This article provides a basic overview of the function and utility of common urodynamic studies (UDS). Continence nurses and other healthcare providers unfamiliar with the concepts involved may find it useful to understand how and why urodynamic studies are undertaken in order to support their own decision-making for patients with continence problems.
This explanation focuses on one centre's approach to undertaking UDS. There often exist minor variations between centres in, for example, choice of monitoring catheters (where solid state probes may be used instead of fluid-filled channels) or the position of the patient during the filling phase. Within this, individual patient requirements represent further modifications to be made, such as in the case of a patient who cannot stand or sit. However, the principles of urodynamics remain broadly the same everywhere.
Further information and guidance may be obtained in the Continence Society's Minimum Standards for Urodynamic Studies (Abrams et al, 2019) and Drake et al's (2018) article, based on the International Continence Society's recommendations. A good basic introduction is provided by Chapple et al (2019).
Put simply, UDS investigate the pressures inside the lower urinary tract when the patient's bladder fills, stores and empties. For the purpose of this discussion, the term UDS broadly applies to the generation of cystometric traces (CMGs) rather than other forms of UDS (indicated in Box 1). The procedure aims to simulate the patient's urinary symptoms in order to obtain a clear diagnostic picture of lower urinary tract functionality. These results may then inform future management by ensuring treatment plans are formulated in line with the specific underlying problem. As an example, UDS can be particularly helpful in defining whether stress urinary incontinence or overactive bladder is the primary cause of the patient's urinary leaks.
| Ambulatory urodynamics | Urodynamic testing equipment is attached to the patient who is then asked to go outside the unit and walk around. Events such as bladder contractions and leaks are recorded both by the testing equipment and the patient, who presses a button on the equipment carried. This form of testing is useful for capturing symptoms that have not been or cannot be evidenced by standard urodynamic studies (UDS) |
| Video urodynamics | Standard urodynamic testing is undertaken under radiological control. In place of sodium chloride or sterile water, a radiopaque fluid is used during the filling phase. X-ray equipment then allows the technician to visualise the urinary tract at the same time as the cystometrogram traces are generated. This is useful when investigating patients where anti-incontinence surgery has failed, there is neurological dysfunction or anti-incontinence surgery is anticipated in the male patient. This test is known as video urodynamics because changes in the lower urinary tract are visualised on the X-ray equipment as the test progresses. This may also be recorded as a video file for the patient's records |
| Urethral pressure profiles and ano-rectal manometry | Some centres use these investigations alongside urodynamic studies in order to augment the clinical information received. Sphincter function is looked at more closely with these tests, which may further refine clinical management |
| Non-invasive flow testing | The patient is asked to attend clinic with a full bladder and is then directed to void into the flow machine funnel. The velocity of the fluid hitting the bottom of the jug is picked up by the transducer and is translated into a voiding curve trace on a printout. This is a common first investigation into voiding difficulties, but will not provide the intravesical bladder information or differential diagnoses as do UDS |
Patient care
Due to the intimate nature of the investigation, it is important to be aware that patients may, understandably, be embarrassed or frightened at the prospect of UDS. The nurse can help the patient overcome this by providing reassurance and focusing on the fact that the short test is the first step in improving their symptoms.
The test involves insertion of fine monitoring catheters into the patient's bladder and rectum which may cause very transient discomfort. The patient may be fearful of experiencing the symptoms (such as leaking) that cause them so much shame and embarrassment while being witnessed by the technician. Finally, the patient may be asked to void into the UDS commode or into a funnel within the clinical environment which is very different from the privacy usually sought when passing urine.
All these issues can conspire to obscure the faithful replication of the patient's usual symptoms, so it is incumbent upon the technician to set the patient at ease in providing privacy, dignity and reassurance as far as possible.
The urodynamic studies procedure
On attendance for the appointment, the patient is invited to bring a frequency volume chart (FVC) detailing 3 days of fluid intake and output. FVC alone can provide some useful information on urinary frequency, episodes and timing of leakage, and diurnal variation in the voiding pattern. Equally, it gives a clear picture of fluid intake type and volumes. The patient is also asked to bring a list of current medications. All of this information is analysed in conjunction with the objective findings of the UDS procedure in order to inform the clinical picture. Generally, and where possible, the patient is asked to temporarily suspend medications that have an impact on bladder function before the test.
A full explanation of the procedure is provided in order to obtain informed consent. It is important for the patient to understand the risks as well as the benefits. Risks include minor transient irritation to genital tissues, risk of urinary tract or environmental infection and failure to gain satisfactory information necessitating a further attendance.
At the appointment, the patient is asked to lie on the examination couch where a post-voiding bladder scan may be obtained. The patient's genitalia are examined before a lubricated 8Ch (Charrière) bladder monitoring catheter (used in both men and women) is inserted urethrally in a aseptic manner. This duel lumen monitoring catheter allows filling of the bladder with sterile fluid by one channel and monitoring bladder pressure by the other. Once this line is secured with surgical tape, the rectal line is then placed in order to sit just beyond the anal margin. The rectal line terminates in a small, soft balloon with a small opening slit cut into the side and is again inserted with lubrication and taped to prevent displacement.
The patient is positioned either on a commode or couch for the filling phase. The other end of the rectal and bladder lines are connected to sensors that convert the pressures from the patient to computer data via a transducer plate. These lines are then flushed with sterile water (some technicians use sodium chloride) to exclude all air from the monitoring channels. The aim of this is to create an unbroken channel of fluid from the patient's bladder to the transducer plate. The presence of air at any point in the channel can obscure the results, so time is taken to ensure that no air is present in the lines. A litre bag of the chosen irrigation fluid is connected to the filling lumen of the bladder line via a pump that regulates bladder filling at a known rate. Once other calibration checks are undertaken, the test begins.
As the patient's bladder fills, the pressure generated within the bladder is detected by the bladder line, creating a trace on the computer screen—the CMG trace. This line may also pick up unwanted pressure changes outside the bladder but within the intra-abdominal space (from talking or breathing etc). The rectal line will sense intra-abdominal pressure changes but not those within the bladder and create a second trace on the screen. When the rectal information is subtracted from the bladder information, what should remain are only the calculated pressure changes within the bladder itself. This is known as the detrusor pressure and forms a third trace on the study.
As the patient's bladder gently fills, the traces produce lines on a graph which also includes other traces indicating fluid-filling rate and volume. Should the patient leak during the filling phase, this is captured by a jug under the commode or couch, which rests on a sensitive pressure plate. The rate and volume of leakage are also recorded as a trace in real time as the study progresses. Once the desired (comfortable and safe) fill volume has been reached or the patient can no longer hold the fluid, the pressure plate under the commode again captures this flow in order to generate a flow pattern on the trace. Wherever possible, the patient should be allowed to void in private before completing the investigation and removing the lines. Results may be shared with the patient once they are again dressed and comfortable.
Aims of urodynamic testing
As stated, UDS are useful in detecting material evidence of detrusor (bladder muscle) overactivity, as well as urodynamic stress incontinence where unwanted leakage happens in the absence of detrusor contractions. In each case, UDS take place following initial but unsuccessful attempts at management with lifestyle changes, medication and pelvic floor exercises. The results of the test may at that point provide clinical evidence for treatment with botulinum A toxin intravesical injections in the case of overactive bladder or surgery for stress incontinence.
Other common applications of UDS include evaluation of voiding difficulties. An example of this is the older male patient with poor flow, where it is important to distinguish between whether this is due to outflow obstruction (from the prostate, or a stricture) or a poorly functioning detrusor that fails to effectively squeeze in order to empty the bladder effectively. Furthermore, UDS are also useful in evaluating intravesical bladder pressures in a patient with neurological disorders. Here, the patient's neurological deficit (for example from a spinal injury) may prevent the usual homeostatic mechanisms from maintaining ‘safe’ bladder pressures. If the patient cannot feel when their bladder is dangerously full or their bladder does not automatically empty when it nears this stage, back pressure to the upper tracts may result. UDS may help monitor for this tendency to prevent damage to renal structure and function.
Conclusion
Although urodynamic testing may at times feel daunting for the patient, it remains a very versatile and useful mainstay of diagnosing lower urinary tract dysfunction. If the urodynamic technician has done their job effectively, at the end of the test most patients find that it was not as unpleasant as expected.
Many patients have suffered with embarrassing symptoms for many months, if not years, and it often takes great bravery to persist in seeking treatment. By reassuring the patient of the value of the test, in addition to ensuring support and sensitivity throughout, the next steps towards symptomatic improvement can be facilitated.