(1)
Functional Urology Unit, Casa Madre Fortunata Toniolo, Bologna, Italy
There are two principal methods of invasive urodynamic investigation:
Conventional urodynamics
Ambulatory urodynamics
Conventional urodynamics usually take place in the urodynamic laboratory and involve artificial bladder filling (Fig. 7.1).
Figure 7.1
Diagram of urodynamic setup
Ambulatory urodynamics is performed outside the clinical setting involving natural filling of the bladder and reproducing the subject’s everyday activities.
7.1 Conventional Urodynamics
Conventional urodynamics include two distinct phases:
Filling phase or cystometry
Voiding phase or pressure-flow study
7.1.1 The Equipment
In the market, there are several urodynamic equipments, all with sophisticated software to help the examiner with the correct use of the instrument during the examination. At the end of the study, all data from the patient are stored on a database for any revaluation of the case and subsequent statistical processing (Fig. 7.2).
Figure 7.2
Multichannel urodynamic equipment (Courtesy of Albyn Medical)
The equipment to conduct conventional urodynamics should have a set of minimum standards including:
Three recording channels, two for pressures and one for flow
Infused volume recorded graphically or numerically
Event annotation method to mark information about sensation and additional comments during the study
Measured (Pves, Pabd, Flow, EMG) and derived (Pdet) signals must be displayed continuously over time with an order varying in the different equipments including (Fig. 7.3):
Figure 7.3
Display of signals
Flow
Voided volume
Pabd
Pves
Pdet
EMG
Inf. volume
Detection ranges
Pressure: 0–250 cmH2O
Flow: 0–50 ml/s
Infused volume: 0–1000 ml
No loss of data for pressures up to 250 cmH2O and flow up to 50 ml/s
7.1.2 Urodynamic Manufacturers and Choice of the Equipment
Table 7.1 includes a comprehensive but incomplete list of urodynamic manufacturers.
Table 7.1
List of major companies involved in the construction of urodynamic equipments
Company | Headquarters |
|---|---|
Laborie | Canada |
Mediwatch – Dantec | United Kingdom |
Medical Measurement System (MMS) | Netherlands |
Albyn Medical | United Kingdom, Spain |
HC Italia | Italy |
Memphis bioMedica | Italy |
Andromeda | Germany |
Neomedix | Australia |
Mindray Medical International | China |
The type of equipment is strictly related to the volume of practice.
Any private practice office should be able to perform uroflowmetry and post-void residual assessment.
Small community hospitals should be able to perform a multichannel urodynamics, while large referral centers should be equipped to perform a more sophisticated testing including integration of fluoroscopy.
On the assumption that urodynamic room should be private and quiet as possible in order to minimize anxiety for the patient, the space available is an important factor in deciding what type of machine is more appropriate for a specific practice. A dedicated UDS room allows for a more elaborated setup, whereas a less sophisticated mobile system is definitely more suitable if one plans to move from a room to another. Recently introduced wireless urodynamic systems allow maximum flexibility for the operator and investigation room setup since the recording unit is close to the patient, whereas the PC display and printer can be located at operator preference (Fig. 7.4).
Figure 7.4
Wireless urodynamic equipment (Courtesy of Albyn Medical)
In addition, a simple uroflow commode may be sufficient in the office or small community hospital, whereas a motorized chair with multiple adjustments will be more appropriate in a referral center where UDS testing on patient with limited mobility (neurogenic bladder) is more common (Fig. 7.5).
Figure 7.5
Electrically adjustable urodynamic chair (Courtesy of Albyn Medical)
7.1.3 The Catheters
There are several commercially available catheters for urodynamic examination. The major difference between them is the method of pressure measurement, namely:
Fluid-filled catheter with external pressure transducer
Air-charged catheter with external pressure transducer
Microtip transducer
Fluid-filled catheters function by recording the pressure into the bladder (Fig. 7.6) and rectum (Fig. 7.7) which is transmitted to the strain gauge of the external transducer through a noncompressible column of water inside the catheter and connecting line.
Figure 7.6
Fluid-filled bladder catheters (Courtesy of Coloplast)
Figure 7.7
Rectal catheter
Advantages of these catheters are that they are at low cost and disposable. The major disadvantage is the potential for signal artifacts due to obstruction of intraluminal air bubble within the catheter (damping phenomenon).
Air-charged catheters (Fig. 7.8) have a small balloon overlying the catheter tip that separates the recording system from the bladder cavity. The catheter is filled with air and the pressure is transmitted directly from the catheter tip to the external transducer. Advantages of these catheters are the absence of classical damping phenomenon and the lack of motion artifacts created by movement of the line. Disadvantages include a slow response to pressure variations and in general an attenuation of the transmitted signal (they are permanently overdamped).
Figure 7.8
Air-charged catheters (Courtesy of Mediwatch)
Microtip catheters (Fig. 7.9) show a small transducer mounted on the tip that detects pressure changes by means of strain. This is converted into an electric signal which is amplified and transmitted to a semiconductor for conversion into a pressure measurement. The major advantage of this catheter is a faster response in pressure change recording and minimal motion artifacts that make them particularly suitable for ambulatory urodynamics. Disadvantages include the cost, the need for sterilization, fragility, and rotation error.
Figure 7.9
Solid-state (microtip) catheters
Footnote 1
The ICS recommends a fluid-filled catheter with external transducer for routine urodynamic testing.
Footnote 2
With any external transduction device (water-filled and air-charged catheters), it is essential to ensure that the transducer is mounted at the level of the superior edge of the pubis symphysis that is considered at the same level of the bladder (zeroing the pressure). A failure to positioning external transducer at this level will result in erroneously high-pressure reading (if below the symphysis pubis) or low (if above the symphysis pubis).
7.2 Preparation of the Patient
Multichannel urodynamic testing requires an optimally informed patient (see Appendix A).
Due to short-time catheterization, prophylactic antibiotics are unnecessary in an uncompromised patient. However, if high incidence of urinary tract infections after urodynamic testing is observed in a given practice, the entire procedure should be strictly rechecked in terms of sterility. Laxatives are also unnecessary since they might cause unwanted bowel overactivity during the test. In any case the patient should be asked to arrive possibly with an empty bowel.
Although voiding is presumably negatively influenced in a situation of mental stress, there is no clear evidence that voiding in unphysiological laboratory circumstances is significantly altered.
However, a quiet ambience with as little number as possible of persons involved is strictly recommended during urodynamic testing.
7.2.1 Setup of the Patient, Step by Step
Step 1: EMG electrode placement
The first step is to position the electrodes on the skin around the patient anus and on the thigh to act as the ground lead.
Step 2: Sterilizing the urethra
Prepare the urethra with Betadine wiping once downward over the meatus and then once on either side of the meatus.
Step 3: Post-void residual urine measurement
Drain the bladder with a catheter to obtain a post-void residual urine measurement. An alternative method is to place the cystometry catheter into the bladder and utilize the filling channel to evacuate the post-void residual with a syringe.
Step 4: Catheter insertion into the bladder and rectum
In female advance the catheter into the bladder eight (8) to ten (10) centimeters. In males, do not advance it more than 24 centimeters.
For rectal placement, apply lubricant around the anal canal. Place the catheter to a depth of approximately ten (10) to fifteen (15) centimeters. You can test whether the placement is correct by asking the patient to tighten his or her anal sphincter. If the pressure shows an upward deviation in catheter pressure reading, the catheter is not deep enough and should be placed a little deeper. As an alternative for female patients, you can check placement of a rectal catheter by positioning a finger in the vagina and feel whether the rectal catheter is sliding along the anterior wall of the rectum in a straight fashion. This ensures more accurate abdominal pressure sensing and reduces the risk of stool affecting the test. If the patient has chronic constipation, i.e., neurogenic patients, an enema before testing eliminates this possibility.
Once inserted, each catheter should be securely fixed and then connected to its respective cable.
Step 5: Flushing (Fig. 7.10a)
Figure 7.10
3-way taps: the key of multichannel urodynamics. Diagram showing position of 3-way taps between transducer and syringe and between transducers and tubing to the patient. Various positions of the taps allow flushing of the tubing, zeroing to atmospheric pressure and internal pressure measurement
Once the catheters are fixed in position and connected to the transducers, the crucial next step is to free them of air inside the channel by flushing with infusion fluid, since any amount of air in the system from the syringe to the tip of the catheter may dampen the recording.
Step 6: Zeroing UDS machine (Fig. 7.10b)
The next step is zeroing the machine. In this procedure the 3-way taps, located at the tip of the syringe and at the beginning of connecting cable and at the dome of the transducer, play a pivotal role. All the transducers are measuring atmospheric pressure (taken as zero) at a given point in relation to the patient bladder. By convention, this point is the superior border of the symphysis pubis.
Both the transducers (Pves and Pabd) are placed at the abovementioned level. The syringe and catheter connection is blocked, while the 3-way taps of the transducers are opened to atmospheric pressure and the “zero all” button is pressed. By this way, all the three lines Pves, Pabd, and Pdet (resulting from the previous two) show “zero” reading.
At this point, the 3-way connector of the cable is open so that the transducers are exposed to internal pressure while are cut off from the atmospheric pressure (Fig. 7.10c). This shows the pressure inside the bladder and rectum according to the patient position (Fig. 7.11).
Figure 7.11
Baseline pressure checking. Expected resting range of abdominal and vesical pressures
It is extremely important that initial pressures are in the expected range (Table 7.2), since if measured pressures lie outside of this range, a technical problem exists which needs to be rectified.
Table 7.2
Initial resting pressures
Plausible values (cmH2O) | Patient position | ||
|---|---|---|---|
Supine | Seating | Standing | |
Pves | 5 | 15 | 30 |
Pabd | 20 | 40 | 50 |
Pdet should show a near-zero value (<6 cmH2O) since Pves and Pabd are equal and detrusor activity is absent with bladder empty. If Pdet results positive or negative, minor corrections can be done by the computer software utilizing the “Pdet to zero” button.
Footnote
The “zero” of the machine can be checked at any time during the test by turning the tap so it is open to atmosphere, if artifacts are suspected.
7.2.2 Microtip and Air-Charged Catheters
Microtip and air-charged catheters are set to “zero” while outside the patient.
For microtip catheters, the reference height is the transducer’s itself, while for air-charged catheters, the reference height is at the position of the internal balloon. Therefore, using these systems is difficult to ensure that intra-abdominal and intravesical lines are equal. This situation is worsened by changing patient position. For example, in supine position the rectal line is likely to be lower than the vesical line, while in standing position, the rectal line may be higher than the vesical line. However, in practical terms, these differences don’t seem to influence significantly the results.
Step 7: Checking the quality of signals (Fig. 7.12).
Figure 7.12
Quality control of the signals: (a) coughing shows Pabd and Pves responding correctly. Pdet shows a typical biphasic artifact due to timing differences between the recording of Pabd and Pves. (b) Coughing shows Pabd not responding correctly. (c) Coughing shows Pves not responding correctly
The quality of signals is checked by asking the patient to gently cough. Both Pabd and Pves respond equally with a rapid peak and rapid drop and the detrusor line should be unaffected.
A small biphasic deflection is normal, but any rise or fall in the detrusor pressure during cough suggests a dampening in the vesical or abdominal system.
The quality of signals should periodically be checked during filling (every 50 ml), at the end of filling, and after voiding to minimize artifacts.
Footnote
Pabd and Pves recordings are “live,” showing minor variations of breathing or talking which should not appear in Pdet.
7.3 Filling Phase (Cystometry)
Once good signal transmission is appreciated, bladder filling can commence.
Usually 0.9 % physiological saline is used.
For a neurologically intact adult, the filling rate is usually 50 ml/min. For neurological patients a less provocative rate such as 10–20 ml/min is recommended. Infusion fluid should be at room temperature (20 °C) since low temperature can induce a false detrusor overactivity particularly at low bladder volume.
During filling the patient should be asked to cough every minute or every 50 ml of filling in order to evaluate a good subtraction of pressure. When lost, the test should be stopped and the lines checked again. The EMG, when recorded, should show a deflection as well.
Filling phase starts when filling commences and ends when the patient in consequence of a strong stimulus decides to empty the bladder or the examiner in front of an adequate filling volume decides for “permission to void.”
The aim of this part of study is to assess:
Detrusor function
Bladder sensation
Bladder compliance
Bladder capacity
Urethral function
7.3.1 Detrusor Function
The normal detrusor function is to allow the bladder filling with little or no changes in pressure.
The presence of involuntary contractions, spontaneous or provoked, during filling of the bladder is defined as detrusor overactivity.
Footnote 1
There is a cutoff value for the significance of an involuntary contraction. Conventionally values lower than 5 cmH2O are considered of little significance.
Footnote 2
Provocative maneuvers are defined as techniques used during urodynamic investigation in an effort to provoke detrusor overactivity. Examples of provocative maneuvers include rapid filling, cool infusion medium, and postural changes.
7.3.1.1 Detrusor Activity
There are two patterns of detrusor overactivity:
- 1.
Phasic detrusor overactivity
- 2.
Terminal detrusor overactivity
The phasic overactivity is defined by fluctuating wave forms which may or may not lead to urinary incontinence (Fig. 7.13).
Figure 7.13
Phasic detrusor overactivity. Waves of detrusor contractions occurring at SD and urgency with a urine leak at latter sensation just before maximum bladder capacity (cystometric capacity) attainment
The occurrence of involuntary detrusor contractions may be observed in normal asymptomatic patients with a rough incidence of 8 %. The condition (also called “occult overactivity”) may be situational due to sensitivity of urethral catheter or to rate of filling or to low temperature of infusate. In most of the cases, however, the significance of this pattern remains unknown.
Terminal detrusor overactivity is defined as a single detrusor contraction occurring at cystometric capacity, which cannot be suppressed and usually results in complete bladder emptying. Characteristic of this condition is the reduction of warning time, i.e., the time that elapses between the strong desire to void and voiding contraction (Fig. 7.14).
