The purpose of this article is to update urologists on contemporary indications and techniques for adult urodynamic testing. The discussion includes examples of specific clinical questions and appropriate urodynamic testing techniques to address these questions. It includes quality control measures and examples of testing pitfalls with troubleshooting methods.
Key points
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Optimal use of urodynamic testing requires the formulation of urodynamic questions.
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The purpose of urodynamic testing is to supplement a patient’s clinical history and physical examination with a series of tests that are designed to assess the storage and voiding phases of micturition using noninvasive and invasive methods.
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Appropriate ancillary staff training and patient preparation are essential to a successful urodynamic examination.
Introduction
Urodynamic testing has become a standard part of the available diagnostic armamentarium for the evaluation of patients with lower urinary tract dysfunction. Optimal use of an urodynamic test requires the formulation of urodynamic questions, namely, “What is the information I need to obtain from the test?” and “What is the most appropriate urodynamic technique to obtain these results?” An understanding of when to use certain urodynamic tests can be derived from the literature, from clinical practice guidelines, and from clinical experience.
Introduction
Urodynamic testing has become a standard part of the available diagnostic armamentarium for the evaluation of patients with lower urinary tract dysfunction. Optimal use of an urodynamic test requires the formulation of urodynamic questions, namely, “What is the information I need to obtain from the test?” and “What is the most appropriate urodynamic technique to obtain these results?” An understanding of when to use certain urodynamic tests can be derived from the literature, from clinical practice guidelines, and from clinical experience.
Urodynamic testing in context
The purpose of urodynamic testing is to supplement a patient’s clinical history and physical examination with a series of tests that are designed to assess the storage and voiding phases of micturition, using noninvasive and invasive methods. Observations seen during these tests and the clinician’s interpretation can help identify potential bladder safety issues (eg, elevated bladder storage pressures), help to guide treatment, predict outcomes, and correlate with patient quality of life.
Before performing a urodynamic test, a clinical evaluation should be completed to identify the relevant urodynamic questions. A thorough history is necessary to obtain a clear understanding of the patient’s complaints, including type of symptoms (ie, urgency, frequency, urge incontinence, stress incontinence, pain, other voiding and storage symptoms), severity and duration of symptoms, bother associated with the symptoms, previous therapies, and relevant medical comorbidities. A physical examination can identify specific findings (pelvic prolapse, urethral diverticulum, pelvic mass), which may contribute to or cause the symptoms of interest. Patients can also be asked to complete a voiding diary to assess objectively fluid intake, voided volumes, episodes of incontinence, and voiding frequency. Pad-weight testing helps quantify the amount of urine lost during incontinence episodes. Data from validated questionnaires help to quantify symptoms and their affect on quality of life. To be most useful, data obtained from a urodynamic test must be considered as supplemental to clinical data. For instance, identification of stress incontinence on a urodynamic test is of limited importance if the patient reports severe urge incontinence as the primary complaint.
Overview of urodynamic testing
Both noninvasive and invasive urodynamic techniques can be used to help qualify and quantify lower urinary tract activity during the micturition cycle. Noninvasive tests include uroflowmetry and postvoid residual (PVR). Invasive tests include cystometry, sphincter electromyography (EMG), videourodynamics (VUDs), pressure-flow study (PFS), and urethral function tests. An appropriately formulated urodynamic question might warrant one or more of these individual procedures to answer the question. We will begin with an overview of noninvasive urodynamic tests. We will then discuss invasive urodynamic tests, with separate sections devoted to the storage and voiding components of the micturition cycle.
Preparing the patient for invasive urodynamic testing can greatly affect usefulness and efficacy of the test. Patients generally tolerate urodynamic testing well, but feelings of anxiety, discomfort, and embarrassment are not rare. Studies of patient experiences with urodynamic testing indicate that more than 70% of patients would be willing to repeat invasive urodynamic testing if medically indicated and most thought the testing was the same or better than they expected it would be. As with all invasive procedures, informed consent should be obtained and all questions addressed.
It is the authors’ practice to distribute standard patient instructions about urodynamics before the testing. These explain the testing procedures using nonmedical terminology, as well as the rationale for the testing. Patients are instructed to maintain their regular diet and to take their scheduled home medications. They are asked to arrive to the clinic with a full bladder to provide a urine specimen and possibly perform an initial noninvasive uroflow study. Poststudy instructions explain that they can resume routine activities and that they may experience mild dysuria, hematuria, and/or increased bladder sensitivity for 24 to 48 hours after the test.
All patients should undergo urinalysis to screen for signs a urinary tract infection at the time of procedure. Patients with a symptomatic infection should have the urodynamic test deferred until the infection has been treated. Limited data exist regarding the usefulness of preprocedural antibiotic administration. The American Urological Association (AUA) Best Practice Statement on Urologic Surgery Antimicrobial Prophylaxis states that antibiotic prophylaxis before urodynamic testing is indicated only in patients with risk factors, specified as advanced age, anatomic anomalies of the urinary tract, poor nutrition status, smoking, chronic corticosteroid use, immunodeficiency, externalized catheters, colonized material, coexistent infection, and recent prolonged hospitalization. Recommended antibiotics include oral fluoroquinolones or trimethoprim-sulfamethoxazole; however, patient allergies, prior urine cultures, and local antibiogram patterns should be considered.
Patients with spinal cord injuries above T6 are at risk for experiencing autonomic dysreflexia (AD) during bladder filling, characterized by an acute increase in blood pressure and bradycardia, accompanied by symptoms such as headache, piloerection, skin pallor, profuse sweating, or skin flushing. Untreated AD can result in intracranial hemorrhage, retinal detachment, seizures, and death. A prior history or the risk for AD should be noted and appropriate preparations and/or precautions followed. Many patients know their typical triggers and these most often involve simulation of the bowel or bladder. Preparations in the urodynamic test suite include monitoring blood pressure and heart rate throughout the study. If symptoms of AD are identified during urodynamic testing, the trigger (usually filling of the bladder or catheter placement) should be removed by draining the bladder and then removing catheters if needed. Additionally, the patient should be placed in reverse Trendelenburg (head up) to take advantage of any gravitational reduction in blood pressure and loosen any tight clothing or restrictive devices. If blood pressure elevation does not resolve, 1 to 2 inches of nitropaste can be applied to the chest and wiped off after blood pressure values normalize.
As with all invasive procedures, certain patients may also experience vasovagal syncope during urodynamic testing. For this reason, some centers have a policy that all patients, male and female, perform the voiding phase of the study in the seated position. In contrast to treatment of AD, vasovagal syncope requires the patient be placed in the Trendelenburg position to increase blood flow to the head and/or chest.
Noninvasive Emptying Assessment
Uroflowmetry (uroflow) is a noninvasive method to measure the flow of urine during micturition. Patients are instructed to void with a comfortably full bladder. Measurements obtained during uroflow are peak flow rate (Qmax), average flow rate, voiding time, voided volume, and flow pattern (eg, flat, bell-shaped curve, saw-tooth, intermittent). Voided volume must be equal to or greater than 150 mL for uroflowmetry results to be valid. A reduced flow rate suggests the presence of bladder outlet obstruction, reduced bladder contractility, or both. Because patients are not always able to complete the voiding phase of multichannel urodynamic testing, noninvasive uroflow can be a useful adjunct after the filling portion of a PFS has been completed.
PVR can be measured directly by draining the bladder with a catheter, or indirectly with bladder ultrasound or fluoroscopy (if radiopaque contrast has been instilled into the bladder before voiding). Bladder outlet obstruction can be due to many causes that can be suggested by clinical history, but cannot be diagnosed with just PVR testing.
Assessment of Bladder Storage Function
Simple cystometry is an inexpensive evaluation that can assess bladder sensation and detrusor behavior during filling. It can be performed in a regular examination suite in either the standing or supine position. The study requires a small sterile catheter (usually 12–14F) and a 60 mL catheter-tip syringe with the plunger removed. Room temperature sterile saline or water is used as the filling fluid. The catheter is inserted per urethra with sterile technique and PVR volume measured. The syringe is attached to the end of the catheter as a funnel. Using gravity, the fluid is gradually poured (approximately 50 mL/min increments) into the funnel to fill the bladder. As filling proceeds, the patient is asked to report their first sensation of bladder filling, normal desire to void, strong desire to void, and maximum bladder capacity. In the authors’ practice, the scripted questions we ask our patients are (1) first sensation, “Tell me when you first feel any fluid or a coolness in your bladder;” (2) first desire to void, “If you’re watching TV, tell me when you would go to the bathroom at the next commercial;” (3) strong desire to void, “Tell me when you can’t wait for the next commercial;” and (4) maximum capacity, “Let me know when you can’t hold any more in your bladder.” Involuntary detrusor contractions can be seen by watching the meniscus in the syringe as a backpressure against gravity. Care should be taken to correlate these observations with any patient movement. If indicated, a full bladder cough stress test can be performed after the catheter is removed.
Complex filling cystometrogram (CMG) allows for measurement of bladder pressure during filling. Single-channel recording of bladder pressure can offer information about bladder sensation, capacity, compliance, and involuntary detrusor contractions. The urodynamic catheter (6–10F) is placed into the bladder and room temperature fluid is instilled at 30 to 50 mL per minute. Bladder sensation (first sensation, normal desire, strong desire, and maximum capacity) is assessed. Studies in healthy volunteers indicate that these sensations are reproducible. Extremes in sensation likely represent a pathologic abnormality.
Commonly, disposable air-charged or water-filled urodynamic pressure-measurement catheters are used to perform cystometry. Air-charged catheters are newer in design; therefore, most prior research was based on water-filled systems. There are notable differences in how each catheter responds to changes transient and sustained pressures and they do not give interchangeable results. However, both catheter types are widely accepted for clinical use, and most observed differences are outside the range of what is generally relevant to urodynamic studies. Standard double- and triple-lumen catheters are available. Double-lumen catheters have one port for fluid inflow and a second port to measure vesical pressure (Pves). Triple-lumen catheters provide a third, more proximal, sensor port, which can be positioned at the level of the external urethral sphincter to measure bladder and urethral pressure simultaneously.
Multichannel urodynamic testing is the stepwise addition of a rectal catheter to a filling CMG, to measure abdominal pressure (Pabd). This allows the testing clinician to incorporate information about the relative contribution of Pabd changes (ie, with cough or Valsalva) to bladder behavior. Rectal catheters come in multiple styles, including fluid-filled rectal balloon and air-charged catheters. Both types of catheters are placed in the rectal vault, proximal to the anal sphincters. Presence of stool in the rectum can affect Pabd readings. In patients without a rectum, the catheter can be placed either in the vaginal vault or in a fecal stoma to allow measurement of the Pabd. Regardless of catheter system, the International Continence Society (ICS) recommends that all urodynamic catheters be zeroed to atmospheric pressure and reference height is set to the level of the upper edge of the pubic symphysis.
In urodynamic terminology, Pves is the measure of the bladder pressure and Pabd is the abdominal pressure measured by the catheter in the rectum. Detrusor pressure (Pdet) is the difference of Pves minus Pabd. Calculation of Pdet is often important as a measure of detrusor muscle function in patients who are able to generate Pabd. Whereas the calculated Pdet represents the viscoelastic properties and tone of the bladder wall, all three tracings (Pves, Pabd, and Pdet) should be evaluated when looking at a urodynamic study to monitor for artifacts and other factors contributing to the Pdet tracing.
Sphincter EMG is an indirect measure of pelvic floor and urethral sphincter muscle contractility. This is a measurement of depolarization of the sphincter muscle membrane. Urodynamic questions that can be answered include information about outlet contraction and relaxation in relation to the timing of other components of the urodynamic study. EMG is typically performed with surface patch electrodes, placed on the perineum. Needle electrodes EMG can be used but are more invasive and uncomfortable.
In a normal urodynamic study, the sphincter EMG has a baseline resting activity that may increase slightly as the bladder fills (guarding reflex). EMG activity will also increase with stress or Valsalva maneuvers. During the first phase of voiding, there should be cessation of activity as the urethral sphincter relaxes. If EMG activity increases with voiding, this may represent detrusor-sphincter dyssynergia (DSD), dysfunctional voiding, or normal attempts to prevent voiding in the presence of an involuntary detrusor contraction. DSD is found in patients with suprasacral spinal cord lesions. As an example, a 58-year-old man with an incomplete C2/3 spinal cord injury demonstrates a strong involuntary detrusor contraction, with DSD based on both increased intraluminal urethral pressure and increased sphincter EMG activity ( Fig. 1 ).
VUDs, or fluorourodynamics, involve synchronous radiographic imaging of the bladder with multichannel urodynamic testing. It was originally (1970) called this because the information was recorded to videotape. Ultrasonography is an alternative imaging modality but not used widely. Fluoroscopy is used to offer dynamic images of the anatomy with maneuvers. Other pathologic findings can be visualized with these images, including vesicoureteral reflux, urinary tract stones, and bladder diverticula.
The use of fluoroscopy offers useful information in complex patients. For example, a 75-year-old man presented for evaluation of stress urinary incontinence, urinary frequency, and recurrent urinary tract infections ( Fig. 2 ). He had a urologic history notable for a robotic-assisted laparoscopic radical prostatectomy for prostate cancer with concomitant bladder diverticulectomy 1 year before presentation. Postoperatively, he developed a bladder neck contracture that was dilated and he now performs obturation daily. Urodynamic evaluation showed first desire to void at 90 mL, strong urge at 121 mL, and capacity of 144 mL. Pdet rose from a baseline of 0 cm H 2 O to 9 cm H 2 O at a volume of 144 mL. Pves, on the other hand, rose from a baseline of 34 cm H 2 O to 48 cm H 2 O at a volume of 144 mL. He had involuntary detrusor contractions at 90 mL and 122 mL, with incontinence. Overall, these findings suggest normal detrusor compliance, reduced bladder capacity, detrusor overactivity, and intrinsic sphincter deficiency. However, fluoroscopy demonstrated a bladder diverticulum and bilateral vesicoureteral reflux (grade II–V on the left side and grade III–V on the right side occurred at 33 mL with 0 cm H 2 O and 70 mL with 3 cm H 2 O, respectively). The diverticulum filled more and the reflux increased bilaterally with voiding. Because of the vesicoureteral reflux, comment cannot be made about the patient’s true bladder compliance because there is no longer a closed pressure reservoir and the bladder pressure may appear falsely safe. Addition of fluoroscopy alters both interpretation and recommended treatment of this patient.
