Indications

Measurement of the flow rate is indicated in women with complaints of difficulty in voiding, neuropathy, a past history of urinary retention and prior to continence surgery. It is advisable for any incontinent woman to exclude voiding difficulties.

Measurements

The flow rate is defined as the volume of urine (in ml) expelled from the bladder each second. The flow time is the total duration of the void and includes interruptions in a non-continuous flow. The maximum flow rate is the maximum measured rate of flow, and the average flow is the volume voided divided by the flow time. The total volume voided can be calculated from the area under the flow curve. The two most useful parameters are the maximum flow rate and the voided volume, which should ideally be greater than 150 ml. However, the Liverpool nomograms (Haylen et al 1989) will allow assessment of flow rates at a lower volume. In women with intermittent flow, the same parameters can be used but time intervals between flow episodes must be discounted. Lower volumes at presentation are more likely in the elderly and those of lower parity with a diagnosis of sensory urgency or detrusor overactivity (Haylen et al 2009).

Equipment

There are three main types of flow meter. The gravimetric transducer measures the weight of urine voided over time and this is converted to a flow rate (Figure 51.2). The rotating disc flow meter has a disc spinning at a constant speed. The voided urine slows the rotating disc. The flow rate is calculated from the amount of power needed to maintain the disc spinning at a constant speed. The capacitance flow meter has a metal strip capacitor attached to a plastic dipstick inserted vertically into the jug containing the voided urine. The rate and volume changes are measured by a change in electrical conductance across the capacitor. This is the most expensive type of flow meter, but is robust and very reliable.

Figure 51.2 Gravimetric urinary flow meter.

Abnormal flow rates

Nomograms for peak and average urine flow rates in women have been constructed from flow rates of 249 normal women (Haylen et al 1989). These allow comparison of a single value with a standard flow rate. A flow rate below 15 ml/s on more than one occasion is taken as abnormal when the voided volume is above 150 ml as flow rates on smaller volumes are less reliable.

A low peak flow rate and a prolonged voiding time suggest a voiding disorder (Figure 51.3). Straining can give abnormal pressure flow patterns (Figure 51.4) showing a high-pressure, low-flow pattern suggestive of obstruction. The cause of voiding dysfunction may be determined by measuring intravesical pressure simultaneously.

Figure 51.3 Urinary flow rate showing a prolonged flow with a low maximum peak flow rate suggestive of a voiding disorder.

Figure 51.4 A high-pressure, low-flow pattern suggesting a voiding disorder.

Indications

Cystometry is indicated in patients with symptoms refractory to conservative or simple treatments, or patients with complex symptoms (National Institute for Health and Clinical Excellence 2006). However, the validity of the conclusions of NICE have been challenged and management without cystometry may be less accurate (Agur et al 2009).

Equipment

Twin-channel cystometry requires two transducers (external or microtip), a recorder and an amplifying unit (Figure 51.5). Bladder pressure is measured using a fluid-filled line attached to an external pressure transducer or a solid-state microtip pressure catheter. A rectal catheter is required to measure abdominal pressure; this is a fluid-filled, 2-mm-diameter catheter covered with a rubber finger cot to prevent blockage with faeces when the catheter is inserted into the rectum (Figure 51.6). The upper edge of the pubic symphysis is the zero reference for all measurements, which are made in centimetres of water (cmH₂O). External transducers are cheaper and less fragile, but the microtip transducer does not suffer from movement artefact.

Figure 51.5 Urodynamic equipment showing the computerized cystometry unit.

Figure 51.6 Pressure lines for cystometry. Clear bladder filling line with blue bladder pressure and red rectal pressure lines.

The bladder is filled using a 12F catheter with a continuous infusion of normal saline at room temperature. The standard filling rate is between 10 and 100 ml/min and is provocative for overactive bladder. Slow-fill cystometry at a rate of 10–20 ml/min is indicated in women with neuropathic bladders. Rapid filling at over 100 ml/min is rarely used, but can be a further provocative test for overactive bladder. There is now an ICS standard for manufacturers to adhere to, and most modern equipment will easily meet this standard. Choice of equipment must be on personal requirements.

Measurements

The parameters measured are the intravesical pressure (measured with the bladder transducer) and the intra-abdominal pressure (measured with the rectal line). The detrusor pressure is obtained by subtracting the abdominal pressure from the intravesical pressure, and is displayed simultaneously. The flow rate, filling and voided volumes are also displayed.

Method

Women attend having completed a bladder diary with a comfortably full bladder. The woman then voids on the flow meter. The woman is then examined and the residual volume is noted on catheterization. During filling, the woman is asked to indicate her first desire to void and the maximal desire to void, and the volumes of these events are noted. There is evidence that women with overactivity may experience different sensations during filling compared with their stress-incontinent comparators (Digesu et al 2009). Systolic detrusor contractions and their association with urgency are noted. Precipitating factors, such as coughing or running water, are also noted. Any symptomatic detrusor pressure rise on standing is again recorded.

At the end of filling, the filling line is removed and the woman stands up. She is asked to cough and leakage is noted. Care must be taken to avoid artefact from the pressure lines moving. Provocative tests for overactive bladder, such as listening to running water and hand washing, are performed at this stage. The woman then transfers to the commode and voids with the pressure lines still in place.

Normal cystometry

The following are parameters of normal bladder function.

Abnormal cystometry

Urodynamic stress incontinence is defined by the ICS as leakage on coughing in the absence of a rise in detrusor pressure (Figure 51.7). It is therefore a diagnosis of exclusion, as cystometry by itself cannot determine bladder neck or urethral function; radiographic imaging or the addition of urethral function tests is required. Urodynamic detrusor overactivity is diagnosed during the filling phase if spontaneous or provoked detrusor contractions occur while the woman is attempting to inhibit micturition (Figure 51.8). Low compliance is diagnosed when the pressure rise is more than 15 cmH₂O on filling the bladder with 500 ml of fluid and does not settle after filling is stopped. These parameters are all given in the ICS good practice document (www.icsoffice.org).

Figure 51.7 Cystometric trace showing urodynamic stress incontinence. The detrusor line remains flat. Each arrow indicates a cough, when leakage occurred.

Figure 51.8 Cystometric trace showing detrusor overactivity. The arrows indicate where the woman complained of urgency and leakage occurred.

Laboratory urodynamics does not provide a diagnosis in 15–25% of symptomatic women. If a laboratory test fails to answer the framed question, the investigator may feel that there is a need to request a further test. A recent study has reaffirmed the importance of urodynamics in women with symptomatic prolapse where 33% had their management changed as a result of urodynamics, including 7% having their surgery changed (Jha et al 2008).

Technique

The woman wears her normal outdoor clothing and has a digital recording system (Figure 51.9). Intravesical and rectal pressures are recorded using microtip pressure transducers at a rate of 1 Hz. The ambulatory recording device can be used in conjunction with an electronic leakage detection system, and when the woman wishes to void, she connects the recorder to a flow meter and then voids. The test can last up to 6 h in clinical practice. The women are encouraged to mobilize and continue normal daily activities, including gentle exercise. Fluids should be encouraged and a minimum intake of 180 ml every 30 min is requested (Salvatore et al 1999). Antibiotic cover is not given as infection rates are less than 1%. At the end of the test, the woman is requested to attend with a full bladder and various provocative manoeuvres are carried out (similar to a standardized pad test). The woman will also keep a diary of events during the investigation, and the analysis occurs with the patient present referencing events recorded in the diary.

Figure 51.9 (A) Ambulatory recording box. (B) Microtip pressure transducers.

This investigation is available in specialist units and tends to be reserved for women in whom routine cystometry gives conflicting or unexpectedly negative results and where simple treatments have failed. This technique is more sensitive to the detection of abnormal overactive bladder in symptomatic women who had previously not been found to have an abnormality on laboratory urodynamics (Webb et al 1991, van Waalwijk van Doorn et al 1996). High rates of overactive bladder have been reported in asymptomatic controls (van Waalwijk et al 1992, Robertson et al 1994, Heslington and Hilton 1996). However, using a strict protocol for investigation and reporting, the high false-positive detection of overactive bladder in asymptomatic women is corrected (Salvatore et al 1996). There is some evidence that overactive bladder which develops after colposuspension may be occult and can be detected before surgery using ambulatory urodynamics (Khullar et al 1995). Ambulatory monitoring is time consuming and sometimes technically difficult. The equipment is expensive and fragile, which is important when women are being discharged home with the equipment in situ. Discomfort is a problem but is usually mild and more common in male than female patients. However, its utility has recently been reaffirmed (Pannek and Pieper 2008).

General radiology

A plain abdominal X-ray is useful when symptoms suggest bladder calculi. Osteitis pubis is a rare complication of the Marshall–Marchetti–Krantz procedure, presenting with suprapubic pain, and is diagnosed on an anteroposterior pelvic X-ray. Sacral and lumbar spine X-rays are indicated if a congenital abnormality is suspected; for example, spina bifida and meningomyelocoele, which are important causes of neuropathic bladder disorders in children. Spinal cord trauma and tumours can also cause disturbances of micturition. Disc prolapse is common and is demonstrated on a myelogram.

Intravenous urography and computed tomography urogram

Intravenous urography is not indicated in most women with lower urinary tract symptoms unless for neuropathic bladder, suspected ureterovaginal fistula or haematuria. More commonly, a computed tomography urogram would be performed; whilst having a higher radiation dose, this also has a higher sensitivity for extrinsic pathology.

Videocystourethrography

Videocystourethrography (VCU) is radiological screening of the bladder synchronized with pressure studies of the bladder, recorded with a sound commentary on video (Figure 51.10). Stanton (1988) reviewed 200 cases of urinary incontinence following failed surgery, and concluded that VCU only had an advantage over cystometry in a few selected groups of women. VCU was indicated in women complaining of postmicturition dribble, which may be due to diverticulum (although magnetic resonance imaging is the gold standard for this diagnosis) (Figure 51.11).

Figure 51.10 Woman undergoing a videocystourethrogram.

Figure 51.11 Videocystourethrography showing a urethral diverticulum.

Micturating cystogram

This investigation also involves radiological screening of the bladder but without pressure or flow measurements, and is therefore less useful in the investigation of incontinence. Its main value is to demonstrate vesicoureteric reflux, and abnormalities of bladder and urethral anatomy (e.g. diverticula, and bladder and urethral fistulae). It is not useful for the assessment of incontinence.

Ultrasound

Ultrasound is becoming more widely used in urogynaecology. Its most simple use is in the estimation of postmicturition residual urine volume and to assess the bladder neck and surrounding area.

Postmicturition urine estimation

This useful technique obviates the need for urethral catheterization with its risk of introducing infection. It is indicated in the investigation of women with voiding difficulties, either idiopathic or before surgery, and also following postoperative catheter removal. The bladder is scanned in two planes and three diameters are measured. As the bladder only approaches a spherical shape when it is full, a correction factor has to be applied. Several different formulae have been devised, and the most common is to multiply the product of three diameters (height × width × depth) by a figure of 0.625 (Hakenberg et al 1983). This has an error rate of 21%, which is acceptable. Ultrasound machines are expensive and not always available in the community setting, in clinics or on the postoperative ward where residual volumes often need to be measured. The bladder scan is a portable ultrasound device designed for the measurement of bladder volume (Figure 51.12). The machine calculates the urine volume using preconfigured settings without the operator needing to perform any mathematical calculations, and results are similar to those obtained with complex ultrasound technology for the assessment of residual urine assessment. These become inaccurate at higher volumes, but this is not of clinical significance as the relevance of a high residual, regardless of the amount, remains. The role of this technique is limited in the immediate postoperative period in a woman with an abdominal wound, and also post partum where lochia can lead to a false-positive result.

Figure 51.12 Portable ultrasound scanner used for detecting postvoid urinary residuals.

Bladder neck position

Ultrasound scanning of the bladder neck has been used as an alternative to radiological screening, and has been reported to give equivalent information to the clinician (Brown et al 1985, Richmond et al 1986).

Ultrasound of the bladder neck has been performed using the transabdominal (White et al 1980), rectal (Shapeero et al 1983), vaginal (Hol et al 1995) and transperineal (Khullar et al 1994a) routes. The transabdominal view of the bladder neck is difficult in obese women, and there is no fixed reference point when assessing bladder neck movement. Transperineal measurement of bladder neck excursion with a specific Valsalva pressure in the antenatal period appears to predict the development of postnatal stress incontinence (King and Freeman 1998).

Vaginal, rectal and perineal probes use the lower border of the public symphysis as a fixed reference. The rectal probe is less acceptable to women, and difficulties arise with rotation of the probe, causing loss of the image.

Transvaginal ultrasound

The vaginal probe has been used successfully to image the bladder neck. Descent of the bladder base, together with bladder neck opening, has been demonstrated in a majority of women with stress incontinence but not in controls (Quinn 1990). However, bladder neck opening also occurs with overactive bladder, and this may be difficult to distinguish from stress incontinence unless there is a concomitant bladder pressure recording. The bladder neck can be compressed by the transvaginal ultrasound probe, preventing urinary leakage (Wise et al 1992). The potential for distortion of the bladder neck by the probe has not been fully assessed. Transvaginal ultrasonography has been used to measure bladder wall thickness (Khullar et al 1994b, 1996a) (Figure 51.13). Women with urodynamically diagnosed overactive bladder were found to have significantly thicker bladder walls than women with urodynamic stress incontinence, and this has been proposed as a screening and diagnostic test. However, the role of this has been challenged recently (Lekskuichai and Dietz 2008).

Figure 51.13 Transvaginal ultrasound picture showing measurement of bladder wall thickness in a woman with a diagnosis of detrusor overactivity.

Perineal ultrasound

Perineal scanning is the most readily available and least expensive technique. It is less likely to cause pelvic distortion, is more acceptable to women and is feasible in obese women (Figure 51.14). The technique has been shown to be as accurate as lateral chain urethrocystography in the assessment of women with failed continence surgery. The equipment is accurate, portable and available in most gynaecology departments (Gordon et al 1989). It may be of use in the determination of causes of failed continence surgery (Creighton et al 1994).

Figure 51.14 Transperineal two-dimensional ultrasound scan of the bladder neck.

Urethral ultrasound

Urethral cysts and diverticula can be examined using ultrasound. The disadvantage of this method is that unless the opening of the diverticulum is seen directly, the two cannot be differentiated. Intraurethral ultrasonography of the urethral sphincter has been described (Schaer et al 1998) and shows an association between decreased sphincter cross-sectional area and urodynamic stress incontinence. This is not used clinically at present.

Three-dimensional ultrasound of the urethra and urethral sphincter has been described (Khullar et al 1994c). This uses a perineal probe which records 150 ultrasound ‘slices’ as the probe scans 90° on its axis. A three-dimensional image is reconstructed, giving views of the urethra and rhabdosphincter (Figure 51.15). The volume of the urethral sphincter is larger in continent women compared with women diagnosed with urodynamic stress incontinence (Athanasiou et al 1995, Khullar et al 1996b). Evidence of damage to the rhabdosphincter is present in some women with severe urodynamic stress incontinence.

Figure 51.15 Three-dimensional scan of a rhabdosphincter.

Urethral pressure measurement

Continence is maintained if the urethral pressure is higher than the intravesical pressure. Many methods of measuring urethral pressure have been used. It is usually measured with a catheter-tip dual-sensor microtransducer, although in the past, infusion catheters using fluid or gas and intraluminal balloons have been tried. The microtransducer system has two transducers which are 6 cm apart, 12 mm long and 1.6–2.3 mm in diameter, mounted on a 7F catheter. These catheters are easy to use but fragile and expensive.

Leak point pressure

Leak point pressures can be detrusor or abdominal. The detrusor leak point pressure is indicated in women who have incontinence and a neuropathic condition, or those who are unable to empty their bladders (McGuire and Brady 1979).

Abdominal leak point pressure is the pressure at which leakage occurs during either a cough or a Valsalva manoeuvre. The pressure can be measured using pressure catheters in the bladder, vagina or rectum. It has been proposed as a measure of urethral resistance of the urethral sphincter to increased intra-abdominal pressure (Robinson and Brocklehurst 1983). It is highly reproducible with a strong correlation with maximum urethral closure pressure. It is not clear whether this test is useful in the evaluation of urinary incontinence.

Indications

Cystoscopy comprises part of the operative technique in continence operations, such as the tension-free vaginal tape (TVT) procedure, to ensure that the TVT introducer needle has not passed through the bladder or in assisting in the placement of injectables such as GAX collagen (Bard) or Macroplastique (Uroplasty).

Technique

Cystoscopy is a sterile technique performed under general or local anaesthetic. If it is used to assess reduced bladder capacity during urodynamic studies, it must be performed under general anaesthetic. The urethra is difficult to examine in women, and this is best done by withdrawing the cystoscope and using a urethroscope sheath. Residual urine should be noted, although it is not always accurate if the woman has not voided recently.

Bladder capacity is the volume at which filling usually stops using a 1-l bag of fluid under gravity feed. Using a 30° or 70° cystoscope, the mucosa should be inspected for abnormalities, such as signs of infection or tumour. A note is made on the state of the bladder and urethral mucosa, and the presence of normally situated ureteric orifices. Interstitial cystitis may be suggested by the presence of splits which bleed on decompression and a reduced capacity (Figure 51.16). If diverticula are present, an attempt must be made to see inside to exclude carcinoma and calculi. Bladder calculi may be present, particularly in women with neuropathic bladder and/or indwelling catheters. Abnormal areas must be biopsied.

Figure 51.16 Cystoscopy with petechial haemorrhage and a Hunner’s ulcer.

Most makes of cystoscope are similar and, as they are often not interchangeable, it is preferable to stick to one type. A standard set should include a cystoscope, urethroscope sheath, 0°, 30° and 70° telescopes, a catheterizing bridge and a fibreoptic light. A set of biopsy forceps is essential, as is a method for dilating the urethra, such as a set of Hegar dilators or an Otis urethrotome. Flexible cystoscopes are more suitable for cystoscopy under local anaesthetic. If flexible cystoscopy has proven suboptimal, a formal rigid cystoscopy should be performed.

Electromyography

Electromyography is the study of bioelectrical potentials generated by smooth and striated muscles, and can be used to evaluate pelvic floor damage in women with urinary or faecal incontinence and prolapse. A motor unit comprises a motor nerve and the fibres it innervates. The electrical potential generated during a contraction is called the ‘motor nerve unit action potential’ and this can be measured using electromyography. If denervation occurs, the remaining nerves sprout collaterals to reinnervate the muscle fibres, thus increasing the dispersion of the motor unit so that more fibres of a particular unit will fire together at one time. This is seen on electromyography as an increase in the amplitude, duration and number of phases of the action potential. If reinnervation is present, polyphasic potentials are seen.

Partial denervation has been proposed as the mechanism by which childbirth contributes to the aetiology of stress incontinence. Allen et al (1990) performed transvaginal electromyography on primiparous women before and after delivery, and detected a highly significant increase in mean motor unit potential duration which was positively associated with birth weight and length of the second stage of labour. Smith et al (1989) studied anal sphincter fibre density in women with stress incontinence and/or prolapse, and found an increased fibre density in all groups compared with normal controls.

Electromyography can be performed using surface electrodes, such as anal or vaginal plugs, and ring electrodes mounted on a urethral catheter, or it can be performed using needle electrodes inserted into the external anal sphincter or periurethral muscles. Single-fibre needles give more selective recordings and allow measurement of motor unit fibre density. A single-fibre reading is more difficult to obtain than concentric needle signals as the sampling area of the needle is less (Kreiger et al 1988), but it can be improved using ultrasound (Fischer et al 2000).

Sacral reflexes

Sacral reflexes indicate the integrity of the sacral reflex arc by measuring the conduction time between a stimulus and an evoked muscle contraction. Electrical stimuli can be applied to the skin over the clitoris while recording from the pelvic floor muscle using an electromyography needle, a ring electrode on a Foley catheter or an anal plug electrode. This technique has been used in the investigation of neurogenic bladder disorders, although its usefulness in the detection of ‘lower motor neurone’ bladder disorders is not clear.