Fig. 3.1
(a–c) Normal-size bladder capacity in three patients on contrast-filled cystogram. (d) Cystogram of underactive bladder in a 54-year-old woman with bladder capacity over 1,200 ml and PVR of 750 ml
Noninvasive measurement of post-void residual urine (PVR) volume via either catheter or ultrasound and uroflowmetry are two first-line urodynamics assessment techniques available to most clinicians (Blaivas and Chancellor 1996). PVR measurement and uroflow testing are simple to learn and of modest expense and may be used before consideration of catheter-based cystometrogram and multichannel urodynamics.
Post-void Residual Urine Volume
Post-void residual refers to the amount of urine left in the bladder after urination. Post-void residual testing is used to assess the degree of bladder dysfunction. There are two types of this test: in-and-out catheterization and transabdominal or pelvic ultrasound.
Acute urinary retention such as immediately after a surgical procedure with anesthesia and narcotics that resolves after a few hours and a single catheterization is not within the scope of UAB or DU. Chronic urinary retention has been defined by the International Continence Society as a PVR >300 mL or rather committing to an absolute volume, stating that it is “non-painful bladder, which remains palpable after the patient has passed urine” (Abrams et al. 2002).
European Urology’s UAB working definition is “the underactive bladder is a symptom complex suggestive of detrusor underactivity and is usually characterized by prolonged urination time with or without a sensation of incomplete bladder emptying, usually with hesitancy, reduced sensation on filling, and a slow stream (Chapple et al. 2015).”
Other definitions of urinary retention and elevated residual urine volume one should be aware of include the National Library of Medicine’s definition of urinary retention as “inability to empty the urinary bladder with voiding (urination).” In the United States the standard medical diagnosis code, ICD-10-CM, has the diagnosis code R33.9 Retention of Urine as:
A disorder characterized by accumulation of urine within the bladder because of the inability to urinate
Inability to empty the urinary bladder with voiding (urination)
Incomplete emptying of the bladder
The Underactive Bladder Foundation (www.underactivebladder.org) working terminology of underactive bladder syndrome is “urinary symptoms including hesitancy, straining and incomplete bladder emptying in the absence of anatomic obstruction.”
Ultrasound Measurement
This test is performed to measure the amount of urine that is left in a patient’s bladder immediately after the patient made attempt to empty it completely. The test is done with ultrasound in the supine position. The clinician will place gel on the skin over the patient’s bladder and then place an ultrasound probe over this area and make a recording (Figs. 3.2 and 3.3). There is no special preparation for this test and the patient may resume usual daily activities immediately following the ultrasound.
Fig. 3.2
Ultrasound post residual urine volume measurement machine
Fig. 3.3
Ultrasound image of bladder being measured for PVR with bladder outlined
Catheterization Measurement
The test is done with a small thin, flexible tube (catheter). After going to the bathroom, the patient will lie flat on the exam table. The entrance to the urethra will be sterilely prepped and the clinician will insert the catheter into the bladder through the urethra. The volume of any urine remaining in the bladder will be drained and measured. There is no special preparation for this study.
Other than complete urinary retention and inability to void, there is no definite consensus between what is normal and abnormal nor a value above which clean intermittent catheterization must be implemented. In older people with less effective bladder emptying, most clinicians even tolerate a greater value for PVR if the patient does not have urinary tract infection and not significantly symptomatic. In general, 150–250 ml is considered by many experts as the threshold and cutoff for being abnormal. There is also a rational argument that PVR should not base not on a single number but rather as a percent of functional bladder capacity. Even for a value of >150–250 ml, further assessment and treatment may not necessarily be undertaken especially if someone would not be a surgical candidate or would not be able to handle catheter care.
Recent ICS guideline (Asimakopoulos et al. 2014) recommends that the interval between voiding and PVR measurement should be short and preferably via ultrasound instead of urethral catheterization. There is no universally accepted definition of a significant residual urine volume. Large PVR >200–300 ml may indicate marked bladder dysfunction and may predispose to unsatisfactory treatment results if, for example, invasive treatment for bladder-outlet obstruction is undertaken. The ICS guideline also concluded that PVR does not seem to be a strong predictor of acute urinary retention and does not specifically indicate the presence of BOO.
Practical Pearls of Post-void Residual Measurement
The time interval between voiding and residual urine estimation should be recorded: this is particular important if the patient is in a diuretic phase.
Poorly drained bladder diverticulum or vesicoureteral reflux offers a problem of interpretation and may indicate a need for surgical treatment if the patient is symptomatic.
The absence of elevated residual urine is clinical valuable, but does not exclude obstruction or bladder dysfunction.
An isolated finding of elevated residual urine volume requires confirmation before being considered significant.
Uroflow
Urinary flow rate represents the net interaction of detrusor contractility and outlet resistance (Fig. 3.4). The flow rate remains an extremely sensitive indicator of lower urinary tract dysfunction, but the Achilles heel of uroflow measurement is that a low flow may be due to UAB, bladder-outlet obstruction, or both (Chancellor et al. 1991). A slow downstream low flow in itself cannot distinguish the cause of upstream bladder dysfunction or outlet obstruction.
Fig. 3.4
Flowmeter
Consistently low flow rates despite adequate voided volumes generally indicate increased outlet resistance, decreased bladder contractility, or both. The minimum voided volume adequate for interpretation of an accurate uroflow is generally considered to be 125 ml (Blaivas and Chancellor 1996). Therefore, in an adult, flow events of less than 125 ml should be interpreted with caution. Nomenclature and some basic concepts bear defining prior to further discussion of different types of flow rates and patterns (Fig. 3.5):
Fig. 3.5
Normal uroflow in a 63-year-old man without voiding symptoms. The patient voided 325 ml over 32 s duration and his maximum flow rate (Qmax) was 27.8 ml/s
Voided volume: The total volume of urine expelled from the bladder.
Flow time: The time over which measurable flow actually occurs.
Maximum flow rate (Qmax): The maximum measured value of the flow rate.
Mean flow rate (Qmean): Volume voided divided by flow time. It is important to note that the average flow rate is only interpretable if flow is continuous and without aberrancy, either at the initiation or termination of voiding.
Flow pattern: Subjective description of the regularity of voiding.
Intermittent flow: Flow pattern where interruptions of varying duration occur between episodes of voiding. The same parameters used to characterize continuous flow may be used to describe intermittent flow only if caution is exercised. In order to quantify flow time, however, the time intervals between flow episodes should be disregarded. Conversely, the voiding time refers to the total duration of micturition, including the intervals between flow episodes.
Maximum Flow Rate
Among the many parameters provided by uroflowmetry, the maximum urinary flow rate (Qmax: ml/s) is regarded by most experts as most useful not only in assessing the degree of impairment but also in monitoring treatment effects. There have been multiple attempts to normalize uroflow parameters for age, sex, and voided or total bladder volume; however, none of the proposed methods have been universally accepted. It is currently assumed that correction or adjustment of the maximum flow rate value is unnecessary if voided volume exceeds 125 ml.
Uroflow Patterns
A normal flow pattern is represented by a bell-shaped curve (Fig. 3.5). Upon comparison, women tend to have a higher mean and maximum flow rate than men. The urinary flow pattern of the patient with bladder-outlet obstruction is typically recognizable by a prolonged flow time accompanied by a sustained, substandard flow rate (Fig. 3.6).
Fig. 3.6
Decreased flow rate in a 79-year-old diabetic woman with urgency, frequency, recurrent urinary tract infections, and a PVR of 150 ml. The flow pattern notes a low Qmax of 10.0 ml/s over 42 s and a voided volume of 300 ml. She has a grade 3 cystocele and a previous pelvic prolapse surgery 15 years ago. The impaired uroflow pattern is abnormal but it cannot differentiate among progressive impaired detrusor contractility with aging or diabetes, urethral obstruction from prolapse or previous surgery, or a combination of the conditions that can contribute to her UAB
Patients with outlet obstruction or impaired detrusor contractility (or both) may in fact eliminate urine by increasing intra-abdominal pressure until outlet resistance is overcome. This pattern of “Valsalva voiding” can often be identified by the urinary flow pattern (Fig. 3.7). In such instances, frequent sharp increases and decreases in the urinary flow rate are noted during the voiding period. Despite a Qmax which may approach normal values, this voiding method is not physiologic and can be detrimental. Valsalva voiding pattern exemplifies the importance of examining not only the flow parameters Qmax, Qmean, and voided volume but also the flow pattern. The parameters in such a case may not accurately reflect the severe nature of voiding dysfunction present in those utilizing Valsalva maneuvers to accomplish voiding (Blaivas and Chancellor 1996).
Fig. 3.7
Normal Qmax of 27.6 ml/s on this uroflow readout and the patient did not have any residual urine volume. But from the tracing, the voiding can be seen to be due to abdominal straining. The urinary stream occurs in spurts with complete interruption between the spurts. This pattern of “Valsalva voiding” points out the value of looking at the flow pattern in addition to just the numeric values of uroflowmetry
The pattern of bladder-outlet obstruction may indeed be more variable and not clearly indicative of obstruction. For example, refer to the equivocal flow rate seen in Fig. 3.8 of a 67-year-old man with moderate voiding symptoms and a PVR of 125 ml. He voided 250 ml with maximum flow rate of 12.5 ml/s. The uroflow in this clinical situation is not diagnostic. Therefore, formal urodynamics evaluation would be necessary in order to determine whether either outlet obstruction or impaired contractility was responsible for the abnormal flow pattern in this patient.
Fig. 3.8
Equivocal flow rate of Qmax at 12.5 ml/s in a 67-year-old man with moderate irritable and obstructive voiding symptoms. He voided 250 ml but had a PVR of 125 ml. The uroflow in this clinical situation is not diagnostic and multichannel pressure-flow urodynamics evaluation would be recommended
It is most useful to ensure that the flow event depicted by the uroflow examination closely approximates the usual voiding event for that patient. Urodynamics evaluation, therefore, ideally should include at least two flow events. In individuals who can initiate voluntary micturition, one event should be at the initiation of the study prior to instrumentation, ideally when the patient arrives with a comfortably, but not excessively, full bladder.
Future Flow
The future of uroflowmetry is already here in Japan. Toto Corporation (Kokura, Japan) the world leader in smart toilet that Japan is famous for have embedded the sensors of flowmeter into top of the line smart toilet (i-Step Newsletter 2013) (Fig. 3.9). The toilet when commanded will sense the volume and flow rate and in a normal sitting or standing positions for women and men and provide readout. The build in flow toilets has been installed in some of the physician’s offices in Japan and provides a more natural flow reading on a regular toilet rather than special urodynamics commode.
Fig. 3.9
Future flowmeter (Toto, Kokura, Japan). The next-generation uroflowmeter build into normal patient bathroom toilet in Doctor Tomohiro Ueda’s specialty clinic in Kyoto, Japan
Practical Pearls of Uroflow
Urinary flow rate varies significantly with the voided volumes. The minimum voided volume adequate for interpretation of an accurate uroflow is generally considered to be ≥125 ml.
It may be helpful to have a urinary flow rate nomogram available in the laboratory for comparison of measured flow rate and voided volume (Siroky et al. 1979).
Because urinary flow rates can vary in an individual from one voiding episode to another, more than one flow rate study should be done when first flow test is equivocal.
In circumstances where doubt remains following an uroflow study, further urodynamics studies are essential to identify the etiology of voiding dysfunction.
Cystometrogram
Cystometry is the method by which the pressure/volume relationship of the bladder is measured. Cystometry (CMG) is used to assess detrusor activity, sensation, capacity, and compliance. Before starting to fill the bladder, the residual urine should be measured. Certain cystometric parameters may be significantly altered by the speed of bladder filling so filling should not be faster than 50 ml/min in most cases. The patient should be awake, unanesthetized, and neither sedated nor taking drugs that affect bladder function (Blaivas and Chancellor 1996; Schafer et al. 2002). Any variations should be specified and recorded (Fig. 3.10).
