Floor Dysfunct 2008;19[7]:899-903, with permission.) |
NONINVASIVE TEST OF BLADDER EMPTYING
Uroflowmetry is a noninvasive test that produces flow rate of the external urinary stream as volume per unit time in milliliter per second (Fig. 12.2).
The patient voids into a flowmeter in privacy, in her preferred position, when the bladder is reasonably full, and a normal sensation of voiding. The patient should confirm that the voiding is representative.
The urine flow is continuously measured and demonstrated graphically (see Fig. 12.2). Maximum flow rate (Qmax) is the measured value of the maximum flow rate correcting for artefacts. Uroflowmetry minimally reports Qmax and volume voided. Total voided volume, shape of the flow curve, Qmax, and average flow (Qave) (voided volume/voiding time) are typical variables used for assessing the bladder emptying function (see Fig. 12.2). If the uroflowmetry values are not normal, it is appropriate to repeat examination to ensure reproducibility. Normal Qmax depends on the voided volume which appears from the Liverpool nomogram (Fig. 12.3).
When voided volume is greater than 150 mL, a Qmax greater than 15 mL/s is normal.
When voided volume is greater than 150 mL, a Qmax greater than 15 mL/s is normal.
The flow curve describes the interaction of the detrusor/bladder function and the urethra function. Uroflowmetry can be used as screening for voiding difficulties. Thus, decreased flow rate and/or long-lasting flow indicates either a weak detrusor and/or urethral obstruction. An intermittent flow curve (Fig. 12.4A) indicates the use of Valsalva during voiding and/or obstruction/weak detrusor or eventually detrusor/sphincter dyssynergia. The specificity of flow rate and pattern regarding the underlying dysfunction is low. In a case of abnormal findings, the test should be repeated to confirm consistency before a diagnosis is confirmed. When a reproducible low Qmax or abnormal flow-curve shape is present, voiding cystometry (pressure/flow study) is indicated to distinguish between obstruction or DU.
 FIGURE 12.4 A 72-year-old woman with increased daytime urinary frequency, nocturia, and recurrent urinary tract infections. The Qmax at the free flow is 7.5 mL/s (A), average flow 1.9 mL/s, total voided volume is 131 mL, and the curve shows an intermittent pattern. The PVR urine was 230 mL. DU was demonstrated at the PFS (B), and the patient was treated with clean intermittent catherization. |
Postvoid Residual Volume
PVR is the remaining intravesical fluid volume determined directly after completion of the voiding. It can be measured either by a transurethral catheter or by ultrasonic scanning.
PVR reading may be erroneously elevated by delayed measurement due to renal input (1 to 14 mL/min) into bladder volume. Upper normal limit “immediate” (e.g., transvaginal ultrasound) has been reported to be 30 mL, whereas studies using urethral catheterization (up to 10 minutes delay) quote upper limits between 50 and 100 mL.
Abnormal PVR requires repeated measurement for confirmation.
The indication for PVR measurement follows uroflowmetry; however, women may have severe VD without an abnormal PVR.12
Decreased Qmax, Qave, and/or increased PVR and/or Valsalva have been reported to be risk factors for VD following midurethral sling placement. However, there is no consensus regarding cutoff levels for the variables.
INVASIVE TEST OF BLADDER FILLING
Cystometry
Cystometry is a measure of the pressure-volume relationship during bladder filling. The aim is to asses bladder sensation, capacity, compliance, and detrusor activity and associated incontinence episodes during bladder filling. Two catheters are placed in the bladder (one double-lumen catheter or two separate catheters). The bladder is filled with saline solution (or x-ray contrast in case of cideo urodynamics) through one of the lumens, and the intravesical pressure is measured through the other. The abdominal pressure is preferably measured in the rectum; however, it can be measured in the vagina or in a stoma if it is not possible in the rectum.
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